Pitted cylinder wall and chipped piston

[1987 Porsche]

I recently purchased a used set of mahle pistons and cylinders from a fellow pelican. I then sent them to Body Motion in NJ to have the tolerances checked, honed, and rings installed on the pistons. Today I was placing the pistons in the cylinders and then on the case and noticed one cylinder wall had some light pitting and one piston had a chip near the top compression ring. I would appreciate your thoughts on how to proceed. Thanks.

Lou

[Walt Fricke]

Send the pictures to Body Motion maybe and ask them their opinion? I doubt either defect was caused by any work they did, so these used parts most likely came this way. Did you inspect them after you purchased them?

Real engine builders might have a different view, but I'd not be too worried about the small pits in the cylinder wall. Are they above where the top ring gets to? But the cylinder could be reconditioned by US Chrome or one of the other outfits which can reNikasil cylinders and bore them to size.

The chip in the piston might be a different story. What you hear about with used pistons is broken lands, or ring lands which have worn too wide.

[Mark Henry]

Tiny pits on nikasil is common and doesn't affect performance. The pit on the piston looks like a casting flaw, likely won't hurt anything. Walt is right about the lands, that would be one of the first checks before getting into the job.

But I don't like the finish on the cylinders, looks way too coarse.
BTW I am an engine builder

[1987 Porsche]

Walt,

Thanks for the reply. Your right, Body Motion did not do this. They were great to deal with and very knowledgeable. These were flaws that I should have noticed prior to sending them out. Hopefully I can continue this build with this particular cylinder and piston. Ill wait to see what the overall consensus is. Thank you

[1987 Porsche]

Walt,

The pits are even with the top ring.

Mark,

The piston chip does run under the top of the ring land. The gap was checked by Body Motion and was good. So you think it may just be a casting flaw?

[1987 Porsche]

Here is a better picture. It runs under the top of the ring land not along the side.

[Walt Fricke]

Interesting flaw.

Some pistons and rings have holes to direct combustion chamber pressure to the rear of the top ring in order to give more outward force/seal on the ring.

My guess is that, since there is no evidence of burning coming down from the piston crown, this wasn't due to an excessively lean mixture - the kind which might burn valves and so on.

Ring gaps don't stay put. And the gap when in a cylinder is going to be narrower than that flaw is wide.

I've run cylinders with a few little pits. I'm cheap, and not really a perfectionist. I've not seen an issue like the piston, though.

[Mark Henry]

I agree it is odd, I can't see it being a chip, I'd say it's a flaw. As long as the ring spins freely, it not a hole and everything is in spec I don't see it causing an issue on a stock-ish engine.
But honestly I've never come across this issue before

[K24madness]

While it’s far from ideal I doubt it would cause any problems. Just make sure the rings move smoothly around that defect.

[dannobee]

I seriously doubt that the piston came from the factory like that. Actually, I'd bet money on it.

The more I looked at it, the more I thought it was detonation damage (although on 911's, it's usually closer to the exhaust valve). Which cylinder was this? Were the numbers marked before disassembly? And does it correspond with the pitting on the cylinder? And what's up with the groove for the CE/head gasket ring? Where did that nastiness come from?

[1987 Porsche]

The pistons and cylinders were marked when I received them. The piston in question is #6 and the cylinder is #3.

[dannobee]

Do any other pistons show damage? If isolated to the one piston, maybe something restricted airflow to #6. Dunno. It’s quite common for pistons to have “anti detonation grooves” machined above the top ring to kill the pressure wave when detonating.
I’ve seen similar damage on 930 pistons, btw.

[Henry Schmidt]

Judging by the corrosion on the the cylinder CE ring groove, my guess is that the Ps&Cs were stored with some moister. The damage to the piston looks like corrosion to me.
If the ring move freely, my guess is that the piston will function properly.
The pitting on the cylinder is minimal and should work as well.
If I was building this engine, I would source another piston if possible, and have the cylinders (all six) coated with Nikasil to achieve a new dimension as well as a more efficient bore material.
That would of course facilitate the need for a ring set better suited to Nikasil.
That said, using what you have is a gamble but may be well worth trying.

[tom1394racing]

Here is a good replacement piston if you decide to go that route.

Mahle 95L67 9.3 CR

[1987 Porsche]

Everyone thanks for the replies. I ended up talking with Tom and will be sending him out my cylinder to find a piston to match.