Oddjob

About 3000 miles since the last time the head was off. Been running 110 leaded for a handful of years now. Haven't seen this much build up before, and certainly haven't had a difficult time cleaning it off. But I can't get the pistons cleaned up. Is it lead?

Lacquer thinner, brake parts cleaner (TCE), toluene and tooth brush, plastic putty knife. I don't want to use mechanical/abrasives due to the risk of damage to the piston.

A little concerned as there is slight build up on the side walls above the #1 ring. Bores look good, so hasn't caused any obvious damage to the cylinder walls.

Ultrasonic?

Other solvents?

951and944S

Do you know for sure the history of these pistons Jim...?

Could they have been ceramic coated and it just burned away...?

You could mask these and glass bead blast just the tops.

Swain does ceramic thermal barrier coating for $26 ea (I use on the NA engines) and they have an extreme duty coating called 'gold coat" specifically for turbo apps.


T

Oddjob

I don't know the full history. They are out of a Steinel built engine that came in the Escort car, and I was told they had a thermal Swain's coating on the tops and a different coating on the skirts. But I can't see anything by looking at them (skirts look like factory to me?). This is the first time I've pulled them out, but the last time I had the head off, the tops didn't look like this. And they cleaned up pretty well without major effort:

Oddjob

Will they clean them, or do you have to send them in blasted ready for coating? Probably worth $26 just to get them cleaned off....! What's their turn around time?

951and944S

I think they do clean but there's an upcharge.

I always clean my own stuff before I send.

Maybe the reason they were so easy to clean the 1st time is the ceramic was still intact (like teflon on a frying pan) and then some tuning issue cause a level of heat or detonation that the coating could not withstand (appearance this time).

Knowing what you divulged in the 2nd post, I'd bead blast the entire piston.
I hit mine with a detergent/acid to remove all oils and open the pores, air dry them and I don't even them come in contact with bodily oils from my hands etc.

Do ceramic on the tops and PC9 on the skirts.

Obviously your block is out, so the piston may grow in outer dimension, you can have your machinist just perform the fine "polishing" stage and then hone with paste.

The PC9 can go as thick as .004" but the kicker is, stock 100mm rings will have too large a gap by the time cylinders are sized to pistons.
You have to get either a custom set (I use Don Weaver at EBS Racing - Total Seal, there should be a reference for ones I have spec'ed before $120) or you have to go to the +.5mm ring.
This is a negative compromise, as while you can grind to the correct gap, the 100.5mm ring will have unacceptable (for me) tension loaded in a 100mm + 004" bore.

You'll have near $200 in the coatings 4 X est $40 ea, not to mention time cleaning, shipping two ways.

Maybe consider the Wossner forged 944T piston and go +.5mm @ $600-ish a set.
Poeltl should be able to get you these PDQ.

T

michaelmount123

If you bead blast pistons, BE SURE to tape off the ring grooves! Otherwise, you chance ruining the ring seal. Ring groove dimensions and surface finish are critical. Masking tape works fine. Cleaning the piston afterwards is another critical step. Since there will be residual bead blast material imbedded in the surface, I wash them in a hot spray washer (virtually all machine shops have this machine) and blast with high pressure air while still hot.

michaelmount123

Strictly my opinion: I wouldn't get anywhere near a wire wheel with a piston. Further, why worry about the piston tops? They're just going to look nasty again after running the engine. I'm afraid those without access to the proper equipment will do more harm than good.

Okay, more food for thought... Any used piston (street or track) is likely worn out and unsuitable for a properly reconditioned engine. I know, I know, your pistons look great and the bores look fine. What will be worn is the ring grooves! I've proven this on the dyno where ring grooves on used pistons were measured with plug gauges and appeared fine, but blow-by was an issue. It took fresh pistons to seal up the cylinders. Porsche always changes pistons during a rebuild and this is why.