What would cause timing chain tensioner failure?

[Guest]

I had my bike running and drove 50 miles before my timing chain skipped the cams and bent two valves. I'm wondering what could go wrong to make this happen after the bike was running fine? My new valves are on the way and I'm looking forward to riding again. However, I'm selling my car and moving to Philadelphia, and feel a little uneasy knowing that my main method of transportation could have a major breakdown for no known reason. TIA.

[Charlie G]

Most (60%?) of the GS's I've worked on have had the tensioner installed improperly and in essence was inoperative. Are you sure it was operating properly?

[JRHemmen]

I mean I don't know how the engine noise compared to other engines, but the bike ran well. I just assumed that if the tensioner was inoperable it would have jumped long before the 50 mile mark.

[tkent02]

How did you install the tensioner? Specifically what did you do with the setscrew?

These GSes are among the most reliable vehicles ever built, but they do need a few things done properly once in a while.

[JRHemmen]

The first time, I simply turned the spring all the way out and pushed the plunger in, then had someone else bolt it in. The second time I did the proper method, locking the plunger down, turning the set screw 1/4 turn out, and tightening the lock nut. However, when I spun the crank by hand it would get slack and then pop back, almost like the valves were hitting, even though the timing was correct. I saw on a thread here where the end of someone's plunger had a little ball worn into it, I'll look for that when I get home.

[tkent02]

However, when I spun the crank by hand it would get slack and then pop back, almost like the valves were hitting,

What was getting slack and popping back? How much tension is on the clock spring?

[JRHemmen]

Oops. Typo. The timing chain would sag and then snap back. I think the timing was off and the valves were hitting. How do I measure that tension? I'm not sure how to describe it to you. Should I wind it until I can't any further and then attach it to the knurled knob?

[tkent02]

No, it's like a turn and a half. I can't remember, there's a specific number of turns. Too loose and the knob will spin around with RPM changes, not sure what too tight would do.

[fastbysuzuki]

Installing the tentioner is pretty simple operation On GS400 and GS425 .
Loosen the locknut and lockscrew on the cam chain tensioner assembly. Push in on the spring-loaded plunger while rotating the large-knurled nut counterclockwise.When the plunger is pushed on as far as possible, secure it with the lockscrew. Make sure the gasket is in place and install the chain tensioner assembly. Torque the bolts to 0.6-0.8 mkg (4.5-6.0 ft.-lb.). Back out the lockscrew approximately 1/4 to 1/2 turn out be sure no More Than 1/2 turn Out to release the spring-loaded plunger. Re-secure the lockscrew with the locknut.
Do Not rotate the clock Spring after installation unless you want to test the operation as below

Rotate the large knurled nut on the camchain tensioner counterclockwise whilest slowly rotating the crankshaft counter-clockwise. This rotation will cause thecam chain to push back against the tensioner plunger. Release the knurlednut and slowly rotate the crankshaft clockwise (normal rotation). The knurled nut should rotate clockwise as the plunger takes up the slack in the cam chain. If the knurled nut does not react as described, the plunger lock-
screw may be too tight or the plunger may be sticking.
If it works as above that's it job done.