760 .20 over piston size?

[EightySeven550]

760 .20 over piston size?

Hello all,
My Uncle and I are rebuilding a 760 motor. It is getting bored .20 over stock.
Does anyone knoW what size pistons I will need?.
Or how do I measure cylinders for piston size?

Thanks all,
Andre & Jim
954-918-5477

 

[Cannibal]

.020" over is .508mm, so you are going to want to get 84.5mm pistons. Get the pistons and bore to fit them. Don't bore it then buy pistons to fit the bore.

 

[EightySeven550]

Thank you so far.
I need to bore the cylinders due to corrosion.
If I bought pistons, how do I know what size to bore the cylinders?
(sorry, I am pretty new at getting machine work done to engines, I've always stuck with stock top ends.)

Thanks again,
Andre
954-918-5477

 

[Cannibal]

.5mm will get out most imperfections. If it looks really bad, you may want to talk to the machine shop you will be using. They can guide you as to whether you can get by with .5 or if you need to go a full 1mm over.

Then buy your pistons and take them to the shop. They will bore and hone to fit your pistons and specs. Depending on the piston mfg, there will be a different piston to sleeve clearance. If you go OE, use Yamaha piston clearance specs, if Wiseco, use their specs. I think WSM and Pro-X use Yamaha specs too, but don't quote me. I don't have the specs myself, but maybe others will chime in.

 

[augustaf]

Chiming! .004" clearance for oem, Prox and Wsm, .006" for Wiseco is usually recommended.