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#4579656 - 11/20/17 12:36 AM BMW S54 Rod Bearing Oil Pressures
SlipperySimon Offline


Registered: 11/19/17
Posts: 4
Loc: South Africa
Greetings all! This is my first post.. I've been following this BITOG forum for many years as a guest...a tremendous wealth of knowledge on this forum! I've been searching the forums for over an hour and haven't come across anyone that's answered this issue adequately, and I'm thinking that this could be a solution for all S54 owners:

As the engine-builder's rule of thumb goes, one should have around 10 psi oil pressure per 1000RPM for standard bearing widths.

As we are all too familiar with, our rod bearings are narrower than the typical rod bearing found in cars.

One can then safely assume then that there's no way our bearings should be experiencing anything under 10psi/1000RPM, and, if anything, should be set to at least 12-14psi/1000RPM.

After taking a look at the TIS documents on checking oil pressure on the S54, it is clearly stipulated that there should be minimum 0.7bar (10.1 psi) at idle speed at operating temperature. It then goes to say that the pressure is then regulated to a constant 4bar (58 psi). This pressure is regulated by a sprung piston situated in the oil pump which limits the output pressure to a maximum of 4bar (58psi), (experts please step in and correct me if I'm wrong here).

At this point it becomes apparent that the bearings are under-lubricated at RPMs over 4800RPM (using a conservative guideline that 12psi are required per 1000RPM)

This makes me think that a far simpler solution to eliminate the rod bearing issues would be to remove the oil pump pressure regulator, or at least modify the existing setup to maintain higher oil pressures at the higher rpm.

1. Does anyone have experience with this or considered this?

2. Why would BMW fit a pressure regulator to the oil pump in the first place?

I just find it really bizarre how this could have been overlooked by the engineers in Germany, as this is the 101 of engine building, and I must be missing something...

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#4579661 - 11/20/17 01:32 AM Re: BMW S54 Rod Bearing Oil Pressures [Re: SlipperySimon]
Colt45ws Offline


Registered: 08/15/06
Posts: 9648
Loc: Central Washington
To increase the pressure, just fit a heavier spring into the pressure regulator. This may or may not be easy depending on its location. You may also be able to 'space' the stock spring tighter with something behind it so it puts more force on the valve, but you have to make sure the valve can still reach its full open position before you bind the coils of the spring.
You need to regulate the pressure to prevent the pump from being damaged by high pressure. Its a positive displacement type pump, which means every rotation it outputs X ccs of fluid. If the oil is cold, there will be quite a lot of resistance to flow through the oil galleries. The pump will keep pumping the same amount fluid in on every rotation increasing the pressure until something gives.


Edited by Colt45ws (11/20/17 01:34 AM)
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#4579699 - 11/20/17 04:45 AM Re: BMW S54 Rod Bearing Oil Pressures [Re: SlipperySimon]
Claud Offline


Registered: 02/11/14
Posts: 593
Loc: Margate England
I would hazard a guess that if BMW think 4 bar is fine then it probably is.
Oil flow is just as important as just pressure. The oil at the bearings need to be constantly replaced to keep the bearing cooled.
If you plug the relief valve my money is on the filter bursting from a cold start, maybe with the oil pump drive breaking as a covering bet.

Claud.

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#4579700 - 11/20/17 04:49 AM Re: BMW S54 Rod Bearing Oil Pressures [Re: Claud]
Shannow Offline


Registered: 12/12/02
Posts: 39924
Loc: 'Stralia
Originally Posted By: Claud
I would hazard a guess that if BMW think 4 bar is fine then it probably is.
Oil flow is just as important as just pressure. The oil at the bearings need to be constantly replaced to keep the bearing cooled.


The temperature in the big end is DUE to the viscous friction in the bearing and the oil.

Heat flow is OUT of the bearing, and into both the con-rod and crankshaft at high RPM.

There has to be enough oil available to replenish the side leakage ...

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#4579720 - 11/20/17 05:34 AM Re: BMW S54 Rod Bearing Oil Pressures [Re: Shannow]
Claud Offline


Registered: 02/11/14
Posts: 593
Loc: Margate England
Originally Posted By: Shannow
Originally Posted By: Claud
I would hazard a guess that if BMW think 4 bar is fine then it probably is.
Oil flow is just as important as just pressure. The oil at the bearings need to be constantly replaced to keep the bearing cooled.


The temperature in the big end is DUE to the viscous friction in the bearing and the oil.

Heat flow is OUT of the bearing, and into both the con-rod and crankshaft at high RPM.

There has to be enough oil available to replenish the side leakage ...


Absolutely, the hot oil needs to be replaced before it breaks down.

Claud.

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#4579725 - 11/20/17 05:43 AM Re: BMW S54 Rod Bearing Oil Pressures [Re: SlipperySimon]
StevieC Offline


Registered: 08/21/08
Posts: 17116
Loc: Ontario, Canada
welcome to BITOG Simon
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#4579917 - 11/20/17 10:08 AM Re: BMW S54 Rod Bearing Oil Pressures [Re: SlipperySimon]
OVERKILL Offline


Registered: 04/28/08
Posts: 36464
Loc: Ontario, Canada
IIRC, the 10psi "rule" applies to the Small Block Chevrolet and is not some universal guideline.

