Wednesday, September 17, 2008

How to Remove Crank Cotters

Disclaimer: I am not a professional bicycle mechanic. This account of my experience is intended for entertainment purposes only (woohoo!), and should not be considered the advice of a professional. In other words, I'm not responsible if you bungle the job!

That being said, let me say (as commenters RB and Giuseppe assured me), that this was not hard at all! Guys, you were right, it was probably the easiest thing I've done on this bike. 

Sheldon Brown, God bless him, can sometimes make things sound much harder than they are. Based on Sheldon's guide, I was certain that I would mush the cotter pin, ruin my crank, and undo all of my good work on the Runwell. While doing the job correctly is important, it is not as hard as some internet bicycle gurus make it sound. That being said, Sheldon's word on the subject is still the standard, and it helped me a great deal. 

You need only three things for this job: 1) a block of wood (I used a scrap of 1" x 8" board) cut to fit under the crank arm to support the arm when you hit the cotter pin; 2) a claw hammer (I padded mine with a small piece of rubber cut from an old tube in case I missed the pin and whacked the frame); and 3) some penetrating oil to lubricate the pin. You can also
 use a piece of soft metal pipe (like copper) instead of a piece of wood, placed under the pin, but I doubt if most folks happen to have a piece of pipe in the correct length just laying about--I sure didn't. I also cut a piece of thin cardboard to protect the bottom bracket if I swung wild, but it proved unecessary.

Here's the setup:

I applied the penetrating oil liberally directly onto the pin a few days before I made the attempt, since I was a little apprehensive and wanted to give myself the best chance of success. Remove the nut and washer on the cotter to access the point where the wedge of the pin meets the flat of the crank axle inside the crank arm and apply the oil directly.

Once the oil has had a chance to work, you're ready to begin. Brace the crank arm on the wood block so that the threaded end of the cotter is pointing up, since this is the end you will strike with the hammer to drive the pin out. Needless to say (I hope), the nut and washer should be removed before you go at the pin with the hammer. With the crank arm braced and the washer and nut removed, all that's left is to whack that little bugger. Strike the pin a hard blow squarely with the hammer--imagine you're trying to drive a nail in just one whack. Grip the hammer as far away from the head as possible, like any good carpenter, since this will help deliver a more powerful blow. Here's what happened after just one strike:

I then tapped the pin gently all the way out, using a little screwdriver as a tap. And that's that. The other side was just the same; one strike and the pin was loose enough to just tap out. No damage to the cotters, the axle, the frame, or the bottom bracket in the process. In fact, unless you're some sort of hulking brute, it's unlikely that whacking the pin will do any sort of damage whatsoever. That's easy for me to say now that I've accomplished it, but this had been a point of some concern. Here are the pins after extraction; the one on the right is the damaged one that was causing my clunk (you can see the stripped threads):

Here's a bit about how cottered cranks work. The pin goes through the crank arm and that flat side gets wedged tight against the flat side of the crank axle (see below). 
The flat of the pin contacting the flat of the axle is what turns the crank when you pedal, and the nut is just there to keep everything snug.
I'll say more about the mechanics of the whole operation and have some better photos when I install the new cotters in a few days (when they arrive in the mail). Hopefully that will go as smoothly as this did. I sound all confident now, but I was quite nervous when I started. Just goes to show that the things you worry about the most usually end up turning out the best (and the things you didn't think to worry about knock you on your arse).


18 comments:

  1. Well done and a nice "howtologue" as well. Now you've no excuse for not getting the "dark side" of that crank clean!

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  2. Thanks!

    As for the other thing, I'm sure I have no idea what you're talking about!

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  3. Thank you for this. I'll come back to it I know. I have a frame sitting under my desk because Sheldon scared me off on the cotter removal. I will need to find all your implements, but at least it now looks like something I could do.

    Thank you!

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  4. Hey, Thom...is there a maker's name on the bottom bracket cup. Your pic shows "Made in England"...is this by Brampton?

    I just realised that your Runwell appears to have the same chainwheel as "The Sun"!

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  5. Well, I...er...hrm, didn't exactly get into the bottom bracket...cough...cough...

    With application of a bit of motor-weight oil through the oil cap, it turns noiselessly, so I figured, why fix it if it ain't broke, right? However, there is a mark on the inside of the chainwheel-side crank arm. I'll try to get a photo or maybe even drawn a little sketch of it, since it's pretty light and barely even there. Forthcoming.

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  6. Do you know how to remove the bottom bracket?

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  7. Yes. Thanks for your question.

    You need a spanner wrench to remove the lock ring and probably an adjustable wrench will work for the BB removable cone (the one on the left). Beware of loose bearings.

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  8. I have taken both cotters out of my two crank arms, one crank arm came off, however the arm on the geared side will not come off still, it seems wedged. I've tried hitting it with a hammer but it won't come loose! Any ideas?

    Cheers, J.

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  9. @ J.: Assuming that your chain has been removed (that's one of those "is the computer plugged in"-type troubleshooting questions), there is nothing mechanical prevening your drive side crank from coming off, it's probably just grease and grime. The gear and crank arm form one piece and it has been my experience that it's always harder to get this side off, perhaps being engineered to fit tighter(?). Get some penetrating oil down where the cotter was and all around the crank axle. Let that sit for 24 hrs. at least, and then just keep at it. A rubber or plastic mallet will work just fine and won't damage the sprocket teeth or mar the chrome. Try pulling on the crank arm while you tap on the top of the sprocket. You can also try having someone hold the frame steady while you pull on the crank. It should come off, just keep at it!

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  10. Yes the chain is off.
    I just wasn't sure if it was being held on in any other way, so i didn't want to keep bashing it with a hammer! I'll get some oil on it and try again!

    Thanks again, J.

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  11. Hi again, I bought a rubber mallet and went hell for leather on the thing, and it came off! Thanks for the advice! I have now sanded the frame down and given it the first coat of primer. I'll post piks once she's finished.

    Thanks again, J.

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  12. thanks, really helped me get the cranks off my old rudge! :D

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  13. Wow, what a nice user friendly piece. My sincerest thank you! With a little input we are functionally capable.

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  14. This was a huge help for me. I had an old '78 Peugot road bike that I could not get the cotters out of. It was really the lines that encourage you to really go at the pin with a single solid hit that helped me. I think that this is a hugely important part, a single solid hit seems to be perfect to unlodge a badly stuck pin.

    Thanks so much!

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  15. I have removed the pins, but the crankshaft is still stuck! How can I remove the crankshaft??

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  16. I too have an old Peugeot road bike, and after reading this I've had a go at the cotter pins, but unfortunately all I've managed to do is mushroom one end of one. Is there much else I can do but smack it harder and buy some new ones if i can't get them back into shape?

    Can they be repaired once they've been mushroomed? (the nut won't go back on the thread.)

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  17. I read the Sheldon piece, wasn't scared off, and mushed the threads on my cotter pins with a bad swing anyway. I was afraid to strike the frame so I struck off-centered. Oh well.

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  18. Thanks for the write up...I'm gonna give it a go and hopefully won't ruin the threads....yikes.

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