I'm doing a 95" with KB's STD 348 Hypertuectics. The boring/honing is done (both with .0013" clearance) but I'm a little concerned about the sizes of these. One is as KB claims (3.8745) and the other is (3.8713). My rep where I bought them seems to think this is perfectly normal, but I think the freak piston should not have made it into a box for market. Wondering if their QC has over/under #'s that are tolerable. A lot of extra ring grinding on the one piston (so much I ended up going over on the second ring, had to order another pack) & I think if one was to get a piston that was larger by .0032" you would need to order an over-sized ring pack. The true piston required no grinding on the scrapers, a slight shave on the second ring & a wee bit more on the 1st to get .028".
Two questions come to mind: 1-Anyone aware of any specs KB's Quality Control might use? 2-Could there possibly be an issue running with one cylinder/piston .0032" smaller then the other?
Thanks in advance!!

 

That is not normal, in this day of cnc you should not be able to measure a difference. I used to work in an automotive engine shop, we bored all the cylinders and honed them to the same dimension and all the pistons would clearance the same. Never needed to size to the piston because they are all the same, if they weren't I would be calling the manufacture. It may be fine but I wouldn't run it, anything coming out that far out of spec could have more issues that you cant see, I would be calling Keith Black and ask him WTF?
Personally I would be running forged pistons they don't cost much more.

 

Thanks for the info Tubeman! I called UEM (Keith Black) a while back & was told I had to contact MidUSA where I bought em. My rep there didn't offer new pistons but sent me a copy of the installation instructions. Still can't figure out how that will fix a freak piston. Every measurement is identical except for the smaller skirt so I think I'm gona run em rather then more downtime arguing with these guys, not to mention I'm overseas. Good analogy on the automotive side of things. Wonder if these people think it's common to bore & fit rings 8 different diameters for one engine???

 

Can't answer the QA/QC KB issue but don't understand why the KB referred you to MidUSA on a QA/QC question since Mid USA just sells the product and doesn't manufacture the product. I would be calling KB/UEMC back and pushing them on the QC issue; doesn't sount right to me and I would not run it until talking to UEMC; they will probably send you another set.

If you do get another set, you can probably set them up tighter than .0013". Don't know what KB says but I bet you could tighten up clearance to .0010". Doesn't sound like much but could help ring seal.

As for running one piston larger than the other and all other things being equal, a non issue. Have bored one cylinder to 3.875" and left the other at 3.750" and run with no issues. The only issue you might have is if the KB pistons are a different weight from the pistons they replaced which could introduce some vibration resulting from the differnce in the reciprocating mass.

 

Your absolutely right Dil & Tubeman! Called UEM again and got the right guy. He recommended not running that piston & is sending some overs out. As you said, UEM also said there may be a deformity I can't see or measure.
You guys probably saved me a catastrophy. Much appreciated!