Bike Hacking (aka "Bicycle Autopsy") - Section 3

Photo 24 - Removing the bearing and ring from inside the cup.

If the bearing ring is rusted and cracked, and the balls fall out, discard them. It is important to take this bearing out, or the crank arm will not be able to slide out through the bottom bracket. Once the left bearing is out, slide the entire crank set out by aiming the chain ring into the middle of the frame while guiding the crank arm through the two bearing cups. Shown in Photo 25, as long as nothing is bent or damaged, the crank set should come right out without having to force it in any way. Place all the bearings and rings in a safe place or bucket of solvent if they need to be cleaned.

Photo 25 - Sliding the one-piece crank out of the bottom bracket.

Removing the three-piece crank is a bit more involved, as there are a few more parts to deal with, and things can get really hard to separate depending on the amount of rust or age of the bike. This time you will definitely need your hammer.  Start by removing the plastic covers in the center of each crank arm if there are any and you will find a 14-mm nut at each end (Photo 26).

Photo 26 - Crank arms are fastened to a shaft with nuts.

Clean out any dirt from the recessed area, and spray a little rust remover in the hole if there is a lot of corrosion inside. To remove these nuts, find the correct size ratchet and turn them in the counter-clockwise direction, as seen in Photo 27. Do not try using a wrench here. The holes are recessed too far and you will only strip the end of the nut. If the nut is really stuck, hold on to one of the crank arms or tie it to the nearest part of the frame so it will not move.

Photo 27 - Remove crank nuts by turning them counter-clockwise.

Taking out these nuts is not normally hard to do unless the threads have been damaged or flattened at the end. In this case, you may be fighting a losing battle. Once you get the two nuts off, the real fun will begin as you attempt to remove the two crank arms. This is probably the most frustrating part of taking apart an old rusty bike, as these two parts have had years to jam into place. Before you start, take a look at how the crank arm is connected to the axel (Photo 28). The square cutout is slightly tapered, so as the nut turns, it pushes the crank arm very tightly against the axel. Even on a brand new bike, a fair amount of force is needed to free the crank arm, so be prepared. If the arm is aluminum, it may come off fairly easy due to the softness of the metal, but you are still going to need a hammer for this operation. Start with the sprocket crank arm first. This will allow you free access to the other arm once it is out of the way. Place the bike up on the workbench so the chain ring is hanging off the end. It should fall to the ground when you finally set it free.

Photo 28 -A square tapered shaft holds the crank arm.

With the bike hanging over the edge of the bench, place a solid rod or wedge-shaped piece of steel against the crank arm through one of the openings in the chain ring, as shown in Photo 29. Place the tool against the crank arm, not directly against the chain ring itself, as the ring will bend from the force. An old socket extension also makes a good tool to bang the crank arms off , but make sure it’s an old one because you will be doing a lot of hammering.

Photo 29 - Some force will be needed to remove the crank arms from the shaft.

If the crank arm is refusing to let go, you may need to get out the torch and put some heat into it first. Apply heat for five to ten minutes all around the middle edges of the crank arm, but not right into the recess where the axel bolt is. The idea is to expand the crank arm away from the axel, and heat makes metal expand. Once you get this arm off, the other one should be a little bit easier, as there is nothing in the way (Photo 30). Use the same technique as before, applying heat if needed.

Photo 30 - With the chain ring out of the way, the left side is easy to remove.

Set your hammer as close to the axel as possible, but be careful not to smash the end of the axel and flatten the bolt. If this all seems to be too much work, you can buy a crank puller, but it will cost you a lot more than a new set of cranks, and may not be able to remove the old rusty ones. Once you manage to get both the arms off, you can now remove the axel and bearings from the frame for cleaning or replacement. For this job, you will need either a pipe wrench or a large adjustable wrench. Start with the left side of the frame. This will be the side with the large notched ring over the smaller threaded cup, as seen in Photo 31.

Photo 31 - Removing the lock nut with a pipe wrench in the counter-clockwise direction.

Grasp one of the notches with the pipe wrench and turn it counter-clockwise until it comes loose, then it should unscrew the rest of the way with little effort. This is the retaining ring that stops the bearing cup from coming loose as you pedal (see Photo 32). Once the retaining ring is gone, you can now remove the inner ring in the same manner. Grip the flat sides of the ring with your wrench and unscrew in the counter-clockwise direction until it is all the way out.

Photo 32 - Removing the bearing cup using an adjustable wrench in a counter-clockwise direction

If the ring is badly corroded, it may be very difficult to get it out. Again, you could try using the torch by heating up the underside of the bottom bracket. It is best to use a wrench that fits snugly on the ring, as it is very easy to strip the edges from excessive force. If all else fails, use a punch and try to hammer the ring into turning enough to get it going with the wrench. If you have to resort to this, make sure you use the torch first. As shown in Photo 33, once the ring is out, you can pull the axel and both bearings out for cleaning.

Section 1   | Section 2   |   Section 3   |   Section 4