Is This 92mm Piston Toast?

[andrew15]

I'm pretty sure that this is a done deal but - Is this piston done for? It's not cracked - just pitted a lot. It's a Mahle 92mm piston and the corresponding cylinder looks like it had part of the lip inside the sealing ring break off and float around for a bit



P.S. Zak is already checking to see if he has a spare - any other leads would be appreciated

Regards,
Andrew M

[911pcars]

Inspect and measure the piston for wear: ring grooves, O.D., and piston pin bore. If they meet spec, then you should be able to reuse. The piston shouldn't have any sharp edges or stress risers. Do the same with the cylinder.

"...part of the lip inside the sealing ring break off and float around for a bit."

Do you mean a piston ring broke off?

Sherwood Lee
http://members.rennlist.org/911pcars

[andrew15]

Thanks Sherwood!

No the piston rings didn't break, they are all fine - The ridge between the CE Gasket on top of the cylinder and the actual cylinder bore broke off. I've tried to demonstrate in the hijacked picture below:



The red portion is what broke off.

Regards,
Andrew M

[andrew15]

Here is a better picture of the damage. There is pitting only on the exhaust side not the intake side:



Thanks,
Andrew M

[emcon5]

Damn. Looks like someone with a drill press got angry with your piston.

Tom

[350HP930]

As minor as the damage is you should also have someone check the connecting rod and pin bushing.

[Steve@Rennsport]

This is not uncommon for this generation of 92's and they are no longer being made like that to prevent these failures from occurring.

[Bobboloo]

Steve,

Could you elaborate?

Are they still using the CE gasket cylinder type?

The reason I ask is because I'm building a motor that I was planning to bore a set of 90mm Mahles out to 92mm and have them re-nickasil plated so I could use 92mm JE pistons. So I'm wondering if I run the risk of the same cylinder type failure as I was looking at going with a 10.3:1 ratio.

[Wayne 962]

Just a guess, but I would say it's unlikely that a piston that had sustained that level of damage would meet spec on the ring grooves. Just a guess though. Tom Woodford at 1-760-731-7535 might have a used one for you. Tell him I said hello!

-Wayne

[Steve@Rennsport]

Originally posted by Bobboloo
Steve,

Could you elaborate?

Are they still using the CE gasket cylinder type?

The reason I ask is because I'm building a motor that I was planning to bore a set of 90mm Mahles out to 92mm and have them re-nickasil plated so I could use 92mm JE pistons. So I'm wondering if I run the risk of the same cylinder type failure as I was looking at going with a 10.3:1 ratio.

Hi Bobby:

Mahle has been making 92's without the CE grooves for a few years now. These fit directly against the heads without any sealing rings, just like the late-model stuff.

From what I've seen, they are more durable than the ones requiring CE rings in these very thin wall cylinders.

I think you'll be just fine; I've done quite a few of these Nikasil and Alusil cylinders with 92mm JE's and Nikasil-plated bores for race engines. IMHO, deck height issues and detonation are the prime contributors to problems here, and just be sure of your CR calculations. I'm assuming that you are running twin-ignition and/or race gas.

[andrew15]

Thanks Guys - I'll check the ring grooves and rods.

[Bobboloo]

Steve,

Yes, twin plug and pump gas.

Thanks for the info.