Exhaust Header Studs Keep Breaking. Help!!!

[cpleninger]

2000 yamaha 350 Warrior - The exhaust studs keep breaking off in the head... Yesterday was the third time I have had to drill them out retapp and replace..... Not running it hard - this is even happening when just driving on pavement.

Yesterday I got frustrated and drilled out the stud holes to 7mm instead of the factory 6mm. Why is this thing breaking studs? It has complete factory exhaust, and the motor mounts are all good, frame is not tweeked or bent

PLEASE HELP..... the next time may cost me a new head.

 

['00 WO-YA!]

#1 problem; they're too small and weak.

 

[Venom]

you may be running to lean causind the header to expand due excessive heat and with exhaut studs overtighten they break...
Just an idea.
With mine it was the oposite they came loose after a 60km ride...

 

[cpleninger]

Venom, Thankyou !!!!! That makes so much sense - My lil bro was telling me that something fell out of the engine and hit his foot a few months back..... When I cleaned the carb we found that air mixture needle was missing. Yup causing the crazy lean mixture and very likely heatin everything up. The needle valve should be here tomorrow, and I will sinch the exhaust flange back down.

I was thinking things weren't moving enough - so I put long 7mm bolts in with compression springs to let that pipe have some movement - but I am scared it is gonna vibrate and strip the holes.

After much thought I think you hit the nail right on the head, cause we never had a problem before that needle valve fell out.

 

[THORrider05]

Check all the motor mounts and bolts. Ive had this issue on my 87 when we first got it.

 

[cpleninger]

when they broke the first time I checked all mounts cusions and bolts - The top mounts were broke.... Replaced em before I took care of the studs the fist time. That was why I was so baffled when this kept happening... As my boy really calmed down on it after the first incident, and does not jump it or even take it off road much anymore. Basically uses it for cheap mode of highway transportation now.

 

[duneracerweston]

Your not gonna stop breaking them why Yamaha thought a m6-1.00 would be strong enough is beyond me. Get you a m8-1.25 and a tap, and oversize them. You wont have any more issues.

 

[THORrider05]

when they broke the first time I checked all mounts cusions and bolts - The top mounts were broke.... Replaced em before I took care of the studs the fist time. That was why I was so baffled when this kept happening... As my boy really calmed down on it after the first incident, and does not jump it or even take it off road much anymore. Basically uses it for cheap mode of highway transportation now.

My 87 had 1 bolt holding the motor in when we got it, broken top motor mount and a broken exhaust stud, got the stud fixed put other bolts in to hold motor but didnt know the top mount was broken. Our 99 never had an issue breaking a stud. Now that my 87 is running again i took the 99 head and put it on my 87 customized the stock upper motor mount and havent had an issue, I just broke the intake boot now cause the airbox didnt have any flex. Also make sure your not over tightening the stud bolts, ive done that and broke one.