Rebuild Help

Well i'm glad my bike didn't sell........had new crank, piston , valves etc and took it for a ride as i was contemplating selling for plated bike and she's done. It's an 04 yz450f. My dilema now is do i use as a parts bike for possibly another yz between 03-05, not sure if some parts would work as spares for a WR or buy a new crate engine which i can't find?? Need to make a decision soon as mechanic has bike apart. So far, case assembly, warped crank, new piston, cylinder etc (cams, valves checkout okay). I'm quite nervous as i had a few hours on bike before it grenaded last year and now am going to have to dump more in. Last year appx 3 grand, re did fork seals etc this year, 1 hour ride now looking at 2500. Need some good advice here.........this bike has been a nightmare. Looking back at the mechanic last year (haven't used since he was an idiot - me as well for buying into his theories) there was a chunk missing out of the bottom of the cylinder but he said not to waste the money as the rings wouldn't come near it no compression lost. In retrospect i'm sure that caused piston instability and caused thousands in damage - lesson learned. Please help! I'd be buying a bike no more than 3500 and aim worried about buying someone elses junk rather than just have this engine completely redone or crate motor if that works.

ya his advise on the piston is no good. You have to be carefull with the guts on the four stroke motors. If its done right they run great, otherwise things can happen like what did with yours. Good luck. If you really like the set up on your bike, here is an option i took. I bought another bike with low hours and a great motor. Then parted out the rest, and ended up making some money on top. Good luck, and keep us up to date.

Depends on where the chunk was missing from. At the sides, it's not important as long as the rings don't cross it. Front or rear is another matter, since the sirt could overlap it if it was large enough, and slipper pistons do not have a surplus of skirt contact to work with.

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