Clunking from bottom of bike - advice please

[Dwn]

I've noticed the last day or two that I have a distinct clunk coming from somewhere around the pedals/bottom bracket.

It only happens when I've been freewheeling and then begin to turn the pedals - the clunk comes just before power starts to go though the cranks.

The pedals themselves feel fine and there is no lateral movement in the crank arms. Does this sound like a bottom bracket problem? Bike is less than 2 years old and done about 2000 miles (although often in wet weather).

In the days when I didn't do much other than pump up tyres and oil the chain occasionally, nothing seemed to go wrong with my bikes. A developing interest in maintenance has coincided with one issue after another!

 

[Cycleops]

Oh dear, sorry, you haven’t had the best luck with mechanicals.
Could be the BB but might also be the freehub. Disconnect the chain and turn the cranks by hand and listen to hear if the noise is still present. Can you feel any roughness? What type of BB do you have?
Similarly remove the back wheel and turn the cassette, is the noise or roughness there? A good flushing out with WD40 might solve the freehub’s problems but the BB will need to be inspected and maybe replaced.

 

[Dwn]

Thanks for the advice - will try that in morning. I don't know the BB type, but have emailed the manufacturer (Decathlon) to ask. It's a Shimano 105 groupset, so guessing that they are the manufacturer.

 

[rogerzilla]

What type of bottom bracket is it? Shimano Hollowtech 2 (external cups), PF30 (larger diameter, bearings inside shell) or something else? PF30 doesn't much like getting wet and this often initiates creaking. HT2 usually copes better but isn't as waterproof as the old UN55 square-taper type.

 

[Cycleops]

if it is a Hollowtech type replacing the bearings is a cheap and very simple affair.

 

[Dwn]

I think it must be Hollowtech 2, going by comparing the photos of new BB's and the outside of the current one (photo attached). Can't make out the writing from the photo but will look closely tomorrow.

 

[Cycleops]

Yes, that’s Hollowtech.

 

[rogerzilla]

Yes, that's HT2. One tool does it all. The main gotcha is forgetting to deal with the annoying secondary retention device, a clip that is intended to retain the LH crank if the pinch bolts come undone.

 

[Dwn]

Looks like this one may be the replacement I need (if it is a bottom bracket problem). Apparently it fits 105 5800/5700 chainsets. The Park Tool bbt-9 seems to be the tool required.

Hopefully will be as straightforward as the YouTube video I just watched on how to remove and replace the BB is!

 

[Dwn]

Thanks for the advice - such a useful forum for beginners!

 

[Ajax Bay]

I'd echo Roger. The symptoms described in the OP wouldn't drive me straight to the 'replace BB' solution.
Yes you have an HT2 chainset/BB but, as @Cycleops suggested, consider and eliminate (or otherwise) other stuff like freehub.

 

[Dwn]

Just had a check and the cassette was indeed loose! I'm a little surprised by that since I thought I had tightened it properly when I changed wheelset, but it definitely needed further tightening. Will go for a cycle this afternoon to confirm.

Thanks everyone.

 

[Dwn]

Went for a short cycle and all seems well but will keep an eye on cassette for the time being. Thanks again

 

[si_c]

Nice easy cheap fix. My thoughts there wouldn't have gone to the BB as there is nothing in there to clunk really.

 

[Dwn]

I was out on my other bike yesterday and same thing happened. I've recently changed the wheelset on both bikes and it's now clear that I just hadn't applied enough force to the cassette lockrings. Lesson now learned.