Cam chain tensioner knob moving

[Remco]

Hi all,

After working on my bike today (GS450L), I started the engine and it was making a strange rattling noise. I noticed that the knob on the cam chain tensioner was moving from left to right fast, while making this rattling noise. The engine runs normally btw.

I switched off the engine and started it again, the sound was gone and the tensioner knob wasn't moving anymore (normal behavior). I pulled the throttle and when it went to 7000 rpm or so the tensioner knob started to heavily move around again. After switching it off, and starting the engine everything was normal again.

Anybody any idea what this can be? As I mentioned, the engine runs ok.

Many thanks in advance for the support!

[Charlie G]

Remco,

If the tensionor is working corrrectly, the knob should rotate a little as the engine is rev'ed back and forth between low and high rev. This dosn't mean that it is adjusted properly, it mean it moves as it should. I have read that it's a common mistake for owners to tighten the set screw down too tight as not to allow the tenisonor rod to move.

cg

[scottmc]

I recommend extreme caution if you feel the tensioner is not functioning properly. A failed tensioner
ruined the engine in my first bike.

[JEEPRUSTY]

There is a series of checks int eh manual for this.
Some experts will be along to address this shortly but My tensioner moves quite far but with no rattles.
The chain or the tensioner mechanism may be worn.

[Billy Ricks]

You should be able to find a link to a pictorial repair guide on Bascliff's website on how to service the tensioner. The pushrod is only supposed to move toward the chain and not back off.

[sedelen]

I don't think your knob should be moving at all, that knob is kept in place by the coiled spring tension, unless it got disconnected from the spring.
The screw held by the lock-nut should be loose enough to allow free movement of your spring loaded push rod. You loosen the lock-nut and tighten the screw when you remove the tensioner, so that it holds your spring loaded push rod in place, and you compress the pushrod in all the way and tighten the set screw when you install it, once installed you loosen the set screw and the pushrod will spring out putting tension on your chain. Now that's an abbreviated procedure in a nut shell.
You should really consult a manual, cam chain tensioners are nothing to tinker with if you don't know about them. Absolutely DO NOT turn over the the engine if you've removed it.

[Billy Ricks]

http://www.bwringer.com/gs/camchaintens.html

A link to Brian's tutorial.

[Remco]

Thanks for all the feedback.

So I can remove the tensioner without being woried about the chain "dropping"? (like what happens when you remove a belt tensioner in a car engine)

[Charlie G]

Thanks for all the feedback.

So I can remove the tensioner without being woried about the chain "dropping"? (like what happens when you remove a belt tensioner in a car engine)

Yes, but don't run the bike without it as the chain may jump timing. I would disagree with some who say the knob shouldn't turn at all. If the tensionor is set properly, I will turn, slightly, as you roll the throttle through RMP levels.

cg

[sedelen]

I pulled the throttle and when it went to 7000 rpm or so the tensioner knob started to heavily move around again. After switching it off, and starting the engine everything was normal again.

You know, I've never really studied the knob on my cam chain tensioner(s) to see if it moved while running, which I don't believe it does (much), because of the spring tension on the knob. Perhaps I should do that next time out to the garage. But one thing I don't understand is how were you able to look at that knob with the rpm at 7K? Hopefully you had the engine under some kind of load at that high an rpm .

[Billy Ricks]

It shouldn't move under throttle. The pushrod is only meant to move in against the chain not out.

[Mekanix]

From experience, the knob will move when the engine rpm change drastically.


If you rev it nice and easy, the same way you would drive the bike then it would hardly be noticeable.

If you rev it quick it will move a little when the engine gets up to high speed 5k +

If you then shut the throttle and have the engine in deceleration that means the crankshaft is slowing down faster than the camshafts.

This causes the chain to go slack in the front for a moment while the back part of the chain which is running on the guide that the tensioner is pushing on is getting pushed hard on.

That's what is making the knob rotate backwards. And the engine vibrating is enough to unlock the knob from its normal position.

Once the engine, chain and cam come into sync again the proper tension is kept and it no longer moves.

Basicaly under acceleration the engine is pulling the chain in front of the engine and the tensionner is taking up the slack. (causes forward movement untill its at its normal position)

On decell the front becomes loose and the back gets tight. (causes reverse movement)


When the engine is running and being reved that much, the vibratrions make it easy for the knob to become "unlocked" from its normal position even against that coiled spring pressure.




In this particular case your tensionner is behaving as if the coil spring is either too weak or has jumped and is no longer holding the knob tight enough.

OR the main spring inside of the tensioner has broken and only the coil spring is holding tension.

good luck

[barnbiketom]

every GS I 've owned the knob moves when the engine is running.

[Billy Ricks]

Okay, I just started mine again and revved it up pretty good and it did rotate counter-clockwise just a bit.