Ok, here is what has been tried :
a. Disassembled crankset, clean all interfaces between chainring bolts, reassemble as tightly as possible. theory was that there was dirt between rings or they were loose.
b. Make sure the middle and outer rings are as close as possible together. There is nothing between these rings but spider arm right now. They have been oriented to be as close as possible together, HOWEVER, there is no shoulder in this gap where the chainrings are getting stuck.
Here are some possible causes that occur to me :
a. There is something wider about the stronglight 93 crank sold with an outer chainguard (really, the guard is just a ring whose teeth were never ground - i cannot see stronglight making special crank arm tangs just for a chainring w/o teeth)
b. Early 1970's stronglight 93's did not work with sedisport. after all ultra-6 freewheels weren't out yet.
solution(a,b) : grind the crankarm tangs down, how much ?
c. For a triple, i may need a special middle ring with shoulders on both sides. Currently using an outer ring in the middle position.
solution(c) : get chainring of what type ??
d. My chain may be too narrow (e.g. maybe 8-speed or 9-speed) or maybe its too flexy and nees to be replaced ?
solution(d) : who makes the widest chain sold today ??
e. This crank was never used as a triple.
solution(e) : get smaller chainring bolts, convert back to 52/42 double
f. Chainline is wrong - VERY doubtful
solution(f) : get axle that is wider or narrower
g. There must be a shoulder between all rings to avoid chain jams
solution(g) : reorient rings so that strangely, middle ring has a countersunk hole that is up against the crankarm spider, doing no good. or get a stronglight ring with shoulders on 2 sides for middle.
Thanx,
- Don Gillies
San Diego, CA