I'm upgrading my oil pump shaft. What does the round metal piece you have to put on the shaft do? Is it necessary to install it? What happens if you don't?
It is a retainer collar. Install it so that it is just below the hole where the shaft goes up to the distributor. Its function is to prevent the oil pump drive shaft from being pulled upwards and out of the pump when you pull the distributor out. It is not necessary, but quite useful. Without it, if the pump shaft sticks in the dist when it is removed, it could come up out of the pump and then fall into the pan.