Is this crank usable or should it be replaced?

Question

I've been suffering from weird noises while pedalling for a couple of weeks. Noise has been isolated to the left foot, its definitely not the right side.

After an inspection revealed no cracks or other badness, I pulled the left crank off with a puller.

The lip around the presser on the right hand side of the image? That's compressed outward, and once I got the crank off the pusher of the puller was wedged in the taper.

The other two sides are only lightly marked. The two sides pictured are the worst damage.

The crank was cleaned and refitted with a light coating of copper slip on the facing surfaces and it seems to be functioning fine. But

Question: Is this crank safe? Or is it vulnerable to further damage?

Answer 1

It's hard to tell if it will be OK, and it will depend on how heavy you are and how much pedaling torque you can produce.

The main problem you are going to face is not the reduction in area of the taper surface, but that the puller will have pushed the edges of the gouged area up, so that the crank will not fit quite properly on the spindle taper. Because of this you may find that you have problems with the crank staying on the spindle.

If you feel inside the taper with a finger tip (my pinkie fits inside a crank taper, and I have fairly big hands) you will feel an raised edge or 'burr' of material around the gouged area. You will want to very carefully file that off with a fine, flat needle file. It will only take a few light strokes to remove it.

When you re-install the crank, torque the retaining bolt up to the maximum allowed. Do a test ride and check that the crank is staying in place. Check the crank regularly when you ride after that. Hopefully it will stay in place.

Answer 2

The damage shown is unlikely to cause a structural problem. Once you reassemble, torquing the arm on very tightly, you should feel no wiggle of either crank arm relative to the other one. If, after some riding, you find some wiggle, torque the arms on more (within spec). As long as there is no wiggle, the damage will not cause any problems. There is not enough alloy missing to weaken, just to potentially maladjust the tapered fit.

The noise you were hearing could have been any of a number of things: a loose crank arm (fairly unlikely if you hadn't removed it recently), a pedal, or the bottom bracket. Check the pedals first -- they should turn freely and without grinding or noise. Service or replace the pedals if not. If the pedals are ok, then test the bottom bracket. Since you have the crank arms off, make sure that the spindle turns freely and without grinding or noise. Also check that it does not have any play by trying to wiggle it up and down or front and back. If there is noise, binding, or play, service the bottom bracket.

In the future, use a crank puller with a smaller push surface. Alternatively, you can loosen the screw in the crank spindle a few turns without removing it and have the puller push on that. If that screw head prevents the puller from threading into the crank arm far enough, you can put a screw with a smaller head into the spindle and push on that. That will extend the spindle enough to prevent the pushing surface from going into the tapered opening in the crank arm.

Answer 3

It may or may not be ok if you tighten the crank down really hard. I had a similar experience so I overtightened the crank to prevent it from making noise, but I ended up damaging the bottom bracket even though it is a much harder material.