[XCR600-RACER]

Can anyone give me some insight on this . I am rebuilding my son's motor due to a bad piston. I thought while I have it apart and have to buy new pistons, gasket kit and other parts I would see if I could bore it a little bit bigger. How big can I go 500, 600? and should I change the heads? This is kind of a father and son project so any info would be greatly appreciated. Please help!

Thanks,
Mark

 

[XCRacer440]

If you don't have to bore it out, then why do it unless your racing? Just put stock pistons and rings back in it, and hone the cylindars. Those Fuji motors usually go forever so I wouldn't start messing with boring and put relyability in jerpardy.

 

[Memphis]

The amount you bore it will make no real difference, only bore it enough to clean up the walls.

 

[yamarx1]

Take it to a machine shop where they can measure the bore and tell you how much wear is in the cylinder. The cylinder will wear more in the middle of the piston stroke then the top or bottom. From there you can determine IF you need to bore it .010 or .020 oversize. You didnt say how many miles are on engine but if its over 4000 m I would guess that it needs a bore. Also be carefull when you replace that head gasket. The small holes go to WATERPUMP side then you may have to flip it once to make the holes line up the best. Common problem to put gskt in wrong and overheat the engine PTO side.

 

[XCR600-RACER]

Thanks for the info. The motor has 4700 miles on it. My son wants to rebuild the entire machine with new front and rear suspension, update the breaking system etc. Should be a fun project. Thanks.