Dave,
what i did was to pull the prop hub off..............poured some straight castor onto the front bearing in which it took 3 applications because the castor kept penetrating into the bearing right past the shield.............then with piston closing off exhaust port fully, i blew through the carb intake.........the bubbles coming out through the castor from the front bearing looked like the local uncared for nieghborhood kid that always had one of those big ol snot bubbles coming out of his nose on one nostril or the other, sometimes both.........

so yeah, it's a lowsy fitting shield, and probably a larger than normal crank to case clearance.