Chain possibly grinding against frame?

[GetHerned]

I've got a Specialized Hardrock base model that's about three months old. I've since replaced the rear cassette with a seven-speed Shimano (I believe this fella ) set. I know that this set is designed for road bikes, but it better fits the way I ride and the mechanic at my local bike store assured me that it would work with my other parts.

Since I've reinstalled the rear wheel, there's been a fairly persistent grinding that I can both hear and feel in the pedals. It's extremely pronounced at low speed, but tends to disappear at high speed. When I stand on the pedals and crank heavily, it's extremely pronounced and accompanied by a loud groaning noise.

I've had the bike in two shops, hoping that the mechanics would find a solution. They've readjusted the front and rear derailleurs, lubed the cables...the second shop took a few links out of my chain, and also said that I ought change to a medium or short-arm derailleur. The bike is now shifting like a champ, but the grinding noise is still persistent.

After today's ride, I discovered that underneath the path of the chain, the paint on my frame is starting to get a bit scraped and worn. It makes sense that the chain is rubbing against the frame - I'm just not sure why.

Is there any way that I can fix this?

[xerxes]

Chains will generally slap the frame if you go over bumps or down curbs, so most people fit a chainstay protector, something like this:

[attachment=1012]

They come in several styles, some are like a thin piece of self adhesive rigid plastic others are a neoprene sleeve, like the one above, that wraps around the stay and velcros together. You can also make one by using some electrical tape or zip ties to hold a length of split garden hose pipe along the top of the chainstay.

I'm not sure about the persistent grinding noise however, have you checked the wheel bearings? Does it happen only when you pedal, or when you freewheel as well?

[GetHerned]

(06-13-2010, 11:57 PM)xerxes Wrote:  I'm not sure about the persistent grinding noise however, have you checked the wheel bearings? Does it happen only when you pedal, or when you freewheel as well?

It's only when I pedal - it disappears in freewheel. I know the wheel bearings are very slightly out of jive, but not enough to create the noise that I'm getting. I also get an extremely crunchy feeling in the pedals - at first I thought it was the chain grinding against the front derailleur, but I've had that thoroughly adjusted and it's not the problem.

Thank you for your responses!

[xerxes]

Quote:It's only when I pedal - it disappears in freewheel.

Have you checked the bottom bracket and pedal bearings?

[GetHerned]

(06-14-2010, 08:44 AM)xerxes Wrote:  

Quote:It's only when I pedal - it disappears in freewheel.

Have you checked the bottom bracket and pedal bearings?

I have not - would a bottom bracket/pedal bearing issue smooth itself out at high RPMs and be more pronounced at low?

Is there anything else you'd suggest I should check? I'm basically compiling as much info as I can for when I take my bike back to the shop - any other suggestions would be fantastic.

[xerxes]

Quote:I have not - would a bottom bracket/pedal bearing issue smooth itself out at high RPMs and be more pronounced at low?

I'm sure if I had the bike in front of me I could find any problems quite quickly, but it's quite difficult via text.

In very general terms, all bearings, headset, wheels, bottom bracket and pedals should be smooth and free, but without any play or slop. If they are not smooth, or their is excessive play, depending on their type and condition, they will need to be either adjusted, or replaced.

[cyclerUK]

Unlikely but check that the top dérailleur jockey wheel is clear of the sprockets.
A jockey wheel would cause a grinding noise if the "B" screw isn't adjusted properly?
You can check this by lifting the bike clear of the ground and turning the pedals.
If you swing the dérailleur down the noise should go away.

[Billy]

Which gear combination are you in when you hear the noise? Put it on the middle ring and run through all seven in the rear, then try it with the inner and outer rings. Any difference?