Are these square taper or?
There are 2 standards used in sq. taper cranks, with the angle of the taper slightly different.
IF it's a used crank, it may have been "messed up" before you got it.
Typical torque, IIRC, is 30 FT-LB. You might just go ahead and exceed that some if 30 isn't doing the job. A 24x series loctite should do the job. That would let you know if the problem is the bolt/nut backing off, or if the taper/spline is damaged.
Fixed gear! Your knees are a lot better than mine!
