Hey guys- in a bind over here. One of the exhaust valves stays open thru the entire cycle of rotation. It first happened when I was winding it out from a good right hand turn, then it like died- just as if ya hit the off switch. Well I yanked the head and found one of the keepers dstroyed. No trouble- so I thought- just go over to my rolling parts chassis and borrow the needed parts. All back together and it doesn't fire- so I grudinly take the head back off and find that the valve still stayed open. I change springs thinkg they're too soft and now cycle it by hand off the engine so I can monitor the valve action and while one exhaust valve snaps shut as it should- the other one stays a little bit open. Could I have a bent valve..............

 

Yeah, you have a bent valve.

 

sounds like it. But thats why you have that parts chassis, also check your piston because if something bent the valve, chances are it was the piston, so it should have some marks in the face of the piston and the face/side of the valve.

 

I'll take some pics. I concluded it's bent because when I tap it down shut I look into the port and canstill see some light- no matter how I turn/ rotate the valve. To the eye everything 'looks' OK, even the valve. I'll look at the piston closer...........

 

If the valve stem is bent by piston hitting it, then you should find out why it happened so that it doesn't happen again. Like loose/worn cam chain skipping a tooth or more on the cam sprocket. Check the cam timing.

 

Either you revved it out too high and the piston hit the valve before it had a chance to close (because the spring wasn't strong enough) or you have a skipping timing chain like Hayashi said. You could have a combo of both if you installed the cam chain a tooth off from the way it should have been.

 

I think I have a good idea- I prolly didn't adequately tighten the locknut on the rockerarm and it came loose leaving the valve out there to get smacked by the piston and thus busting the keeper on the other end after having bent the valve. I'll look closer and snap pics when I get a moment...............

 

I doubt it... I've done that before and all it does is back off and not open the valve. Now, if the lock nut fell off and wedged itself inside the spring coils and wouldn't let the spring go all the way down, the rocker might have destroyed the keeper and let the valve fall down into the cylinder to be smacked by the piston. That would be some really bad luck on your part for that nut to find its way into the spring. I would think the quad would have been progressively running worse until it finally stopped though.

 

Took a look at everything last night- there was a small, clean spot on the top of the piston, very small- wouldn't come out in a picture, evidently where the piston smaked the valve. The springs off the donor engine seem stiffer- I'm gonna try those out and not go so gung ho on the valve adjustment. I don't think I was off a tooth on the timming chain- the thing ran like a scalded cat right up to that fateful valve event.............

 

OK guys- got everything back together with the new valve and man it runs great- even idles. B4 I couldn't get it to idle for jack, now it runs great all over, and I mean all over; power is on tap anytime. I forgot how much fun this thing is![img]i/expressions/face-icon-small-happy.gif[/img]