ISO crusty mechanics with cottered crank skills....

Pulled my first set of them last week and mushroomed the cotters upon removal. I'm really not keen on a. finding a new set of cotters, and b. filing the flats to fit, so I'm wondering if I have options for making things work. As it stands, I can't thread the nuts onto either cotter. Can I clean up the threads (I don't have a tap and die set)? Can I dremel off the mushroomed part and expect a nut to thread onto the cotter (there is enough room to do this)?

Thanks for the help.

They are $2 a set at https://www.biketoolsetc.com.
My local bike shops had most sizes in stock. You will want to get the right size.

Did a set recently following the advice given by Sheldon Brown on his site (Support the crank with a pipe before beating on the pins, etc.). Re-used my old ones. Just loosened the nut a bit before banging on them, so the ends did not get flattened too much.

How difficult would it be too replace the cottered cranks with modern ones? Obviously you would also need a new chainring, but would you need a new bottom bracket as well?

You successfully did the hardest part of the job, which is getting those buggers out. I salute you as I have been stymied on more than one occassion by cottered cranks.

The install is a piece of cake in comparison. At most, 5 minutes of filing a new cotter. Be sure to press the new cotters in and use lots of grease on the friction fit so they will come out again in the future.

I've done this a few times and I have to say the easiest, best way of removing and replacing cotters is with a cotter press. It is a far better way of doing it vs. the "hammer mechanic" brain set that I normally do things with. Bikesmith Designs and Fabricationshttps://www.bikesmithdesign.com/ has a ultra quality cotter press. Bikesmith also has cotter pins.

I would totally agree about the press, and generally look for any excuse whatsoever to buy a new tool, but I'd need to do a lot of cottered cranks to justify a $50 tool. I'm still wondering about my $20 lockring wrench.

San Rensho, thanks for the reassurance. I'll get off my ass and go buy some new ones.

One of those would be neat, and make life easier... but if you're good with a hammer then that's all you really need IMO.

I tried this home-made press, which didn't get the cotter out, but it did bend it. You might be able to use it to press the new cotter in.

Get a socket that just fits over threaded end of the cotter. Get a big c-clamp and use it between the rounded end of the cotter and the socket over the threaded end of the cotter.

I've removed two sets of cottered cranks over the years but never installed a set. The main purpose for removing them was to replace them and their bottom bracket with something newer and 1/3 the weight so I really didn't care what happened to the cotters. And yes it's a lot of work with a BIG hammer and a support pipe and the pipe was only there to protect the frame.

Grease, or better yet anti-seize, on the cotters themselves is a good idea. However you want the spindle and the spindle bore through the crank to be as clean and dry as possible.

From the Bikesmith Cotter Press page;

Installation

Installed properly, there should be enough friction between the spindle and bore to eliminate movement. The cotter will only be loaded in compression, evenly across the face, and be easily removed.

Without this friction, the only thing resisting movement will be the relatively soft cotter, loaded in shear. When you see grooves across the cotter face, either the cotter wasn't tight enough, there was grease between the spindle and the bore or both.

1. Avoid chromed spindles. Sandblasting or sandpaper can help if you don't have a choice.

2. Make sure spindle and spindle bore are clean and dry.

3. Use anti-seize or grease on cotter.

4. Install FIRMLY with a cotter press. As you tighten the cotter, the wrench will move smoothly and with gradually increasing resistance, till you get to a point where force required to move the wrench suddenly increases. That's when you stop.

When installing cotters, I suggest holding your wrench with your thumb near the bolt head, to keep you from applying too much leverage. This tool is so powerful that one fellow mushroomed the fat end of a cotter.

Years after tourists had alloy cotterless cranks, many racers were still using the more reliable (when installed properly) cottered cranks.

How long ago was this? I think it shows the great conservatism of racers in the past. That certainly isn't true today.

Removal of cotters isn't usually hard, but it demands finesse and attentiveness to the job at hand. I think cottered cranks have gotten an undeserved bad rep. They are so simple; nothing more than a wedge, an inclined plane and screw.
There are perfectly valid reasons for replacing cottered cranks, such as substituting a lighter assembly. They don't diminish the utility of cottered cranks.