judgetread 758 Posted December 3, 2015 Id get the autosol out and polish it til you can see your teeth in it. You are talking about tthe piston yeh? not anything else? 2 Ando81 and dougie77 reacted to this Share this post Link to post Share on other sites
Ando81 2,950 Posted December 3, 2015 I'm glad he didn't recommend for me to stroke it 2 Outback Jack and judgetread reacted to this Share this post Link to post Share on other sites
hendrixhc 10,922 Posted December 3, 2015 No ill leave all the perverted stuff to unfamilia. i just like shiny metal! 1 Ando81 reacted to this Share this post Link to post Share on other sites
deankxf 20,362 Posted December 4, 2015 could of been a scratch from a piston ring being installed 1 gerg reacted to this Share this post Link to post Share on other sites
CHESTNUTXE 7,363 Posted December 4, 2015 That mark on the piston is from putting the ring on incorrect,it was put on by hand and slid around the rim and the sharp end has cut the top of the piston as it goes over the piston then into its grove,i have seen this so many times on engines. 4 bear351c, Ando81, Outback Jack and 1 other reacted to this Share this post Link to post Share on other sites
bear351c 10,276 Posted December 4, 2015 Yep. me too. And ring expanders are SO expensive...................not.! 1 Outback Jack reacted to this Share this post Link to post Share on other sites
Nath 1,975 Posted December 4, 2015 Yep. me too. And ring expanders are SO expensive...................not.! Yeah I hear the price on sex toys is going up. Share this post Link to post Share on other sites
Ando81 2,950 Posted December 4, 2015 could of been a scratch from a piston ring being installed  I'm pretty sure you've knocked the nail on the head there mate! Well done Share this post Link to post Share on other sites
Lord_fahrquhar 2,580 Posted December 11, 2015 If only the plumber could remove their crack as easily 1 Outback Jack reacted to this Share this post Link to post Share on other sites
Ando81 2,950 Posted December 11, 2015 Ha ha, some plumbers would need a lot of wet & dry to remove the crack 1 Outback Jack reacted to this Share this post Link to post Share on other sites
slydog 7,873 Posted December 12, 2015 What's your cyl head like ? Have you measured the chambers ? You could end up with WAAAAAAAAAAAY to much comp on too small a camshaft and have nothing but a rattle tin. Compression HAS to match engine components and use which means measuring needs to be done not guess work. If it's been decked the block or head that is it WILL have a effect on compression. Â Â 1 Ando81 reacted to this Share this post Link to post Share on other sites
Ando81 2,950 Posted December 12, 2015 The bloke at the machine shop is going to double check it all for me. He's done quite a few warm crossies for speedway blokes and seems to know his shit. From what you're saying, I now understand why he insisted he looked at my cylinder head and cam specs before he would put the pistons in for me. He must be going to cc the chambers in the head before he makes a ticking time bomb. Thanks for the handy tip mate 1 Outback Jack reacted to this Share this post Link to post Share on other sites
slydog 7,873 Posted December 12, 2015 It's not hard for you to do bro,if I can do it any one can.You need a syringe with cc gradients and a CD cover or flat perpex to cover a chamber. Small hole in 1 corner then lite smear of assembly grease or vaso around chamber to create seal,add fluid be it trans fluid or water and measure when it's full. apply the math and there's your chamber size.Add your 40th head gasket and your piston dish,bore size and your set. Â It's math but easy enough to do. 1 Ando81 reacted to this Share this post Link to post Share on other sites
ando76 4,354 Posted December 12, 2015 Or use doctor Google and type in compression ratio calculator and bam. Add your figures and you have it sorted 1 Outback Jack reacted to this Share this post Link to post Share on other sites
FORD_MAN 1,026 Posted December 13, 2015 your current RA4103X .040 pistons has a 28cc dish. 3.72" bore, 3.91" stroke, gasket bore 3.75" x 0.041", Head ??cc, new piston ??cc  Hypertec do a 20.5cc, acl made 4102 & 4105 is 15cc, https://www.uempistons.com/index.php?main_page=calculators&type=comp&zenid=794fcc0c0ddca582949a420331659388 2 Ando81 and slydog reacted to this Share this post Link to post Share on other sites
Ando81 2,950 Posted December 13, 2015 Thanks mate, I'll have to get around to measuring the head and do the sums. Great link too by the way 1 slydog reacted to this Share this post Link to post Share on other sites
Ando81 2,950 Posted December 13, 2015 So I put in the figures into a calculator and with a 50 cc E2 head it said my compression ratio with flat top Pistons would be 11.5:1 Does that sound about right and would it be ok for a 208@50 cam with 110 degree lobe separation? Share this post Link to post Share on other sites
slydog 7,873 Posted December 13, 2015 Ohhhhh I'm far from keen on that comp with that camshaft.Not enough overlap to bleed off un-needed compression IMO. Â Â Id like to see 10.1 - 10.5 at most with that camshaft. Share this post Link to post Share on other sites
ando76 4,354 Posted December 13, 2015 Get it up about the 230@50 and it will love that Comp. Me - I don't mind a dish piston at all. I'd rather have a dish piston and zero deck height than a flat top .030 or more down from the deck. Dish helps with squish, especially with the open chamber of the E2 head. But each to their own. 2 Outback Jack and slydog reacted to this Share this post Link to post Share on other sites
Ando81 2,950 Posted December 13, 2015 All comments taken on board thanks lads. I might let the machine shop decide for me. I reckon my calculations may be wrong as that number seems pretty high to me. Share this post Link to post Share on other sites
PRO250 1,506 Posted December 13, 2015 11.5 with flat tops is easy I managed 13.5 once would have been  a mint methanol engine I recon Share this post Link to post Share on other sites
wagoon 2,429 Posted December 13, 2015 I dont think your sums are wrong. My head is 42cc combustion chamber and piston is 29cc with a bit of work so not exactly sure on cc, but it hasnt been skimmed a lot. I was told my comp is 10.3-10.5 by my machinist. Share this post Link to post Share on other sites
wagoon 2,429 Posted December 13, 2015 My machinist had a choice to use either 20cc or 29cc dish pistons but didnt want to use the 20cc as it would make the CR around 11 and wouldnt suit pump fuel. Share this post Link to post Share on other sites
Ando81 2,950 Posted December 13, 2015 Did I mention that I'm going straight gas with this motor? Can I get away with higher comp with gas? And I am well aware that some gas is way better quality than other suppliers. Share this post Link to post Share on other sites