Strange clonking with low rpm

Hey everybody,

I know there are quite a few topics on strange engine sounds of the cb500. Haven't just found a solution to mine yet. So I have a cb500R, past 70000 on the clock.

The thing is, at low RPMs (2-4k) there is a clonking at a pace of few times a second while accelerating. Happens at least on gears 1-3. The pace goes up with rpm, don't really notice it after 4k. Would it be just the sound, I wouldn't worry too much, but I can feel it every time through the foot pegs.

It doesn't seem to be the engine or chains, since this doesn't happen when I pull the clutch. Changed the oils two weeks back.

Any ideas?

without hearing it its hard to tell. could you do a video?

Have a look at the chain and front drive sprocket (behind the panel just down by your left foot). I'm betting that the sprocket teeth are hooked, which means a new sprocket - and really you should replace the chain and all sprockets together.
Of course, it might be just a case of chain tension!!
Regards,
Phil

It could also be the camchain tensioner, there are some threads on this in the not too distant past

teamster1975 wrote:It could also be the camchain tensioner, there are some threads on this in the not too distant past

thats what i was thinking.

My bike chugs a bit if I'm accelerating in low revs - I think when the revs are low and you open the throttle up you can just hear it working hard. If it doesn't happen when holding a constant speed in the same rev range that could be it. Of course if it sounds metallic then maybe there is something rattling.

Recorded some of the sounds today while driving, now i just need to figure out a way to let you guys here them

Definitely less clonking with constant speed, but it's there again when under higher stress like when going up a hill. I'm not sure whether it dies out with higher rpm or just that I can't hear/feel it anymore. And now that I've been listening to it for a day, it seems more speed related than rpm related.

Gotta check the front drive sprocket, just need the right tools for it.

upload it to youtube.

Let's see how well this turned out. Had to do this in silence due to working conditions. If you can't make out the sound I'll post a new video later tonight.

Hmm, it's a burbley sounding engine, I can't pick out any metallic sounds or anything too horrible. Sounds like the burbling is less detectable at high revs because the sounds merge, and it's louder with the throttle open because more mixture is drawn in per rev. I'm no expert, but given the mileage and the sound I'd check:

1st the carb balance - if it's skewed off it's going to sound a bit uneven and probably vibrate more, also this is a relatively easy check to do.

2nd the valve clearances - not a job I've done yet and live in fear of doing. Means bike off the road for a week while you measure and buy shims, and requires careful mathematical working out.

Ok, this is weird. Drove over to a friend's house tonight, checked the chain and front drive sprocket. Nothing really out of place there, just some dirt on the sides. Rolled the chain around on neutral and found nothing wrong. Replaced the cover and drove home. Absolutely no clonking the way home.

I'm gonna clean and lube the chains and check tension. Let's see if that does the trick.

amjuuz wrote:
I'm gonna clean and lube the chains and check tension. Let's see if that does the trick.

do you think you could have a tight spot in the chain?

Tricky. wrote:

amjuuz wrote:
I'm gonna clean and lube the chains and check tension. Let's see if that does the trick.

do you think you could have a tight spot in the chain?

Sure it's possible. Like I said, I'm still learning More time during the weekend to work on the bike...

been away so missed this post. my cb was like that when my chain was too tight. make sure you adjust the chain at the tightest point,you can find this by rotating the wheel and feeling the slack in the chain

newbie alert
Seems as if a good lubing for the chains did the trick. The bike works like a dream atm. Gotta gove the chain and sprockets a good clean once I have the time and get back on the road

Nice to know it was a simple problem and not something serious!