Need help with a noise

[CNY rider]

I've got a new knock/tap coming from my Legend that's got me baffled.

Background: I recently completed an upgrade from 9 speed triple to 10 speed triple.
Over the winter I put on the new 10sp crankset, FD, and 10 speed chain. Rode it without any problems.

Last night I completed the package: Shifters, rear der, and new cables all around. When I'm in the large ring I now get a gentle knock or tap when the left crankarm comes around about 1000, just where you're delivering maximum power. Coincidentally that's also when the right arm is passing the FD cage; at first I thought it was hitting the back of the crankarm but there is actually a couple of mm of clearance. It does NOT make the sound when in the middle ring, no matter how hard I pedal. Also the sound is not torque dependent; it really doesn't matter if I pedal hard or not, it just makes the sound as long as I am on the large front ring.

Any suggestions? I don't want to come to Saratoga with an embarassing noisy bike!!

[Louis]

When I'm in the large ring I now get a gentle knock or tap when the left crankarm comes around about 1000, just where you're delivering maximum power. Coincidentally that's also when the right arm is passing the FD cage; at first I thought it was hitting the back of the crankarm but there is actually a couple of mm of clearance.

That was going to be my guess also - back of right crank arm hitting Fder cage. Are you absolutely sure that that is not what is happening due to deflection under load? When in the big ring does it not make the noise under low to medium load, but does make it under heavy load? Maybe the clearance is not what you think it is. Did you look for scrape marks? Try putting something on the back of the arm where it passes the cage - anything that would be affected by the cage, maybe some Scotch tape. That will confirm or rule out this particular explanation.

The one advantage of friction Fder - I can make the noise go away by trimming, which is the final proof that it is the cage / arm. Unfotunately, you can't do that.

Good Luck
Louis

[Ken Robb]

could the end of the cable be hitting the crank?

[CNY rider]

Louis I will have to look again as I ride home today, but it seems to do it even under light pedaling so I don't think I am flexing the frame and making the right crank hit the FD.

Ken that was my first thought too, but it's not the FD cable.

Thanks guys!

[Louis]

Last resort - rollers and an assistant with a mechanic's stethoscope.

[Too Tall]

Last resort - rollers and an assistant with a mechanic's stethoscope.
Oh you really caved on that one...too easy :rolleyes:

No no, disassemble clean chase prep. and examine every frickin' nut n bolt put it back together only to find the tick tick is still there arrrrrrrrg.

[William]

Chain ring bolts all tightened down?

Mess with your cleats recently?

The last time I had a similar situation it sounded like it was coming from every where but the BB. Tried everything to no avail. Then new BB, noise gone.

Go figure.



William

[rounder]

could the end of the cable be hitting the crank?

yeah...that's what i was wondering...that happened to me.

[CNY rider]

The answer is.......

The bottom of the FD cage was just low enough to skim a tooth from the middle ring when the chain was on the big ring.

A slight adjustment of the limit screw moved the inside of the cage just enough to get it away from the teeth of the middle ring.

Maybe this will help someone find their incredible annoying mystery sound in the future. :beer:

[manet]

The answer is.......

The bottom of the FD cage was just low enough to skim a tooth from the middle ring when the chain was on the big ring.

A slight adjustment of the limit screw moved the inside of the cage just enough to get it away from the teeth of the middle ring.

Maybe this will help someone find their incredible annoying mystery sound in the future. :beer:

ure crazy... file the teeth