How to Repair a Bicycle Bell Crank

A bell crank is a linkage system that changes the direction of movement to create a mechanical advantage. Three-speed bicycles typically use this type of linkage to produce torque so the bicyclist can get more power at higher speeds. Repairing a back tire on this type of gearing system requires adjustment to the bell crank when it is reassembled. Although the adjustment is not difficult, there is a specific procedure to follow that is not readily apparent by simply taking apart the bell crank.

Things You'll Need

  • Allen wrench, 5 mm
  • Screwdriver
  • Pliers
  • Cable cutter
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Instructions

    • 1

      Push the bell crank housing back onto the rear tire axle. Fixing a flat tire on the rear of the bike requires removing the bell crank, so after the tire is fixed the bell crank must be reinstalled. Insert the bell crank housing onto the push rod that is attached to the rear axle. Tighten the Allen screw on the back of the bell crank housing to fasten it to the bike.

    • 2

      Unscrew and remove the bell crank cover. Insert the cable coming from the gearshift lever at the front of the bike through the cable-adjusting bolt, into the bell crank housing. The cable-adjusting bolt is located at the front of the bell crank assembly. Tighten the cable-adjusting bolt with your fingers.

    • 3

      Loosen the fixing nut with your fingers. The fixing nut is located next to the cable fixing plate inside the bell crank assembly. Slip the cable through the cable fixing plate and through the fixing nut. Grab the end of cable you just threaded with a pair of pliers. Loosen the cable-adjusting bolt from Step 2 while simultaneously pulling the cable tight with pliers, and then tighten down the fixing nut with your fingers. Be sure the cable is tight between the fixing plate and the cable-adjusting bolt. When you are satisfied that the cable is seated properly, tighten the cable-adjusting bolt. Cut off any excess cable where it exits through the fixing nut.

    • 4

      Set the gearshift lever at the front of the bike to second gear. Look down on the bell crank housing from above to properly see the adjustment window, so you can see the push rod from Step 1 through the adjustment window. Turn the cable-adjusting nut until the red line on the push rod lines up with the mark on the adjustment window.

    • 5

      Move the gearshift lever from second gear to third gear, and then from third gear to first gear. Then move the gearshift lever between third and first gear several times. Finally, set the gearshift lever back to second gear and verify that the red line on the push rod is still aligned with the mark on the adjustment window. Tighten the cable-adjusting nut to complete the adjustment. The cable-adjusting nut is located next to the cable-adjusting bolt.