If you hear clunking noises or feel heavy metal knocks coming from between your bicycle cranks, chances are high the cranks have loosened or the bottom bracket spline has bent and needs to be replaced. Before you remove the cranks, try a quick fix of simply tightening the crank hex screws. If this does not work, remove the cranks and replace the bottom bracket. This task requires approximately two hours in a home workshop.
- Skill level:
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Things you need
- Bicycle work stand
- Two 8-mm Allen wrench
- Bottom bracket remover
- Chain tool
- Chain link pin
Place the bike into the stand. Shift the gears so the chain is on the largest chain ring and the smallest gear in the cluster off the rear wheel. Insert the 8-mm wrench into the hex screw in the centre of the crank on one side of the bicycle. Insert the other on the opposite side and use opposing force to tighten the cranks. Check for any clunking noise or side-to-side movement. If none is present, do not proceed. If present, proceed with the other steps.
Slide the chain tool over one link pin on the chain and turn the handle clockwise to force the link pin out of the chain. Pull the chain off the bicycle.
Insert an 8-mm Allen wrench into the hex bolt in the centre of the cranks. Place another on the opposite side. Use opposing force to loosen and unscrew the hex screws. Pull the cranks off the bicycle.
Look at the splines coming out of the bottom bracket. The splines are where the cranks attach to the bicycle. If there are bends or degradation to the spline metal, the bottom bracket needs to be replaced. Push the bottom bracket remover tool onto the spline and pull the unit out of the middle of the frame.
Insert the new bottom bracket and place the cranks back onto the splines. Insert the hex screws and use the 8-mm wrenches to tighten the cranks back onto the bicycle. Use opposing force to tighten the cranks as tight as possible.
Thread the chain over the gear cluster and the chain rings. Push the link pin into the link where the old pin was pushed out. Slide the chain tool over the link pin and turn the handle clockwise to push the pin into the chain, closing it around the chain rings and gear cluster.
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