I am replacing the motor in my 96 750 super sport xi. The motor I removed from the ski has a crankshaft diameter of 18mm where the pto coupler screws to. The motor I ordered has a 20mm shaft where the coupler screws on to. Can anyone tell me if a pto coupler with a 20mm inside diameter will still match up to the coupler on the drive shaft or is it bigger than one with an 18mm inside diameter?