787 piston size

[Black67tb]

I have a 1996 gtx. 787 engine. My SBT pistons are not marked anyplace on them. One is no good. Had the cylinders honed and measured. Was told the bores were 83mm. I would like to know what size of piston do l need?
Thanks

 

[mikidymac]

Standard bore is 82.0 mm so it’s not uncommon for SBT to bore out to the maximum of 1.00 over which would be 83.00 mm. If you have a trashed piston typically just a home isn’t enough to get within the correct piston to cylinder clearance.

Also what caused the piston to fail.

 

[Black67tb]

Water damage. But If my cylinders are a good , decent bore (83mm), with a good finish, and not out of round, what size of piston do l need to order?

 

[mikidymac]

You would need 1.00 mm over which is what SBT bores all their cylinders to.

Just know that is the biggest oversized you can go.

Finally how did you get water into the engine?

 

[Black67tb]

Leak in a gasket. Want to thank you for your replies.

 

[etemplet]

You're gonna have to measure that bore size and as you said, check for taper, out of round, etc... I can tell you that 1mm overbore on WSM is (3.2655") or close to that. WSM pistons need .0045" to .005" clearance so 3.270" is pretty much spot on. Of course, that is minimum sizes so you can get away with bigger. Be sure to chamfer the cylinder ports while you have them removed. Good Luck !