TWO Broken Rocker Arms. GS700E.

All four pistons are moving up and down. No worries there.

Got the intake cam out. Cam chain is broken. That end of the chain lifted right out. Still have to remove the exhaust cam. Chain is still engaged with the exhaust cam sprocket.

Oddly, the cam chain tensioner still looks good, at least what I can see of it. It pivots forward and back but I didn't try to pull it out.


I've been reading that crankshaft has to be lifted out to replace the cam chain. Is that strictly true, or can a 'split' chain be fed in and a master link used?

[posplayr]

See if the rotor turns on the other side of the crank.
Sounds like a broken crank.

put straw into the plug holes to see if they move

See if the rotor turns on the other side of the crank.
Sounds like a broken crank.

This just in:

Pulled the plugs - all looks great in all 4 holes (well, what tiny bit you can see). All 4 #1 valves move nicely by hand (pressing 'em by hand against the spring pressure). All sound like they're seating nicely (not binding against a bend in a stem).

Pulled the ignition cover, 19mm socket on crank bolt, turns very nicely, no noises, no binding BUT....

Cams aren't turning at all. Camchain is either off the crank sprocket (is that even possible?) or broken. And, either I got lucky and all the OTHER valves are in a position to not hit their pistons, or all of the vulnerable ones are ALREADY bent out of the way...

I'll start pulling cams and try to see down in the cavity. Before I pull the head...

Sigh.

Well, that's what I'm kinda thinking. SOMEthing stopped the valves from moving so that the rotating cam lobe broke the rocker.

I'm curious - how would a failed tensioner let this happen? I always thought the tensioner was on the trailing run of the camchain and only kept a push on it to keep the chain from slapping around on the 'unloaded' run. The crank rotation is always pulling the chain around against the resistance of the valve springs, so the chain run from crank to exhaust cam and the run from exhaust cam to intake cam are always under tension. How does a failed tensioner let the cams get out of time, unless the chain jumps a tooth I guess.

Sigh.

It is on the trailing run....Until you back off the throttle.....Billy

I'll try and rotate the crankshaft via a wrench on a bolt under the ignition cover too. Maybe even watch the marks on the ends of the cams to see if they're properly lined up.

Hopefully by this evening, I'll have more results from more troubleshooting...

Thanks to everyone for the help and insights.

Kirk

No point in turning the crank as the valves are closed. It does not matter where the piston is......Blow air into the plug hole and see where it comes out......Billy

With that much slack in the chain the piston will hit the valve. Then the valve is bent. THEN the valve is unable to move and the rocker broke.
An unfortunate series of events.

The heads coming off
If you broke rockers you bent valves.
Your cam chain tensioner failed miserably.

Well, that's what I'm kinda thinking. SOMEthing stopped the valves from moving so that the rotating cam lobe broke the rocker.

I'm curious - how would a failed tensioner let this happen? I always thought the tensioner was on the trailing run of the camchain and only kept a push on it to keep the chain from slapping around on the 'unloaded' run. The crank rotation is always pulling the chain around against the resistance of the valve springs, so the chain run from crank to exhaust cam and the run from exhaust cam to intake cam are always under tension. How does a failed tensioner let the cams get out of time, unless the chain jumps a tooth I guess.

Sigh.

[posplayr]

The heads coming off
If you broke rockers you bent valves.
Your cam chain tensioner failed miserably.

I think taking the head off is a given

The heads coming off
If you broke rockers you bent valves.
Your cam chain tensioner failed miserably.

Billy, I'm thinking you're right.

The only odd bit (to me) is BREAKING the rockers. That just seems SO outside my frame of experience, limited as it is... Bending the valves, sure, but breaking the arms, wow.

But, you're right as to my next steps - pulling the plug and trying to visual, and then blowing the compressed air. I'll try and rotate the crankshaft via a wrench on a bolt under the ignition cover too. Maybe even watch the marks on the ends of the cams to see if they're properly lined up.

Hopefully by this evening, I'll have more results from more troubleshooting...

Thanks to everyone for the help and insights.

Kirk

It appears that the timing chain tensioner backed off for some reason and the cam timing went out the window. Pull the spark plug out and blow air into the cylinder. With the rockers out of the way, there should not be any air coming out of the intake or exhaust.....If the valves are bent there is no reason to play with anything else, the head has to come off......Billy

Looks trashed, better sell it cheap while you can. I'll give you $100 for it now, even though I know the engine is shot.


Just kidding, PM me if you need a couple of rocker arms.

/\/\ac

[Steve]

If you haven't removed the tensioner yet, I would think that's a bit too much play in the cam chain.

.

That's all I could come up with - piston stuck, cam tries to open valves into stationary piston and valves bend / rocker breaks. Repeat for other rocker.

Otherwise, a piston smacking a valve usually just bends the valve and/or breaks the piston, not breaking the rocker.

We'll see...

Related to this - upon disassembly, how loose should the cam chain be? That is, during this effort, I was able to rotate the intake cam a bit and you can see the slack that developed across the top of the two cam sprockets. This doesn't seem normal to me, but I didn't do any further investigating yet. Actually, it wasn't until I was reviewing the photos that I noticed it and got to thinking....