The backplate that comes with the motor is too deep for the case and grinds on the rod. It's easy to check----take the back-plate off, If you have the deep back-plate, you will be able to see were the rod is worn from grinding on the face of the back-plate---There will also be thousands of scratches on the face of backplate----the metal that comes off act's like sandpaper in your engine. O.S. needs to correct the back-plate or include a brass shim washer between the case and back-plate for this motor. No motor should have a rod that grinds on the back-plate.