Bicycle Mechanics - Left Crank/Pedal Thump

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Portis

06-28-04, 08:01 PM

I have had a chronic "thunk" on my left side. I have tightened the crank and pedal continually and it seems to go away for a day or two only to return. How do I troubleshoot this to isolate the problem. I see no symptom without me on the bike pedaling. IOW, i can pedal it in the stand all day and it is symptom free.

I imagine the BB is the next suspect but why does it seem to go away when i tighten the pedal or crank?

seely

06-28-04, 09:00 PM

It probably goes away because your crank is loosening up? Is it square taper? If it is I would suspect that the hole on the crank arm is worn and slightly rounded out. If this is the case as it works itself ever so slightly loose you start to get some play in the arm.