Ebay P&C evaluation
 

I got this new set of Alusil pistons and cylinders on Ebay and they were delivered today. Well, I unpacked them and they do look new but they aren't a matched set. I brought them up to the shop and began to take some measurements and everything looks good and I do believe they are indeed new but there was one cylinder from a different height group (group 6 instead of 5) and it measured to be .0008" taller than the rest. I also had two heavy pistons. The pistons weighed at:

656.5
654.1
653.8
659.8
653.4
659.7

The ring to land clearance was .07mm on all of them as well. So any thoughts? Are these usable as-is? It seems like .001" could easily be sanded off the cylinder and the heavy pistons could be installed on opposing cylinders to balance each other. Any other measurements I should be looking at? Comments would be appreciated.

Also, I got 190k miles from my previous set of Alusil pistons so it doesn't bother me to throw another set in there. They were also a pretty good discount over new Mahle's.

Bullet Bob,
Porsche factory spec's for piston weights use a range of 8 grams. These pistons fall within the 8 gram spec. Obviously assemble with the heavier pistons opposite on down to the lightest.
Doesn't seem like much of a challenge to fit the taller cylinder.
I would check the diameter of the pistons vs. the cylinders.
The tolerance for each size group is 0.025mm to 0.045mm, Piston to cylinder diameter.
More important than the other dimensions.
I can be more specific if you'll share the piston and cylinder size.

I measured all of the pistons and they were all within 94.980mm and 94.983mm. I haven't yet measured the cylinders but I will tomorrow.

Thanks,
Bob

Bob,
From my Bentley, 94.980 to 94.985mm pistons are paired with code 1 cylinders measuring 95.005 to 95.010mm.
Good luck,

I had a closer look at the P&Cs and half of them are paired with the matching cylinder but there are a few that are off (#3 piston w/ #5 cylinder). I'm not sure if I am doing it correctly but I am going based on the numbers stamped on the cylinder skirt and the piston dome. The pistons have a + or - on the dome along with a number and the cylinders have the height class and diameter class stampings.

Getting accurate measurements on the cylinder ID is pretty tricky. Would .001" difference make or break one of these engines?

Thanks,
Bob

Good Morning Bob,
Looking at the specs for KS pistons and cylinders, we see a tolerance of .025mm to .045mm.
Translated to inches we get .025mm is right at .001" and .045mm is just under .002".
I would suggest any cylinder measurements be accurate to .0001", one ten thousandths.
Your pistons are from 94.980mm to 94.983mm, a difference of .000118", or just over one ten thousandth from the smallest to the largest.
If the cylinders run from 95.005mm to 95.010mm to match the pistons you have, I would match the smaller pistons with the smaller cylinders and the larger pistons with the larger bores to keep the clearances as close to one thou as possible.
Yes, we are talking about very small tolerances, but worth your time to match pistons with cylinders.
You wouldn't want some clearances running 8 ten thou and others running 12 ten thou when you could make them all closer to 10 ten thou by carefully matching them.
I hope this is useful info.