I'm in the process of rebuilding the bottom end of my mc18. I had a big end bearing fail and a piston was distroyed in the process. So, I have a spare crank, new bearings and new seals. Problem is, the spline on the end of my spare crank ( where the primary drive gear goes on) is shorter than the crank that came out of the motor. Also, the primary drive gear is thinner and smaller in diameter than the one I took off the crank

Primary drive gear




Ends of the two crankshafts (broken one first)




Why are they different? They both have the same bearing and seals, they both fit into the cases perfectly, both primary drive gears fit on the end of the crank and the taper on the flywheel ends are the same as well. I am worried that the smaller drive gear wont engage properly on the clutch gear. Can I use this spare crank or do I get the original one rebuilt, assuming that the pins are all ok? Off to go clean more parts. Thanks heaps for any help, appreciate it!