Alan 91 C2

The machine shop media blasted the pistons, so now the skirt has a roughened surface. What are my options?

I expected the piston crowns to be blasted, but not the skirt. Are these skirt coated by Mahle, or are they just raw/machined aluminum?

Alan 91 C2

What is the normal treatment for the piston skirts? I guess I can clean the skirts up with some ScotchBrite red scuff paint pads to minimize the skirt growth.

In all my previous rebuild work, I cleaned the pistons, wire brushed the tops,and only used solvent on the skirts.

any comments?

onevoice

It was not uncommon a long time ago to blast the entire piston, but I have not seen that done lately. The roughness should not be a problem if it was done with small media. You can talk to the shop, but they've probably been doing it that way for 50 years. It's more on the side of low buck tractor repair than general Porsche rebuild, but will get you down the road.

For a precision rebuilder, it is completely unacceptable.

Of course $4-5k for a set of P&Cs is unacceptable also. If they measure in spec, and the ring side gap is good, I'd use them. Clean them very well, IIRC there were questions in the past about blast media embedding in AL parts and finding its way out when the motor is run.