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SPArKy_Dave

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  1. SPArKy_Dave

    XD Headlight Glass

    XD's used Ford Granada headlights - made by Bosch. Some place in the UK, may have NOS or reproduction parts for the lights? I believe I have or had, a NOS XD headlight seal somewhere. I had a NOS glass too, but sold it yrs ago.
  2. SPArKy_Dave

    Dielectric Grease - the good and the bad (tech article)

    Dielectric Grease, of some description. The factory, usually has a white paste grease in there.
  3. Use of greases in connection protection seems to be a controversial topic. Some claim dielectric grease is conductive or abrasive, containing silica that increases wear. (It doesn't contain silica). The most frequent Internet complaint is that dielectric grease insulates connections, making connections less conductive. Some call pure silicone grease an "insulating grease". The general basis for this claim is in the word "dielectric" used in the name. The word dielectric is assumed to mean the connection will have future problems because "dielectrics" are insulators. Generally, authors predict greases with powdered metal (in slang "conductive greases") will improve or maintain connection quality over time while dielectric greases will isolate connections because "that is what dielectrics do". History My first experience with silicone grease was in the 1960's as a lubricant in record turntables. It was also commonly used as a lubricant and protectant on turret-type television tuners, where channel coil packs or "strips" were mounted in a rotary turret. Rotating the turret moved different channel strips over stationary contacts to select each channel, and the clear silicon grease (which replaced a green or red petroleum grease) lubed the contacts and kept air off the plated surfaces. Later, RCA, Motorola, and Magnavox, facing field failures from bad electrical contact connections in new modular televisions recommended pure silicon grease as a contact protectant. They sent kits that included pure silicone to be directly applied to module contacts. This 100% pure silicone dielectric grease reduced connection issues between circuit modules, pins, and sockets. Hundreds of thousands of TV sets with hundreds of connections in each TV were living with silicone grease on signal and high voltage connections. Silicone grease also lubricated frequently-switched gold or silver plated contacts, and low voltage signal level module contacts. Silicone grease was also used directly on high voltage CRT anode connectors to prevent or reduce corona. My second experience was in the CATV industry. As a systems engineer, I was drawn into signal loss, radiation, and ingress problems in CATV/MATV systems. Problems centered around dry connections that corroded, and around aluminum trunk cable shield connections protected by Noalox, a grease people often call "conductive". All of these problems were eliminated by "non-conductive" silicone grease. The initial grease and sealer I brought into the systems was a white Teflon-silicone grease from a company in Elyria, Ohio. While that grease solved problems, it was expensive to apply to tens of thousands of fittings. It also was unsightly, service personal would leave white fingerprints everywhere. After consulting with several grease manufacturers, I switched to a GE 100% pure silicone dielectric grease in all CATV fittings. We used that grease without incident for many years in hundreds of thousands of connectors, completely flooding F connectors that were directly exposed to snow or rain. I continue to use silicone dielectric grease today. I use it as a lubricant on coaxial connector O-rings and threads. I use it to lube stainless bolts and nuts, to prevent galling. I use it for plug-in connections, in particular in my automotive hobby. I also use silicone dielectric grease for battery terminal connection preservation, coating it directly on the battery post. I use it in liberal amounts on ground connections, to inhibit corrosion on stainless-to-zinc (galvanized), lead-to-lead, stainless-to-copper, and stainless-to-aluminum electrical connections. I have never found a problem with silicone dielectric compound increasing resistance or increasing wear. We use it in new equipment production to lubricate and preserve contact plating in very low current meter switches. It has never caused shorts across insulation, I use it on spark plug HV boots on race engines and in high voltage connectors. I also use directly on contacts in my EFI system, including low voltage sensors. Silicone vs. Petroleum Grease Petroleum grease (Vaseline) was recommended (and was apparently used) on low power antenna installations years ago. While people report using it without problems, I never use it in my installations. The primary shortfall of Vaseline is the very low melting point. Most brands or types liquefy at around 100 degrees F, just above human body temperature. While this may be a medical benefit when coating human skin, it is a serious problem with connector applications. Any heat will cause Vaseline to run and eventually dry out over time. A second petroleum jelly issue is Vaseline's release of flammable vapor, even at low temperatures. A cotton ball soaked in Vaseline will burn a very long time, and actually makes a good fire starter. Since connectors are often near insulation or other things that can act like wicks, petroleum jelly is not the best thing. This is especially true since grease migrates in warm temperatures. Typical Applications for Greases Heat sinks Internet forums thrive on myths. Forums often claim dielectric grease thermally insulates connections. Forums also claim dielectric grease electrically insulates connections, such as in connectors and on battery posts. Neither is true. Here is a test using a 35-watt dissipation resistor. The resistor is mounted to the heatsink with a stack of Belleville washers. These washers are conical spring washers. They maintain a constant pressure when partially collapsed. Proper Belleville washer implementation ensures compression or pressure against the heatsink is essentially the same between tests. The Belleville eliminats cap screw torque as a factor in results. Here is measured data of a few sample greases with 30 watts heat dissipation: Type Sink F Device F Delta degrees Percent (aprox) Bare lightly scuffed 62.0 63.9 1.9 3.1% Heat sink compound thick 55.9 57.6 1.7 3.0% Bare polished 61.6 63.0 1.4 2.3% Vaseline 62.5 63.1 0.6 1.0% Dielectric grease 62.3 62.8 0.5 0.8% Heat sink compound thinly applied 56.2 56.6 0.4 0.7% Best result is at bottom. All greases were tested under "scuffed" conditions by roughing the heatsink with ~300 grit paper. Using too much dense grease, like thick heatsink compound, greatly increased thermal resistance. This occurred because compression pressure was not enough to force excess grease out of the area between the heatsink and the resistor tab. When the layer was thinned to a light "wipe" of grease, thermal resistance fell off significantly. There is essentially no difference between Permatex Dielectric Tune Up Grease and a special heatsink compound used on high-power transistors. Even Vaseline, at 1%, is better than bare metal-on-metal. Connectors In radio frequency low power installations, in particular at low frequencies and/or when the connector has very little air gap, completely flooding the connector is perfectly acceptable. Flooding a connector is not acceptable at high power, because most greases will carburize when subjected to an arc. Greases also change the dielectric constant, lowering the dielectric constant in the connector. This may create an impedance bump at very high frequencies, the problem's effect on the system being entirely dependent on the length of the bump in electrical degrees and the amount of the bump. (Not all things that show on a TDR meaningfuly alter performance, but they do indicate a potential problem.) In regular low voltage multiple-pin circuit connectors, such as automotive applications, flooding with a proper insulating grease of low-viscosity dielectric grease is perfectly acceptable unless a manufacturer recommends against it. The grease should have good stability and not contain metals in any form, and be specifically designed for use as a dielectric grease. This generally is a silicone dielectric grease, although some Teflon based greases are acceptable. In single low-voltage terminals or connections, such as metal-to-metal joints, grounds, or battery posts, almost any pure grease of light viscosity will be acceptable. Caution should be used with greases containing metallic powders to be sure any metal is compatible with the embedded grease metal. Connection enhancement from embedded metal powder is very minor, if it exists at all, and unless you match the grease to the connector material, risk of interaction with base metals might increase. In single high voltage connections, such as spark plug boots or other high voltage connectors (x-ray, neon sign, or HV power lines), only pure dielectric silicone greases should be used. Generally a light coating or wipe is all that is required. Dielectric grease will actually increase voltage breakdown across insulators, especially in the presence of moisture. Never use or allow a metalized grease around HV connections. The important physical characteristic is that any grease must have low enough viscosity to push out of the way at contact points, be water or liquid resistant, and be stable enough to remain in place as a protectant against moisture and air for a long time. It will not do any good to apply a grease that does not do required functions of excluding air and moisture, and lubricating the interface to prevent galling or fretting, for extended periods of time. Contrary toInternet rumors, advertisements, and articles low viscosity silicone dielectric grease will NOT insulate pressure connections. Silicone dielectric grease will prolong connection life as well as, and have just as good conduction performance, as a properly selected metallic powder grease (conductive grease). On the other hand, and improperly selected "conductive" grease can actually cause connection problems. Switches, Movable Contacts, and Relays Unless you are absolutely sure what you are doing is OK, do only what a switch or relay manufacturer suggests. There are some cases where very high current contacts can be lubricated, or should be lubricated, to prolong or extend life. There are many cases where lubricating contacts accelerates failure. As a general rule, low-viscosity greases can be directly applied to low-voltage contacts. Low-voltage generally would include consideration of opening or closing transient voltages, such as opening arcs from inductance back-pulse. Contact arcs have the ability to alter composition of greases. Silicone greases can be converted by arcs to silicone carbide, which is highly abrasive. For this reason, silicone grease should be avoided when contacts are "hot switched" and have any chance of arcing. Insulating and Conducting Grease Both dielectric grease and "conductive" greases (anti-seize) are insulators. The primary difference between dielectric greases and "conductive" greases is that "conductive" greases and anti-seize greases include some amount of finely-powdered metal. The finely powdered metal is suspended by insulating grease, so it does not conduct. The suspended metal powder does lower the voltage breakdown of any arc paths through the grease. Articles claim sparkplug threads are insulated by anti-seize, causing sparkplug or ignition fault indications. This is obviously wrong for several reasons, most predominantly because of voltages and currents involved. I suspect the real problem was anti-seize contaminated the plug insulator. Tests here show anti-seize and other metal-loaded "conductive greases" reduce high voltage breakdown voltages of air paths or surface path resistances of insulators significantly. Fingerprints on, or worse yet slathering of "conductive grease" on insulators or insulation, seriously