Singlespeed & Fixed Gear - Back pressure question
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02-26-12, 01:23 PM
I noticed today that my bottom bracket, crank, chainring, chain, cog or rear hub is making a grinding-crunchy sound when I back pressure as I'm slowing down. If I just use brakes, and slow down then there is no noise and the drive train runs smooth as silk.
So I'm assuming its somewhere in the engagement of the chainring/chain.
There is play in the chain, but not that much, maybe 2" on the bottom. The top play is less than 1/4" an inch. By comparison my wife's Fuji Betsy (traditional track dropouts) has about an inch of play on the top and 2-2 1/2" of play on the bottom.
Chain alignment looks good between the rear cog and chainring, but I did notice my chainring is just a little - like 1/16th to 1/32nd of an inch narrower than the chain linkage per tooth. Its just over halfway basically. On the rear cog, the chain-to-tooth fit is exact.
02-26-12, 01:52 PM
2" at the bottom with <1/4" at the top? That's weird.
Generally this is just an issue with the rollers of the chain engaging the rear cog. Under lighter chain tension it's normal to have a small amount of play, that can also lead to noise when backpedaling.
If it's bothering you go ahead and increase the tension a little bit.
02-26-12, 02:53 PM
I would take your cranks off and clean your spindles, also make sure your chainring bolts are tight.
02-26-12, 03:18 PM
02-26-12, 07:22 PM
You very well could have a damaged link (or several) in your chain, typically caused by repeated breaking your chain with a chain breaker tool. Actually, sometimes all it takes is one time where the link isn't put back together just right and there is some play in that one link. I've had this problem before too and it literally drove me crazy to the point where I would wake up at night thinking about it.
What chain are you using? The problem is much more common with KMC K710 chains and others with "mushroomed" pins.
02-27-12, 06:13 PM
Sram PC7X-Ni chain. It's a sub-200 mile drive train so far. I removed the wheel last night just to see if there was any stuck or funky links but nothing felt readily apparent. I'm still wondering if I'm getting play between the chain and the crank teeth when I'm braking. Lateral movement of some sort since there's just enough room in there to get some wiggle (I'm guessing 1/16th of an inch.
02-27-12, 07:51 PM
You won't always be able to feel a slightly damaged link with your hand. Some play between your chain and chainring/cog is normal, otherwise your drivetrain would barely move.
02-27-12, 08:39 PM
My bike does this exact same thing, its because my spindles are dirty. If you hear the creak when applying back pressure, does it creak again when you mash your pedals forward?
02-27-12, 08:54 PM
Nope, it goes stone quiet on forward stroke pressure. It is specific to back pressure at stops or when slowing. Its chainring/chain oriented because it sounds exactly like the chain itself is grinding on the teeth of the chainring. I'm going to pick up a second chain and see if I can eliminate it that way.
Go figure that after this little annoyance my wife goes and destroys her cheap ass freewheel on her Fuji. So I flipped her to the fixed cog (after tightening down the lock ring properly) and her first comment. "Isn't that (pointing at my rear freewheel) the same size as mine? Why can't I just use yours since you aren't?" Mine is a $90 White Industries ENO freewheel. Lesigh. The things we do for love and 14 year marriages.
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