This has happened to me maybe three or four times in 40 years of riding: You're cheerfully pedaling along, and suddenly the non-drive side crank arm is rattling around loose on the spindle. It's not like it gets a little bit loose then rapidly gets worse--it gets very loose all at once. I seems to me that the crankarm fixing bolt gradually works its way loose until it's just finger-tight, but the arm itself stays pressed onto the spindle until suddenly it breaks loose, maybe as a result of standing up on the pedals to climb over a rise. Has this happened to others? Does anyone have any insight as to why it happens?

Anyway, it happened to me again last weekend about 20 miles into a 50-mile ride (returning from an overnight stop at a friend's house on a run from near Bellows Falls, Vermont to Amherst, NH and back). I was on my Gitane TdF, and it was a rainy Sunday with no obvious opportunities to borrow a 14mm socket wrench. I had just resigned myself to screwing the bolt in finger-tight and destroying the crank arm in the process of finishing the ride when I had a brainstorm while passing a place where the local utility had cut down a bunch of trees.

We pulled off the road and I lay the bike on its side with the drive-side spindle centered over the stump of a small oak tree. My friend Dave held it there while I found a two-foot length of oak, maybe four inches in diameter, that was sawn off square at both ends. I positioned the non-drive-side crank arm on the spindle, with the bolt removed and WHAM! brought the butt of the length of oak down on spindle end of the crank arm as if it were the business end of a wooden mallet.

To my surprise, that solved the problem. It pushed the crankarm far enough onto the tapered spindle that it stayed tight for the rest of the ride--no play at all, and no damage to the crankarm or spindle, as I determined by disassembling them later. The key, I think, was having the other end of the spindle resting solidly on the stump, so all of the force was transmitted into the spindle and arm, rather than the bearings and cups.

That said, I think I'm going to convert all of my bikes from 14mm hex bolts to those more modern 8mm bolts with the integral dust cover. They may be slightly non-original, but my folding allen wrench has an 8mm attachment. Even if this only happens once every ten years or so, it's a failure mode I can do without.