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!