Join Date: Jan 2005
Location: San Juan Capistrano
Why oil pumps break
I can't read the procedure that Papajam posted, but I'll bet it addresses this problem:
The mounting flange for Alfa oil pumps are at an angle relative to the shaft. There is a fat O ring between the pump's mounting face and the surface it attaches to at the bottom of the front cover. If you simply tighten the 3 bolts that hold the pump to the cover, you will often find that the shaft won't turn easily. The problem is either that the parts either have some tolerance in the angle between the shaft axis and the mounting surfaces, or that the pump "rocks" a bit on the O ring as it is tightened. Either way, this misalignment puts a bending stress on the shaft, the hole where the pin goes is the weakest point, and it will fatigue. This generally happens within the first few hundred miles after a pump is installed.
Sure, new shafts may fatigue more readily than old ones - I'm not saying the heat treating stuff isn't true, or doesn't contribute. And, no, I can't explain why a pump would die after 40,000 miles (maybe it was only slightly misaligned)
But, the best way to install an oil pump is with the front cover off the block, tightening the three bolts slowly, and checking that the shaft will turn freely. I put some loctite on the bolts, and tighten them just snug - not super tight - tinkering with the relative tightness of the 3 bolts to ensure that the shaft is turning OK.
If you engine is assembled, in theory you can use a large screwdriver in the distributor drive to wobble the shaft within the lash of the drive gears to ensure that it isn't binding. I have never tried this - it would seem to take two people - one standing up feeling the shaft rotation, and one on his back under the car tightening the oil pump bolts.
San Juan Capistrano, CA
'65 Guilia Sprint GT