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I am getting a nasty clunky/grindy sound from my drive train, mainly when its under load. can also feel it through both peddles.

so I'm thinking it is either, A. the chain and chainring not marrying up properly, or B. a problem with the BB.

wondering if anyone might have any ideas or experience of this before? like I said, it seems pronounced when the drive train is under load then as the peddling eases it goes away. could the bearings in the BB be grinding? or is it more likely to be the chain grinding on the teeth of the chainring?

am thinking about swapping out the drive train, found a deore xt groupset minus brakes for 320 but wanted to hold off till next month as I just splashed out on New forks.

any ideas or advice would be welcome.

It doesn't work for everything but ages back I put this together.. weird I did it cos my bikes always squeak haha

Might help the process of debugging the strange noise. - sounds like bb to me but quite often you have to eliminate 10 things to find the one thing which s causing the issue.

Im 99.9% sure its your bb! i get bikes with the same symptons everyday in at our workshop! its normally a flat spot on a bearing so its still in the race but grinding when it starts flexing (under load)

what bike do you ride? it will give us info as to what type of bb you have
i.e...
a sealed bb or a semi sealed or a cheap 3 piece?

Very handy

Karve - that's a good flowchart you've got there! Did you make it yourself, or is it a well-known thing? Personally the only flow-chart I've had to use is this one:

It came from this thread

http://www.essexhertsmtb.co.uk/mountain ... 66-15.html

I should update it as I have a few more to add in there - ie it took ages for me recently to work out it wasn't my pivots squeaking but my saddle rails. If anyone want to add to it - change stuff out let me know

hah ha thats a sweet diag

Tom, its a trek marlin. I tried to have a peek today but the dust cap on the chainring side crank wouldn't budge so couldn't get the crank off to get at the BB. it was ok last Sunday when I was out riding. then today, rode to the shops and heard it. sounds like a grinding clunk. constant though, not just one clunk per rev, but all the time when under load, then as the load eases it goes away until I change up gear and put load back on. that's what made me think it could be the chain on the chainring.

gonna have another go at the crank tomorrow and see if I can get to the BB. clean it and re-grease it. like I said, I intend to change out the drivetrain to a XT 2x10 but wanted to wait a bit to do it.

thanks for the flow chart too. that points to a BB problem

Make sure your chain and chainring are clean before you do anything? And where are you based? Ur welcome to come along to my work and I'll have a look for ya! I'm in Harlow don't know where u are so don't know how far it is!

I'm in chafford hundred tom, thanks for the offer. chain and chainring are clean and lubed. its a square taper BB I believe. been reading up, and "creaking" would be a good description of the sound/feel I'm getting.

really need to get past the crank fixing bolt, then I can get th BB out and give it a good clean and re-grease.

might have to bash the credit card and do the upgrade sooner rather than later.

cheers for your advice and thoughts everyone

Had the same noise last week........bought a new BB £30.00...........job done...noise gone

Paul, your bike is a fairly new buy isn't it? If so it sound like it is just a case of giving the BB tapers a clear and a bit of grease and then tightening everything back up to the correct torque (after checking these hasn't been any damage to the crank from shifting about on the BB axel).
When the BB and/or chainset are newly fitted they will often require a bit of tightening after the first few rides as the bed in, especially for cotterless (square tapered) BB's. This is one of the reasons when splined systems were introduced.

Thanks for the advice and opinions people. I stripped out the BB today, cleaned it all up, lubed and greased it and put it back together, and hey presto. no creaking! maybe I shoulda just gone there in the first place.

drive train upgrade will be planned for next month. deore XT 2x10. lovely.