took my dynamo/generator off to replace my left crank seal, but now I cant get it back on.

I removed it with the recommended bolt which I bought off of boltdepot.com

I don't know If its supposed to press on with something or pound on.

I did try getting it on by torquing the timing advancer, but that didnt work.

Armature locks to crank by the machine taper. It's a very common method to lock something to a shaft and locate it concentrically. Many machine tools use tapers as well as the armature and flywheels on Yamahas.

en.wikipedia.org/wiki/Machine_taper

Shaft and hole need to be clean and dry with no burrs, rust, etc. Same with crank key and keyway. Key sometimes shifts in groove preventing armature from sliding on all the way.

Also make sure puller bolt didn't "mushroom" end of crankshaft.

Do not pound. If everything is clean, armature will lock on taper pretty well with a little shove... then tightening mounting bolt to spec locks it solidly to crank. (Key is mostly an "assembly aid" to index for timing. Taper locks the armature to crank.)

Has the crank key turned up out the back of the groove & still trapped by the groove & stopping the armature going on. Should just slide on no problem if you line up the key.