OriginalSterm

Looking for tolerance group 1 piston. I may need 2, but I know one for sure. I'm waiting to get this second engine totally apart, but the first one I pulled was in pretty bad shape.


If you cannot use tolerance 1 pistons in a tolerance 0 cylinder (if it turns out that's what I now have), does anyone have a set of 4 tolerance 0 pistons? Or does it make more sense to remove enough material (nikasil) to make this a tolerance 1 block again?

Peckster

What does tolerance group mean? Is that like first and second oversize?

There was a guy in Ottawa selling pistons on ebay recently, not sure if they are still there.

Jeremy Himsel

I've got a couple that are in great shape. They are group 1's. BTW, your block is alusil, not nikasil.

Jeremy Himsel

Just read your other post on your block having Nikasil coating, my bad. Most stock blocks are group 1 specs so you should use 1 pistons.

OriginalSterm

yeah, this block was pretty messed up. we had a local guy who was willing to give nikasil a shot if we could find the correct rings, which we did (964 oem). I have not measured the cylinders yet, hopefully he still has the dimensions, but i'm thinking he may not have given me tolerance 1 specs.

If tolerance 1 pistons will work, how much do you want for 1 or 2 of the pistons?

OriginalSterm

pistons:
the tolerance grouping is how tight the tolerances are held. tolerance 0 is 99.98 +/- 0, tolerance 1 is 99.99 +/-.005(mahle) +/-.007(kolbenschmidt), and tolerance 2 is 100

cylinder:
tolerance group 0 is 100 +/-0, tolerance 1 is 100.01 +/-.005, tolerance 2 is 100.02

pk951

Didn't BMW have problems with Nikasil coatings a few years back in there engines?

OriginalSterm

yes, but i believe the problem was sulfur content related. poor quality gas caused problems with these engines fairly quickly. i think gov't regulations limit the amount of sulfur in our gas now (i could be wrong).

pk951

Original Sterm
Yes that seems to be right, about the sulfur in the gas causeing the problem, what about porsche engines 911 not having that problem?

OriginalSterm

might be the quality or grade of the nikasil blend. i'm not sure what percentage of each component is required for "nikasil", or if there even are grades. could have been a process related issue as well, i don't really know enough about it.

dand86951

Just saw your other post and made a comment there, but inregards what you can do, I think it would be worth taking your group 1 pistons to a good shop and have them chuck the piston in a lathe with soft jaws and try to emery cloth sand the pistons down. You only have to get about .0004" off to put you back in spec. Since you have Nikasil you don't have to worry so much about the skirt coating. A good grinding shop may be able to give you exactly the dimension you need. I believe the ring grooves have enough tolerance to work ok.