A variety of things can cause the pedals and cranks on your bike to get stuck. The most common are a worn or improperly adjusted component and damage from spills. As a novice bike mechanic, you can identify the cause and choose whether to correct the problem or enlist the services of a repair shop.
Evaluation
The basic elements of the pedal system on your bike are the front and rear sprockets and the chain. To determine the cause of stuck pedals, it's necessary to evaluate the system. You do this by first loosening the rear axle nuts or a quick-release lever so you can move the rear wheel forward and lift the chain off the rear sprocket. Ask an assistant to lift the back of the bike as you attempt to rotate the rear wheel by hand. If the wheel doesn't rotate, the problem is a freewheel, and not the pedals. You replace freewheels using a tool that's specific to the rear sprocket, such as a lock ring tool or a spline wrench. Depending on the type of freewheel, unscrew it from the hub or pull it out by hand and install a new one in the reverse order. If the rear wheel rotates, the next step is inspecting the pedals.
Pedals
Pedals are often the first things to hit when you take a spill on one side. Each pedal has a threaded stem that fits into the end of a crank arm. Small bearings at each end of the pedal allow it to rotate. Looking down the long axis of a crank arm, the pedal should be perpendicular to the arm. A bent or rusted pedal that doesn't rotate needs to be replaced. You remove a pedal using a thin cone wrench on the flats of the stem where it meets the crank arm. The right pedal is removed counterclockwise and the left pedal is removed clockwise.
Chain and Cranks
Bicycle chains that are not properly adjusted and lubricated can stretch. A badly worn or stretched chain can lift off the front sprocket and wedge between the sprocket and the bicycle frame. In most cases, the chain lifts off at the underside of the sprocket, and you might not see this when sitting on the bike. Dislodge the chain and take it off the bike. Rotate the pedal cranks by hand to make sure another problem does not exist. Install a new chain and make sure it's adjusted to the correct deflection and lubricated regularly. Although crank arms are not a direct cause of sticking pedals, the arms must be attached securely to avoid causing problems with the bottom bracket. Include a check of the crank arm bolts in your evaluation. The bolts are located where the arms attach at each side of the bottom bracket. Depending on the type of bottom bracket, you tighten the bolts using a metric socket or spline wrench. On some bikes, the left crank arm has a cotter bolt that you tighten with an Allen key.
Bottom Bracket
A bottom bracket is the primary component of the pedal system on your bike. The bracket is located within the hub at the base of the bicycle frame. A chainring attaches at the right side of the bottom bracket spindle and a pedal crank attaches at the left side. The spindle rotates on bearings inside the bracket as you pedal. Newer bottom brackets have sealed bearings that cannot be serviced. Older bikes have ball bearings that can fail when not properly lubricated. If the pedal cranks are stuck when the chain is off the sprocket, the bottom bracket or bearings need to be replaced. Typically, you service a bottom bracket using a lock ring tool and a wrench that's specific to the bracket. Single-speed cranks do have a bottom bracket, but consist of a single piece of steel that comprises the cranks and the spindle. The spindle rotates on ball bearings inside the hub. If a single-speed crank is stuck when the chain is off the sprocket, the bearings need to be replaced. Loosen the large nut on the right side of the bottom bracket using an adjustable wrench to remove a single-speed crank.
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