degrades high voltage hold off. "Conductive" grease could trigger an ignition misfire warning code if a single fingerprint bridges the spark plug insulator. Other articles tell people to use conductive grease on connections, such as between battery terminals and an automotive battery. Tests show this claim is completely wishful thinking, and the type of grease has virtually no impact on terminal-to-post voltage drop. Again, we have a direct contradiction. People reporting anti-seize insulates a spark plug from the cylinder head are calling people liars who report conductive grease enhances a battery terminal connection, or vice versa. Generally, when two groups provide exactly opposite claims, at least one notion or claim is wrong. In this case, both are wrong. Neither group appears to understand resistance, current, and voltage. Permatex Grease Nye Grease super lube All of these dielectric greases, and virtually all from other manufacturers, both improve insulation and preserve electrical connections. They do this by sealing contaminants, moisture, and air out of connections. They also seal insulators, keeping moisture and contaminants out of insulation. They are as effective at preserving connections as "conductive" grease, and will not harm insulation. Historic Applications of Silicone Dielectric Grease Silicone Dielectric Grease (and lubricant) is a low viscosity grease. The normal temperature range is from around -40F up to +500F degrees. Silicone Dielectric Grease is far superior to petroleum jelly or Vaseline for preserving connections. Silicone grease has been around for a long time. It was used in the following applications: Application Prevention Junction Materials Early turret and rotary switch television tuners tarnish, wear, friction gold and silver flashed contacts Low power potentiometers or volume controls wear, electrical noise, friction carbon and brass Low voltage or non-arcing switches tarnish, wear, friction gold or silver flash or plating Connector pins tarnish, wear, fretting cadmium, zinc, silver, or gold surfaces Bolted connections tarnish, corrosion, friction lead, copper, aluminum, stainless, zinc Grommets and O-rings wear, tear, air and water leaks rubber or silicone based sealing rings Thermal conductivity aide fills air voids and seals out moisture aluminum, copper, beryllium, mica, silicone One incorrect logic is the "dielectric" in "dielectric grease" means the grease should only be used to insulate. All greases work by the low viscosity allowing the grease to completely push out of areas with metal-to-metal contact. Dielectric grease is just better at holding off high voltages over long paths. Conductive Grease Conductive greases and anti-seize compounds have a suspended base metal powder. The suspended metal powder is a fraction of the area occupied by insulating grease, and so the grease still insulates the connection. The grease does not conduct. The working theory of "conductive" grease is when pressure is applied, the grease squeezes out of the way. This leaves a fine metal powder that theoretically pierces oxides or fills voids. Using aluminum and copper blocks with various surface conditions, I've never been able to actually verify connection improvement from specialized conductive greases. In my tests, it appeared the grease simply carried most of the suspended powder away. Any remaining powder has never been enough to reliably reduce voltage drop across clamped connections. The change in voltage drop has always been indefinable, even with careful repeats of clamping pressure. I'd appreciate anyone having useful data sending me a copy. The suspended powder creates a problem that does not exist with dielectric grease. The suspended metal must be fully compatible with the metals being clamped. This means conductive grease is application specific. If the metals being clamped are incompatible with the grease's suspended metal powder, the connection will eventually fail. This is what happened in our CATV system connectors. The connections were a mix of copper, aluminum, and steel. The cable shields were aluminum, the trunk center conductors cables were copper clad aluminum. Drop cables were aluminum shields and connectors, with copper clad steel centers. Our records showed a much higher incidence of corrosion failure using conductive grease. Corrosion failure rate dropped significantly, almost to zero, when we switched to pure dielectric grease. In bolted or clamped connections, I have no opinion if conductive greases help or are necessary. I feel like they help, but I'm not sure if that is true. I use Noalox on clamped aluminum slip joints in antennas because it is generally less expensive than silicone dielectric greases and it appears to last longer. I NEVER use conductive greases on push fit electrical connectors, or if I am unsure of metal to grease compatibility. Conductive greases should specifically match materials being clamped. Conductive greases should never be used in low pressure electrical connectors, or in connectors with multiple terminals. Conductive greases should only be used in connections that are well-isolated from connections with differing voltages, and never in high voltage connections. They never belong in RF or signal connectors, unless they are bolted connections and the material compatible grease does not bridge insulation. https://www.w8ji.com/dielectric_grease_vs_conductive_grease.htm
  4. Understanding, Testing and Calibration of Ignition Coil Dwell Time Aim of this article: Most aftermarket engine management systems incorporate basic settings that relate to the control of the ignition coils. It’s been our experience that very few people really seem to understand the implications of getting these wrong or the benefits of optimising them. We hope to explain fully, in simple terms, what coil dwell control is all about; the systems used, coil and vehicle characteristics effecting it, effects on ignition performance and most importantly how to test and work out the optimum settings for a given coil. For the electrical ‘purists’ out there, some of my descriptions will be verging on oversimplification so please be tolerant. The article is not aimed at those with a PhD in electrical engineering! Dwell time is really only relevant to inductive ignition systems (so called ‘conventional’ systems), this information does not relate to Capacitor Discharge Ignition (CDI). I will also avoid coil and ignition discussions that depart from what’s needed to understand dwell control. Energy storage and measuring, coil selection, voltage demand vs availability, CDI, multi-sparking, high voltage diodes, effect of system loadings, spark formation phases etc. will be topics discussed in future articles. What is “dwell”: Dwell, or ‘dwell time’ in ignition systems refers to the period of time that the coil is turned on, ie that current is flowing through the primary winding and the magnetic field is building up in the coil. In the now obsolete points systems (Kettering systems) it is the time the points are closed, in our modern systems it is when the transistor (or other electronic switching device such as a MOSFET or IGBT) is on. Ignition coil basics: An ignition coil in an inductive systems works by ‘mutual inductance’. It consists of two coils that are wound around the same iron core (helps to concentrate the lines of magnetic force). The two coils are known as the primary and secondary windings. Secondary windings have thousands of turns of very fine wire that needs to carry high voltage (around 35 Kv is typical) but very little current (80 mA is typical spark current). One end goes to the High Tension tower ‘HT tower’ and the other is grounded or linked to the ignition terminal internally (very common) The primary winding has fewer turns of thicker wire as it carries a large current (7A is typical for a modern High Energy Ignition {HEI} system) and has ignition voltage on one side (+ terminal), the other (- terminal) is connected to a switching device (called a ‘driver’ quite often). The primary winding is switched on and current begins to flow through it producing a magnetic field (this takes time to build up!), this magnetic field surrounds both coils. When the primary current is turned off the magnetic field collapses rapidly around both coils and this induces a high voltage into the secondary winding to produce the spark. The high voltage produced is basically (but not only) a function of how many turns the secondary has compared to the primary, called the ‘turns ratio’ (1:80 is typical) Example of coil winding specs, From a common High Energy Ignition (HEI) Coil - Primary turns 135 Secondary turns 11000 Turns ratio 81.48 Of interest is the fact that if we have 1:80 ratios we are not multiplying battery voltage by 80 to get our high voltage, rather we are multiplying the primary induced voltage, think of it as a ‘spike’ if it helps, by 80. This means that any thing that reduces primary voltage will affect the HT voltage. Primary voltage usually lies in the 300- 400V range and is electronically ‘clamped’ in most systems to prevent the switching device being damaged. Have you ever wondered how the engine analyser machines used in workshops safely ‘kill’ cylinders for testing when they only connect to the coil primary with a small wire (without damaging coils or frying the tester with hi current)? Ok you probably haven’t! They simple clamp the primary voltage when required to a low level like 50V; the coils then produce a voltage that’s too weak to fire the plug. What coil characteristics effect dwell requirements: If you have a long straight piece of wire and connect it to a battery then the current flowing will reach its maximum level almost instantly. The current level that will be reached depends on the wires resistance (measured in ohm’s ‘Ω’, easily read with a multi meter). However, when the same piece of wire is wound in a tight coil it obtains a property called inductance (not measurable directly with a typical multi meter, measured in Henry’s ‘H’ or the smaller unit of milli Henry ‘mH’,). The property of inductance affects the rate at which the current level in the coil can build up, the peak current level is still limited by the wires resistance. Inductance depends on many coil design factors such as diameter, height, number of turns, core diameter, core material etc. and this is why coils cannot be substituted when replacing based on their resistance alone. Long piece of copper wire 13V applied and current rise time recorded Amps on vertical Y scale Milliseconds on X time scale Same piece of wire wound into a coil without any solid core (hollow, just air inside the brass & plastic former) 13V applied and current rise time recorded Amps on vertical Y scale Milliseconds on X time scale Same piece of wire wound into a coil with iron core fitted 13V applied and current rise time recorded Amps on vertical Y scale Milliseconds on X time scale Note how long the coil took to get to a certain current level, like 5 Amps, in each of the above traces, now picture if we had to power it up for just the right amount of time to reach this target current level. You can see how different coils would have very different dwell requirements! Coil inductance has a very large effect and dwell control settings must be measured by trial, especially when all the other variables that will be mentioned later come into play. Example of coil winding specs, From a common High Energy Ignition (HEI) Coil - Primary resistance 0.4 Ω Primary inductance 3.5 mH Secondary resistance 7.8 KΩ Secondary inductance 23.7 H Why is dwell important: Inductive ignition systems store their energy in a magnetic field and the correct dwell will allow this field to reach its maximum strength within the design limits of the coil. Design limits exceeded! Power dissipation in the coil exceeds design limits, the plastic bobbin melts and the epoxy filler brakes down. Expanding material and gasses rupture the casing. As mentioned, the coil stores energy in a magnetic field and the level of this is dependant on coil current. For anyone actually interested, the energy stored is measured in Joules and is ½ the inductance x the current squared. This means a small reduction in current makes a HUGE difference to energy (as it’s squared). Correct dwell control has a direct effect on current level and therefore energy stored… OK so who cares? Well, have a look at the following pictures that show the effect of coil current on spark appearance and duration. YOU should care! Coil current effect on spark appearance (achieved with dwell settings) Sparks shown are using the same HEI coil at 13 volts and firing it into a spark gap of 5 mm. The difference was the coil current of 2 vs 7 Amps. 2 Amps of coil primary current 7 Amps of coil primary current The LH ‘stringy’ looking spark could only jump a 6mm gap before extinguishing. The RH ‘fat’ spark jumps a 22mm gap before the temporary test equipment setup fails as shown next- Spectacular, if it’s not your coil! This coil has more voltage reserve than is required to jump the test gap used so it ‘flashes’ down the HT tower to the primary terminals. NEVER let this happen, it spells death to ignition components and even vehicle electronics systems. Also, NEVER open circuit a HT lead etc when bench testing or on a vehicle (perhaps your attempting to knock out a cylinder), the stored coil energy will dissipate back into the system and damage the switching electronics. Besides, many modern coils can generate more open circuit voltage than their insulation can withstand and they will internally break down. What occurs is a carburizing of the potting material leading to a conductive path for future short circuits. When the coil voltage demand is high, such as when you accelerate suddenly, the fault can occur. 