Every time I twist the throttle (even gently) and the bike accelerates there is very pronounced chatter sound from the engine. I've had it since I bought the bike two years ago and it seems to get worse over time. It is louder and more pronounced to the point it is constant when I am going steadily. It almost resembles sound of a loose bolt fast shaken in a tin can.

The valves were checked and adjusted about 800 miles ago and should be ok. When idling (and the chatter in question is not there) I hear very faint crackling from valves when I lean close to the engine, and I believe that sound is normal.  When I did my valves I also checked the cam chain adjuster (adjuster assembly, #10 at the picture below) and it appeared to be fully operational (extending forward and not retracting back when pushed).

I think it may be the cam chain tensioner (pictured #8 here), or cam chain guides (eitehr #2 or #5, or both)





Any other ideas?
Also BTW, how hard it is to replace those tensioners? Do I take the engine out? I may try replacing those unless you folks point me onto different direction.


TIA
P.S. The bike is 1999, and has under 10k miles.

5 is easy, 2 you have to take off the top end.
And I doubt its that, have yout tried your drive chain ... final drive chain. Uneven stretch has my vote.
At high speed you have cam chain problems ... trust me, low speed will be much worse.
The oil when you changed it last didn't have chunks of rubber in it did it.
Cool.
Buddha.

Quote from: reminor on August 29, 2008, 08:10:58 AM
Every time I twist the throttle (even gently) and the bike accelerates there is very pronounced chatter sound from the engine. I've had it since I bought the bike two years ago and it seems to get worse over time. It is louder and more pronounced to the point it is constant when I am at 60-80 mph and going steadily. It almost resembles sound of a loose bolt fast shaken in a tin can.
Any other ideas?

P.S. The bike is 1999, and has under 10k miles. 

Gas knock.

yeah i'd dump that tank of gas into your car and fill it up with the good stuff

89/91

I am gassing the bike regularly (I happen to ride a lot lately). So it is not old gas. Filled up yesterday at Hess. No difference. Though... You guys giving me new ideas  . Maybe it is detonation related. Though I know how detonation pings sound (in the car engine) and my sound does not come close. It is more like rattling and chattering noise than pinging noise. Similar to a driving chain dragged on a washboard: "Hr-r-r-r-r-r"

Forgot to mention I have a DIY ignition advancer, maybe I should try un-do that adjustment first (2 minute deal anyway). The bike is pulling strong, starts no problem. All fine, but that noise. 

The chain has less than 1000 miles on it. Serviced and checked two days ago, again. The tension appears normal. No apparent wear, still shiny.

No rubber in the oil when changed last time (before winterizing). The old oil was in great shape with no large particles, just cloudy/muddy in a normal way.


Could that be transmission?

I just figured out one I think important detail about the problem. No matter what gear I am at the chatter starts almost exactly at 4000rpms and is gone by approx. 4300rpm. So it must be related to the engine, not the final drive chain or transmission (obviously my speed is different at 4k rpms depends on the gear).

Any thoughts? Is it just a "gremlin"?

Sounds like you have a vibrating gas tank to me.

Mine vibrates right at 4k RPM. 

Ride along at a slow enough speed that you can hear the noise clearly.  Then, slide forward as far as you can and grip the tank as hard as you can.  Does the noise go away or get quieter?  If so, check all the rubber tank pads and make sure you have good rubber around the tank edge.

Yup vibrating gas tank.
Cool.
Buddha.

If its not the gas tank, could it be the cam shaft vibration/float I've read about here on the boards? 

Cam shaft does not vibrate, it clacks ... distinct a sorta semi metallic clack clack ... silence, then clack clack ...
Cool.
Buddha.

Thanks guys! Your suggestions are clearing up my mind. Indeed if the speed of chatter does not increase (I think) with the revvs going up from 4000rpms to 4300rpms  it means it is some kind of resonation/vibration induced sound, not the engine related. I will investigae the gas tank idea and let you know.

This may be old news, but a piece of flexible tubing can be helpful in diagnosing the location of a noise.  Hold one end to your ear and use the other end to "probe" around the engine.  Kind of like a stethoscope for an engine.  This can help to mask background noise and make the offending noise source more prominent.  A funnel on one end can be used to cup over your ear.  Not easy to do while riding, but with a little assistance, you could investigate the source of the sound a little closer.

Just a thought...

Quote from: reminor on September 02, 2008, 08:19:51 AM
Thanks guys! Your suggestions are clearing up my mind. Indeed if the speed of chatter does not increase (I think) with the revvs going up from 4000rpms to 4300rpms  it means it is some kind of resonation/vibration induced sound, not the engine related. I will investigae the gas tank idea and let you know.

When the tank is less than half full, I get some engine resonance on my bike around 4000 rpm. I find the sound diminishes if I squeeze the tank really tight with my legs. To help determine if it is a tank resonance issue, you may want to see if leg pressure has any effect.

I tried (repeatedly) to press against the tank when heard the noise but nothing seemed to tame the chatter. I swear I tried hard. My b%lls still hurt from squishing on the tank