model 130-7 won't move chain when engaged in carriage

the opener can move the carriage back and forth if door is disengaged with manual release, but cannot when carriage is engaged. On the drive gear at the motor head their appears to be a pin about 1" long that appears that it should go through the motor shaft. Ours stick out about an inch from the edge of the shaft assembly. when the door is connected to the carriage the motor shaft spins but the gear does not turn. I'm guessing this is a shear pin that has broken because the door got jammed ? How do I find the proper replacement. Don;t have a manual for this opener

The pin may have just worked it's way out...you may try putting it back in. If that doesn't work then pull the pin out and try looking at a local tool or hardware store...a lot of times they'll have different size pins. If none of that works you can always replace the entire #1200011 Drive Shaft Assembly. Hope this helps.