M90 options

eriknetherlands said:
Is there a way to check the "health" of the oil pump before reinstalling it into the block?

If it was running on it's last legs, I'd be devastated if it dies while running the engine in.
Click to expand...
Hey, good question. How about just replacing it with a new one as a pre-emptive risk mitigation measure?
 
are they even available? being an M90 block, is the oil pump any different vs a bog std M30?
I know my block came with an oilcooler, and it is advised to keep it; does that change the oil pump specs? 2 extra oil hoses and a small radiator does add more friction -> would it thus have a higher capacity pump compared to std M30's?
 
Here are the part numbers for the M90 up to May 1982. The xxx468 pump is also what was used on the 1984+ 635s so it seems they are interchangeable.\\

It is not exactly clear to me how one might test the oil pump...

Screenshot 2026-05-12 at 10.52.53 AM.png
 
Yes, I kept the original engine and followed the book to check with a feeler gauge the clearance inside the gears of the oil pump. I suspect it is the same approach (maybe different specifications) on the later engines.

I recall reading that the oil pump drive gear bolt(s) can loosen, so you may want to check options for securing, including safety wiring the nut to the gear.
 
Thanks for the tips on the play in the oil pump and the possible loosening of the oil pump drive gear.
I'll see if i can dig up specs for the gap of the gears.
Digging into the oil pump drive gear, google found me this solution from VAC:

Anyone have any experience with this kit? @sfdon - do you use this kit or similar in your m90 builds?

I'll have my engine builder check with VAC if it would also work on the m90 oilpump.
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Use a different approach?
We use a M3 B35 pump and an original pick up for a Coupe
Now we have a modern pump that has the correct pump pick up
Make sure you relieve the shaft hole in the Housing a tiny bit
 
Jimmi said:
Hey, good question. How about just replacing it with a new one as a pre-emptive risk mitigation measure?
Click to expand...
With the today´s quality, i prever to keep as much old parts as possible.
I have driven good with that strategie over the years.
If the oilpump has the correct pressure before knock down, i wouldn´t open it and bolt her back in as they is.
Just check the sprocket for wear.

Breiti
 
sfdon said:
Use a different approach?
We use a M3 B35 pump and an original pick up for a Coupe
Now we have a modern pump that has the correct pump pick up
Make sure you relieve the shaft hole in the Housing a tiny bit
Click to expand...
I'll look into the m3 B35 pump and see if I can find a partnumber for it and if it's is available via the dealer.
I also noted earlier.posta from you on the oilpumps as this one, helpfull to understand the variations:
Post in thread 'Oil pump difference M30b30 to M30b35 swap' https://e9coupe.com/forum/threads/oil-pump-difference-m30b30-to-m30b35-swap.46776/post-412413

Can you explain a bit more on the modification "to relieve the shaft hole in the housing..."?

I've reviewed this youtube of a m30b35 oilmpump rebuild, and the only 'bingo' in my brain would be the hole where the red line points towards, or it's mirror friend on then opposite side in thenother housing half. But those holes act like bearing surfaces for the rotor axle; i can't understand why "relieving" that hole would be a good idea?
Screenshot_20260514_123650_Samsung Internet.jpg

What am I missing? (Likely more then just one thing :-) ! ).

Youtube link:
 
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