why are some oil pump shafts different on the pump ends,some are male and others female,also Ive noticed on the pump covers some have a dimple to push in the pump on the cover and others dont.also the gear the timing chain is on could go 2 ways and the wrong way would cause alignment of gear and chain problems.These sound unusual but ive disassembled a motor and the gear teeth seem worn on 1 side real bad and it doesnt seem aligned propely.They obviously arent all interchangeable like I thought.