2 and 4 Amp extremes of current level are used here to clearly show an effect. To achieve these the dwell time only had to be altered just over 3 milliseconds for this particular coil! Another way to view the effect of low coil current is to see the effect on an engines spark duration (the time the spark is ‘firing’ across the spark plugs electrodes). This is a good comparative indication of stored coil energy. For this demonstration we fired the coil into a fixed spark gap whilst measuring the voltage and time. Coil current effect on spark duration (achieved with dwell settings) 2 Amps of coil primary current Milliseconds on X time scale KV on Y voltage scale Spark duration of only 0.5 ms 7 Amps of coil primary current Milliseconds on X time scale KV on Y voltage scale Spark duration of 1.4 ms now As you’ll read in another Dec article, spark plugs are actually very inefficient at transferring energy to the mixture so we need to give them all we can. Dwell control methods for Aftermarket ECU’s: 1. Using a modern ‘Closed loop’ electronic ignition module (No ECU Dwell map)– LH, Bosch BIM 137 RH, Bosch BIM 024 Common ignition modules such as Bosch’s BIM 137 {008}, BIM 024 {021} units and Fords TFI have sophisticated closed loop control of dwell. In brief, these actually monitor the coil current and adjust the dwell to ensure the target level is always reached (about 7 amps is usual), this allows for RPM, temperature, voltage, coil tolerances etc. Should the current rise above the target then the modules transistor will partially turn off to limit the current and this can be seen as a ‘flat’ section on the top of the current trace when viewing. They even limit the maximum dwell so that they don’t turn on too early and not leave enough spark time. Yes, if needed, at higher RPM they do actually extend the coil turn on point right into the preceding spark period and interrupt the spark before it finished, about 0.6 ms of spark time is sufficient at high engine speed for good combustion due to the excellent mixture formation in the cylinders. A final feature is the shutting down of coil current if the input signal is not showing engine RPM (ignition is left on but the engine is not running). Coil current trace shows BIM 024 current limiting, normal at low RPM in these. This module adjusts its dwell continuously and will maintain the set maximum current under most conditions. These modules are often used in aftermarket applications as they are very simple to set up in theory (no dwell mapping required) and readily available. They are a good choice if your ECU has limited control ability or you lack the coil dwell data or equipment you will need to test the requirements yourself, discussed later. Important notes on using closed loop ignition modules- · You need to use coils that are compatible with the module (eg. Bosch BIM 137 module works well with Bosch HEC715 or HEC716 coil). · Do not use an inductive sensor triggered type (like BIM 024) with your ECU. Internally these modules use the slope of the sensor input signal in their dwell setting process and if triggered with a square wave it will not have dwell control available. Only use modules from Hall Effect systems (eg. BIM 137). · The Hall Effect triggered module type internally converts the square wave input signal (from your ECU now) into a saw tooth voltage and uses this new sloping signal in their dwell setting process. The limit they can adjust their dwell will be restricted If you do not give them a long enough pulse. · To expand on this; these modules fire when the input signal goes from Hi to Lo, so if you have a Hi period of the triggering pulse say 3 ms long before you wish to fire then this will be the maximum dwell time that can achieved. Set up your ECU so the pulse Hi time is always longer than the greatest dwell time needed. Down side of using full closed loop ignition modules in an aftermarket system is that- · You can’t alter the coil current limit if your application allows (detailed later) · Dwell control at very low coil firing rates (eg an engine with one coil/module per cylinder at idle speed) may be outside it’s ability and dwell is often way too long. Coil destruction results. The solution may be an aftermarket alternative such as those from ‘M&W ignitions’. · Expensive if you need multiple units (eg an engine with one coil/module per cylinder) 2. Mapped dwell (ECU has actual control of the dwell)- This is when the ECU sets the dwell based on an internal map. The main variable is battery voltage as this has a major effect on the time needed to allow a coil to reach our target current level. The map has to be programmed correctly for the particular coil used. Nearly all production vehicles now use this method. NEVER substitute the coil for another type on a mapped system. The ECU will not know you have done this and will still turn the coil on for a certain time, if your new coil charges quicker (lower inductance) then the coil or ECU will be damaged. If a slower charging coil is fitted (higher inductance) you will get a poor spark. The ECU controls a switching device (transistor usually) to switch the coil on for the exact time it needs to reach the desired current level before turning it of for the spark. The transistor (known as ‘end stage’ or ‘driver’ also) may be mounted inside ECU, mounted external or even be built into the coils as is common. This is the type of dwell control we will concentrate on in this article now and will detail the calibration process. These are not ‘modules’, they are driver transistors. The LH unit (Bosch BIM 200) is two drivers in a single housing. The RH unit is a Mitsubishi J121. What many do not realise is that these basic drivers also have internal over-current protection (clamping) that limits the maximum coil current you can use them to switch. The exact level is very temperature dependant, driver specific and subject to tolerance but is usually less than 7 – 9 Amps. Most coils that have the drivers internally built in (like many Coil On Plug ‘COP’ coils) have this over-current protection also and some even have thermal protection that will reduce their heat dissipation temporarily until under control (eg Mitsubishi 380 vehicle coils). NEVER have your dwell set long enough so that the driver is clamping the current, seen as a ‘flat’ section on the top of the current trace when viewing. Drivers (not modules) are generally not designed to limit current in normal continuous operation and they will fail very quickly. If you doubt this then just put an input signal into one constantly so it’s forced to limit the coil current, you can boil water with them! One topic rarely considered is the primary voltage level that is clamped by the driver also, we have already made mention of primary voltages effect on secondary voltage. As this is designed into the drivers the only way to optimise this is to bench test various types and record the primary voltages. As an example a J121 driver tested at 310V primary clamp but a stand alone transistor (from an old ignition module) tested at 402V, it also had no over-current protection so care would be needed when setting up. Ultimately the most flexible driver device would be able to handle both high current and have a high primary voltage clamp (did I mention cheap and reliable?). Generally, off the shelf items such as Bosch’s and Mitsubishi’s are more than sufficient to do the job, however it is also possible to use discrete drivers from the major semi-conductor manufacturers (inc. Bosch). If your ECU has the driver incorporated then the decisions already made for you! Why do we need a dwell ‘map’: We’ve discussed the effects of coil design (inductance) on dwell time but now we need to examine other factors. The single largest variable is supply voltage, see the dwell time figures vs voltage below! Dwell map from a Motec setup. This adjusts dwell time with battery voltage; note the RPM column is just repeated. RPM doesn’t alter the basic dwell time so this 3D table could be a simple 2D curve of voltage vs dwell time. We’ll talk about more complex tables soon. Testing the dwell requirements of a coil: There are two main approaches, testing a coil on the bench or doing it in the vehicle. Bench testing coils will provide a wide range of good data, useful for future reference should you wish to experiment with different current levels. Bench testing also allows a large voltage range to be applied conveniently. Final confirmation needs to be done on the vehicle regardless! Equipment required- Oscilloscope, most any will do as it only needs a single channel and we’re measuring relatively slow signals. The ability to freeze the picture and measure with cursors is very handy and will save much time. Variable power supply (7 – 16V is the test range needed) that will not dip in voltage when the high coil demand is placed on it, most ‘switch mode’ supplies are very bad for this. It is best to test the output on a scope before getting too far into you’re testing (much less than 1V drop at peak coil current is required). We often connect some very large capacitors (bigger is better) across the supply to smooth the output; another option is to use a flat automotive battery to act as the capacitor, the only catch is you must start testing at low voltages and work up (as battery will charge) It will only work over limited range but can help if supply is poor and capacitors are unavailable. Current probe, clamp type (DC, hall principle usually used) for the scope. These can vary wildly in cost so shop around, you need to measure 0- 10 Amps typically. There are also inexpensive kits available from electronic suppliers like Jaycar that may do the job (see links page). Using series shunts is also possible, but be very careful as any extra resistance can have an effect. Signal (function) generator, not necessarily essential. Used to trigger the driver and allow the monitoring of coil current. Getting the figures on the bench- The coil to be tested needs to be powered from the variable supply and switched via the driver. A current probe and scope are used to monitor the coil current. The driver can be ideally triggered from the signal generator or even just ‘flashed’ on manually. Most drivers require a certain of current to drive them (20 – 40 mA typically), never apply direct power, at the very least use an automotive ‘test lamp’, equivalent small wattage globe or a