you can run any size bell you want that wont make this "clicking" you guys are talking about. If it does it when there is no play in the teeth or when there is a ton of play in the teeth that kinda makes it seem that its got nothin got do with the spur gear or the clutch bell....... The brakes on these things are famous for making "clicking" sounds when there not set up right. Or maybe a bad bearing? How about the drive shafts from the transmission to the diffs? Are all your tires the same size? You should never ever run 2 different tires on these things then your just putting extra stress on things. It just doesnt sound like a spur gear problem to me. Broken clutch spring? Bad clutch bearings? Is your clutch touching your flywheel? What size is the spur gear? If its the bigger gear of the 2 then you have to put the transmission spacer in to stop the gear from rubbing on the chassis. Or is the spur gear rubbing on the clutch bell? Do you have a worn out diff cup or stub axle? Hows your muffler bearing?