Re: Chain Skipping problem fixed by grinding sprocket teeth.
Peter Cole 3 May 2005 20:13:55
Me wrote:> Most of us know that a chain skipping problem is usually caused by> worn sprocket teeth (rounded teeth causing the chain rollers to roll> over them too early and skip). I was all set to head to the LBS (local> bike shop) and cough up $100.00 or more to get new chainrings,> cassette, and chain installed but remembered reading a couple of> websites that mentioned fixing the problem by filing or grinding the> pressure side of the sprocket teeth flat again. So I figured I'd give> it a try. If I screwed it up and it didn't work, I wouldn't lose> anything anyway because I was going to replace the parts anyway.
I didn't take long at all to buzz the> pressure side of the teeth on my 24 tooth granny gear flat again. I> jumped on my bike and went looking for a steep hill to check my work. I> was totally surprised there was no skipping at all. Has anyone else> done this? How many miles can I expect to get?
Not very many. It's an OK fix to buy you the time you need to find a good deal on replacement chainrings. Most chainrings are so expensive you could throw the crank away...
remembered reading a couple of>> websites that mentioned fixing the problem by filing or grinding the>> pressure side of the sprocket teeth flat again. So I figured I'd give>> it a try.> ...>> I didn't take long at all to buzz the>> pressure side of the teeth on my 24 tooth granny gear flat again. I>> jumped on my bike and went looking for a steep hill to check my work.> I>> was totally surprised there was no skipping at all. Has anyone else>> done this? How many miles can I expect to get?>
This is a very difficult operation to do without changing the ring's> effective pitch. If you change the ring's pitch, you quickly wreck> both the ring and the chain, which in turn wears out your other rings.> This happens because a mismatch in pitch causes the chain's load to be> borne by a single tooth and roller at a time.>
Of course, by the time you have reasons to contemplate such a crude> fix, most of the damage has probably been done already.>
Your improvised repair seems like a good way to wring the last miles> out of a tired drivetrain, and with any luck it will serve you for a> useful amount of extra time. When the time comes that you have to> replace anything, though, do yourself a favor and replace everything> together-- the chain, cassette, and all three rings.
Why the rings, assuming they're not yet causing the chain to skip?
-- Benjamin Lewis
Although the moon is smaller than the earth, it is farther away.
Because the old knackered chain will have worn them into an effective> pitch length that doesn't match the new chain. So the old rings will> quickly wear the new chain, which will then trash the new cassette.
OK, dumb question time. You have a fixed number of teeth on the chainring, and a fixed diameter. How can you change the pitch (distance between the teeth) that the chain sees? Aside from nominal variations caused by inconsistent grinding of the teeth?
If you're causing the chain to ride lower on the chainring, I can see where that would cause a problem (because the distance between each tooth would, in fact, be smaller at a point closer to the chainring's center).
Because the old knackered chain will have worn them into an>> effective pitch length that doesn't match the new chain. So the>> old rings will quickly wear the new chain, which will then trash>> the new cassette.
OK, dumb question time. You have a fixed number of teeth on the> chainring, and a fixed diameter. How can you change the pitch> (distance between the teeth) that the chain sees? Aside from> nominal variations caused by inconsistent grinding of the teeth?
A worn chain has a larger pitch and therefore rides higher on the cogs than a new chain would. In this process wear pockets, at the radius on which the chain rides on exit, are formed. It is this larger pitch into which the out-of-pitch chain rolls with every passage after entering on the base circle. This generates ramps to the larger radius (greater pitch) on which a new chain rolls up under load and prevents engagement of incoming rollers.
If you're causing the chain to ride lower on the chainring, I can> see where that would cause a problem (because the distance between> each tooth would, in fact, be smaller at a point closer to the> chainring's center).
This is primarily a problem for driven sprockets, not driving sprockets that are forcefully engaged under load. However, chain suck on driving sprockets is another problem.
Meanwhile, because most sprockets are case hardened, modifying cogs to accept a new chain is a short term fix because the sprocket is most likely worn into the soft core if that is necessary.