The oil pressure relief spec pressure simply means that the bypass cracks at that point, it doesn't mean that's the maximum pressure you are going to see. It is very possible; probable even, to observe pressures significantly higher than the relief as the pump over-drives the relief circuit and continues to build pressure in the rest of the system.
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#4579932 - 11/20/17 10:19 AM Re: BMW S54 Rod Bearing Oil Pressures [Re: SlipperySimon]
BrocLuno Online   content


Registered: 09/06/15
Posts: 5526
Loc: Kalifornia Kollective
+1 smile

And, yes and no. Most USA V8's have somewhat similar bearing sizes, so it has become a rule of thumb for USA engines. But all bets are off on bearings with other sizes and different clearances...

I'd just run a good high HTHS oil in the appropriate grade and keep it clean. If you want to do track days, think about loosening the clearances by a few thou and be done with it laugh


Edited by BrocLuno (11/20/17 10:19 AM)
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#4580006 - 11/20/17 11:30 AM Re: BMW S54 Rod Bearing Oil Pressures [Re: SlipperySimon]
andyd Online   content


Registered: 09/25/04
Posts: 7162
Loc: Marshfield , MA
The displacement 3.2L is the same as the the M30 in my '83 533i that puts out only 160 hp. The trouble is that oil needs to changed more often. These cars are victims of poor care and hard usage. Most have a tender cooling system that contributes to overheats.Replacing plastic parts before 100K is advisable. Having a tank split open at full hoon will often result in a major overheat. Something about the new stuff being more bio degradable in the waste stream.
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#4580012 - 11/20/17 11:34 AM Re: BMW S54 Rod Bearing Oil Pressures [Re: SlipperySimon]
BrocLuno Online   content


Registered: 09/06/15
Posts: 5526
Loc: Kalifornia Kollective
More biodegradable yes, but it starts as soon as they roll off the line ... frown
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#4580029 - 11/20/17 11:47 AM Re: BMW S54 Rod Bearing Oil Pressures [Re: SlipperySimon]
ARCOgraphite Offline


Registered: 05/17/09
Posts: 11970
Loc: N.H, U.S.A.
Worry more about HTHS rating of your Oil.
Mains pressure just puts oil into the bearings and provides little bearing cooling as there should be minimal heat transfer due to windage in this situation.
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#4580143 - 11/20/17 02:37 PM Re: BMW S54 Rod Bearing Oil Pressures [Re: BrocLuno]
Shannow Offline


Registered: 12/12/02
Posts: 39924
Loc: 'Stralia
Originally Posted By: BrocLuno
+1 smile

And, yes and no. Most USA V8's have somewhat similar bearing sizes, so it has become a rule of thumb for USA engines. But all bets are off on bearings with other sizes and different clearances...

I'd just run a good high HTHS oil in the appropriate grade and keep it clean. If you want to do track days, think about loosening the clearances by a few thou and be done with it laugh


Reinforcing this...tTry to find an oil that has a high HTHS for it's grade, and drop back on Kinematic viscosity a little.

For example I'd use
https://www.redlineoil.com/Content/files/tech/15W50_MO_PROD_INFO.pdf

over either
https://www.mobil.com/english-gb/passenger-vehicle-lube/pds/glxxmobil-1-extended-life-10w60
https://msdspds.castrol.com/bpglis/FusionPDS.nsf/Files/B97CA7A6D4E6B82580257F8E006DA735/$File/BPXE-A9VFNF.pdf

As you get the same protection (HTHS) with about 15% lower KV, which means less pressure loss along the oil galleries and the feed port through the main to big end transfer port...a little bit, but in the right direction.

Also, being highly additised, when the oil film IS in distress, there's additives to help out.

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#4580184 - 11/20/17 03:31 PM Re: BMW S54 Rod Bearing Oil Pressures [Re: SlipperySimon]
1JZ_E46 Offline


Registered: 04/04/16
Posts: 1229
Loc: Oregon
I was told by someone with lots of knowledge on the S54 (has a 900 horsepower one in his race car - big turbo, nitrous) that the rod bearing issues are due to low-RPM, daily driving. S54 bearings seem to live long lives at the track in high-RPM high-oil pressure use. FWIW, he has stock bearings in his car with no issues.
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#4580245 - 11/20/17 04:46 PM Re: BMW S54 Rod Bearing Oil Pressures [Re: SlipperySimon]
rooflessVW Online   content


Registered: 12/24/11
Posts: 4078
Loc: North Carolina
The rod bearing "issues" in the S54 and S85 are, in my opinion, due to people driving with their foot to the floor while the engine is cold. If the people that daily drove and short tripped them did so with 0W-40 in the sump, they'd probably be fine.
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#4581318 - 11/21/17 07:04 PM Re: BMW S54 Rod Bearing Oil Pressures [Re: rooflessVW]
Garak Offline


Registered: 12/05/09
Posts: 24620
Loc: Regina, Saskatchewan, Canada
You mean people buy a car like this and don't drive it as more than a grocery getter? wink Yes, I understand the irony, given that my G37 rarely sees above 60 mph.
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