Clicking in just one chainring

Question

I wonder if anyone can suggest any reason why I might be getting a regular clicking (two to each crank revolution, at the same place each time) from the crank/BB area of my bike. I understand these things can be difficult to diagnose, but just hoping I can be guided down the most likely paths.

I recently took the bike to a shop and they said the only thing they could do was replace the free wheel, which I found odd as the sound is unmistakably coming from the front end of the drive train. I can't spot anything visually wrong as I turn the crank, but the clicking only happens in the second chainring, not the first or third. I've had a good look at this chainring and it doesn't look excessively worn, although there is the odd tooth that is clearly much more pointed that the rest, to the point of resembling knives. Also the chain runs clear of the front derailleur, so I'm guessing that can't play a part in this.

Could it be that the chainring just needs replacing? Any other suggestions gratefully received! Thanks.

Answer 1

Inspect the teeth of the chainring for damage. A single one might be damaged from hitting some obstacle. It may then produce a click when taking up the chain at the top and again as it drops the chain at the bottom of the turn.

The best way to do this would be to suspend the bike and have the chainrings at eye-level. Don't turn the bike upside down because it could change the conditions under which the clicking appears. Also try out whether the clicking appears when the crank is turned backwards.

Good luck and patience because sources of noises are notoriously hard to spot.

Answer 2

Also check the left/right position of the tip of the suspect teeth. Sometimes a chain can sit on top for a brief instant, then the chain drops once the load increases.

Its even possible a minor Burr on a tooth can cause this same effect.

You can also get more miles out of your crankset by using the bigger chainring a bit more - it has pretty minimal wear by comparison with your middle ring.

As for changing the single chainring, that depends whether your crankset is bolted together or rivetted. Many MTB triples are rivetted because it decreases production costs. Drilling out rivets tends to not work because they're enormous, hard to re-rivet, and chainring bolts don't fit.
So clean it and look for bolts, and if you're lucky shop around for a suitable chainring with the same bolt hole pattern and count, and ideally the same number of teeth, though you can go plus or minus 2 well enough.