The 'primary' gear of the Mini is the first gear out of the engine that transfers the power to the transmission. The clutch disc is slip splinned onto this gear. The large ID gear rotates on the nose of the crankshaft and has bronze bushes for the bearing surface. As these bushes wear, not only do you get noise from the gearbox area but the chances of destroying a much more expensive gearbox, etc. increases dramatically. The bush on the 'front' is at the end closest to the engine and has NO flange. It has the bigger ID of the two bushes. It takes a lot of load as this is the driven end where it engages the idler gear.