'05 top and bottom rebuild - What service?

A friend wants me to do a complete rebuild (top and bottom) on his YZ. His cases are broken (chain derailment) so that needs opening for sure. What should I do/look for in the top end? He bought the bike used and from the looks of the bike it has lead a pretty hard life. Should I automatically replace things such as the timing chain? What 4 stroke specific tools do I need?

Sorry in advance for the stupid questions. None of my bikes have valves so I need some educating here. Thanks!


well...i could try to type out over half of the owners manual for a yz450f or you could just get a hold of one and that will answer about 99% of your questions. The owners manual will be great because it will give you all of the specs and tolorences of the whole engine, top to bottom.

Thanks Mike, that would be my first step. What I was hoping for here was perhaps a list of likely problem areas inside the engine. I figured people here would have that type of information. I know these bikes are pretty bomb proof, but I thought perhaps there where specifics I should pay extra attention to. Thanks again. The new manual in on its way.

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