What would cause engine to jam while cranking??

To time it, you need to make sure no1 is on compression. To do that, pull the no1 plug, stick your finger in the hole, and bump the engine until you BEGIN to feel compression. If you have not done this you may need to "go round" once to be sure. When you feel compression, watch the marks, bump or wrench the engine NOT clear to TDC, but rather so the marks are where you want initial timing, AKA 10BTC or whatever. Stick the dist in with the rotor in the direction closest you can get to no1. Rotate the dist CW (retarded) and then slowly advanced (CCW on a SB) until the points just open or the reluctor is aligned with the center of the pickup. No plug the no1 wire into the cap where the rotor is "just approaching," and wire the rest accordingly. Start it up