Oil Pump piston and compression spring

[Joe Boston]

I am in the process of assembling M90 engine and was checking the oil pump and noticed this piston with a compression spring. I noticed that there was no tension. For some reason my pump doesn't have item 22 i only have in the diagram items 20, 21,23,24.
Has anyone had experience in changing out this piston?

[keehn]

I have not worked on this system, but item 22 looks VERY important.

I've shared what the blue service manual has on the oil pump. Note that item 22 is present.

[Joe Boston]

very interesting Keehn...thanks for the reference of the manual.
I have another M30B28 motor and removed the oil pan and i have the same type of oil pump. no part the looks like item 22 in the diagram.

I believe the plug (#22) was for old production pumps. close up look there is no thread to screw on the plug. the clip hold a spring pocket to allow the flow of oil. Perhaps

[keehn]

Joe,

This looks to be a "technical update" (TU) to the oil pump design. Clearly, your engine must work fine, so I wonder if the exploded diagram simply shows the pre/post TU by design? It's a head-scratcher to me.

Regardless, I'll be doing a complete top and bottom rebuild of my 76 M30B30 this winter and I'll make sure to document what I find.

[Lock]

I took a look at the oil pump I removed from the M30B35 I had, and it's identical to the picture Joe posted. So you're right it's probably a technical update and your book is showing early pumps.