Hot Rods Shoebox starter

I am helping a buddy with his shoebox that has a new power master starter. When turning over the bendex kicks out and disengages the drive but still spins the starter motor. So we pull the starter to take a look, looks ok but can’t seem to spin the shaft by hand. Is it a bad new starter or l am missing something.

 

What kind of starter is it and what engine.

 

It’s a 12v power master starter on 50 flathead ford v8