Help with unknown problem

[G-manUK]

Hi People,

I wonder if anyone out there can help me with a bike problem I've got.
I'm a leisure cyclist on a hybrid bike and I get this issue normally about 20-30 mins into a ride. I start getting a knocking/banging noise coming from the chain area. Normally starts softly and gradually gets louder. The chain isn't hitting anything that would cause the noise.
Could this be the chain stretching over time, and slipping on the chainring?
Any ideas? I'm using a relatively new KMC half silver chain.

Thanks

 

[gbb]

Hi Gman, and welcome...
1/2 hour in is a bit confusing, but it could well be your BB (botton bracket). Thats the bearings that support your crank axle. Sometimes, as wear sets in, the bearings dont seat properly and jam, causing a knock / bang.
Could be other things like your chain slipping on the chainrings, but i'd have thought it would happen more regularly.
Cant think how much a LBS would charge to replace a BB...they're not very expensive.
Perhaps a visit to them is in order to get some advice ?

 

[chillyuk]

Are you certain it is from the transmission. Bike noises have a habit of coming from one place and sounding as if from another! You say a nearly new chain, did you change your freewheel or casette at the same time.

Does the noise stop if you stop pedalling and just freewheel.

 

[colinr]

I had something like this and it was handlebars, though I would've sworn blind it was in the transmission.

 

[Sam Kennedy]

Try This:
Stand over your bike and hold the front brake, push the bike backwards and forwards(with the brake still on), if you get the sound, then it is most likely your handlebars like colinr said.

 

[G-manUK]

Thanks for quick replies everyone. It's definitely not handlebars, and yes, only happens when peddling. Seems to be worse when chain is straining (eg going uphill)

 

[Virtual DBP]

LBS would probably charge about £40 fitted. i had one replaced recently and i'm sure that was the figure i paid.

 

[HLaB]

LBS would probably charge about £40 fitted. i had one replaced recently and i'm sure that was the figure i paid.

For a BB ? I can't remember what I paid but I think it was £14 for the BB, £7 to fit.

 

[Paulus]

Mrs P had a similar problem and it took me a while to trace it, but it was the rear wheel bearings. I took the bearings out, cleaned and re greased the hub and problem solved. See if there is any play on the rear axle.

 

[Randochap]

Could be BB ... or pedal. Drivetrain noises can be difficult to diagnose without experience. Suggest you take it in to LBS.

 

[G-manUK]

If it was the BB, shouldn't I still hear it when reverse peddling? There's no noise when I do this.

 

[purplepolly]

I start getting a knocking/banging noise coming from the chain area. Normally starts softly and gradually gets louder. The chain isn't hitting anything that would cause the noise.

Is there a rack? If so check that the fittings are all tight. (I speak from recent experience here - spent a couple of weeks wondering what an intermittent clunking was before I thought to check the rack)

 

[Mortiroloboy]

check the free hub too, could be starting to wear?

 

[accountantpete]

It'll probably be a heat build up somewhere along the line due to insufficent gease/oil.

I'd get the LBS to service the bottom bracket and hubs (helps anyway) and then see how it goes.

 

[Smoothhound]

Do you have a suspension seatpost?

I had a similar problem a couple of years back that I swore was the transmission and it turned about to be the suspension seatpost which creaked in time to my pedal stroke. I had similar symptoms including the delayed effect - I guess it was warming up? It was worse on the hills and under strain because you shift your weight around a bit more.

I have read since (probably here) that you can get a similar problem even with regular seatposts/saddles that may not be tightened correctly.

HTH