resistor in series with the drivers input terminal to limit the current. If you have basic electronics knowledge you can measure the voltage dropped across the driver and determine that it is fully on. If you do not turn on the driver fully (too low a drive signal) then the coil current will be limited and the driver will overheat, this can be an issue when setting up your ECU also, many allow you to set the drive current, Motec for example has a 20mA or 40 mA selectable level. Record the coil current rise time at particular supply voltages and note the time to reach various current levels. This is where the freeze and measure ability of a scope can save lots of time. In theory you could actually dispense with the scope and use a multimeter with ‘peak hold detection’ but this would require a very careful use of a signal generator to adjust the drive signal duration to the correct coil current is reached and then record this signal duration. Chances of failure would be high. Be very careful testing and only pulse the coil briefly as there may be no protection at all (depending on your driver choice) and thermal dissipation will be high, allow cooling time and check driver for temperature rise. A HEI coil tested at 10V supply Rise time to 7 Amps is 5.4 ms A HEI coil tested at 13V supply Rise time to 7 Amps is 3.6 ms We can use the above traces to check the time required to reach other current levels also if we wish. Sample data generated for some common coils (more test points than actually required) Getting the figures on the vehicle- The difficulty with doing the testing on the vehicle is in being able to isolate the coil power supply so that it can be varied from an external supply. If you can achieve this by tapping in at the supply origin and therefore using most of the existing vehicles coil wiring the harnesses voltage drop will be compensated. Engine operating temperature can also be achieved and calibrated. The job is made a lot easier with ECU’s that incorporate a self test where it can drive the coils at an adjustable frequency and period (eg. Motec again), they can be varied to simulate different dwell times to observe the peak current level. This also ensures that any losses in the drivers and wiring are adjusted for. Testing solely on the vehicle like this is a lot of work and generally just doing the following vehicle confirmation and final trimming will give the same results and is therefore recommended. Confirming the application on the vehicle- Once the basic voltage dependant dwell map (or curve) is programmed with the data gathered then it must be checked on the vehicle. This is necessary to allow for vehicle supply voltage drop and temperature effects. Actual coil supply voltage measured in a vehicle. At peak coil current the voltage dropped about a volt (ignore the vertical spike from ignition interference), not ideal, I’d like much less. Less than 1V drop is just acceptable though. This is just the coil supply side, voltage drops also occur in the switching side, particularly across the driver where 2 volts is not uncommon (characteristic of the Darlington transistor often used). The ECU’s only monitor the voltage at the ECU, not at the actual coil etc. It is essential to confirm and fine tune the dwell on the vehicle under normal running conditions. Confirmation at normal operating voltage and temperature is easily performed with the current clamp and scope to ensure your target current level is being reached at all times. Test at high RPM- ensure that if the start of dwell is interrupting an occurring spark, that sufficient time is still left for it (no less than 0.6 ms typically). This effect can be seen by looking for coil current that is not starting at zero Amps but has a ‘step’ at the start. What is occurring is that there is still energy remaining in the coil so we are only really ‘topping it up’. This phenomenon is usually only an issue if a single coil and distributor is used, not on a COP or a Dual Fire System (DFS) as the coil doesn’t fire as often on these, the operating frequency of the coil is lower. Very high inductance coils (slow charging) could also exaggerate the effect. Have a good look at coil current during cranking also; ensure it’s still acceptable as the battery voltage plummets under cranking. Dwell requirements are often so long that we need to compromise with what’s achievable. Actual battery voltage measured in a vehicle under cranking conditions. Starter motor is disabled here to clearly show the big voltage drop as the starter first engages and then the ripple as each cylinder pushes against compression. Selecting the coil current level to use: The only way to guarantee reliable service is to set the coil primary current to the same level that is used in the vehicles the components are used on. Vehicle and component manufacturers do many severe tests to check reliability. If you use aftermarket or cheap replacement coils then you’re on your own! There are gains to be had by raising the coil current slightly but long term component endurance will be a gamble. Manufacturers have to be conservative for a reliability margin and to allow for manufacturing tolerances, they really know their limits. We have tested some COP systems that run reliably with 12 Amps (Toyota) However, the coil selected may now be used in an aftermarket application that gives greater time between sparks than it was designed for, like a distributor system coil used in a COP or DFS system, this allows the coil to cool down between firings. Unfortunately, in any system the higher the engine RPM, the greater the temperature build up, as there is less time without current flow to cool down. Another thermal consideration is for example, the mounting location; this may increase the components temperature as in when mounted directly on the engine above each cylinder. Temperatures can easily reach 80ºC under the bonnet. Higher coil current flow will increase the resistive losses in the coil by a squared function (I²R), so a small increase in resistance for a given current passing will have much larger effect on the power losses and therefore heat dissipation. Temperature will increase the resistance of the coil and wiring, ‘0.393 % per ºC’ is copper’s temperature characteristics so at 100 ºC its 39% higher, drivers actually have lower losses at higher temperature (semi-conductor materials used) and so help cancel out some of the temperature effect on losses. Operating temperature conditions can be checked at other voltages, besides those normally uncounted, by running with the alternator disabled and headlights etc. on to reduce the battery voltage gradually. Also be cautious of a sudden change in the coils current rise time as in this diagram. The coil may have reached ‘magnetic saturation’ and this can cause a rapid increase in current and power losses. Your possible coil current range will usually be limited by your driver choice as most have inbuilt protection as discussed previously. Mapping for temperature and other factors: Car manufacturer’s ECU’s can incorporate approximated coil temperature as an ignition variable to allow for power losses and voltage drops. If your ECU has the flexibility for more complex tables and you have decided to push the limits (or just want to guarantee reliability) you could reduce the dwell at high temperature, sustained load and high RPM. Dwell optimising for starting conditions and cold temperatures is also possible. Maximum RPM before current will drop off, based on dwell: When the dwell time to reach a certain current level is known, we can work out how many RPM could be reached before the coil current will be reduced from our target due to lack of available charging time. We can do this for any number of cylinders the coil must fire. The table below is based on the earlier dwell figures. The formula used, I suggest you put in an Excel spreadsheet - (1000 / (Dwell time + min burn time)) x 120, divide this by number of cylinders supported by the coil. Dwell time = time to reach your target current in ms Min burn time = min time left for the spark to occur, 0.6 ms is suggested NEVER use a BIM 024 module as a driver transistor: It is not uncommon to see BIM 024 modules used as driver transistors in aftermarket systems, particularly multi coil applications as it’s a cost effective module. NEVER do this, it is a full ‘closed loop’ module that’s expecting to be triggered by a sinusoidal shaped input (AC voltage) from a distributor mounted sensor, not from a square wave out of an ECU. Please re-read the previous section on closed loop module operation if this is not clear! When it’s used incorrectly strange things can happen at certain RPM and input pulse widths, there is also generally excessive current limiting periods and therefore heat build up. The result could be poor and difficult to diagnose ignition performance or component failure. Driving a BIM 024 with a square wave Module is wired to a HEC 715 coil, driven by a signal generator at a frequency that is equivalent to a 4 cylinder at 1000 RPM or an 8 cylinder at 500 RPM. In this example, to illustrate the problem, we have varied the pulse time (dwell) Red is the transistor drive signal from generator Blue is the coil current Note that the coil current flow does not coincide with when the drive signal is high; it would if we used a normal driver transistor! (note also the uneven coil dwell times) In the lower trace, with the same frequency but a longer pulse applied, the device behaves exactly as expected. Many other strange characteristics appear at different settings. Generally lower RPM and shorter dwell settings make it worse. Disclaimer: You have been WARNED! Before you race out and start testing read the whole article and if you are unsure about anything then seek further help before continuing. Due to the DIY nature of this article and variations from system to system there may be some challenges you have to overcome and further research required. The article is a guide - not a guarantee! DTec accepts no responsibility should you decide to undertake any modification - it’s entirely at your own risk. Be aware also that automotive equipment manufacturers will not give warranty if their components are used in the incorrect, un-specified application, nor should they! Please keep an eye out for further DTec articles at and visit our links page for references to further information. Appendix Dwell control methods background: The following “points systems” information and dwell extension methods only gives enthusiasts some interesting background insight; please don’t get ‘bogged down’ in it. Points systems (also called contact or Kettering)- The earlier ignitions had a fixed dwell, these were mechanical ‘points’ systems. The dwell is set by the relationship of the contact points to the rotating distributor cam and does not vary. The limiting factor is how fast we can reliably open (for a spark) and then close the points to let the coil primary current build up again, points ‘bounce’ and durability are issues. What’s happening is the points are closed for a certain number of degrees of distributor rotation but the coil needs a certain amount of time, not cam angle. At high speed the same degrees of cam angle pass in a shorter time. The result is that at high RPM, the coil cannot be turned on long enough (dwell too short) to reach full current and ignition performance falls off. All this and we haven’t even mentioned the lack of voltage compensation! Performance is made worse by another limiting factor, points can only switch a small amount of current reliably (generally 4-5 Amps) and coils for these systems have a high inductance and therefore take a long time to charge up. This is due to coil resistance needing to be high (therefore lots of wire turns) to limit the current and protect the points, the later addition of a ‘ballast’ resistor in systems was to externally limit the current and free up the coil designer to use lower inductance coils. Bypassing the ballast to boost performance when cranking (low battery voltage) was a later addition! Effect of high RPM on points systems Coil primary current measured 4590 RPM on a 4 cylinder Amps on vertical Y scale Milliseconds on X time scale There is simply not enough time available to charge the coil fully so coil current falls rapidly. Nominaly on this old system it’s 4 Amps, not 2.6 Amps as above. The ‘peak current’ plot below reveals the diminishing primary current clearly. Peak coil current plotted vs RPM · Amps on vertical Y scale · RPM on X scale This is a 4 cylinder, the problems twice as great on a V8! Standard points only just do the job on these. Don’t use points unless your forced to do so. Points dwell extension - Twin point distributors used 2 points in parallel that are carefully timed so one closes just after the other opens and therefore gives a long dwell (compared to single points). Improvement, sure, but still basically has all the same problems except high RPM performance is improved. Besides, very few are ever set up correctly when serviced and usually only operate as a single point system. Early electronic ignition with dwell control- Many early electronic systems had a dwell time that was controlled (some were still fixed angle), but it was a simple pre-determined change based on RPM. The early transistors used to handle only about the same current as points could. At least it allowed the maintenance intensive points to be replaced with electronic sensors in most cases. Enjoy!
