The left crank kept falling off and I've kept on managing to put it back on but finally it wouldn't go. Think the threading is just absolutely kackered. So I ended up taking it to a shop to have a look at and a possible replacement crank. The only one advised to purchase was the Shimano FC-M622 175mm but it is near enough impossible to find and alot of places has discontinued the product. Does anyone know of any other cranks i could purchase instead of this one? Thanks, Tom.
If your rings are still in good condition, it's likely that you can replace just the left crank. https://www.sjscycles.co.uk/cranks-left/ Lists some that are available now. If you have (as your model number implies) a Hollowtech II crankset, any mountain crank using the same system will fit. As the main spindle is quite a hard steel, it doesn't usually get damaged from this type of problem. Remember, you can't look at both sides of the bike at the same time! (unless you use a mirror).
In addition, make sure you are installing the cranks correctly. Hollowtech 2 cranks are very robust and shouldn’t just spontaneously fall off.
- Loosen and tighten the two pinch bolts in very small increments, 1/4 turn max at a time. Make sure to alternate sides.
- It is imperative to use a torque wrench on these two bolts. If the tension is uneven, the crank won’t clamp on properly and is very liable to fall off. If you can’t access a torque wrench, tighten the bolts pretty much as hard as you can go with a regular length Allen key. If the threads strip out, your suspicion was correct: the threads were damaged.
- Use threadlocker on the bolts.