Originally Posted by CliffordK

I'm not exactly sure what is worn.

Years ago I was using one of the bottle generators. The toothed wheel on the generator engaged the tire near the top of the wheel and had worn smooth. So, I was able to simply remove that toothed wheel and turn it upside down, giving me almost new teeth to engage the tire once again.

I'm not sure if it was supposed to be reversible, but it was close enough that it worked fine.