Bicycle Mechanics - Roughness/"crunchiness" in my drivetrain

Hey all. For the last couple months, I've been noticing a slightly bumpy or grating feeling in my drivetrain. It's pretty subtle, but it's definitely there, and I've been trying to figure out what it's from. Well, I took a careful look at my rear derailer and freewheel, and noticed that my chain isn't meshing quite perfectly with my freewheel cog teeth. If I get my derailer lined up perfectly (friction shifting), the feeling goes away when spinning the pedals by hand with the bike off the ground, but I can still feel it a bit when riding - not surprising given the much greater force involved. If the derailer is even the slightest bit off, though, I can feel it even in my hands. I can see it happening, too - the chain slips very slightly as each link 'settles' into a better fit than it engages the cog with.

This probably seems like an obvious wear problem, but I'm not one hundred percent certain. The freewheel doesn't really look worn to me - there's no "shark tooth" effect, and no worn-down looking cogs. However, I don't really know how many miles there were on this freewheel before I got the bike - I've probably put around 1500 miles on it since I purchased it, used. The chain is one that I bought, but it only has around 500, maybe 600 miles on it, and it didn't appear to have any stretch when I measured it. For what its worth, the chain is a "z" chain, and was pretty darn cheap. Did I skimp too much on the chain?

So, what do y'all think? Is it time for a new (better) chain? A new freewheel? If the latter, I have a quick question about that, too. Right now I'm using a six-speed freewheel. My frame has 126mm spacing, so the logical thing to do would be to upgrade to a seven-speed when I replace the freewheel. If I do so, will I be able to just screw it on and be all set, or will I need to re-dish my wheel or reposition the washers on my hub or anything like that? I'm hoping not, but you gotta do what you gotta do.

Thanks a lot!

If the dish is OK now there won't be a need to change it. A 7-speed freewheel would make a good upgrade, just be sure to get the gearing you need. If the chain is dirty, cleaning and lubing may reduce the noise.


Al

for what its worth, i bought a brand new bike this spring, did alot of hilly single track, after 400 kms i started to hear noises from the drivetrain
i checked the crank, chainrings chain, freewheel...
long story short, the shimano hg 9speed chain was stretched about 4mm longer than a new chain
i put on an sram chain and that solved the problem.
i also understand that the sram chains are stronger than shimano chains.
also a factor i am sure is the fact that i wiegh about 195 lbs.

Chain and freewheel should be replaced together. Probably the reason that you've been feeling this grittiness is that the freewheel had worn enough to fit the old chain (and vice versa), but the new chain now doesn't match the freewheel. If you decide to replace the freewheel, get a new chain just in case this one's become too worn, then try them both. With a new chain and freewheel, you shouldn't have any problems.

Thanks for the replies. If I do get a new freewheel, then I would definitely purchase a new chain at the same time. No question at all. Anyway, cleanliness isn't really the issue - I cleaned it last week! That freewheel has never been cleaner (while I've owned it). Hrm. Paycheck tomorrow. Perhaps it's time for that upgrade to seven speed :rolleyes:. I've got my eye on one of those 14-34 "Megarange" freewheels. Or maybe a 13-14. Oh, the possibilities!