In this article, I’m going to show you how to how to adjust a wobble crank arm. Wobbling crank arms are mainly caused by long period of riding. If you do not solve this problem, you may fall from the bike directly and get hurt while you are traveling at a very fast speed.
Before we begin, you shall know that bikes have two types of cranks, namely cotterless and cottered. And the later type is often found on older bikes. You can identify these from the cotter bolts that thread through the top of the crank arm. A cotterless crank has a hex bolt in the center at the top of the crank arm. No matter what kind of type your crank is, you should check the tightness of your crank every other month to make sure the safety of riding.
How to adjust crank arm?
Firstly, remove the nuts from the cotter bolts that thread through the crank with an adjustable wrench, because a worn cotter can cause a loose crank.
Place a cotter pin press over the crank. Use the finger to tighten the press bolt clockwise on the cotter pin press until you can’t turn it. Keep on turning the cotter pin press bolt with an adjustable wrench to push the cotter bolt off the crank.
Put a drive pin punch against the cotter bolt if the end is sheared off from damage or from attempting to drive it from the crank with a hammer. Hold the drive pin punch with vise grip or locking pliers to avoid accidentally hitting your fingers. Strike the dive pin punch with the hammer until it drives the cotter bolt from the crank.
Drill a 1/4-inch hole on the center of the cotter bolt. Place the drive pin punch against the cotter bolt once again. Strike it with a hammer to push the cotter bolt off the crank.
Strike the crank with a propane torch as a last resort if all other options have failed to remove the cotter bolt. Don’t heat the crank so hard that it becomes red hot, only hot enough where you could no longer touch it. Position the drive pin against the cotter bolt once again and strike it with a hammer to remove it from the crank.
Apply axle grease to a new cotter bolt. Place the cotter pin press over the crank with the bolt attached to the cotter pin press against the non-threaded end of the cotter bolt. Use the finger to tighten the press bolt counterclockwise on the cotter pin press until you can no longer turn it. Continue to screw the cotter pin press bolt with an adjustable wrench to push the cotter bolt into the crank. Insert the cotter bolt into the crank and tap it into the crank with the hammer if you do not have a cotter pin press.
Place the nut onto the cotter and tighten it with the adjustable wrench. Do not over tighten the nut, as you could strip the threads on the bolt.
As for cotterless cranks, it would be much easier.
Pry the plastic protector cap from the crank arm with a wide-bladed slotted screwdriver. The protector cap covers the hex-head bolt that holds the crank arm to the crank and keeps the crank tight. Some older bicycle models may have a threaded dust cap, and you can remove the dust cap with a hex key.
Insert a hex key into the hex-head bolt. If you have an older, male-threaded spindle, fit a metric socket and socket wrench over the bolt. Turn the bolt clockwise to tighten the crank.
Replace the plastic protector cap onto the crank arm.
Tighten the other side of the crank by repeating the steps on the opposite crank arm.