Crank 'knock' - what is it?

[griffter]

Hi all, I'd welcome opinions please. I have a red b'twin triban 3 and the right crank arm knocks and slips slightly when pushing up hill. It's done it more or less since new, but having dragged the bike out for the winter I want to fix it. Crank arms are tight, chain rings are tight and pedals are fine. It's only the right arm which knocks and it all but disappears after 10-15 miles. There is no obvious play anywhere I can find.

I'm going to change the bottom bracket unless anyone has any other ideas?

Thanks.

[Barchettaman]

Before changing the BB, remove it, clean the cups, grease the metal cup (not the plastic one) and replace. Worth a go.

[Black can man]

Sounds like the bottom bracket , i changed mine with a new chain & cassette , soon sorted it ,


May be worth asking your LBS to have a look. The guy near me is as miserable as sin but he know's what he's doing with bikes.Worth his weight in gold.

[griffter]

Thanks both, have removed the BB. It's a sealed cartridge, so no bearings to grease.
The lock rings, or whatever you call them, were only finger tight in the frame, so it could have been slipping in the frame.
However it feels rough when turned by hand on the spindle, so for the sake of £15 I've ordered a new UN55 from crc.
Hopefully that will do the trick, but I'll never know whether it was the bearings or being loose in the frame that was the cause..

[matt-ITR]

If it is slipping, then that won't be the BB.

Most like the freehub or possibly the gears/chain.

[griffter]

I agree with you in theory (!) but in practice it's had a new freehub when I fitted new wheels. If it was the chain or gears, why would it only do it on the right hand crank stroke?

I'll report back when I've fitted the new BB.

Thanks.

[griffter]

New BB solved it. Whether the 'slip' was worn bearings (the old one was rough when turned by hand once removed) or whether the old cartridge was moving slightly in the BB tube because it was only finger tight, I don't know.

Thanks for views.