I'm looking at a thrift-store frame for beater bike conversion. It's got a decent enough frame, and isn't looking too bad for $20. But, it has cottered cranks. I've read Sheldon Brown's stuff on cotters, and read on this forum what a pain they are to work with, so here's my question:

Should the cottered cranks fail, will I be able to replace them with normal cotterless cranks? And, if not, will I be able to replace the BB with a new one that does accept cotterless cranks, like a square taper shimano? The frame is Japanese, I believe, so I shouldn't have to worry about French or Italian threading. Is an old frame compatible with modern BB's?

although i admit my knowledge on this subject is weak, one of my favorite bikes was a thrift store conversion with (previously) cottered cranks. nobody has been able to identify the frame yet, but it definitely had cottered cranks. i had to get the bottom bracket replaced and throw a new crankset on there. ever since that easy fix, this bike has seriously ruled. i got a new crankset off my friends old singlespeed he converted fixed for free, and the BB cost me $25. the bike itself was $12.50. total cost = $37.50 for days and days of fun!

If the cotters are in good shape, you should be able to get a lot of life out of them. They aren't really inferior from a performance stand point, just from a maintenence and installation standpoint. You can definately put cotterless cranks on there, you'll just need to change your BB and crankset.

Good luck!

Japanese and other asian bikes use standard ISO/English bottom brackets, any modern BB will fit that frame.

Sheldon "Oldies" Brown

Sounds like cottered cranks are nothing to be afraid of... thanks for the advice all.

Sheldon, you are looking fine.

My '68 Raleigh project came with cotters, I tried EVERYTHING I could find on the net and at the shop I was working at at the time, one side invariably came loose every 2 or 3 rides. Replacing the cotter made it even worse...since you can't *get* high quality cotters anymore, they're only available in cheap-ass pot metal flavor.

I'm not sure if Japanese frames use their own standard for BB size/threading, but I'm guessing not...just standard 68mm English. I replaced the old unsealed cottered nonsense with a used Tiagra set someone was throwing away (but nevertheless in great working condition). You'll wanna double check BB size with some calipers to be sure, but there probably won't be an issue upgrading.

I installed an early Shimano 105 crank on a '73 Raleigh Sports I built up and "modernized".
I used the original Raleigh BB cups with a 70mm (italian frame) Shimano 600 BB axle I had lying around (thankfully I saved it!). I had to use smaller ball bearing to make it work, but work it does!

alright ... since i talked a little smack about cottered cranks over the weekend i feel like i should throw in my two cents. but first, i should clarify something. i give bike advise from the perspective of someone who knows enough to find the problems, but does not know enough to solve all of them. i also assume that people want to get on the road as quickly and as cheaply as possible. if you know lots about bikes and have time and money to burn, nothing i think of as a problem will be one for you.

now that that is out of the way, if the cranks are in good working order and you don't feel the need to change the chain ring or get into the BB shell to do some greasing, you may get many miles out of these cranks.

problems arise if you want to dismantle the cranks. assuming you can get the pin out in the first place, it will be hard to get it to fit back in as snuggly as it was before and, as someone mentioned, new pins of good quality are hard to come by.

i doubt that cottered cranks which are in good working order are mechanically inferior to cotterless cranks (esp. if we're talking about a beater) but this is only true as long as the pin holds up ... and since the pin works by being forced into a hole that is too small for it, the cranks will only work properly for the life of the pin ... which is relatively short since, in order to function, it has to be sort of smushed into place - and thus compromised.

if you have the inclination and money to change the cranks (and, most likely, the BB and spindle) try to make sure you will have the right threads to do so. i don't know how to figure this out for sure so i wouldn't do it. but that's just me ... cheap, mechanically disinclined and lazy.

I've got cottered cranks on my Maserati conversion. They function fine, but aren't preferable. I disassembled them in order to overhaul the BB, and when I reassembled them I found it nearly impossible to get the cranks perfectly 180 degrees from each other. Right now they are about 175 degrees off.. Good enough, but not great.

Plus, I stripped the threads off one of the cotters. Its in, and the bolt is tight, but next time I disassemble it it'll need a new cotter. I'll probably just leave it all assembled until I replace the BB and the cranks as a set.

So yeah, they are a hassle, but not impossible to work with.

Also, I've got to say that Sheldon's post is about as non sequiter as I've ever seen out of him. "Here is some advice, and here is a photo of me in drag." Yes!

peace,
sam

I've done it, and you can too!

I rode around for a few months on the cottered cranks that came with my frame. They started getting loose so that was an excuse to pick up a new BB and cranks rather than fool around with cotters. I did the switch and the bike's still going strong.

You were doing well until the last sentence. Cottered cranks with properly installed cotters are at least as reliable as cotterless cranks. Problems with them are generally caused by improper installation of the cotters.

Either they weren't installed tight enough, or when filed to fit, the surface that is supposed to be flat wound up curved. (Filing a flat surface and keeping it flat requires a bit of skill and technique that not everybody has learned.)

Cottered cranks didn't go out of fashion because of durability or reliability issues. They went out because they were heavier (can't make 'em out of aluminum) and difficult to remove for service.

See: https://sheldonbrown.com/cotters

Sheldon "Inertial Impact Alignment Instrument" Brown

P.S., nice job on the fjords of Norway!

The cotters shouldn't be smushed, like you'd smush a rivet, they are just pressed into place. You really need to use a little force to get them in right. Whoever said that mini-sledges have no place in bicycle maintainence never had to work with cotters.

For filing flat stuff, and keeping it flat, I like to clamp a flat file in a vice, and then run the filed item over it like a lapping stone. You can also go the other route, clamping the item to be filed, but that is more likely to cause a sloped surface.

I'm all in favor of the cotter going the way of the dinosaur, but if you've got em, you might as well work with them.

peace,
sam

man ... called out by my hero ...

thanks for the compliments on the fjords ... obviously i spend more time with them than cottered cranks.