Bottom Bracket Clunk - sorted

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maxglide
Posts: 178
Joined: 19 May 2013, 5:35pm

Bottom Bracket Clunk - sorted

Postby maxglide » 22 Mar 2019, 6:07pm

I've had this occur on two different bikes:

At each rotation at the 12 o'clock position, the right crank makes a loud clunk. The immediate thought is a dodgy BB, although in the first instance, it happened on a new bike. After a few rides, it disappeared never to return.

Fast forward a couple of years to last week, and it happened again on a different bike. Same noise, same position. Not in possession of either a crank puller nor a BB tool, the only option was to mess with the pedals & crank bolt.

The pedals were removed, threads WD-40'd, cleaned & greased, then screwed in firmly with the 15mm spanner. Same for the crank bolt with a 14mm socket. These were screwed back in gorilla tight. Just returned from a ride and the noise is gorn. Didn't hear that clunk once.

Brucey
Posts: 34864
Joined: 4 Jan 2012, 6:25pm

Re: Bottom Bracket Clunk - sorted

Postby Brucey » 22 Mar 2019, 6:17pm

it still might have been a dodgy bottom bracket. The reason the RH BB cup screws into the frame using a LH thread is so that the RH cup doesn't tend to back out (precess) of the frame in use. In fact it may self-tighten. Pedal threads are similarly handed, and for similar reasons; however if the spanner flats extend as far as the crank, they may inhibit beneficial precession, and leave the pedal flapping around in the crank until it is tightened using a spanner.

It is SOP to check all the fastenings around the BB on a new bike, after a few hundred miles of use.

cheers
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