There is a split line, very well hidden with the fine CNC machining.Where the BME logo is there is a prop outline and the split cuts right through the center of the prop. The crank works the same as anything else for installation. Exception being the rear bearing presses in from the inside like always but no seal is needed as the crank stub for the clutch gets cut shorter. The other unanodized piece goes over a third bearing that installs on the crank after the crank is installed. Slide the bearing on then the piece of aluminum and drill and tap the three holes to hold the bearing block in place. The milled slot is for the timing sensor to glue to. Now I wish I could come up with one or two cases like these for the 61cc twins I have here.