The Unknown Squeak - Can't Track It Down!

Hey guys,

I've been searching in the forums for "noises", "squeaks" and "squeals" and I haven't quite found the results I was looking for. But I'm sure one person on here has had heard this noise.

My bike is a 1981 KZ650 CSR (H1)

It's a low frequency (like 3-4 Hz), modulating squeak that kind of sounds like rubber rubbing against metal or glass. The noise really doesn't really increase in frequency that much. I can hear it from 10 mph all the way until the wind prevents me from hearing it(so like 65+). On the bike it feels like it's traveling from somewhere - where I don't know. I can't locate it while riding.

The first thing I thought of was the chain, but it's new and I lubed it up real nice. I recently installed my new 26 tooth sprocket, so I was wondering about the cush drive these bikes have and if it was contributing. I don't think the gearing change would be stressing my transmission anymore than it normally would; I still try to run in lower gears to keep the bike from bogging. It's not like I'm dealing with increased torque in the rear.

Being on the formula SAE team when I was at school really helped diagnosing engine problems because we ran a 4 cylinder, the F4i, but I have never heard anything like this in my life. It's just really strange and kind of worrying.

Anyone have any thoughts?

-Ian


Ian Duckett
Milton, VT

*UPDATE*

The noise sounds more like scratching but it's still periodic, like I mentioned before. After riding today that's what I concluded. Low frequency scratching. Yum.

Also, pulling the clutch does NOT supress it, nor does changing into a different gear, or loading the transmission with full throttle vs. no throttle...

It sounds like something's trying to get out of my motor!! More ponies perhaps? Ahahahahah no...

Anyone have any ideas?

Tach cable? Speedo cable? Tunibrium balancer? Are all the hexagonal fasteners secured?

What about the actual speedo or tach? May want to try and spin the cable and see if you can replicate the noise. Other things that ride on rubber mounts- gas tank, seat, cam chain sprockets,...? Also the 81 had a different cam chain tensioner, perhaps the cause. Is it only while riding or can you hear it in a certain rev range?

Yea it seems to be only when riding. I'll check the cables this afternoon and get back to you guys. Thanks!

*Edit*

So I decided to do this before work this morning. I took the cables completely off and drove to work. I still heard the noise, but it's only when rolling. I'm going to guess it's something with the front wheel.

This afternoon the bike is going up and I'm going to spin the front wheel, check out the bearings, and check the speedo assy.

-Ian

could it be a warped brake disc? does the freq increase with a speed increase? I had a warped disc and it made a scratching / rubbing noise.

I'll have to look into that as well. At first I didn't think that was it because I tried braking hard in the front and it didn't seem to make the noise any louder/intense. I'll take it off and take a look at it for sure!

Some times the pads will lay on the rotor and cause a noise. My front brake lever has some play where it goes on the perch and will rattle like hell and I have to rest my pinkie finger on it to keep it from vibrating at certain speeds.

hi-just a thought, make sure your front sprockets not come loose i had this last year, makes a real strange noise
good luck

HAHA!! I FOUND IT!

Just as I expected, the noise was traveling from somewhere. Where might you say? The sprocket carrier bearing!!

I was hearing and feeling the noise and vibration on the left case cover.

Before I had put the bike up on the centerstand and gone through the gears, but it wasn't loading the rear sprocket bearing much, so I couldn't hear the noise. I decided to try it again, just for the hell of it, so i violently hammered down in 5th and... Voila! :woohoo:

Apparently, after putting my 26 tooth sprocket on, I didn't tighten the rear axle enough. Leaning the bike in ze turns created some axial and off-axis loading on the bearing - producing some REALLY BAD noises. Towards the end of that poor bearing's life, it basically sounded like I was turning steel on a lathe. :ohmy:

I'm really really glad I found it because a $35 bearing is worth much much less than my life. I mean, not much really could have happened, but when your bike doesn't respond the way you want it to, you might be in trouble given the perfect situation.

Thanks for all your input guys, I really appreciate it. This one's in the books.

-Ian

Bearings will definitely hum when they're going bad, glad you found it! You really don't want anything locking up on a bike, that's for sure.