Your oil pump will fail., And it will kill your engine. Options

[Valy]

I'm rebuilding a 2.0L and posted a lot of pictures in a different thread.
One of the pictures showed the oil pump and Jake immediately noticed that the pump failed. Went back to the engine and saw how the oil pump touched the cam gear and shred off the nits holding it.




Being such an anal guy, I took same time today to understand why did the oil pump fail?



The red axle in the picture above it the one that protruded through the pump cover. There's nothing that holds it in place except the friction between it and the cover!
So Why does it move?
This red axle goes into a cavity of the oil pump case (rightmost in the figure). The cavity is almost snug-fit to the axle but oil can infiltrate around the axle into the cavity. When the pump works, there is a bit of oil pressure in the pump that causes the oil in the cavity to push the axle out; just like a hydraulic piston. The force is small but it's constantly there. As the axle moves, more oil flows in and that keeps pushing the axle out.
Over the time, that axle is pushed out of the pump cover until it starts touching the cam gear, shredding the nits that hold it. Eventually, the nits will brake or the axle will block the movement of the camshaft and something else will brake or your camshaft bearings will give due to the vibration inducted by the hits.

The aftermarket oil pumps are build differently, with no axle that can protrude into the motor, making them a good upgrade to your old original pump.

Make yourself a note to replace that old oil pump at the first occasion. I will even recommend to create that occasion before it's too late.

[Valy]

So I did some research on the possible replacements for our old oil pumps.
As I understand it, we need the type 1 pump with 8mm studs, built for flat cam.
Or original pump gear is 24mm so anything this size and bigger will be nice.

Some recommend the Melling pumps. Those pumps look solid but have a major problem: the pump body is made of cast iron. This results in a different heat expansion rate compared with the aluminum case (aluminum expands more). The result is a bigger gap between the case and pump when the engine is warm. Can be fixed by adding an elastic o-ring between the pump and case.

The other option is the Schadek pump that has a more desirable aluminum body and is much cheaper (IMG:style_emoticons/default/smile.gif). There are also lots of good reviews for this pump.

Both pumps are available in different gear sizes, including the 26mm and High Volume 30mm gear.

Anyone is welcomed to comment on the options or just add more.