parksung

When I get off the seat and peddle harder, I notice a grinding on the chain, as if it might even come off. I usually ride harder in 5th gear, and I haven't noticed it in other gears.

Does this call for a new pulley, derailleur, etc. or just a tuneup to tighten some parts?

spwelton

Probably the chain is rubbing the front derailler. It just needs adjusted. Most bike shops will do it for dirt cheap or there's a ton of good info on the internet on how to do it yourself. Basically though, there's a barrel adjuster on teh cable going to the front derailler. Turning that will adjust it in or out slightly. See if turning that a bit and watching the derailler to see if its rubbing makes the sound go away.

cny-bikeman

Rubbing of the chain on FD is usually described as scraping rather than grinding. If the grinding is a feeling as well as sound then your cog may be worn. BUT we need more info - what do youi mean by "5th gear." Do you mean the 5th cog on a 5 speed freewheel, and if so is it the small cog? Do you have just a 5 speed bike or do you have a 10 speed and ride that cog hard on the large chainwheel also?

parksung

it's the 5th cog on 5 speed freewheel, the small cog. it's a 10 speed bike. the grinding sounds like the chain isn't on completely, and it seems to be coming from the pulley or RD

due ruote 

More info may be needed to answer your question. Are you on the large or small chainring? If the small, you are doing what's called cross-chaining ie. going from the inner front to the outer rear. This and its inverse are best avoided; ideally you want your chainline as straight as possible, given, of course, that most gears necessitate a slight angle one way or the other. That said, cross-chaining is less of an issue with a 5-speed freewheel.
If it really only grinds when you stand and pedal hard, my guess would have been that you're flexing the frame a bit, causing the front derailleur to rub, probably only on one of the downstrokes. If that's the case, you can trim (move slightly without actually shifting) the front der. to stop the rubbing.
If it's really not the front der. but something in the rear, it's possible that you're cross-chaining and the chain is rubbing the 4th position cog slightly.
I doubt that the noise is coming from your rear derailleur per se.

cny-bikeman

OK, that helps. If you ride hard in that gear the odds are very high that it is worn (and possibly the chain as well). If so it's of course going to show up much more when you stand on the pedals. Aside from cross chaining even the small chainwheel on the typical 10 speed (42 tooth for example) combined with a 14 tooth rear cog is a fairly high gear -81 inches vs 100 inches for a 52/14. Accelerating in that gear (or trying to) is going to wear the bike faster and will not get you in shape better.

Unless one is sprinting out of the saddle, shifting to a higher gear is done when one reaches an appropriate minimum speed for that gear or are reving too fast for the gear one is in, not when one wants to go faster. Even out of the saddle in an 81 inch gear you should be going a good a good 18+ mph, and 21+ or so in a 100 inch gear.

Again, I don't see a scenario where the pulleys would be a factor - unless you have extreme frame flex when out of the saddle, you are riding the small/small combo, and the chain is therefore coming onto the lower pulley at a bad angle.