73’ xs650 256 engine questions

[thrashin]

I just picked up a 79’ xs650 with what appears to be a 73’ engine. I’ve pulled the engine and began to tear it down. It looks as if the head gasket blew pretty good. No damage any where else I see. Valves look good pistons are worn but not destroyed and bores aren’t bad. Rods have no knock and minimal radial movement. (If anyone has a tolerance on side to side radial movement at the connecting rod please share)

So I’m looking at piston kits and measured the bores last night at 2.955” which appears to be 3rd oversized 75mm. Where can I get a piston to have these jugs rebored and cleaned up? Would JE 700cc kit be more than 75mm? I wouldn’t mind a little extra pep. If not is there a better route?

Also noticed a crack in the clutch cover. Appears that the clutch pressure plate was rubing heavily on the side cover. Also have some silicone on the opposite side of where the pushrod and seal protrude. Contemplating splitting the cases but now would be the time to do so if necessary. Feel free to share thiyghts and opinions. Thanks

 

[wera90ex]

I used these guys a while back http://xscycle.ca/pistonkits.html.

 

[TwoManyXS1Bs]

Try Gary at: http://www.hoosracing.com

 

[5twins]

I think your bores and pistons may be stock. The stock bore on these is just a hair over 75mm or 2.953". The oversize pistons come in .25 or 1/4mm increments. That means a 1st oversize piston would be 75.25mm or 2.963". That won't even fit in the bore you have now. The wear limit on a stock bore is 75.1mm or 2.957". At 2.955", you're not even there yet.

 

[thrashin]

Thanks for the info, guess I was searching pistons and seen 75mm. Assumed that was the oversized bore. I still want to clean them up. The bottom of the cylinders are showing some vertical wear. Pistons skirts look worn pretty good too. What if I do a stock over sized piston and do the no cylinder base gasket or mill some off of the cylinders? Not sure what the stock compression ration is or could be. Need more research.