Has anyone had to rebuild a YFZ? I've heard that u have to rebuild them because of the compression ratio and the piston has no skirts.

IS THIS TRUE?

 

no its not true. You wont have to rebuild it any time soon.

 

I am rebuilding mine this winter.

 

Mine has had to be rebuilt twice now, both times were top-end problems, and the motor is stock!! I've also been hearing of some people haveing valvetrain issues as well.

 

Damn sounds like you got a lemon.

 

No actually he doesn't have a lemon, well yes he does, but no more than a lot of other YFZ's. This is a very common problem with these, I have personally had to rebuild mine 4 times. All due to a lack of lubrication to the top end, I've had the wrist pin seize and I've had the cam bearings seize. I spoke with Curtis Sparks about this issue, and he said it is a common problem, and they are working on a fix for it. What we did to mine was, line bore the cam journals to loosen them up just a bit, we also drilled out the banjo bolts on the oil line that goes to the head to allow for better flow. Sparks also said to not use Yamahalube oil, so I switched to Maxima Maxum4, it has been 3 or 4 months now since I had a problem with it, so I am thinking it is cured. Also make sure you warm it up some before driving it, when we spoke to Yamaha about it they said it needs to be warmed up for 10 minutes before riding, of course they were just looking for an excuse as to why it was breaking, but I do recommend you let it idle for a couple of minutes before riding.

 

i think the rings are smoked in mine...

 

i know a lot of people have had a problem with a plastic/rubber plug comin out. it's located on the top of the motor, facing forward or the right side (when sitting on the bike). there is the head of a bolt sticking out the side. a lot of guys have had the plug jus blow out and oil goes everywhere. other than that i've never heard of a problem with the motor.