Flywheel collet slipping on the crankshaft
 

Ok, I picked up an old XXX-NT stadium truck to play around with at the track. I have a OS CV in it, the one with the old square head that's red. The engine runs like a champ, will idle all day and has plenty of power.
All of the sudden, the flywheel would just spin on the crank when I try to start it. Pulled the engine yesterday and to get a closer look and saw that the collet is slipping on the crank. Pulled everything apart and put a completely different clutch setup on it I pulled off of another engine. Different collet, flywheel, clutch bell, everything. It was nice and tight.
Throw it on the starter box and fire it up, runs for a second and stalls. Go to fire it up again and it's just spinning the flywheel again. I didn't mess with it anymore beyond that point.
I have another complete clutch setup I'm going to try this evening. If that slips as well, what can I do to get it to grab? I feel like a total noob asking this, but I've never had the problem before.
I'm concerned that the crank may be worn down a bit from it slipping and I may not be able to get it to grab.

Use threadlock and get it TIGHT.

File the slot in the collet a little wider. If the crank is worn down a little the collet may not be able to close enough. If you do this you may have to put a shim on before the collet as the flywheel will slide on further when you tighten it

Makes perfect sense, I will give this a shot.

Thanks