My longest ride was yesterday - 20 miles. The eccentricity in my (3-piece) crankshaft made my left crank fall off. Today, I discovered the reason:

The quad splines on the crankshaft are tapered, from thick inboard to thinner outboard. The aluminum crank arms are designed to press tightly onto the quad splines when the nuts are screwed clockwise onto the crankshaft threads. This tightening essentially makes the three pieces of the crank fit together so tightly that they rotate together en masse like a one-piece crank. I had put five inboard bushings between the left radial ball bearing and the left crank arm in order to prevent the left crank arm from striking the front fork. While these bushings (washers) kept the left crank arm far enough to the left to prevent striking the fork, they also added an undesireable gap between the left crank arm and the quad splines on the left side of the crank shaft.

My mechanic gave me brass shims to essentially increase the "thickness" of the quad splines. I will put them onto my left crank and ride twenty miles this weekend.

Then I will know if the shims solve the crankshaft wobble problem. The only other thing I can think of to fix this problem is to find a thinner fork so I can throw away those five bushings.

Man, I hope this works so I can become a distance rider instead of a bicycle mechanic!!