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Loose Crank arm on mountain bike...? |
The last mountain bike I bought, the Left crank arm came loose and fell off during a ride... I had checked it when I got it home from the store... it was tight, so I figured I'd upgrade and get a more expensive bike that was less likely to work loose... was out riding my new bike and the same thing happened... Could I possibly be doing something that is causeing this, or am I just gonna have to deal with retightening my left crank arm every other day??? You can have the most expensive bike on the planet and the crankarm will still fall off if it works loose. Depending on the material the crankarm is made of, a crankarm that is ridden loose may flare at the point at which it meets the spindle and may never tighten properly again. Try this: Once you have verified that the part of your crankarm that seats on the bottom bracket spindle is NOT damaged from being ridden while loose, put a drop of light-duty thread-locking compound (like blue Loc-tite) on the threads. Make sure that there is no grease or anything else on the BB spindle before putting on the crankarm. Put on the fastening bolt and tighten it down until the crankarm seats most of the way. Finish tightening it down with a torque wrench. Check with your crank manufacturer for proper torque specs, but the average alloy crank, for example is good at 30 ft-lbs. If you are concerned about your crankarms working loose again, simply check them with the torque wrench from time to time. Hope this helps. The exact same thing happened to my then-new mountain bike a few years ago.. The threading on the bottom bracket was stripped due to improper assembly, so no matter how much the crank arm was tightened, it keeps working itself loose. It was under warranty so the bike shop that I purchased it from fixed it for free. They swapped out the bottom bracket and put on a new crankset (including new chainrings). This time it was properly installed and the crank hasn't loosened after 4 years of my abuse. :-D Take your bike back to the shop you bought it from and have them fix it. Good luck! |
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