98RedBird

iTrader: (77)

I went with a set of Diamond Forged pistons a while back and had the cylinders bored/honed to match the pistons. The machine shop had each piston numbered to each cylinder which I followed when I installed them. I got to thinking... You'd figure that the manufacturers would keep a pretty close eye on making sure each piston left the factory with pretty much perfect identical dimensions between pistons in a set just in case someone only followed the installation sheet that comes with the pistons rather than measuring each piston. For those of you who have dealt with them, how much variation is there within a set of pistons from a company like Diamond, Mahle, ect... And is it enough to cause a problem if each piston is not individually measured? Just wondering...

427

iTrader: (3)

Sounds like you found a good machinist.
Pistons can vary up to .001 that I have seen, although that was not a Diamond. Its best to run a micrometer over all the pistons to check size, I think your lucky to find someone who checks.

Kurt

98RedBird

iTrader: (77)

I felt the same way, but on the flip side, I was very curious to see how many people don't check and just cut and install. Evidently it's not too big a deal or we'd be seeing a lot more issues resulting from incorrect piston to wall clearances...

98RedBird

iTrader: (77)

By the way, when spraying large shots of nitrous 150+ will .001" make a difference? Just wondering.

Old SStroker

Good thoughts, Kurt. I like that machinist already.

Jon

427

iTrader: (3)

The problems with clearance may only be oil consumption or noise. You would see cars in the 60's and 70's that just ran better than others stock from the dealer. The best ones probably had the most time in them, or came out right from dumb luck.
On the additional .001 hurting a nitrous engine. Some people will set up a nitrous race engine loose to counteract the thermal shock of a big nitrous hit. I am one of them.....

Kurt

RoDan

yeah! and the trick was to buy the cars built on Tuesday and Wednesday right? The Monday and Friday cars just sucked! Probably due to workers being hung over from the weekend on Monday, and wanting to get done early on Friday...

01z28auto

On a gen 1 406 I was doing this weekend,the speed-pro pistons varied .0005. 7 out of 8 measured 4.1532-4.1533,and one measured 4.1537. It's really pretty close,but just wanted to show the difference in the 1 piston. That's why good shops want the pistons to bore/hone to fit each individually.

Sales2@Texas-speed

iTrader: (5)

I agree with Kurt and Jon (No H)! But you'd be amazed how many individuals and even shops we distribute to that don't mic each piston, or even worse just go by the number and machine the block before they even have the pistons!

racecar

Pistons are never perfectly the same size, and the cylinders in your block are not either. If you use a dial bore gauge, you can detect small differences in cylinder bores.
The solution is simple; match the smallest piston to the smallest hole, and next and next. Then your clearance will have a chance of being consistant.

GuitsBoy

iTrader: (4)

A good quality CNC should be accurate to within a couple of ten-thousandths of an inch. Assuming that the piston set was manufactured during the same run, using the same fixtures and same tooling it should be tighter than a .001 tolerance. Although if the pistons were pulled out of a pile and not necessarily manufactured back to back, or somebody sharpened or replaced a broken endmill, you could easily have a .001 discrepancy or more.