paul1980

hi guys can any one help with my problem, I split the engine on my ty 80 to have main bearing and seals etc, but when it came to put it together the main gear sprocket locks up, but only as I tighten the engine casing screws, if I loosen them it's free but just that miner tightening of it locks back up again, it will go round but with alot of force, what could this be? Many thanks paul