Bicycle Mechanics - Chain tension
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I work part time for a local bike rental. I'm the sole mechanic for about 250 bikes. Primarily, we rent out the beach cruisers. My number one time consumers are loose and broken chains. What I have noticed is that whenever I tighten a chain, or even replace one, It never has a uniform tension. If I crank it around a half turn, the chain is tight. Another half turn, and the chain seems loose again. Thinking a stretched chain, I'd replace it, yet the problem still persists. I've even gone as far as rebuilding the rear and crank hubs, replacing bearing sets and races. The cups are a little gunked up sometimes, but seem to be in good enough condition after a good cleaning. They're just not as easy for me to replace out, so I have to leave them in. Any ideas?
07-20-00, 10:40 AM
Usally a beach cruiser is a single speed bike. The problem you described is caused from the single front sprocket being uneven, or not centered when it is installed on the cranks. Sometimes, the center hole on the sprocket is a little too big. There are a couple things you can try. By lightly tapping a hammer on the sprocket you can try to center the sprocket on the crank. In this method you do not have to overhaul the bottom bracket. But be careful! Tapping too hard can result in a bent sprocket or damaged chain. The other option is to remove the crank arm and loosen the inside adjusting cone that holds the sprocket, and try to center the sprocket on the crank arm. The problem with this option is that the sprocket moves off center everytime you tighten it.
Very seldom is the problem caused from the rear sprocket in my experience.
Also try a serrated lock washer on the rear wheel, one that bites into the frame of the bike. This will reduce the rear wheel from slipping forward when people rent them.
Just a side note: Don't get discouraged! Some bikes are next to impossible to center the front sprocket. I have wasted many an hour trying without success! Good luck!
Thanks for the info. I have recently ordered a couple boxes of the serrated washers and they seem to be helping with the intial loosening of the chain. I'll take a closer look at the sprocket setup closer. There might be a chance that I have it a little over tightened. Holding the cone and tightening that hex is kinduva pain in the ***. I'll have to find the sweet spot. Most of the bikes with these symptoms don't have the bent cranks, but I'll look closer. Bottom line is, these tourists out here really do treat these bikes like their somone elses. The bikes get a lot of hours on them and get beat up pretty bad sometimes. There's only so much I can do. That, and these aren't really your top-of-the-line bikes here. Again, thanks for the response.
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