Cotter pins were getting getting loose and cranks had some play in them. Tried different sized pins with no success.

​​​​​​Breaking off a small piece of hacksaw blade. That fit into the spindle slot for the cotter pin and allowed the crank arm to slide over, then inserting the cotter with the piece of hacksaw blade inbetween the spindle and the cotter pin.

This way the crank never got loose in over a year of riding. There was no problem taking the crank off when needed.