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Old 09-06-10, 10:34 AM   #1
hobbsc
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cottered crank removal

I'm helping a friend re-build an AMF Hercules which I believe to be a Raleigh made model (based on the dropouts and the age of the bike). We've been trying to get to the bottom bracket to either replace or overhaul it and we've had a hell of a time with the cottered cranks.

The pins are stuck in the cranks very tightly and no amount of WD-40, hammering, and foul language can persuade them to leave their home. I don't believe they've ever been removed since initial installation. We'd like to salvage them as they're still in good condition, but I'm not sure how to remove them short of breaking the crankset.

Does anyone have ideas for removing the cranks without damaging them?

Thanks a ton!
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Old 09-06-10, 10:45 AM   #2
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Archimedes said "give me a lever..., and a fulcrum and I shall move the world. Just as a lever would be useless without a fulcrum, hammering without an anvil, or other means of concentrating the force won't get you anywhere. You need to support the crank arm and provide inertial resistance, or all you'll do is mash the pin, and damage the BB bearings.

I don't know what tools you have, but you'll need a piece of 3/4" or 1" steel pipe a few inches long, or a block of hardwood with a hole drilled in the end. You'll also need a heavy vise, or other mass. If you have a helper it'll be easier, or if you have a repair stand you can use that, but your pipe will have to be long enough to reach the floor.

Support the crank arm over the pipe with the large end of the cotter pin inside. Support the other end of the pipe in your vise, or an anvil, or a plate on the floor. Don't put the end of the pipe directly on the floor, it'll score it). Now the goal is to deliver a solid blow to the pin and send it hurtling down the pipe. You don't want repeated smaller blows which will only mushroom the pin, but one devastating shot.

If you've already mushroomed the cotter pin, file off the spread section, and use a punch to drive the cotter out.
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Old 09-06-10, 10:53 AM   #3
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Actually, I worked on a lot of these in the 70's and there are a couple of amendments to the above techniques.

First, hammer the threaded part of the cotter back and forth until it breaks off. No need then to worry about mushrooming, and you will get a more solid blow, as well as the hole in the crank holding your punch in place. Then try tapping the crank arm close to the BB spindle a few times toward the center of the bike. That can help break the pin free. then go to FB's instructions.
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Old 09-06-10, 12:08 PM   #4
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Less

If your Bike Shop has a Cotter press, rather than brute force, you may be able to Re use the cotters..
if you destroy the cotters you have to buy new ones, they are not a No Brainer to replace.

It is common to carefully File the Wedge on the cotter to get the fit right.. and it is soft metal. there were special cotter vises to hold the round cotter in a bench vise..
But with a vise to hold it you can accommodate that.

so after per shaping the cotter to fit, a few modest hammer blows tightens it,
then you snug down the nut,
don't try to pull it in with the wrench on the nut..

Now you know why nobody strips the cranks off those bikes
when they are locked up and abandoned.

Last edited by fietsbob; 09-06-10 at 12:15 PM.
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Old 09-06-10, 12:32 PM   #5
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After you've screwed around with it long enough, mushroomed it, dented the crank and the paint job with your hammer, nailed your thumb, and yelled at the kids, just drill out the center of the pin. It's soft metal. It'll pop right out then.
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Old 09-06-10, 12:54 PM   #6
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It's interesting to see how knowhow disappears when certain jobs drop out of the mainstream. Until the early seventies, cottered cranks were the norm, and shops stocked the 3 or 4 standard size replacement cotters. Removal was easy, you backed off the nut to the top of the thread, dollied the crank, and gave the pin one well directed blow. 95% of the time out it popped. Then you removed the nut and pushed it free. Most times the thread was OK, and if the cotter was in good shape you could reuse it. Otherwise you replaced both cotters, to ensure that the taper angle was the same, and the cranks sat 180° apart.

For those few stubborn ones, tapping the arm on the spindle as cny-bikeman suggested helped, but could be damaging to the BB bearings. Otherwise, cut off the screw, braced up the arm more rigidly to protect the BB, and got out the 4# mallet, and punch. No mechanic of that era could keep a job, if cotters got the best of him.

When training new mechanics, I found the biggest problem is that they were afraid to deliver a hard enough blow, especially if dealing with a mushroomed pin where a punch was needed. It seems people are afraid to apply full power with their other hand in line with the hammer. I solved that by having them hold the punch with Vise-grips, and freed of worrying about their other hand, most would nail it with their next shot.
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Old 09-06-10, 02:28 PM   #7
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I had a bb axle snap on one bike - I've had it with hammering on the crank, no matter how well it's supported. Maybe back in the day the cotterpins popped out for any well trained, fully equiped mechanic, but after sitting around for 40 years 50% of the cotterpins on the filthy dirty, neglected bikes I come across are pretty pissed and they don't like being hammered on. I've had a bike shop mushroom a cotterpin with a 50 pound, three foot long cotter press.

Nothing is easier than drilling it out. Start with a 1/8th inch bit, and work up from there. Takes a second, the metal is so soft. By the time I got to the bike store, asked them to use their giant cotter press, paid my bill, and drove back - I can remove them myself, kiss the kids, trim my nails, and have a gin and tonic.

Now, if it's the cotter pin I installed when I rebuilt the bottom bracket last year, then yes, a tap at the right angle, with the right strength pops it right out.

Last edited by sciencemonster; 09-06-10 at 02:36 PM.
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Old 09-07-10, 02:07 PM   #8
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Actually I should have mentioned drilling as the final step. It's worth it to try one good wack or two 1st, as even the soft metal takes a while to get through.
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