Cracked piston?

[judgetread 758]

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?

[Ando81 2,949]

I'm glad he didn't recommend for me to stroke it

[hendrixhc 10,921]

No ill leave all the perverted stuff to unfamilia. i just like shiny metal!

[gerg 10,871]

Happy times!

[deankxf 20,294]

could of been a scratch from a piston ring being installed

[CHESTNUTXE 7,317]

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.

[bear351c 10,271]

Yep. me too.  And ring expanders are SO expensive...................not.!

[Nath 1,975]

Yep. me too.  And ring expanders are SO expensive...................not.!

Yeah I hear the price on sex toys is going up.

[Ando81 2,949]

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

[Lord_fahrquhar 2,580]

If only the plumber could remove their crack as easily

[Ando81 2,949]

Ha ha, some plumbers would need a lot of wet & dry to remove the crack

[slydog 7,873]

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.   

[Ando81 2,949]

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

[slydog 7,873]

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.

 

It's math but easy enough to do.

[ando76 4,354]

Or use doctor Google and type in compression ratio calculator and bam. Add your figures and you have it sorted

[FORD_MAN 1,026]

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

[Ando81 2,949]

Thanks mate, I'll have to get around to measuring the head and do the sums. Great link too by the way

[Ando81 2,949]

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?

[slydog 7,873]

Ohhhhh I'm far from keen on that comp with that camshaft.Not enough overlap to bleed off un-needed compression IMO.

 

 

Id like to see 10.1 - 10.5 at most with that camshaft.

[ando76 4,354]

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.

[Ando81 2,949]

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.

[PRO250 1,506]

11.5 with flat tops is easy I managed 13.5 once would have been  a mint methanol engine I recon

[wagoon 2,429]

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.

[wagoon 2,429]

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.

[Ando81 2,949]

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.