cam sprocket, valves, help

[Vumad]

I have a 2002 warrior 350. I was riding at the track when I lost power and got a bad engine rattle. I took off the valve covers and found the lock nut on my exhaust valve had come off. I believe the nut was the rattle, and the screw backing out was the loss of power. I bought a new screw and nut and placed them in. My understanding was the exhaust asjustment for the warrior was 0.006-? so I adjusted it to 0.007 TDC cold. I checked the compression and got 155psi on my old guage. The quad seemed to idle well. It sounded to me like it had a bit of a puffing sound that didn't seem normal (don't know how else to describe it). It seemed to respec correct, so I took it on the street. It had very good power in 1st, 2nd and 3rd gears. It didn't sound completely healthy in the high RPM in 4th and 5th gear. I let off the gas for a second, and when I hit the gas again it completely shut off. After I pushed it home, I took off the cam sprocket cover (which previously everything looked healthy). The cam sprocket turns when I hit start but the cam does not. One of the holes in the sprocket appears to have flexed and I believe the lock bent out and the sprocket is spinning freely on the cam. I haven't done anything else with the quad since I have seen this. The shop guys told me the sprocket would have broke if the valve was adjusted too tight. They told me to put a new sprocket in it and readjust it again.

Any insight on this? I don't want to throw parts at a quad with a problem, but I also don't want to tear apart a top end with 155PSI for no reason. I was going to take the advice and simply order the sprocket and try again, but I just don't see why the sprocket would have broke, and am afraid something greater is the problem. I can't recheck the compression to see if the valves are burnt up w/o it... Advice? Help...

I'm going to be buying a YFZ 450 very soon or I'd just tear it apart and put a hotcam in it. I'm going to keep the bike as a spare/friend bike and want to keep it simple and cheap. It's important to me to make it as reliable as it once was.

Thanks

 

[Motorheads5]

Pull the head off and look it over. All you are out is a head gasket. You don't have to disturb the base gasket, then you will know if the valve is possibly bent or if any contact has taken place in there.

 

[WFO Speedracer]

It sounds to me like you have locked up the camshaft in the head,this could be due to low oil or something may have stopped up the small oil line going to the head,I have seen this a few times on Yamaha 350's .When the cam locked up the rest of the motor tried to keep spinning which is why the cam sprocket distorted and is now spinning freely.Your best bet is to find a used head off Ebay and go from there.This is my diagnosis without ever seeing the unit,by all means pull the head and do a proper inspection.

 

[Vumad]

It sounds to me like you have locked up the camshaft in the head,this could be due to low oil or something may have stopped up the small oil line going to the head,I have seen this a few times on Yamaha 350's .When the cam locked up the rest of the motor tried to keep spinning which is why the cam sprocket distorted and is now spinning freely.Your best bet is to find a used head off Ebay and go from there.This is my diagnosis without ever seeing the unit,by all means pull the head and do a proper inspection.

I think you have a very valid concern. Something like this is why I don't want to just put a new sprocket on it. However, I do know that there is oil flow, as I hit the start button before I put the valve covers back on (before the spocket broke) and had oil flow.

 

[WFO Speedracer]

Take the cam sprocket bolt out,find a spacer or large washer to go on it,the spacer is important because you want to be ablt to get the bolt back out! Reinstall the bolt into the cam shaft without the sprocket on it,now make sure your piston is at BDC,if in doubt find the TDC mark on the flywheel and turn the engine 180 degrees from there,be sure to hold the cam chain up while you rotate the engine.Now with the cam bolt reinstalled with the spacer see if you can rotate the camshaft,if you cannot fairly easily rotate the camshaft you have found your problem.There will of course be resistance from the valve springs but it should turn without a lot of force.

 

[Vumad]

It turned with almost no resistance when I adjested the valves. I suppose it could have locked up right after I adjusted the valves... I put fresh oil and filter in it before I ran it.

Good advice that doesn't require parts. I'll give it a shot. Thanks.

I don't think this is going to end up being it. Anyone else have ideas as to why this part would have broken?

 

[WFO Speedracer]

It turned with almost no resistance when I adjested the valves. I suppose it could have locked up right after I adjusted the valves... I put fresh oil and filter in it before I ran it.

Good advice that doesn't require parts. I'll give it a shot. Thanks.

I don't think this is going to end up being it. Anyone else have ideas as to why this part would have broken?

You didn't by chance put the filter in backwards did you? I have seen that one quite a few times,what you describe is what happens when you do that,the camshaft and rockers are the first components to fail when there is a lack of oil pressure.