  5. Ford's Electronic Distributorless Ignition System - Ignition controller - EDIS (Ford) - reference and timing The purpose of this test is to evaluate the correct operation of the ECM and EDIS module based on the voltage and frequency of both the PIP and SAW signals during engine run conditions. How to perform the test View connection guidance notes. Use manufacturer data to identify the functions of the ignition circuits. Connect PicoScope channel A to the ignition unit output signal circuit. Connect PicoScope channel B to the return signal circuit from control unit to ignition unit. Start the engine and allow it to idle. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform. Start the scope to see live data. With your live waveforms on screen stop the scope. Use the Waveform Buffer, Zoom and Measuring tools to examine your waveform. Example waveform Waveform notes PIP: Profile Ignition Pick-up SAW: Spark Advance Word Profile Ignition Pick-up (PIP) is the signal sent from the Electronic Distributorless Ignition System (EDIS) to the Electronic Control Module (ECM). It is the digitally modified version of the alternating current (AC) signal that originates from the Crank Angle Sensor (CAS). The PIP signal is a squarewave switched at 12 volts and is the ECM's reference for the engine's speed and position. When received by the ECM, the PIP signal is modified to take into account the ignition's timing advance and is then fed back to the EDIS unit. The returned signal is called the SAW signal, and is in the form of a 5 volt squarewave. Both signals can be seen in the example waveform with the PIP signal in blue and the SAW signal in red. Further guidance The EDIS module, fitted to the distributorless range of Ford vehicles, works in conjunction with the main EEC IV ECM. Its function is to collect the alternating current (AC) signal from the crank angle sensor and modify it into a digital square wave. This signal is known as the Profile Ignition Pick-up (PIP) signal. The PIP signal tells the ECM the exact position of the engine and this signal is then further modified into the Spark Advance Word (SAW) signal that is adjusted to compensate for any timing advance that the ECM decides is necessary. The advance is determined by the engine speed and the engine load. The returning SAW signal to the EDIS unit determines when the earth return circuit is released from the coil negative in order to fire the coils. As there is only one SAW signal that triggers the coil for cylinders 1 and 4, the point of ignition is calculated by the EDIS unit for cylinders 2 and 3. The ignition timing is set at 10° before Top Dead Centre (TDC) as its base setting, which occurs when the engine is cranking, at idle, or operating in Limited Operation Strategy (LOS). If one of the SAW signals is outside its operating window, the EDIS module uses the width of the previous signal; if however, the unit sees 5 or more errant signals, the ignition timing reverts to 10° before TDC. As with all double-ended coil configurations, a wasted spark system is used that fires the plugs even when they are on the exhaust stroke. The above figure shows the basic wiring diagram for the EDIS system.
  6. "Understanding Standard and Signature PIP Thick Film Ignition" Ford is really clever, but TFi has some major issues because its not understood well. It was born as an external "Hall" crank sensor EECIII but DuraSpark Brown Box DS II system in the 5.0 CFi /5.8/6.6 liter 2-bbl 1980-1984 Lincolns, 83-84 Mercury Cougars's and 83-84 CA Tbirds and some/most 351M and 400 California Bronco's and F-trucks and E-vans. Just single synchronized Spark only system . Since the harmonic balancer is 6-3/4" on everything, the 80-84, external D2-II Crank triggered parts can be used to fix up a TFi that isn't Dual Synch. But in 1984, Ford Had a Better Idea TFi = Thick Film Ignition PIP = Profile Ignition Pickup, the sensor inside the distributor. The PIP system uses a Hall cell magnetic sensor, which is a prox sensor, a distance ranging device that generates a reference and zero voltage as the Shutter Wheel passes between it and the Magnet. It is three parts. TFi's are Dual Synch for Sequential Injection 5.0's, but Single Synch Bank fire on 5.0/5.8 trucks till about 1995. They are not the same. The one year only 84.5 to 85 Automatic TFi was similarly unique. Get the wrong parts not up to quality, and the sensor will stop transmitting. Replacement parts have a terrible reputation. Ford OEM, reasonable, although they too are suffering from some approved supplier problems. If the distributor is not forming a Square wave to the Injectors and another modified square wave to the SPOUT , the car will break down at various RPMs. If its not working, then you have to get an aftermarket Hall Sensor and you must check the PIP Shutter wheel for magnetic quality and the spacing of the narrow shutter. later Ford 5.0 distributors are solid, no mechanical or vacuum advance. Just a simple rotor with PIP gates and a Hall Effect sensor. The signal should be stable (Without Scatter) the module is this the shutter wheel that forms the PIP signal is this the shutter wheel triggers a square wave electrical signal using the Hall Effect sensor See https://www.w8ji.com/distributor_stabbing.htm Plug Wires A quick word about plug wiring. Never dress spark plug wires from high energy ignitions in a bundle. Electric field and magnetic field coupling can cause enough cross-talk to spark an unwanted plug even with good wires. Never dress two adjacent distributor post wires next to each other for any distance. For example, in a 1-3-7-2-6-5-4-8 Ford firing order, never dress wires 1 and 3 or wires 6 and 5 next to each other for any distance. The reason for this is simple. If adjacent post wires ever cross-talk, you can fire a cylinder 90 degrees ahead of time. Cross-firing adjacent posts can be a worse case scenario, firing a cylinder while the cylinder is full of unburned fuel and air (and soon to be on the way up). Adjacent firing cylinders are 90 degrees out of phase mechanically. With 20 degrees running spark advance, a cross fire can ignite a the next cylinder with 110 degrees spark advance! That much advance is never good at high speeds. Resistance is generally a very poor way to test wires. Most meters measure resistance with voltages well below 9 volts. The spark is thousands of times higher voltage! An open wire or high resistance at 9 volts can behave perfectly at 20kV, and a low-ohm wire test can behave poorly. Although high resistance conductors should be avoided, resistance measurements with typical low voltage meters actually have very little to do with high voltage wire performance. A simple meter test will neither guarantee a wire is bad or good! A visual inspection for cracks, holes, or burns is actually much more reliable than a meter. Unless you have a proper tester or know how to test visually, if you have any doubts about wire condition, change them. Distributors There is a lot of misinformation about distributors. One myth is that the distributor position in the block, or the particular tooth in the block, determines timing and rotor sync. Some people even claim they move the distributor one tooth and pick up speed or ET, or the car pulls better. I'll show you why, even though some claim things like that, it cannot be correct for any distributor system that has the ignition spark timing pickup or trigger located inside the distributor. While this is specifically about the common Ford TFI system, system basics also apply to most other systems. My experience with ignitions started early. In the early 1960's, I hand built a tachometer and solid state ignition for my dad's 1957 Ford. While still driven by the points, and still using the stock coil, four early transistors reduced the point current. I just wanted to see how power transistors would work in ignitions, since they were starting to appear in some car radios. TFI Thick Film Ignition Mounting The TFI is a module that replaces the electrical function of breaker points. The TFI module is nothing but a solid state off-and-on switch controlled by a small signal. In early Ford computer systems (before crank trigger systems), a shutter wheel interrupts the flux path of a small permanent magnet to a Hall effect cell. The path interruption by the steel blade of a shutter wheel changes the Hall cell's conduction state. The computer looks at this voltage, which is called the PIP (profiled ignition pickup) signal. This signal replaces the mechanical cam on a breaker points distributor. The computer rapidly and continually learns the sequence of the pulses, smoothing them while also learning number one pulse postion, and then modifies the timing of evenly-spaced, but much longer, pulses sent to the TFI module. The TFI replaces the metal contacts on "points", which are an electrical equivalent of the old mechanical cam operated normally closed switch contacts in breaker points. The TFI is closed, just like breaker points, when the computer supplies an ignition dwell signal. The steady dwell current, just as with old points systems, builds a magnetic field in the ignition coil core. The dwell signal disappears at the moment the computer wants spark. This removes coil magnetic charging and field holding current. The collapsing magnetic field causes an extremely high secondary voltage. We could accurately say this is a magnetic discharge system, as opposed to a capacitor discharge system. Because it is a magnetic storage system, and not a capacitor storage system, the coil operation is much different. Because the operation is different, optimum coil design has to be much different. Most of the current limiting is in the ignition coil. A bad coil or the wrong coil is extremely rough on the the TFI module. When steady direct current voltages are applied to inductors, current will build. Eventually current reaches a maximum value that is limited by static and dynamic resistances. Heat is always current squared times resistance, so heat is produced by current through the resistance. Every bit of operating heat produced inside the TFI module, and in the ignition coil, is caused by resistances and average current through those resistances. Current while "charging" the coil is primarily limited by coil inductance, and not by resistance. While inductance does not contribute to coil heating, it does limit TFI current through much of the field charging (dwell) cycle. Shorted turns, or the wrong coil (too low of inductance), will increase TFI heating by increasing dwell current. An ohmmeter is not a good test of ignition coil functionality. Shorted turns, or the wrong coil (too low of inductance), can increase TFI heating without