Bicycle Mechanics - what's that grinding sound?

Hi everyone I have a question, on my mountain bike when I am in first gear and pedal I can hear the chain grinding as I pedal, It used to do it for a while and then it was OK, it only happens in this gear ,the rest of them it doesn't happen, is this a problem with the chain.

Haven’t you changed your chain yet? It could be the chain hitting the front derailleur, have a look while the bike is stationary.

Gordon, I havent changed it yet, I have been busy But will change it ASAP:)

If you are in the large ring in the front and the large gear in the back, then you are what is called all crossed up, this is a no-no.

Kind of like Buzzbomb said...

If you are running the largest chainring in the front and the largest cog in the back/smallest chainring in the front and smallest cog in the back, you are running cross-over gear combos. These combos will not hurt anything, but can cause the "grinding" or metal rubbing metal sound that you might be hearing. The derrailleurs can usually be adjusted to eliminate this noise, but if there is some in these combos it isn't a big deal. You lso shouldn't be worried about running these combos. If you catch yourself in them and there isn't an ooportunity to shift out of them, don't worry. People say it is a no-no, but you won't cause any damage by running the combos inadvertantly every once in a while. The noise is caused by the chain rubbing against the inside of the front derailleur cage. This rubbing should be visible when holding the bike stationary and pedaling backward. If your rear deraillaur is not adjusted correctly you could be hearing the chain skippnig against the next cog, though this isn't likely to be the cause of the noise in your case.
As long as your chain is cleaned correctly, the rubbing should be coming from the chain and front derailleur. I don't see why it would be a chain replacement issue unless it is very used. I still couldn't see how this in itself would cause grinding though. Try measuring your chain with a ruler if you don't have a chain checker. If you place the end of the ruler in the middle of one pin, the other end of the ruler (12 inch) should be in the middle of another pin. I believe it is 24 half links? An 1/8 inch too long is plenty enough to mean the chain should be changed.

-Moab

Cross-chaining actually will wear out your gearset much more quickly if you persist running big-big or small-small. It also imposes additonal wear on the rollers and pins. And, if your chain is a link too short, you will have further troubles in shifting. But I'm thinking that's not your problem...

When you say first gear, presumably that means on the small chainring on the front and the large cog on the rear (which is A-OK, by the way). It is likley that your low-gear limit screw needs a tiny tweak to allow the derailleur cage to drop a little further than it has and thereby clear the chain as the links run past it. It's also likely you will need to adjust the cable to get this adjustment.

Originally posted by Rowan
Cross-chaining actually will wear out your gearset much more quickly if you persist running big-big or small-small. It also imposes additonal wear on the rollers and pins. And, if your chain is a link too short, you will have further troubles in shifting. But I'm thinking that's not your problem...

When you say first gear, presumably that means on the small chainring on the front and the large cog on the rear (which is A-OK, by the way). It is likley that your low-gear limit screw needs a tiny tweak to allow the derailleur cage to drop a little further than it has and thereby clear the chain as the links run past it. It's also likely you will need to adjust the cable to get this adjustment.

Thanks everyone, Rowan where would I find this low -gear screw?

there are 2 limit adjustment screws on the top of the front der cage. the ones for the rear der are at the pack of the parallelogram. there are 'H' and 'L' marked next to these screws

Thanks everyone, I have found the screws turned them and I cranked the pedals by hand, so far it seems to be working, but I have yet to ride it since I turned the screws, I will keep everyone updated.