Bicycle Mechanics - Drilling Cotter Pins

Hi all

I've got a stuck cotter pin, and it's bent a little and deformed in the process of trying to remove it. I tried direct application of a Large Hammer, and then tried a punch, but no luck. The one time I tried to drill out a cotter before, I damaged the cranks as well, and I really don't want to do that.

I guess that a smart first move will be to remove the chainrings, so that I've got the best possible access to the cotter, but what then? Should I be drilling from the threaded end of the cotter, or should I be starting from the large end? I can't quite get it straight in my mind as to the physics of the drilling releasing the pin, so it's tricky for me to figure out. Help?

If you are doing all this with the bike in a stand try having another person hold the frame so the crank rests on solidly mounted vise while you use a solid punch and that Large Hammer.

The shock of the impact is what loosens ithe cotter and having the frame in a bike stand absorbs some of that shock.

Good luck!

Hi all

I've got a stuck cotter pin, and it's bent a little and deformed in the process of trying to remove it. I tried direct application of a Large Hammer, and then tried a punch, but no luck. The one time I tried to drill out a cotter before, I damaged the cranks as well, and I really don't want to do that.

I guess that a smart first move will be to remove the chainrings, so that I've got the best possible access to the cotter, but what then? Should I be drilling from the threaded end of the cotter, or should I be starting from the large end? I can't quite get it straight in my mind as to the physics of the drilling releasing the pin, so it's tricky for me to figure out. Help?

See: http://sheldonbrown.com/cotters

When I have needed to drill, I have done it from the broken end.

Sheldon "Cotters" Brown

Spray some PB-blaster down the cotter-pin hole and let it soak in overnight. Then pound out using a pipe to support the underside of the crank. I find leaving the nut halfway on the cotter gives you a larger target and flatter surface to hit with the hammer.

I find leaving the nut halfway on the cotter gives you a larger target and flatter surface to hit with the hammer.

Hindsight is a wonderful thing! I've removed every other cotter bar one with a single blow, without the nut left on, and it's made me complacent. Next time (which will be soon), I'll be soaking it first with WD40, and leaving the nut on.

Thanks all for your help. If I can't shift it, I'll have to drill again, but VERY carefully. The double Stronglight crankset is in near mint condition, and is probably worth what I paid for the whole bike. I don't want to kill it.....

soak it with a good penetrating lube ( silikroil or PB blaster) Apply some heat t0o the crank arm itself around the cotterpin trying not to heat up the cotter pin or bb spindle. then use a punch and hammer to knock what is left out.