I would like to post a little warning for those of you considering a big bore kit. I have an 86 XR600R that I have had since about 89. About 2 years ago I installed a 660 cylinder & piston kit and an "all around" cam. Have an FMF pipe and a Baja Designs street legal kit. I don't know if the trannies are the same on the later 600/650s but mine can't handle the power. I broke the trans. twice. 1st time broke a peg off of 3rd gear. It broke a piece off of the inside of the case, broke off the bottom of the new sleeve, and bent the piston. I rebuilt the whole thing again. 2nd time I kind of got lucky and it only broke a peg off of 2nd gear with no engine damage. I have not been riding this bike hard. The power is so fun but I can't afford the money or frustration of rebuilding this thing every year. I feel like I have to unload this thing now. Also if you install a bigger cam with a rebuilt, (most are rebuilt) you MUST use hardened rockers. Learned that the hard way. The manufacturer didn't mention it. Also my first rebuilt cam appeared to be porous and chewed up one of the stock rockers. The second cam (from a different manufacturer, also rebuilt) broke in great with hardened rockers. I am curious if any one else has had simmilar problems with the power up kit or tranny problems. Also If anybody want's a go at this bike let me know. I had the case fixed and the top end is all new. Sorry this is so long winded.