My son bought a used 450. Ran great for about 4 months but then jumped timing. Piston took out all three intake valves and cracked the valve guides. Cam shaft bearing surfaces look to be a little scratched up and discolored. My question would be is this a common failure for this machine and is there anything I can do to prevent if from happening again. Thanks in advance for any words of wisdom

 

Hmm.. Only way I can see it doing that is if the timing chain became, extremely loose. I would think it would have been ticking and making noise. I do not believe it is a common issue. Prevention would be teach him to listen to the engine and beware of any odd noises. My bro had a 400ex and we noticed the steady ticking. Took it apart and found guides for the chain had broke loose.

 

Thanks Koopa, unfortunately we are to familiar with this clicking noise. We had problems with another yamaha with the self adjuster not working. I have heard him rev the engine pretty good from a cold start. This happend with in a minute of the first start of the day. He may have over reved it. Thanks for the input

 

Eeeek. Ya, reving on a cold start before getting oil good and circulated is a bad idea. I hope you get it working.

One thing I thought of that is a known issue is fixed by the "oil mod". It's a flaw where the wrist pin does not get lubed properly. Google "yfz oil mod" and you'll find plenty of info. I think you could have succumbed to this problem.