The parts book tells me what #3073 and #3074 are, but I'm having trouble figuring out where they go. What is the crank case arm?
The part that laps over the frame. One bolt from the top, the other in the side to attach to the frame.
The photo shows white arrow pointing to what I think is the crankcase arm
Of course! I should have thought of that.
Steve, The "top" is the short one with a castle nut and cotter key. It goes where the white arrow is pointing in the photo above. The "side" one is the long one that goes thru the side of the frame and thru the wood block and crankcase arm. It also has a castle nut and cotter key. The long one is only supposed to be "snug" and then locked with the cotter key.
It is good practice to also make the top one up to no play but not tight. When the frame flexes on uneven surfaces it is these bolts with the strap over the nose of the pan that allow the assembly to give enough to not twist the pan and ultimately crack the nose and arms.
The top one is tight, with cotter. The side long bolt castle nut is just snug with cotter. Make sure the wood block is tight, it needs to be a friction fit between the inner frame rail and the crankcase arm.