u sure its not the brake binding?

if thats ok, id personally just fire it up... but thats me.... does it bind at all when the pinions are turned, as per when the engine is running? if not then it should be ok shouldnt it? and maybe a bit of running will smooth it out...? i dont want u to fry another spur on my word, but i cant see what else could be the prob.

gears are free from debris etc arent they? try a tiny spot of grease for 1st run maybe? watch loads of stuff doesnt stick to it tho and kill the gears...