Crankshafts. The 5-speed crankshafts are interchangeable, until the CB500, which has bigger bearings and won't fit the 450 cases. (There were changes, through the years, in the bearings, I think). 450 cranks that are tight enough, but noisy at idle, can be quieted by using a thin shim (.010-.020") between the inner primary drive gear and the bearing. It "walks" the gears onto a little different pattern, which "carries" the bearing lash over a little. The crank doesn't rock as much in the drive side bearing. Watch out for cracked upper frame tubes, just above the rear most weld of the web material under the backbone. Loose cranks cause that crack, very early on. Honda added a doubler, somewhere around 1970, to reduce the cracking. Back