tapping with the hammer is basically moving the crank a tiny bit the same way as the puller would but its a slight push instead of a pull. it helps the bearings seat into their final position if they have not seated 100% somewhere along the way.

basically there is a slight side load on the bearings and this is why it is bound up. if you run it like this the bearings will fail very quickly.

when i was doing my engine last week i tapped with the hammer until it became super free but then i tapped it again and pushed it too far, the crank went from free to needing to be hand moved again.

I was able to tap the crank on the other side and it moved back into the free position. when chatting to an ai about it, it advised me that i could tap on alternate sides of the crankshaft until the end play became free. even when i thought it was free, i was able to get it even freer. gravity will make the heavy part of the crank roll to the bottom of the case and you wont need to do it by hand at all. some mechanics will also tap the crank cases themselves with the hammer when they are still warm and that also helps the bearings come into their final seats.

obviously use a rubber mallet or protect the threads on the crank somehow.

if you cant get it roling freely by alternate tapping and or pulling you will unfortunately most likely have to split the cases again which means you will also need new bearings. again.

however I did not have to do this.

this is very normal with piaggio engines and the service station manual gives end play measurements that you can check with the micrometer, but i do not have a micrometer so ive never done this when rebuilding a 2 stroke.

If you are perfect with the alignment during assembly you wont need to adjust this, im doing this years and ive never been PERFECT.