I have recently had this problem with two different cranks, both older cranks that were new to me.
I wonder what brand/model cranks? Perhaps some are prone, some others immune?
Originally Posted by
jimmuller
On the question of Loctite, I would not think the bolt is coming unscrewed. I sure wouldn't put Loctite on the taper itself!
Yeah, I meant on the threads.
Originally Posted by
trailangel
Stop retighten the cranks or you will ruin them. The bolts are not loosening, the crank arms are working their way further up the spindle.
I am beginning to suspect THIS. Gonna Loctite (
capitalized as otherwise the spellchecker keeps trying to change it to "lactate", not going to try that on my cranks 
) the bolts and hope for the best. If the crank arms deteriorate, I might be shopping for some Campy cranks as most of the rest of the bike is Campy. I happen to have an extra set of Stronglight 93's... but on an Italian bike???
Perhaps Avocet cranks are just soft? NEVER had this before on any cranks -- my own, friends' or the 100's I worked on in my bike-shop days; not even Maxy cranks which I always presumed where made of alumibutter.
Plus I should also check w/VO on the taper type on their bottom brackets.