cloudjessie42

Being new to cycling, I won't know many of the more technical terms to describe the problem I'm having with my crankset, but anyways:

I ride an old GT Talera (late 80s to early 90s), the crankset and front derailer is Shimano 200GS, and rear derailer is a newer Shimano Tourney. My problem is this: I noticed the chainrings spin in an elliptical pattern when the pedals are cranked, is this a result of wear and many years of use, or rather is this how this particular derailer was designed?

I ask because I have a problem with the chainring when I shift into the largest ring, the chain rubs against it slightly, no matter how I trim the derailer. I also notice the chainring wobbles side to side (from a top-down perspective), which causes the chainrub. Is there an easy fix for this besides buying a new crankset?

dabac

Chainrings and cranks, particularly of your vintage and price range, aren't rocket science. Some excentricity is to be expected. Bolted chainrings can be adjusted by loosening the bolts, identifying the point of maximum deviation and then tapping the chainring gently towards the bb.


The derailer has nothing to do with how your chainrings move.

There was a set of chainrings that were designed to be out of round called biopace plenty of years ago, but I don't think yours are those. If it's just the odd mm or so I'd put it down to the original assembly not being any better than that.

And this is a problem because it causes what?

Then I really wonder how you trim the derailer. Adjusting wire tension won't do a thing if the limit screws are set too tight. Some triple cranksets can be difficult to get to both run cleanly and to shift crisply. It's also dependent on what rear sprocket you're on. Chain rub while cross chaining is easiest addressed by not cross chaining.

I believe sheldonbrown.com has a page about straightening chainwheels, try that.

cloudjessie42

Thanks, the problem seems to be that the chainring wobbles side to side, so much so that it always rubs against the front derailer no matter how I would adjust it. I will take a look at the page for straightening chainrings, thanks.