This is not a complete analysis of the perils of oil pump cross-fitment.
There are *at least* two oil pump configurations.
The "A" is a later configuration than the "B".
At this time, I DO NOT recommend mounting an "A" pump to an early motor.
More info will be posted as I get it further figured out.
Stopintime needed a set of primary gears, and I had a set.
There are different oil pump gears, so to attempt avoidance of that beartrap, I sent an oil pump with the matching gear.
The trans-atlantic shipment arrived intact, and I figured the whole deal was sorted.
His mechanic went to assemble the bits to his motor, and that's where it all went sideways.....
So, to try and figure out where the train went off the rails, I gathered up a bunch of parts.
You like pictures, right?
Here's two of the scoundrels, I've arbitrarily named them "A" and "B".
Both 33 teeth on the primary, so they're from small case 33:61 motors.
"A" has 25 teeth on the oil pump drive gear, matching "A" pump has 40 teeth, fairly large ones at that.
25:40 is a 0.625:1 reduction.
"B" has 30 teeth on the oil pump drive gear, matching "B" pump has 58 teeth, smaller ones.
30/58 is a 0.517:1 reduction.
So "B" turns ~83% as fast as "A".
Here's a pic of the back sides, the dramatic tooth size difference is easily seen.
Here they are mounted up on a '99 M750 motor (10mm engine bolts, weak area at neutral switch, and 3 phase charging)
The "A" pump can be removed/mounted easily, even with the clutch basket/primary installed.
The "B" pump *cannot*.
I did both with the crank primary gear installed on that motor, YMMV.
The "B" pump is a serious beyotch, as with the larger gear it will just *barely* clear.
Pic below shows the position where it hangs up, and the orientation required to clear is shown within the green circle.
Requires patience and gentle wiggling to get it through the tight spot.
IMO, this could easily be a total no-go if the crank is shimmed a bit toward the alternator.