BROKE THE 686 NICE AND EASY. WENT OUT RIDING AND BOOM! TOP OF VALVE COVER GONE BY THE CAM, BROKE ONE BOLT HOLE OFF THE CAM, DESTROYED THE GEAR AND DECOMPRESSION STUFF AND EVEN BROKE THE MIDDLE ROCKER ARM! WHAT WOULD CAUSE THIS? LOOKE LIKE THE WHOLE THING JUST CAME APART AND IT RAN GREAT UNTIL THAT. ANYONE KNOW WHERE I CAN GET A VALVE COVER PRETTY CHEAP. MAYBE TIME FOR A R1 MOTOR, LOL. THE DECOMPRESSION PIN WAS STILL THERE SO IT WASNT THAT. SHOULD I PULL THE HEAD AND SEE IF VALVES GOT BENT? THANKS

 

how were you riding it when it broke?

 

Ouch! Been there, Sounds like one of the cam gear bolts came loose. Good luck finding a vavle cover, I had to buy a new head. Yamaha doesn't sell them separate.

 

TURN OFF YOUR CAPS YOU FOOL

 

Half to three-quarter throttle on a flat. Just doesnt make any sense to me. Why would it break the cam if the bolt came loose? I think the cam broke first, but I guess I'll never know. I have e-mailed east coast atv to see if they have one. I dont want to replace the head because I have so much money into the port work. I about went over the nose when this all happened, I mean it just shut down NOW. I also cant figure out why it would break the center intake rocker arm. Unless the piston came up and hit it??

 

Firefly is right,

Yamaha won't seel only the cover. The head and cover is machined together not to be changed. If you change one, then u have to change the other. If you find a used one, you probably have a pretty nice bike, i wouldn't take the chance of half-a$$ing it.

 

Anyone know what kind of money I am talking about here???? Does anyone have one laying around that they do not need?? Please help me guys, its almost riding time. What about cams? I do not want anyone to say Hotcam's at the moment but what about this web cam I hear about?

 

You'll have to tear it down to know for sure how much. I think a head is about 500. Check on the parts fische at Riva Racing or Alba to be sure.

If a cam gear bolt backed out its not the cams fault, it would be whoever assembled it. It requires loc tite and a certain torque spec. Do you still have your stock cam? If not the webb cam is going to cost you a good bit more without the stock core charge. The Webb 736/737 is a little smaller than the cam you had/have.

 

It sounds like something wasn't put together right. Possibly the cam gear bolt was tightened past the torque spec and cracked the cam.

You CAN NOT use a different cover on your head. The head and cover are matched. If you need a new cover you need a new head with it.

 

I agree, I have seen a few of em with the cam ear broken off mid thread. The cover is half the cam journal, I have seen people running unmathed sets but I wouldnt screw around with it if your looking for reliability.