Maybe those idle moments of pleasure reading in the no plot Factory Shop manual have paid off....

In the 616/NA 617 manual it says that if you have " oil noises" ( which I have no idea what they were referring to " at start up then you have the option of screwing in a different ( and implied LATER ) model oil relief in the oil pump. They come with differnt size holes, pointed different directions, and at different BAR ratings....