JE or CP Pistons in Stock Barrells???

[K24madness]

I keep hearing conflicting reports of the success of using JE or CP pistons made of 2618 alloy in stock barrels because of the expansion properties of them. Can anyone that has used them please chime in.

Thanks
Tom

[Steve@Rennsport]

Tom,

2618 does expand at different rates than the proprietary Mahle alloy so they do need more clearance, however the most important aspect is the design of the forging and what running clearances are specified in application.

We use JE & CP's but they are made to our specifications so they run tighter than most off-the-shelf applications.

[JeremyD]

I would use JE's with Nickies or Mahles with Mahles.

If you are dead set on JE's with Mahles - then I would defer the entire build to someone like Steve Weiner who can do it right with the clearances or you'll get a motor that either preassurizes the case or has piston slap - or wears incredibly fast or all three.

[K24madness]

Originally Posted by Steve@Rennsport

Tom,

2618 does expand at different rates than the proprietary Mahle alloy so they do need more clearance, however the most important aspect is the design of the forging and what running clearances are specified in application.

We use JE & CP's but they are made to our specifications so they run tighter than most off-the-shelf applications.

I am having custom pistons made.

I spoke to CP and they will take my barrels and measure them just to confirm the sizing. They told me .0018-0020 is what they are going to set them for. Does this sound right to you Steve?

CP will scan my current piston so I can maintain the same combustion chamber floor. The piston will use the X forging with narrow pins and MIL lightning. This should be a strong light piston.

[haycait911]

Originally Posted by JeremyD

I would use JE's with Nickies or Mahles with Mahles.

If you are dead set on JE's with Mahles - then I would defer the entire build to someone like Steve Weiner who can do it right with the clearances or you'll get a motor that either preassurizes the case or has piston slap - or wears incredibly fast or all three.

how does the pressurizing of the case happen? what is the piston/cylinder relationship that causes this? thanks Don.

[Flieger]

I would suspect excessive piston/cylinder wall clearance allowing combustion gas blow-by could cause the case to pressurize.

On the other hand, I suppose tight pistons could trap air in the case if the breather is not sufficient.

Wouldn't the rings have a seal no matter what, largely negating the importance of piston/cylinder wall clearance other than preventing "slap"?

[JeremyD]

Yes - unless you have your end ring gap dead on - and your piston to cylinder clearance precise - you may be subjected to piston blow by. As the pistons increase in temp - they expand in the jug [in some cases faster the the jug] which can tighten up the tolerances.

IF the tolerance is too loose [piston to cylinder] you get some slap, especially during warm up. If you have it too tight - when the piston starts expanding it can create excessive wear.

Do what you want - but this was an expensive lesson for me.