Bicycle Mechanics - Crank keeps coming loose

The crank on the left hand side of my bike keeps coming lose and will eventually fall completely off. I got a new bolt that attaches the crank to the bike but it doesn't seen to help. I also have a really hard time of getting the crank back on. What do i need to do to fix this problem?

The damage may have already been done, and the square crank 'hole' (I am sorry, I cannot think of the term for it), and will no longer sit tight on the crank axel because it has now become more rounded than square. If that is the case, it will always move from now on... thereby causing more wear. Your crank axel will have also suffered some wear from this movement... but it is harder than the crank, so it wll be less.

But try this... and hope.

Grease both the axel and crank... grease the bolt thread, and then go for broke when tightening them up. I mean really lean on the wrench. You can do this because you have greased everything.

This a new trick I recently learned from the good members of this forum!

I'm afraid the damage is done if you rode at all on the crank while it was even slightly loose. I recently learned (also through experience) that cranks are made of relatively soft aluminum, and the tapered spindle on which the crank fits is made of hard steel. The force of your foot deformed the crank, and it won't ever seat again. I got a used left crank, and now my bike has mismatched cranks. It's mildly amusing, and works fine.

Since these are supposed to be a square TAPER, why couldn't one use some shim stock to tighten them up? use a piece of say .002"? on each side.
Available at real auto parts stores.

Since these are supposed to be a square TAPER, why couldn't one use some shim stock to tighten them up? use a piece of say .002"? on each side.
Available at real auto parts stores.

Gosh, at my shop we sell new replacement left cranks for $10. Don't waste part of your life trying to "rig-job" it. I've seen all kinds of junk wedged in there but short of welding it on (seen that too, with cheapie steel arms) it's gonna come off.

Get a new one.

And when you get the replacement crank arm, install it with the correct torque to prevent damage to the new one. These things have to go on TIGHT.

What kind of crank is it? More info needed.

Gosh, at my shop we sell new replacement left cranks for $10. Don't waste part of your life trying to "rig-job" it. I've seen all kinds of junk wedged in there but short of welding it on (seen that too, with cheapie steel arms) it's gonna come off.

Get a new one.

I could've given you one for free if you walked into mine ;) We have a whole stack of just odds and ends, they're not new but they work.