bottom cog?if its the bottom pully thats come off it will of thrown the drive belt & its possible the the cambelt may of got damaged.that might be why its running cr*p.if i was u i would'nt start it till u know if the cambelts ok,cause if that comes off or snaps,u will be looking at cylinder head off,new cambelt & tensioners & anywhere up to 16 valves bent
bob
February 2007