I have managed to break a crank.... advice?

[MontyVeda]

Buy a crank removal tool - I know you are concerned that the threads in the crank was damaged but the tool is steel and the crank is Al alloy: it would have done the business. But you surely need this tool in your box. How else will you remove the crankset you currently have fitted?

if you don't tighten the bolts sufficiently, the cranks will most definitely loosen when you ride it... don't ask me how i know this

 

[classic33]

As a matter of interest, has anyone ever broken, or heard of someone breaking, a cottered steel crank? I've seen a couple of bent ones resulting from crash damage, but never one actually break.

Yes, took a while to remove from the bottom bracket. Broke on one side of the crank, opposite the cotterpin.