Broken Rocker Arm...How difficult a repair?

[scottmc]

Bike: 1984 Suzuki GS(X)400.

Cliff notes: I had a tensioner fail, and opened the engine cover to check the damage.

After testing 3 of 4 valves, they all seemed to be within clearance between .03mm-.08mm. However as I went to turn I rotated the crankshaft forward, to test the last valve. (Top left, if you are sitting on the bike), I heard a BING.

A rocker arm flew through the air, and it was suddenly clear where the problem was.

My question is what do I do next? How do I approach this job?

Note: This bike represents my first attempt at anything mechanical, and I am a starving student at the moment.

[Curly]

That's a 4 valve per cylinder, right? I believe it's a big bolt on the outside of the head that holds all the valves on, I have four. One for the intake and exhaust on 1&2, and the same on the right for 3&4. It's a ~6" bolt, holding the two rockers. Might only be one for you I guess? Is it a 2 cylinder?

[SqDancerLynn1]

Rocker arm is easy to fix.... The question is WHY did it break ????
Piston may have hit a valve ????

[scottmc]

Rocker arm is easy to fix.... The question is WHY did it break ????
Piston may have hit a valve ????

I think so... but I don't know. This can happen with a camshaft tensioner failure apparently

What would be the best procedure to diagnose this? I was thinking that if I manage to replace the rocker arm, I can simply recheck the clearance on the valve and re-shim as necessary. If this doesn't work, then I have a bent valve and must replace it.

Also, when you rotate the camshaft by hand via the advance governor, should you be able to continuously rotate it clockwise? I can rotate the camshaft chain clockwise, till a full revolution of the chain but only once then it 'stops' and I have to reverse anti-clockwise. Is this normal?

[SqDancerLynn1]

SHould be able to keep turning the motor.. MAKE SURE the cams are in time !!!! I would suggest a close look at the valve keeper height.. Probably have a broken valve and it jambs the motor

[scottmc]

SHould be able to keep turning the motor.. MAKE SURE the cams are in time !!!! I would suggest a close look at the valve keeper height.. Probably have a broken valve and it jambs the motor

Damn...If I have a broken valve is this a whole new ball game? My understanding is the tools, parts are quite expensive.

[scottmc]

That's a 4 valve per cylinder, right? I believe it's a big bolt on the outside of the head that holds all the valves on, I have four. One for the intake and exhaust on 1&2, and the same on the right for 3&4. It's a ~6" bolt, holding the two rockers. Might only be one for you I guess? Is it a 2 cylinder?

Yes, two cylinders.

This type of repair does not seem to be covered in the manuals though....

[Dave8338]

Lynn brings up the "keeper point". WHY did you break a rocker. It takes a fair amount of force or "just the wrong chain of events" to snap a rocker. It is usually a valve to piston combo, but I have had stranger things happen.

1. Where were you spinning the poor thing at, when this happened?
2. Is the cam chain tensioner functioning correctly?
3. How does the piston / cylinder walls look on that cylinder?
4. You have to remove the valve(s) so check it for turueness. NO amount of "not perfect" is acceptable, when you are dealing with the valve train.
5. Check the valve clearances and timing on the whole package, once you've completed the above.

YES...you need a head gasket, so order one of them and get going.

[scottmc]

Lynn brings up the "keeper point". WHY did you break a rocker. It takes a fair amount of force or "just the wrong chain of events" to snap a rocker. It is usually a valve to piston combo, but I have had stranger things happen.

1. Where were you spinning the poor thing at, when this happened?
2. Is the cam chain tensioner functioning correctly?
3. How does the piston / cylinder walls look on that cylinder?
4. You have to remove the valve(s) so check it for turueness. NO amount of "not perfect" is acceptable, when you are dealing with the valve train.
5. Check the valve clearances and timing on the whole package, once you've completed the above.

YES...you need a head gasket, so order one of them and get going.

Awesome list, ....

(1) 6000rpm
(2) All these problems were caused by a failed cam tensioner, which has now been replaced.
(3) I have yet to investigate
(4) On my List.

So I have to check all the valves, replace the rocker, make sure the piston and piston wall are not damaged and re-time everything? That should prove an interesting challenge!

What kind of costs and I looking at? As a student funds are VERY tight, a NOS tensioner cost me 90 dollars. I just need an understanding before I get really into things if its over $300, I just won't be able to afford it now.

[scottmc]

Okay... I was following this thread.

http://www.thegsresources.com/_forum/showthread.php?t=161316&highlight=removing+valves

It looks like I am in for some work.

I will start a new thread with pictures once I start going at it. I may need a fair bit of advice, and the thread could serve as a useful guide for others in my position.

It's August 15, and I need to get this done before September 6th.

I think I can get this done with a little help.