turning piston diameter down

A friend of mine has a set of JE gas ported pistons that are .060 0ver .They have lite scratches on the skirts. He's going to toss them. Could they be turned down to a .030 over size? and if so at what cost.

Is it possible to clean them up at .055" over?

Brian

Pistons are not round top to bottom. AND, there is different diameters, so to speak, at the egg shape. As such, it is not a one cut deal on a lathe.

But, never machined a piston myself, may it is possible. Be interested to hear from real experience.

I'm sure they would clean up at .055 .I just never heard of it being done or how the piston would beheld to do the turning.

Years ago I had a set of .060 over oem pistons turned undersized so they would check legal for a NHRA stocker. It was done somewhere in Detroit, but the engine builder never revealed his source. Whoever did the job cam ground them to the same specs as TRW pistons. Going fast in a NHRA stocker was never cheap.

I had a set of 9second Phils pistons hard anadised in SO CA to save them, he had a bad set of solid lifters that the tops started failing allowing pieces of them to get embedded into the forged Ross pistons skirts, they where 4.080 340 pistons and he didn't want to go to the next size bigger so we saved them by doing what we had done That company was a aerospace company and they won't do them anymore that company made them exactly the same size as they where new, we could of had another .0010 to .0030 added onto the diameter of the skirts for no extra costs
On your deal I wouldn't hesitate a second to look at some of the current coatings out there now to save them
Don't take a chance on doing anything not proven, it ain't worth it to take a chance on any Hi Po motor parts

Finish on piston has a lot to do with how they run also. We were shocked on our hi reving 2 strokes engines what a difference finer or coarser finish would do on power. We would make one in the cnc lathe and dyno an engine. Depending what the power was like we would change it and try again. We tried different finish on the turning getting better and also getting worse on our results. Once we found what we like we ran all of our pistons this way. That is one advantage of having everything in house.

Another thing to keep in mind is that the two different alloys will look a lot different on the skirts, the tight alloy look a lot worse after use than the looser alloys do with the same abuse
My message is to measure them to see if there hurt or not
Don't always trust your eyeballs when it comes to judging race parts Check them out thoroughly first before making any decisions on race parts, just like you should on women

Got a pic of the worst one?

If they are just lightly scuffed I'd use them..
I have used some fairly ruff ones.. just use
a stone on them.. you will be surprised.. I have
had 1 set coated and they are still working well
on a street engine

If the skirts are the only thing wrong why not just get the skirts coated???

How much does the coating add in thickness?

I had .004 added to a set.. they can add more

I would say all if not all NASCAR engine builders turn their own pistons.

I talked to a engine builder and had him look at them, he said he'd run them as is . This of coarse changed my game plan of getting a free set of $800. pistons as the owner of them was there also. Now he's peed as he bough a new set on advice of another builder.

Make him a offer of a little less than 40% and
see what happens(this based on how they look)

No, the only team turning any pistons is Hendrick.

Fellaz, what about the ring fitment. Won't the inside diameter of the ring pinch the piston inner groove?

Only if you don't check the back clearances properly
I shoot for .005 minimum with the rings pushed all the way into the ring lands, 1st,2nd and 3rd rings
If it has more than .025 it is time for ring spacers

I talked to him last Wednesday and he said after he thought about what the engine guy said about still being usable , he said he was going to keep them. I'll bring it up once in awhile as he probably won;t ever use them as his block is bored to the next oversize.

Cut them loose and forget about them. Not worth the time and money to consider them at this point.

They can set under my bench just as well as his. LOL

Really?

Last I heard couple years ago.

A place called Combustion Technologies was roughing their billets, then finished in house.

Childress tried to, then gave up.

Most are on Mahle or Pankl these days.

Designing/making pistons not as easy as it sounds, the machining and inspection equipment is spendy.

U
Maybe just the tops then

Yes, some cut pockets & dishes a little deeper, but not so much that it ruins top groove flatness.