showing on an ohmmeter. If the TFI module did not have some current limiting, it would generate no more than 5-10 watts of heat. The TFI module has some current limiting that functions like old-time ballast resistors and ballast wiring. This resistance causes additional heating in the TFI module. The TFI module generates most of the heat at idle or low speeds. This is because the "on" (dwell) duty cycle is highest, while current limiting effects of inductance (which does not produce heat) is lowest. The conventional Ford distributor with TFI module depends heavily on engine fan airflow for cooling. Altering airflow in any way that reduces air across the engine front and across the distributor will increase TFI module temperature. The TFI module surface looks like this: The above surface is unacceptable. The lumpy, dirty, surface will prevent the module from having good contact. This will cause the module to run hotter. Cleaning the surface with a light solvent, such as 100% alcohol, lacquer thinner, mineral spirits, or almost any fast evaporating paint thinner, will remove the old, dry, lumpy, thermal compound. A clean surface, ready for a new TFI module, should look like this: Ford, for some reason, does not machine the surface very well. Because air insulates heat, the surface requires a **thin** layer of heatsink compound or pure silicone dielectric compound between the clean TFI module surface and clean distributor surface. Contrary to Internet rumors, pure silicone dielectric compounds work almost as well as dedicated heat sink compounds. The grease functions to fill ridges, displacing any trapped air that would thermally insulate the module from the distributor. The grease has to be able to work down into the grooves and push air out. A thick layer of thick compound is actually as bad as no compound at all. Do not use too much compound. Use just enough to fill the grooves fully. Nothing will transfer heat out of the module than direct metal to metal contact. Heat sink compound, although much better than air gaps, still has several times the thermal resistance of metal-to-metal contact. For best life: Clean the surfaces Apply a light uniform coating of suitable high temperature heatsink or pure silicone grease. It is important that the grease completely pushes out of all metal-to-metal contact areas, and the grease not run or melt at modest temperatures Fasten the TFI module #6 hex screws snugly with a hand driver, but not so much as to hurt the fasteners Use a little silicon dielectric tune up grease in all the connectors. This should be 100% pure silicon. It will keep air and moisture out The TFI module will NOT cause a PIP module failure, and a PIP module failure will not cause a TFI module failure. The PIP wiring just passes through the TFI to reach the wiring harness without any important connections to TFI module electronics. Distributor Operation The PIP system uses a Hall cell sensor. A shutter wheel interrupts the magnetic field from the magnet to the Hall cell. The block circuit is: The functional description is: The PIP triggers a timing reference signal as any wheel tooth enters the center area of the cell-to-magnet shutter wheel gap. If the magnet loads up with iron trash, timing will become erratic. Enough trash can cause random PIP failure, shutting the computer down. The wheel looks like this. The firing order is for the 302 HO camshaft: The actual wheel pattern looks like this. All teeth except 1 are the same size: This drawing is for a standard HO firing order of 1-3-7-2-6-5-4-8. This would be a view from the hall cell side of the distributor. PIP triggers (the leading end of the wheel teeth) occur exactly 45 distributor degrees from each other, for a total of 360 distributor degrees. Since the distributor turns at half crankshaft speed, firing pulses occur every 90 crankshaft degrees. Trigger edges, even for narrow tooth number 1, are all exactly the same distance apart. Only the trailing edge of number 1 changes. Decreasing #1 tooth width increases the shutter wheel air gap to cylinder three, which increases Hall cell dwell time after number 1 blocking tooth clears. Notice the number 1 trigger tooth is narrower, causing a wide gap after the number eight trigger edge before the PIP's dwell. The computer watches for a longer open window to learn when number 1 is coming up. The computer knows how fast the wheel is spinning, and how far apart magnetic field blocking intervals occur. The EEC recognizes number one because of the longer gap after number one hits, which makes number one shorter off-time than the other PIP signals. Since the ignition firing queue is at the leading edge passing through the Hall sensor gap, the leading tooth edge determines initial timing. Here is an oscilloscope view of the PIP signal. The display is set up so the plugs appear in sequence from left-to-right, air gap is at the top, and the vane is at the bottom: Low signal is the vane blocking the hall cell. High signals are gaps. Notice the long gap after 1. The measured timing of the trace above is: RPM Time for one turn Perfect time between sparks Time range between start lows 8 vane 8 gap 1 vane 1 gap 3 vane 3 gap 7 vane 7 gap 585 204.8 mS 25.64 mS 25.4-25.9 mS 12.7 mS 12.3 mS 8.5 mS 16.7 mS 12.6 mS 12.3 mS 12.4 mS 12.4 mS The entire timing relationship is between Hall cell position in relationship to the shutter wheel position. Timing has nothing to do with the stabbed distributor tooth, or the distributor housing to block position. As long as you can rotate the housing to align the tailing edge of the narrow tooth to the Hall sensor trigger point, timing will be correct. Taking the distributor out and moving it one tooth will only change the required final housing position, it will not change anything else. Re-stabbing will not change rotor phase, it will not change timing. Changing the stabbed position only moves the distributor housing position where proper timing occurs. If you want to stab properly, put the engine about 10* BTDC, the distributor housing in a good position for adjustment rotation, and the leading edge of the shutter wheel number 1 tooth in the center of the hall cell gap. This will also point the trailing portion of the rotor contact blade at post number 1 inside the distributor cap. The Hall cell gets power through, and returns PIP signal through, these three terminals: Make sure these female terminals are clean, and give them a light coating of dielectric grease. The cell wires pass right through to the terminals. For maximum life and reliability, push a small amount of Permatex 100% pure silicone dielectric tune-up compound into the terminals. Don't listen to anyone who tells you dielectric compound will insulate the terminals!! Timing is set by the relationship of the distributor housing to the shutter wheel: Contrary to rumors, the stab position is totally meaningless for distributor rotor to terminal synchronization or timing. Stab Position and Initial Timing The stab position only changes the position where the housing produces the correct timing. If you can rotate the distributor housing to the required position for proper timing without bumping into anything, and if the wires reach, you can slap the distributor in at any position on any tooth you like. In the case this Ford TFI system, all you would have to do is make sure the rotor's knife edge contact is near the exiting side of number one cap terminal when the crankshaft is set at the desired initial timing on the compression cycle for number one. A PROPER installation for a 5.0 HO with EEC IV would be: Premark the cap number 1 position on the edge of the distributor's lower insulated cap wall Set the crank at about 10 BTC on compression for #1 Install then rotor and position it late from the position 1 mark (clockwise top view) Position the distributor body so the TFI wires reach, and so you can swing the distributor each way with clearance Stab the distributor and watch the rotor move If the rotor moves so far you cannot turn the body to align near the tailing edge of the rotor contact with number 1 cap terminal (with a little overlap), move the initial starting position and repeat a new stab starting from step 3 Install plug wires so cylinder 1 is on the cap terminal marked 1 Time the engine with the spout removed. If the distributor hits anything before reaching the target timing, you will have to move the distributor gear one or more teeth opposite the direction you moved the distributor housing when it hit something Shutter narrow tooth in gap by magnet when rotor trailing edge is at post 1 This is what you want with the distributor seated. Rotor Phasing Anything done to the distributor externally, including the particular tooth stabbed, will not change rotor phasing, or the rotor tip position in relationship to the cap terminals when spark occurs. Rotor phasing, or the position of distributor rotor to cap terminal at spark, is controlled by shutter wheel-to-rotor relative position, the pickup position, and the position (clocking) of the cap on the distributor body. To change phasing, you have to relocate the rotor relative to mounting shaft and shutter wheel assembly, clock the hall cell with the vacuum advance lock (if the distributor allows this), or relocate the cap's clocking position on the distributor body. Moving (clocking) the cap is often easiest. Shortening the vacuum advance lock bar will make the spark fire with an earlier rotor position. You will have to retime the distributor if anything is altered. When the housing is rotated in the block, the cap and pickup rotate together the same degrees. This changes the timing of cam to housing, which changes the timing. Rotating housing to block always changes timing, but does not change rotor to cap phasing. When we pick a new tooth, it changes the shaft position relative to cam. This changes the timing of shaft to housing, which changes timing. Rotating housing position will move it right back, as long as it can rotate without obstructions. Picking a new tooth cannot change rotor phasing or anything else. A new tooth simply requires a new housing position to produce the exact same results. The tooth stabbed simply determines housing position for optimum timing. Change this position relative to affects Timing Rotor Phase Housing Position (for same timing) Housing block X Gear tooth stabbed cam X X Rotor clocking shaft X Cap clocking housing X Pickup clocking housing X X X Shutter clocking shaft X X X Note: A crank trigger system mechanically separates the trigger point for the spark distribution. The spark timing is from a crankshaft reference, while the distribution is from the cam. Because spark trigger reference is mechanically independent of spark distribution, rotor phase will vary with either distributor rotation (rotor and cap relationship) or anything that affects timing (such as crank sensor position). Be sure rotor phase is visually checked to center the rotor on the correct cap pin when mid range on timing. If the operating timing range is between ten degrees and 38 degrees, set the crank to 24 degrees BTDC on number 1 and center the rotor on terminal post 1 visually. This will make the rotor have a maximum error of 14 degrees as timing varies between 10 degrees and 38 degrees. If you make an error or have uncertainty, try to make the error in favor of the maximum advance setting aligning. The distributor has the following rules: Pickup, housing, and cap rotation as a group only changes timing The tooth stabbed only changes timing for a given pickup, housing, and cap position. It simply moves the housing to a new position for the same timing Rotating the cap alone only changes rotor to cap phase, it does not change timing Rotating the base plate and pickup assembly alone changes timing and rotor phase Rotating the shutter to the shaft position changes timing and rotor phase, it is exactly the same change as moving the plate assembly except opposite direction This is how distributors with pickups inside work. The rules above include optical, breaker points, and magnetic effect systems.
  7. SPArKy_Dave

