Open Road

Hey, all you parts hoarders, I am in need of one piston that is in the first oversized tolerance group. I have an S4 block that I am rebuilding, and I discovered one of the cylinders has some corrosion in it and will need to be bored out a little. There are no oversized pistons available from 928 International or from Porsche dealers. I am hoping someone may have one hiding away someplace or may know of a resource I would be very grateful. I'd hate for this block to not get rebuilt.

Here are the part numbers:
928-103-0430-59 (100.48mm)
928-103-0430-69 (100.49mm)
928-103-0430-79 (100.50mm)



Here is the cylinder and piston damage

Good luck.

Or time to go big-bore 104 mm…

good luck Mike, been following your thread on TOS. Hope you can find just the one.

you might want to have that bore skimmed just to see if it will clean up. not all the way to the oversized dims but split the difference between the current bore. I'd hate for you to scrounge around and pay top dollar for one piston only to find the block won't clean up. S4 blocks are not good for strokers. 85-86 blocks are thicker & better choice for a stroker.

Thank you for all the feedback.

@maddog2020 I brought the S4 block to the machine shop that will be doing the work. They looked at the surface damage. The current bore diameter is 100.00mm. The damage was not something that would be able to be cleaned up by honing alone. They recommended removing enough material to require a 1st oversized piston. They recommended going to 100.500 - 100.520mm bore.