GS650G Slight engine tapping

[Daedalus Wren]

This just started a week ago. When riding my bike between 4000 and 5000 rpm I hear a slight tapping in the engine. Nothing that is felt with my hand on the engine but loud enough to hear with my full face helmet on. This too only happens at cruising throttle while the engine is warm. Releasing or increasing the throttle within the effected range kills the noise. The oil is up and every gear within the same rpm range produces the same tapping so I know it is not the gear box or final drive. Furthermore, it is not a rapid tap as more then one cylinder would produce and the only maintenance that has been done recently was a Valve shim job three weeks ago and carburetor setup and balance two weeks ago. Performance does not seem to be effected at all by this but it is a little disconcerting. Any help would be greatly appreciated. Thanks

[tom203]

I'm unclear how you ruled out secondary drive- increasing/decreasing throttle changes load here irrespective of gearbox position.
When you did carb "setup" did you inspect camchain tensioner to make sure lock nut and lock screw were set correct?

[tkent02]

the only maintenance that has been done recently was a Valve shim job three weeks ago and carburetor setup and balance two weeks ago.

I would re check the valve clearances just to be safe. Carb balance, too, sometimes noises come from this, not sure why.

These engines, noisy as they are usually run quietly at the middle RPMs.

Any other noises at idle? Clutch in or out?

[Daedalus Wren]

Just got off the road with it and fine tuned my RPM range where the noise is heard. 3400 - 4500 RPM. The automatic cam chain tensioner was inspected and was fully operational. The shims were just done because of another tapping noise, which was cured by the job, but a totally different sharper tap was the noise then. and so true you are about the mid range being normally the smoothest, quietest range. No other noises can be heard out of the normal. Clutch in, out makes no discernible difference.

As far as my assumption that the primary drive was the culprit of the noise. I figured this because of the RPM range in-which the noise was heard. The range does not change, whereas the speed of the transmission and driven gears turn at different speeds as the gears are changed. Proportionately, the drive shaft and speed increases. To me this would mean that were it the transmission or final drive, the tapping would not remain steady within a given RPM range but would travel. Now I could be wrong and if so would indeed accept correction. Thanks

[tom203]

Will it make this tapping at 4k in neutral -bike not moving?

[Daedalus Wren]

That is the strange thing, it will not make this noise without a slight load on the engine. (like cruising produces) but not under any other condition that I can find.. I'm off Thursday so unless I have something more definitive I will be popping her top and checking the valve lash again.

[tkent02]

You sem to know what you are doing, not intending to imply otherwise, but you did release the setscrew on the cam chain tensioner? And did you use the Suzuki manual procedure for setting the valve clearances, or the incorrect Clymer's procedure?

These don't seem likely but It's all I can think of right now.

[Daedalus Wren]

When I inspected and actuated the cam chain tensioner it did not involve locking the tensioner with the set screw. I merely loosened the tensioner by hand while pressing down on the chain between the cams to verify that it was indeed relaxing and then turning the crank by way of 19 mm wrench, verified that the tensioner did indeed remove the slack from the chain till taut. Now, as for the method I used for the valve lash setting. I did indeed use a Clymer manual to measure the lash. I did just acquire the Suzuki shop manual for this bike and see the incorrect procedure. I will be without a doubt, re-doing the Valve measurements and hoping that this solves the issue. Thank you for your assessment and the possible issue causing the problem. I will keep you all posted as to what I find.

[tom203]

When you say.." loosened the tensioner my hand", do you mean you rotated the knurled knob counterclockwise (standing on right side) ?
Anyways, my first thought was that locking setscrew was backed off too much and the plunger might be vibrating in the tensioner assambly at this rpm range.

[Daedalus Wren]

As far as the tensioner is concerned, "loosening it by hand" meant precisely what you described and not loosening any other component of the assembly.

Now, as for the possibility of the plunger vibrating, I assume since the spring loaded adjuster will only allow the pushrod to travel in one direction (that of pressure application on the chain guide) that the pushrod could not in fact vibrate unless the tensioner was not working correctly. However, if the cam chain was beyond its serviceable length and the tensioner was no longer able to apply tension, perhaps the guide and or chain could be slapping. This is another avenue I will explore (measuring the chains 20 pitch length) when I have her top off.. Thanks.