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Old 02-14-10, 10:31 PM   #1
FasterthanU
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Banging from drivetrain on singlespeeds/fixies...

Hey dudes,

What is the cause of regular and periodic banging from the drivetrain on singlespeeds and fixies? Is it the sound of a side plate on the chain being lifted up onto the teeth on the cogs and then slapping back down on the cog when the chain tension forces it back down? Sometimes the banging is regular on a particular bike. Other times, it occurs at particular moments. For instance, on my current setup, it happens sometimes on the first pedal stroke after I've been coasting for awhile, or when I take off from a standstill. The sound is clearly a "bang." Let me know. -FTU
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Old 02-14-10, 10:44 PM   #2
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Hey dudes,

What is the cause of regular and periodic banging from the drivetrain on singlespeeds and fixies? Is it the sound of a side plate on the chain being lifted up onto the teeth on the cogs and then slapping back down on the cog when the chain tension forces it back down? Sometimes the banging is regular on a particular bike. Other times, it occurs at particular moments. For instance, on my current setup, it happens sometimes on the first pedal stroke after I've been coasting for awhile, or when I take off from a standstill. The sound is clearly a "bang." Let me know. -FTU
If it's a freewheel problem that won't apply to fixed gears. Banging - how's the chain tension? How's the freewheel? Has it been through a winter? Getting a hollow sound when you freewheel it?
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Old 02-14-10, 10:49 PM   #3
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I can understand grinding noises... but banging noises on a SS/fixed?
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Old 02-14-10, 11:21 PM   #4
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I'm running a new shimano freewheel. Chainline is decent. Tension is pretty good-- not too tight or loose. I've had this problem with brand new BMX bikes. It's similar to grinding from a chain that's too tight, but it's only occurring at certain times (as I mentioned). Again, it sounds like a "bang"
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Old 02-15-10, 01:05 AM   #5
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Broken axle?
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Old 02-15-10, 01:20 AM   #6
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Chainwheel or sprockets out of round/nonconcentric? Binding chain link?
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Old 02-15-10, 02:56 AM   #7
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On a single speed or multi speed if you snap the crank arms forward from freewheeling to driving the chain can snap pretty aggresively depending on how hard you do it. I try not to do this but occasionally I do it mildly. When that happens there's an audible snap sound from the chain as it hits hard after taking up the slack. Learn to NOT do this and ease into the forward drive mode so the chain transitions from no load to full load smoothly rather than with a snap.

Although a fixie doesn't freewheel there's still enough slack in the chain that if the rider transitions from dragging back to powerfully surgeing ahead that the chain will see pretty much the same snapping forces as the forward limit of the chain is hit.
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Old 02-15-10, 11:37 AM   #8
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What is the cause of regular and periodic banging from the drivetrain on singlespeeds and fixies? Is it the sound of a side plate on the chain being lifted up onto the teeth on the cogs and then slapping back down on the cog when the chain tension forces it back down?
I was dealing with the same noise for a while, and it invariably happened right after bunny-hopping. It was indeed the side plate of the chain being caught by the cog's teeth. What probably made the problem worse was a too-low chain tension and the fact that I used ramped cogs, both as chain guides and for the cog itself. I'm not sure whether the chain was getting caught by the teeth on the driving cog or the guides. I fixed the problem by switching to a 1/8" chain and SS-specific cogs, which allowed me to ditch the guides and use a slightly lower chain tension.

You might want to check the chain. The side plates on mine got all chewed up after only 50 miles!
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Old 02-15-10, 12:58 PM   #9
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Ah, yeah, if the chainline is a little off and/or the tension is a little too loose and depending on what you're using for gears then the side plates may tend to hang up on the teeth.

My first single speed was cobbled up from geared bike bits and used spacers to locate the rear cog. But because I had so much adjustment room to work with I was able to get the chainline all spot on with the crank ring. However I was using a cog from a broken apart old uniglide cassete that just had the tooth crests twisted to aid shifting. To avoid the side plates trying to catch on the tooth tops I likely ground and polished smooth the tips so they were tapered. Before I did this I'd get the odd occasion where the chain would hang up on the tooth and then snap home with a sharp crack. After lightly tapering the tips I seldom got it happening and it wasn't that loud. And in those cases it may well have been some grit or small pebble caught in the chain while riding in the wet. In the dry and when freshly cleaned it never did make any sort of sounds at all.
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