    Help with dizzy wiring!

    When looking at the outside of the distributor - In order from left to right - Hall Effect Ground Hall Effect Power PIP Signal Output
  8. SPArKy_Dave

    GROUP BUY - DBA 4000 Series Disc Rotors

    Yeah that'd be awesome, it's definitely worth asking, for sure. Here's all the Ford numbers up to e-series - DBA4132S - EF/EL fronts 4000 series slotted heat treated rotors DBA4133 - EF/EL heat treated solid rears DBA4133S - slotted heat treated rear DBA4130S - EA-ED fronts 4000 series slotted heat treated DBA4111B - EA-ED and XG/XH heat treated solid rears DBA4111BS - heat treated slotted rear DBA4107S - XB-XG fronts 4000 series slotted heat treated rotors DBA4109 - XE/XF heat treated solid rear DBA4109S - XE/XF heat treated slotted rears DBA4108 - XD heat treated solid rear DBA4108S - XD heat treated slotted rears DBA4103 - XA-XC heat treated solid rear DBA4103S - XA-XC heat treated solid rears DBA4106HS - XW-XB up to 10/75 - heat treated slotted fronts H = Hub type without H = Hat type (DBA do a Hub type and a Hat type - assume hat type, is for race applications? - separate bolt on outer discs?)
  9. EXPRESSIONS OF INTEREST - potential group buy, of DBA 4000 Series slotted rotors, for XH's and e-series, and/or x-series. They're the Aussie Made premo heat treated T3 rotors, designed for Motorsport use, and/or fantastic on road stopping power. I've been running a set for a few yrs now with Bendix Ultimate pads, and they've been pretty awesome. Not one hint of warping. Unfortunately, DBA stopped making them for x-series and e-series, a few years ago. But they'll do a run of 25 sets as a special group buy, IF we can get the interest. Coupled with some QFM HPX or similar pads, they're about as good as you can get, if staying with the standard brake setup. The expected price would be north of $200 per rotor. These are NOT cheapo chinese made disc rotors. If the interest is there, we can also look at packaging them with NOK Brand Hub seals, and/or Timken wheel bearings (both the Genuine Ford OEM Brands) Any suggestions are welcomed.
  10. SPArKy_Dave

    GROUP BUY - DBA 4000 Series Disc Rotors

    I wonder if DBA, would still entertain a group buy? I'm not actually sure they even cast the rotors here in Australia anymore?
  11. This is interesting... since they're basically the same transmission, I'd guess they can be built for x-series too? https://www.hemiperformance.com.au/shop/reconditioned-hp-powermaxx-borg-warner-35-bw35-max-stall-converter-gearbox-package-race-spec-400-hp.html
  12. The clutch-pack size/diameter will always be the limiting factor, but... among other things, to up their power handling - use the BW51 3bolt rear servo assy, (either in a BW51 case, or modify an earlier case) fit the wider bands, Fit a lighter check valve spring to the front servo, to allow faster apply/release, fit heavier springs in the primary/secondary regulator valves to up the line/clamping pressure, and if you're really keen, reinforce the case around the bell-housing attachment area. Plus use the earlier Ford F-type fluid, as it should increase the friction/clamping ability of the clutches. Merry Christmas Rear servo Front servo spring Front Servo Primary/Secondary Regulator Valve (line pressure) springs
  13. Originally posted by user DEANKDX Copied over from another forum, due to importance. I bought this set http://cgi.ebay.com....rack=true��last August 2011 figuring the main issue would be wear sooner than TRW branded stuff. i did not expect a FAILURE in a part i assumed was one solid cast. seems they are manufactured in 2 parts... and the thin section of the broken part is approx 1mm which surprises me it lasted the 10,000km it did. this failed on a slow intersection turn without warning(approx 15kmh). you could only imagine what could happen if it failed at highway speeds. i'll be changing at minimum the other side one as precaution to a TRW brand which are closer to $50 each(still cheaper than a tow truck let alone a life or injury) THIS DISGUSTS ME TOTALLY, And although i know you get what you pay for.... you shouldn't be able to buy at any cost something so inferior (worn originals would be safer) if you have any suggestions for AUTHORITIES to contact regarding this i'd like to get the word out to prevent this crap from ending up on our roads. i plan to contact vic roads and RACV to pass this on to whoever will listen.
  14. Please excuse the fragmented nature, of the below info... I progressively update this post with copy/paste info, as I find it across the net. (latest updates - 09/03/20 and 24/08/20) _____________________________________________________________________________________________________ https://www.hemiperformance.com.au/shop/shop-by-category/transmission/manual-4-speed.html XB, all models including GT with 2v heads had the BW 0503-003. XC/XD 4.1/4.9 had the BW 0503-009 XC/XD 5.8 0503-008. 003 is 1st 2.82, 2nd 1.84, 3rd 1.32, 4th 1.00 - (4.9) 006 is 1st 3.06 - possibly (3.3/4.1) not sure on ratio's yet 009 is 1st 3.06, 2nd 1.84, 3rd 1.32, 4th 1.00 - (4.9) 008 is 1st 2.46, 2nd 1.78, 3rd 1.27, 4th 1.00 - (5.8) Ford never published the codes for XE and XF but the 1st gear ratios are XE 6 cyl. carb 3.43 XE efi & 302 3.06 XE 351 2.46 XF efi 3.40 XF carb 3.50 Other numbers XB Single Rail - 74DA-7003-AB 0503 006 3192 0503-006-3013 XD Single Rail? 78DA-7003-CB 0503-014 (8096) 76 DA 7003 AA 05 03 009 84 DA 7003 BA 0503 038 xd/e/f 0503 carby 1st-3.43 2nd-1.99 3rd-1.43 4th-1.00 rev-3.29 0503 efi 1st-3.50 2nd-1.99 3rd-1.32 4th-1.00 rev-3.47 0506 1st-3.47 2nd-1.96 3rd-1.26 4th-1.00 rev-3.37 0507 5spe 1st-3.47 2nd-1.96 3rd-1.26 4th-1.00 5th-0.79 rev-3.37 xa/b/c 0503-009 (4.1/4.9) 1st-3.06 2nd-1.84 3rd-1.32 4th-1.00 0503-008 (5.8) 1st-2.46 2nd-1.78 3rd-1.27 4th-1.00 A 250 or 302 single rail is rated to 285lb/ft, similar to a stock T5. A 351 single rail is rated to 325lb/ft which is the same as a Z-type T5. A std. wide ratio Toploader is rated at 375lb/ft and a bull nose 425lb/ft. BW single rail differences. All have same mounting flange, which is the same as the 3 speed box except for one bolt. Valiant has longer, finer input shaft, same output I think. Valiant has a short shifter shaft with a dogleg intermediate rod to clear the Valiant crossmember. Valiant has 2.84 first gear, so does cortina. Cortina has foward mounted shifter and short shift shaft with no intermediate shaft, extension housing is different to cater for this. Falcons all have rear mounted shifter and long shift shaft with no intermediate shaft. There are several ratio sets in falcons, from 2.54 first gear fitted to 351s, to 3.47 on xf type sixes. The highest torque rated box is the 351 at around 350lbsft. BW single rail. Valiant has 23 spline input shaft which is longer than the Falcon/Cortina box Valiant has different extension housing with different mounting and shifter to Ford types. P76 single rail is very similar to Valiant type, not seen many so couldn't say exactly what the differences are, if any. Repair kits should be the same, but you'd need to be a bit careful when its comes to extension housing output shaft seal. As far as I know all Valiants had same 2.84 first gear ratio gear-set. Falcons and Cortinas have quite a few gear-sets, I know of - 2.54 first gear (for 351s) also highest torque handing because of larger input gear. 2.84 first gear seen in Cortina six 3.06 first gear in 302s and six's until XE 3.54 first gear in later sixes. One extension housing in Falcon with corresponding shifter position. One extension housing in Cortinas with corresponding shifter position. This is what I was able to find off the net, and from books in the local library, for the 0503 :- Falcon XA & Leyland P76 2.78/1.93/1.36/1.00 Falcon XB & Charger E48 2.82/1.84/1.32/1.00 Falcon XC/XD/XE 3.06/1.84/1.32/1.00 Valiant VJ-CM 3.32/2.00/1.43/1.00 Falcon XE (4.1 carb only) 3.43/1.99/1.43/1.00 However, Ford used a 10-spline 1&1/16th" input shaft, but Chrysler and Leyland used a 23-spline 1&1/32nd" input shaft. Other XE Falcons got the "new" 0506 4-speed, or it's relative the 0507 5-speed. Single rails came in 4 variations depending what engine they were designed to be fitted behind. All are physically identical on the outside and are interchangable. To check which type you have, look at the small tag on the side of the box. 74DA 7003 A (up to 11/74) 74DA 7003 AB (11/74 onwards) 0503-006 (3.3/4.1) 0503-003 (4.9) 0503-009 (4.9) 1st-3.06 2nd-1.84 3rd-1.32 4th-1.00 74DA 7003 BA 0503-008 (5.8 inc GT) 1st-2.46 2nd-1.78 3rd-1.27 4th-1.00
  15. SPArKy_Dave

    Panko's Mk1 Escort (Round 2)

    https://www.ebay.co.uk/itm/FORD-SIERRA-GRANADA-CAPRI-TYPE-9-GEARBOX-TAIL-CASE-HOUSING-1096055/173926220330?hash=item287ecf822a:g:Qu4AAOSw3G1c-noJ https://www.firstmotion.co.uk/ford-type-9-gearbox-parts-spares/ http://www.gt6.ca/5speed/index.html
  16. SPArKy_Dave

    Boingk's F250 4x4

    An alcohol fueled stove? This reminds me of a simpsons episode -
  17. SPArKy_Dave

    Decoding your F-truck VIN/Chassis no.

