My brother took his YFZ to get dyno tuned and during one of the pulls, one of the valves broke.
He is going to pick it up tomorrow so we dont know the full extent of the damage yet, but he is most likely going to need some head work, and possibly a new cylinder (we wre thinking big bore).
Has anyone ever had something like this happen? The quad was just serviced in November and ridden only once since.
Also, does anyone have a recommendation on parts or selling any parts he may need right now?

What are the mods on the yfz. I don't think it is really common to break valves in the yfz's. Maybe, but I don't hear much about it. If he was running a bigger cam than the springs could handle, it might cause a valve to break. I would also check the damage, whether or not it hit the piston. If the springs were weak, it could have floated the valve into the piston.

You say it was serviced. What was done during the service, before he rode it the one time?? Who did the service work? Was it timed right?? Did a cam bearing get spun?? Just some things I would check I guess as you tear it apart.

I'm no engine builder by any means, just some suggestions.

i have had 2 seperate yfz's spin the intake cam flang causing valve to piston issues. you may check to see if this was a problem for you.. i get them welded now.

later aaron

Norcal what ever came of the prob let us know?