I have a mega 16/15/3 bl motor I bought used.I haven't had a chance to try it yet but when I turn the shaft by hand it sorta catches,not like a grind but more like you would expect from a brush like some resistance when you try to put magnets together and there polarity doesn't match-not totally smooth going around.Is this normal?The reason I ask is because I also have a Hacker B20 22s and when you turn it by hand it is totally smooth.Just want to know if this is ok. thanks

Swift, that is completely normal for the Mega motors. See Megas are six pole motors and Hackers are two pole motors. What this mean is that the rotor has either 2 slots or 6 slots. Take a look at the Mega Motors usa home page they can explain far better than I could or maybe someone else can explain the whole idea, but dont worry the cogging effect that you feel when you spin the motor is normal for a Mega motor.
Viper

Swift, I also recommend that you check out this website its all electric and you can get a much better explanation there.
http://www.ezonemag.com Check it out I think it will help.
Viper

It's perfectly normal, and commonly known as "cogging." The magnets are extremely strong in these motors, and that's what's causing the phenomenon.