    The VIN on the engine or car will be 6 characters long, for example, JG63UM or AL1JYM. These are decoded as follows; First character = Product source. A = USA, C = UK, J = Australia and S and U = Japan. Second character = Assembly plant. G = Broadmeadows - (Passenger), L = Broadmeadows – (Truck), H = Brisbane and K = Sydney 3rd & 4th characters = Body Series See below 5th & 6th characters = year and month of production respectively Therefore; A = USA source L = Assembled at Broadmeadows Truck plant 1J = F100 4x2 Y = 1981 M = March F-Series Body Codes 1J = F100 4x2 4K = F100 4x4 1T = F100 Bronco 2J = F250 3J = F350 5K = F350 4x4 4J = F500 6J = F600 1K = F700 2K = F750 3K = F800 and F8000 Now onto the engines. The engine codes for the F series trucks are unique and not linked to the passenger vehicles and are also relevant to the years of manufacture. Therefore, for the following years, the codes apply as follows; 1970 Engine D = 4.0 litre (240 CID petrol 6 cylinder) E = 4.9 litre (300 CID petrol 6 cylinder) T = 5.4 litre (330 CID petrol 8 cylinder) Transmission 4 = 4 speed 5 = 5 speed 1971 Same as above except for; Transmission 3 = 3 speed column shift B = 3 speed floor shift automatic 1972 Same as above 1973 Engine D = 4.0 litre (240 CID petrol 6 cylinder) E = 4.9 litre (300 CID petrol 6 cylinder) Transmission 4 = 4 speed B = 3 speed floor shift automatic 1974 (US Drive line) Engine L = 4.0 litre (240 CID petrol 6 cylinder) E = 4.9 litre (300 CID petrol 6 cylinder) Transmission L = 4 speed manual floor shift B = 3 speed floor shift automatic 1974 (Local Drive line) Engine L = 4.0 litre (250 CID petrol 6 cylinder) Y = 4.9 litre (302 CID petrol 8 cylinder) Transmission L = 4 speed manual floor shift R = 3 speed automatic 1975 Same as above except for; Engine E = 4.9 litre (300 CID petrol 6 cylinder) 1976 Engine L = 4.0 litre (250 CID petrol 6 cylinder) Y = 4.9 litre (302 CID petrol 8 cylinder) E = 4.9 litre (300 CID petrol 6 cylinder) Transmission L = 4 speed manual floor shift R = 3 speed automatic 1977 Same as above except for the 300 CID engine is no longer available 1978 Engine B = 5.8 litre (Pre-ADR 36) C = 5.8 litre (Post ADR 36) Y = 4.9 litre (2 wheel drive only) X = 4.9 litre (4 wheel drive only) L = 4.1 litre (Pre-ADR 36) H = 4.1 litre (Post ADR 36) Transmission L = 4 speed manual floor shift R = 3 speed Cruisomatic column shift 1979 & 1980 Same as above 1981 and onwards Engine W = 4.1 litre 6 cylinder C = 5.8 litre 8 cylinder (carburetor version) T = 5.0 litre (fuel injected) Transmission L = 4 speed manual floor shift R = 3 speed Cruisomatic column shift Now back to the model code. I will start with the easy ones first being the 1978 to 1981 F series trucks. As shown above, the ute in question had a model code of 62112 and it is this number that can be used in conjunction with the following code breaker to find out what you have. Model Digits 1 & 2 = Product line (more on this later!) Digit 3 = Year of manufacture (actually applies to all F series trucks) Digit 4 = Body style 1 – F100 Chassis Cab 2 – F100/250 Style Side Body 3 – F100 Ambulance and F350 Chassis cab Digit 5 = Series 1 – F100 Short Wheel Base 2 – F100 Long Wheel Base of F250 3 – F350 Short Wheel Base 4 – F350 Long Wheel Base So from the above model code of 62112, this equates to; F100 S-Cab, 1981 build year, F100 Chassis Cab, F100 Long Wheel Base of F250. Now onto the pre 1978 model codes. According to the book, there are heaps of model codes, especially so for the years of 1970 through to 1972 as the codes covered the F100 all the way up to the F700. Therefore, I am only going to cover a year that is more applicable, namely 1976. 62611 – F100A C.Cab 2972 mm W/B 2586 kg GVM 62612 – F100A S.Cab 3379 mm W/B 2586 kg GVM 62621 – F100A S.Box 2972 mm W/B 2586 kg GVM 62622 – F100A S.Box 3379 mm W/B 2586 kg GVM 62632 – F100A Ambulance 3379 mm W/B 2717 kg GVM 74611 – F250A 2WD C.Cab 3379 mm W/B 3448 kg GVM 74612 – F250A 2WD S.Box 3379 mm W/B 3448 kg GVM 73613 – F250A 4WD C.Cab 3379 mm W/B 3493 kg GVM 73614 – F250A 4WD S.Box 3379 mm W/B 3493 kg GVM 74631 – F350A C.Cab 3480 mm W/B 4536 kg GVM 74632 – F350A C.Cab 4089 mm W/B 4536 kg GVM As you can see, the two first numbers (Product Line) change according to the type of vehicle required. (info, courtesy of 'Paull', from Ford Australia Forums)
  18. SPArKy_Dave

    Xd aircon

    Yes I guess so, a broken b-series blend-door shaft, results in the HVAC system blowing both hot AND cold at the same time. (often each temperature extreme, out differing vents) Hence - schrodingers blend-door shafts. E-series mid/high series do it too, but it's the blend-door motor which fails, generating the dreaded E2 climate control error code. Both are dash-out fixes.
  19. SPArKy_Dave

    Xd aircon

    Glad someone understands my autistic humour.
  20. SPArKy_Dave

    Xd aircon

    B-series have schrodingers blend-door shafts...
  21. SPArKy_Dave

    Xd aircon

    Only... sometimes it doesn't.
  22. SPArKy_Dave

    Xd aircon

    329-412 is an Ashdown-Ingram number, equivalent to the 9041. TX9041 2 tonnage 4.4degrees Superheat TX9015 1.5 tonnage 2.8degrees Superheat I'd stick with the TXV you have, and start there. In a nutshell, the higher capacity TXV's (tonnage) requires a higher superheat, to ensure all the refrigerant gets boiled to a vapour within the evap core, before reaching the compressor. Since liquids don't compress, the compressor will not fair well, if it has to deal with liquid refrigerant. 12.000 Btu = 1 Ton When air is cooled or heated, the heating or cooling of the air is called sensible heating, and heating or cooling of water vapor in the air is called latent heating. The cooling process takes place at the evaporator. As warm moist air moves across the coil the water vapor condenses and is removed from the air, this is commonly seen as water dripping from an air conditioning system. A large amount of energy is required to heat or cool the water in the air. It is therefore important that we know both temperature and relative humidity of the air to calculate how much heating or cooling is taking place. This is especially important to get a more accurate system efficiency calculation. The amount of heat (sensible and latent) in air is referred to as enthalpy. R12 and R134a refrigerants are pure refrigerants - ie, azeotropic. Hychill, is a Zeotropic refrigerant (blend of R600a - isobutane and R290 - propane). Zeotropic refrigerants have a wider evaporating/condensing temp range. When evaporating, the most volatile component will boil off first and the least volatile component will boil off last. The opposite happens when gas condenses into liquid. for a given pressure, the temperature will change in the liquid-vapor mixture region. This results in a gliding evaporation and condensing temperature along the heat transfer surface. In practice, the saturation temperature at the inlet of the evaporator will be lower than at the outlet. In the condenser, the saturation temperature at the inlet will be higher than at the outlet.
  23. SPArKy_Dave

    Boingk's F250 4x4

    You're saying, it had 125 thou ring gaps? It actually ran like that! And I thought my F-truck ring gaps were bad at 45thou, against a 20thou stock service limit. Cleveland's are amazing... I prefer soft cast rings, (which preserve the bore's), any day of the week! So 3-6thou piston to cylinder wall gaps? (half that, over the circumference) What mic's and dial bore gauge, do you have? I've got a set of Mitutoyo 103 series mics, and I'm looking at their bore gauge options, atm. Spoke to their local rep, the other week.
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