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Old 07-14-14, 04:09 PM   #1
WFRTony
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Timing Chainring Wear

On our last ride, I started to notice a popping sound/sensation through the pedal when we started from a dead stop. I just got done cleaning the bike and giving it a once over before RAGBRAI next weekend, and I noticed that a few of the teeth on the timing chainrings appear to be worn. The teeth that show the most wear are the ones that are engaged when we first start out with left pedal (which we have always done). Is this wear going to give us problems on RAGBRAI? Shall we switch to the right pedal when we start? Can I remove the chainrings and time them so the worn teeth are not engaged when we start?

If I need new chainrings, am I going to have a hard time finding them? It is a 1996 Shimano XT 8-speed.
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Old 07-14-14, 05:21 PM   #2
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I would personally replace the rings and chain. Don't think they can be rotated, I think the five arm pattern allows the rings to be mounted in only one position. Plus, every rotation still puts the worn teeth through the chain regardless of where you start. Short rides around home, ride it til it breaks...400 miles across Iowa backroads, invest in the peace of mind. Replacement shouldn't be a problem, some inexpensive rings of the right BCD and a "cheap" chain should do.

If it's making noise now, don't think I would trust it. IMO.
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Old 07-14-14, 08:29 PM   #3
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I'm guessing you removed the sync chain when you cleaned the bike? If so, and if the chain has been on there for a long time then the quick fix to eliminate the pitch difference between the chain and rings is to advance the chain by a single tooth.

Is this wear going to give us problems on RAGBRAI? So long as you get the original chain back in the original orientation / synchronization with the timing rings and can adjust out any slack in the sync chain it will work just fine.

Shall we switch to the right pedal when we start? Doesn't matter....

Can I remove the chainrings and time them so the worn teeth are not engaged when we start? Actually, unless someone else has done this once before, you can swap a set of well-worn timing rings from front back / back to front and have, in essence, a brand new set of timing rings. However, you'll need a new sync chain (takes 1.5 standard chains in most cases) as the old chain will have stretched too much to work on the fresh teeth with correct pitch.

If I need new chainrings, am I going to have a hard time finding them? It is a 1996 Shimano XT 8-speed. It shouldn't be too hard; they're basically middle / small chain rings. You just need to match the 4 or 5 arm configuration and bolt circle diameter with the replacement rings. You can use non-ramped and pinned rings or rings with ramps and pins; it doesn't matter. You can also use pretty much any matched pair of chain rings using anywhere from 34t - 42t; 38t - 42t are the norm.
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Old 07-15-14, 08:36 AM   #4
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I did not remove the chain, but I did notice that there is a lot of slack in the timing chain. I am going to try and take the slack out of the chain and see if it helps. Swapping the front and rear rings and a new chain will be Plan B.

Thanks for your help!!!
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