Bad History With Crank Arms

[DaveM]

If you are generally strong/heavy/rough on the pedals, this is not an uncommon problem. But you should be able to avoid it. The key is never letting the crank arm get loose it the first place. If it starts to loosen and you ride on it, then the hole in the arm gets flared out of shape and you can never get it to seat properly again.

Get a new left crank arm. Very lightly grease the the BB spindle (axle) before installing. You can use locktite on the bolt threads. But the main thing is to get the crank installed to the right torque, not to prevent the bolt from unthreading.

If you can borrow/buy a torque wrench, they are helpful for getting the crank on correctly. If not, the trick isn't to crank the arm down as tight as humanly possible. More important is to get it tight and check it occasionally in case it has started to loosen up.

I'm not sure how much difference there is, but a better quality crank arm probably uses slightly better quality aluminum than a shop's $5.99 no name crank.

Lastly, watch how good riders clear obstacles. You may see when they spin the pedals in lower gears and when they crank on high ones. Spinning can make you a much better rider when used properly.