Oil Pump Shim Advice

[Craig Bower]

I am in the process of freshening up a fairly low mileage m90 and have run into a conundrum. The only information that I have been able to locate about shimming the oil pump seems to refer to new a new chain and sprocket and says to shim the pump up until the drive chain deflects slightly under light pressure. Seems a subjective for engine machine work. My chain and sprocket look to be in great shape but I really don’t have a good reference dimension to measure the chain against for stretch. I did find one reference stating that reused chains and sprockets should have additional clearance than new but no mention of what it should be. It seems that new chains are readily available but the pump sprockets are no longer available.
Thoughts or suggestions?

 

[lloyd]

FWIW, for lack of any specifics, it has been suggested that for the M10 engine oil pump chain, 5mm deflection under light tension (~10 ft./lbs.) works. https://www.bmw2002faq.com/forums/topic/68899-oil-pump-chain-tension-how-tight-is-too-tight/

My own practice has been to keep things "understressed" and avoid freeplay or preload, a la Goldilocks . Inevitably, as soon as the chain and sprockets are "run-in" some play will return. Perhaps if you start with "a modicum" of free play, the chain will not develop as much slack as if it started out as "extra taut." But I think not.

I should add that once upon a time these chains were available with a master link, making replacement fairly simple, without regard to pump removal, and as an alternative to adding shims. It is not the best substitute for addressing already worn driving teeth . . . . .

 

[sfdon]

You should need about 7 mm’s of shims after you upgrade to the m30b35 small gear.
Thick shims are NLA but can be found on eBay.
Two different chains
Three different gears
Must open up shaft area when converting to front late pump to rear early pump
655 chain is b35
656 chain is early


correct is long chain= big gear splined or bolt on 46 link this is early
44 tooth chain is late for small gear spline and tensioner [b35] version.

 

[sfdon]

At the shop on m90 engines we go-
44 link
Small splined gear
B35 front pump
B34 rear pump
Relieved shaft hole
Stamped not cast crank stand off
Original pickup can
3mm shims and 1 mm shims

Best high pressure regulation and highest low rpm oil pressure.

 

[Craig Bower]

I appreciate the information from both Lloyd and Don on this. I am a little confused with Don’s reference to the stamped not cast stand off. My engine has a cast iron bracket at the center (#4) main bearing cap then flat sheet metal bracket attaches to the oil pick up casting. Is this the stamped sheet metal bracket?
Do you know if the splined hole in the small gear is smaller in diameter than the pilot hole in the bolt on gear? If so, then I could machine the small splined gear to fit the old bolt on pump.
I find it interesting that shims come in 1mm or 3mm increments when this engine came from the factory with shims that are approximately .004”. or a tenth the thickness what is now available and we are instructed to provide “some deflection under light pressure”. It seems that the factory was being more accurate originally.

 

[sfdon]

That amazing cast piece and special long bolts were soon replaced by a cheap stamped piece. Available today but you will need two regular bolts.

 

[sfdon]

Btw- shims are: mm
.3
.2
.15
.1

 

[sfdon]

The three gears....

 

[Craig Bower]

Thanks for the photo. From here, it doesn’t look like the BMW engineers wanted me remachining their new sprocket to match the old pump.
What is the logic behind the stamped pickup bracket other than limiting the number of extraneous pieces and hardware?

 

[sfdon]

Thanks for the photo. From here, it doesn’t look like the BMW engineers wanted me remachining their new sprocket to match the old pump.
What is the logic behind the stamped pickup bracket other than limiting the number of extraneous pieces and hardware?

Money... that’s the logic.

My favorite is the plenum support of the e23 of 1982. One year only.
34 pieces......

http://www.realoem.com/bmw/enUS/showparts?id=6633-USA-06-1981-E23-BMW-733i&diagId=11_0824

Most replaced by another simple stamped bracket.