What would cause engine to jam while cranking??
Make sure the ignition is OFF
LOL I have to tell you guys everything?. Actually sometimes I static time with the ignition ON. I get the dist retarded, points closed, and "rig" a gap or neon lamp to the coil wire, then move the dist until I get a spark. With practice, you can do the same thing with breakerless. Sometimes I just listen for the "click" of the spark if it's quiet.
My neighbor just could not believe it years ago. Had a 351 in a Ford pickup he restored, was out there for an hour screwing around. I went out, stuck my finger in, pulled the dist, argued with the oil pump drive, and timed it I looked around, and said "start it up." He was flabbergasted by that statement, and it STARTED!!
I first learned all this in about 1972