One thing that I've seen often in bike repair and experienced myself was to have a crank arm just falling off the bike. Now if that doesn't ruin your day, imagine a few days later riding along all proud of having fixed the problem, riding with joy, birds singing in the trees, life is good....and the darn thing falls off again! Of course this happens in the middle of nowhere with no handy tools at hand. Option A: Pedal with one leg Option B: walk and push the bike home.
To prevent this from happening in the first place, take the time to tightened the nut attaching the crank arms to the axle at least once a year. This can be done with a 14mm socket ratchet wrench. If your crank arm just keeps on falling off, even after you've asked your muscle building neighbour to tighten that nut as if his life depended on it, there is one simple reason. When the crank arm is loose and you pedal with it, you damage the four corners of it's socket that rest in the axle. Somehow this damage causes the crank arm to wiggle enough to unscrew the nut little by little until it just falls off again. You will have no choice but to replace it. You can try locktite, but I've had no success with that either. Bring the old crank arm with you to make sure you buy the same size, that's unless you have a leg shorter than the other!
Til next time, ride safe and Godspeed.
Gerry
