Noise puzzle
 

OK, here's one that's got me thinking!

My XT600E has started making a strange noise while running. It's a kind of slightly metallic sha-sha-sha sound (sorry for the crap description), similar to when you are passing regularly-spaced trees and the sound of the bike is reflected back at you. The sound is not unlike a loose washer vibrating. Fairly quiet, but just audible over the engine/exhaust at 40-60 mph. That's the best I can do! The puzzle is the frequency. At 40 mph, it happens at approximately 4 to the second, and varies with the bike's road speed. It is there with the clutch in and the engine dead, and carries on getting slower and slower until the bike stops. It's obviously chassis rather than engine.

The frequency is the puzzle. My maths (which could well be as rubbish as my descriptions) says that the wheels are turning at 8 (front) or 9 (rear) revolutions per second, which kind of rules them out, unless some strange feature is making the noise happen every second revolution.

My only answer is the chain, which at ~100 links with a 45T sprocket will make a full revolution at approximately half the rear wheel speed, or about 4 per second at 40. Does this make any sense at all?

It's n ot a big problem (yet) but I would like to put it right before it gets worse and starts wearing something important. Any comments or suggestions welcome. I should add that I have checked the bike over and nothing is obviously loose or rubbing.

Many thanks.

If it sounds like a loose washer vibrating it may be some kind of a resonance related thing, try to locate the sound when you ride and touch stuff, like the mirrors, speedo, tank, plastics and so on.. if the sound goes away you have found what is causing the noise.
More ideas.. Is your chain worn or loose? Chain slap? Is your chain slide (on the fork) worn through, do you have metal to metal contact when the chain slaps the fork?

Resonance was my first thought, and I have done everything you mentioned - nothing loose or vibrating at all. And a loose mirror wouldn't vibrate at this frequency either, would have thought. I've had the tank, seat and tailpiece off to check for loose things - nothing.

I'm now 100% convinced it's the chain. I've checked everything over this morning - tension, chain line, the lot. No sounds while I was turning the wheel by hand, but when I got it on the paddock stand and let it idle in 1st, there was the noise again. I dribbled some Scottoil on the chain as it was turning, and the noise reduced quite a lot. Nothing seems to be touching that I can see, except the chain on the plastic slider (which it always has done without a rider on board). The only thing that has changed is the addition of a rear rack and small topbox.

It's possible that the extra weight and drag of the topbox have caused the suspension to compress more than before and the chain to rub on the lower slider (I am no lightweight and the preload was set fairly low) and that, combined with a dry chain (not lubed for 2-3 weeks) have caused the friction and the noise. I've lubed the chain and jacked the preload up to near maximum, and I will take it for a run this afternoon to see if that has fixed it. If it has, I'm suspecting a tight link in the chain, and I may well need a new one.

Thanks for the input, GS600.

It's the chain! also, check the chain rollers/sliders...when they are bad it makes that sound! ;)


Vando :innocent:

Hi Vando

Looks like you are right - I've just been out for a few miles and the noise has gone. The chain slider is pretty worn, so I suppose that should go on my shopping list too.

Cheers, and thanks to GS too.

Rich

Glad I could help!

The worn chain slider and rollers make the chain literally JUMP around and thus making that noise!

That noise was one of the things that made me want to get an enclosed chain guide for my XT... :)

I will however fabricate a strong engine case guard that fits between the engine case and the front sprocket to avoid any chain damage like those when the chain just jumps out of place and gets tangled up in the front...

This happened to me on my 2002 DT125R.. I was lucky tho, I could still manage to make a small incision on the engine cover for the clutch spring to gold on to...


Vando :innocent:

I think I will probably wait until it is new chain and sprox time, and then replace the lot.

I've jacked up the rear preload to about 0.75 of maximum. It was almost on the minimum before, and I hadn't altered it since I bought it last year. The previous owner was bigger than me, and I reckoned if it was OK for him it would be fine for me too. Wrong! Increasing the preload has made the whole bike feel much tighter and it's much more stable when leaned over at silly angles.

I should have known something was wrong when I stopped to give a guy a lift to get some petrol about 10 days ago. It's the first time I had taken a passenger on the XT and it was awful - the front wheel was almost in the air, and it didn't want to go round corners. My old XT350 was fine with a passenger, so something had to be wrong.

A couple of hours well spent today, I think.

The noise you're describing is the same as an overtightened chain.
The chain tension must be checked with the bike 'laden' & then rolled forward or back to find the tightest point.
By raising the rear shock preload, the swingarm geometry is altered & causes the chain to have more slack, which could be why the noise went away.
Bob

proper wheel alignment should get rid of tight spots on a good condition chain you can load the suspension with a ratchet strap through the wheel and over the seat to check for the right slack in the chain :cool4:

Great for loading the suspension, but makes it hard to spin the wheel to check the whole length of the chain, I would have thought.

:(

Fair point. The the slack in the chain was 35mm half-way on the bottom run, but I did it unladen, as per the manual. That's how I have always set it, and I've never had the noise (or any chain problems) before. The fact that it started immediately after I had fitted a rack and topbox (total weight possibly 10kg) makes me think it was the chain rubbing on the lower slider, which is well worn.

The unladen method of checking chain adjustment in the manual is for convenience.
You will notice that when weight is applied, the chain tightens.

well i'd have thought you would have checked for tight spots and alignment first then do the under load check for correct slack :rolleyes2:
the manual is half correct on the standard settings it may be correct but if the pre-load has been changed by a large amount that will affect the sag so the no load should be set to the high value of slack.

I assumed that the 30-40mm recommended slack took that into account. You are right - the laden method is better in mechanical terms and the manual is the more convenient way. But I have adjusted chains the unladen way for nearly 40 years now and I've never had a problem. Each to his own, I guess.

Sure. I just had a funny picture in my head of someone wrapping a strap round the rear wheel and then wondering why the wheel wouldn't go round. It was an attempt at humour - sorry if it missed.