Where can I purchase a single crank arm?

Hi all, new the forums. Don't know alot about bikes so bear with me.

I was wondering if anyone could give me some advice. I recently added cycling to my training routine but i've had some (plenty of!) problems with the second hand bike I bought. The latest one being the left crank arm, of which i've found has been completely worn out from the previous person not putting it on properly. I've taken it to a repair shop, but they don't do the crank arm alone, only whole crank sets - way too expensive and not needed. However, they're willing to repair it if I can provide the parts.

My question is, does anyone know of any websites/stores in the UK, that do mail/delivery of 165mm crank arms with diamond taper? - for a mountain bike.

Probably nowhere. Occasionally a single crank arm shows up on Ebay, but the chances of it being exactly the one you need are slim.

You'll get back on that bike faster if you try for a complete crank set. A local shop should be able to order one for you.

I know there are all sorts of formulations for what some people think is the "correct" crank arm length for different size people ...

But, IMO, unless you are shorter than 4'10" (147cm), you may as well consider replacement cranks in a longer length -- particularly if this is really for a mountain bike -- because most people use a longer crank arm length on their MTB than on their ROAD bike.

The problem with getting only a single crank arm which uses a square taper BB is that there really wasn't a "standard" ... so, the odds of locating a match are against you.

So, while 'I' actually have an orphan 165mm left hand crank arm that I could send you, the offset from the bike's centerline might not be the same as the offset of your current crank arm.

Now, since it is your LEFT crank arm that is damaged, you can probably SHIM the crank arm's taper with some BRASS STOCK (about 1" x 1/64"?) to get it to fit snugly on the BB spindle.

You can buy brass stock from a hobby shop ... you will just need a pair of PLIERS to bend the brass ... and, a FLAT FILE to clean/trim the edges.

You'll want to bend the brass stock into an L-channel that you'll fit over two faces of the BB's spindle ... then, wedge the spindle-plus-shim into the crank arm, or vice-versa ...

SOME trial-and-error may be required because the object is to have the arm rotate in a plane that is parallel to the bike's centerline ... you can test the viability by making some test shims cut from a a plastic talc bottle or laundry-type (or, equivalent) jug before buying some brass stock -- brass is probably easier to work with than most of the other options while being hard enough that it won't deform when held in place as a shim ...

While shimming the crank arm is far from a perfect solution to your crank's problem, it is an inexpensive, DIY project which will get you back on the road after only a little time & effort.