Shaving the pistons....

[BobT-47P15]

A fellow told me the other day he bought a set of new pistons for his

48 P15. They were larger than the stock size. So he took them to a

machinist who said they have to be machined down to the needed size.

But, he said, there are not many guys around nowadays who could or would do that.

However, the man did machine them to original dimension.

So, now, I guess they would be ok if the cylinders did not need to be

bored out to oversize. If bored, then I suppose a sleeve would be needed

to bring back to original specs??

Have you ever heard of machining the pistons down in size??

[greg g]

Yea but. Our stock pistons are oval ground to allow the skirt to expand with heat and contact the cylinders. I wonder it a turned piston would work as well.

[Plymouthy Adams]

took the words right out of my mouth Greg...

[Suddensix]

Back in the day when I was in the parts business you could buy "semi" pistons that were way oversize then you would turn them to fit your application. Usually reserved for odd ball engines.

[Norm's Coupe]

Yea but. Our stock pistons are oval ground to allow the skirt to expand with heat and contact the cylinders. I wonder it a turned piston would work as well.

Have no idea if the old pistons in my coupe were oval shape or not. Looked round to me, however don't know if they were the originals either.

That said. If you buy new pistons regardless if over bored they look round to me to. At least the ones we put in were round. They are over sized to match the bore in the block though. So, with that in mind if you used shaved pistons to fit the new ground round piston port, why wouldn't that work out as well.

Reason I say this is, you can't put an oval shape into a round hole. It would be like trying to put a square peg in a round hole.

[BobT-47P15]

The fellow said he paid three hundred something (maybe 385) for those pistons that had to be ground. Don't know where he got them.

[greg g]

Top of the piston is round. skirt area is oval ground, probably opposite of the wristpin and so slight you wouldn't notice if you weren't looking. I think it's a matter of .0003 If the piston were to grow semetrically it would get stuck on the cylinder. Or at least cause a lot of friction.

[Niel Hoback]

If you ground the OD of the pistons, would you not also have to deepen the ring grooves?

[Don Coatney]

If you ground the OD of the pistons, would you not also have to deepen the ring grooves?

I would think so.

And I agree the piston shirt is ground slightly oblong to help eliminate piston slap. But you will not see it with the naked eye. You will see it very clearly with calipers.