Bicycle Mechanics - Crazy Crank Clank
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05-20-12, 09:32 PM
I am being driven mad by a mysterious clanking noise on a Trek FX 7.7. It seems to be emanating from the left crank, though with an aluminum frame it's always a little difficult to pinpoint. The clank only happens when I'm applying torque, and not always then. It's inconsistent, but seems to be getting more and more persistent. Happens on both the large and middle chainring (I don't use the smallest, so I don't know about that one).
I've checked the bolts and nothing obvious is loose.
The bike is a 2010 model that was purchased in 2011 and then sold to me after having been used very little. I, on the other hand, have used it daily since February of this year.
If anyone has suggestions for diagnosing or eliminating, I would be grateful.
Thanks in advance,
05-20-12, 10:13 PM
You state that you have checked the "bolts". Have you checked the pedals as well? Clean and grease both pedal and crank threads and torque them correctly with a proper pedal wrench. I prefer to use stainless pedal washers as well. Also clean and adjust the pedal bearings if they are serviceable. If no joy, suggest you swap out your pedals, with platform type if available to eliminate clipless cleat issues, if used, as well as pedal problems.
05-21-12, 01:02 AM
Yeah, pedals. If the crank arm bolts aren't loose, that's the next thing to check. For some reason it took me a long time to get that fixed in my brain. I'm sure I'd be embarrassed if I had to count the times I tore apart a crankset and bottom bracket chasing a noise like that, only to find it in a pedal after there was nothing else left to check. I finally learned. I hope.
05-21-12, 11:37 AM
I'm lazy and cheap so I do the easy/free things first if nothing's immediately obvious. Pulling apart a crankset and bottom bracket is a lot of work, checking bolts and pedals isn't.
05-21-12, 12:58 PM
When it regards a bike, a clank implies to me a loud, almost scary sound. Most drive trains sounds are more often described as clicking or creaking. If the sound is very loud I would advise you determine the cause as soon as possible. If tightening all bolts and the pedals does not eliminate it then I advise you to take it to a shop. If you had BB tools and knowledge to use them I would assume you would have already tried that route, and most good mechanics can trace a noise pretty quickly.
05-21-12, 01:52 PM
a clank almost sounds like a broken frame
05-21-12, 02:21 PM
Or a left crank hitting a kickstand. Didn't say if there was a kickstand.
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