78mm pistons

[Satch39]

Hey all,
I've been around for a bit, but haven't posted a whole lot. I've done some business with quite a few members. This is my first thread.

So to get down to it, I bought a set of 78mm cast pistons out of Japan, on eBay. When I took them to the machine shop I'm using, the machinist asked me if there was a recommended over bore for the cast piston vs. a forged piston. Does anyone have any recommendations on this? I tried emailing the seller, but I didn't get an answer. Any help would be appreciated.

Thanks
Satch

 

[TwoManyXS1Bs]

The factory pistons were also cast, and your size difference is very small, so just use the same piston/bore clearance and ring gaps as published in your manual...

 

[Satch39]

Thanks 2many!! I had the .002" from the manual, but my machinist was questioning the cast vs forged. I'll let him know they were cast originally!!

 

[gggGary]

Word is the OEM piston maker makes the ebay pistons. Probably on a bit better machines these days. My machinist has bored 6 or 7 sets now and hasn't seen ANY variation in piston size set to set. He uses the factory spec. IMHO It is a good sign your guy asked!

 

[Satch39]

I'm pretty confident in my machinist, but most of his experience is motocross and racing, that's why I drove an hour away to use his services. I'm glad he asked and that we have a community here that is so quick to help out! Thanks guys!!