Red Oil Pressure Light comes on when idling (right after rod bearing replacement)

[BMWahba]

So stay away from extra clearance bearings?

[MTiz]

I think I'm just going to buy a car cover and park it until I can save up to do the rod bearings again.

...might see a white M3 on marketplace soon

[sapote]

You could raise the idle rpm. What rpm does the low pressure light turn off at?

Not good, as higher idle rpm will eat the tranny R , 1st (and 2nd if SMG) fast. For longer synchro life run low idle rpm.

[sapote]

So stay away from extra clearance bearings?

Why deviate from the factory spec? I'm sure the designers had spent many hours testing to arrive at the spec. I see no reasons to increase the clearance.

[heinzboehmer]

I think I'm just going to buy a car cover and park it until I can save up to do the rod bearings again.

...might see a white M3 on marketplace soon

Oooor your could get all the parts new from FCP for free and do your first project on the car. Take your time, rent a tech angle and you should be good. Bearings sound really daunting but are actually very straightforward.

[ClevoCapri]

If you put some heavy oil in it like a 20w50 and the oil light stays off at idle. It would be a fair indicator that the bearing clearance increase has upset the engine. I would be replacing with the correct size either way.

[MTiz]

Quick update: FCP Euro is more than willing to do a warranty swap with stock clearance bearings, meaning I can save some money on that end. However, their BMW Catalog Manager does not believe the additional clearance bearings would cause me to have low pressure at idle. He believes an o-ring on the oil pickup tube could have gotten nicked during installation.

Unfortunately, there's no way of knowing without tearing the car apart again so that's coming up in the near future. What a nightmare.

[terra]

Why deviate from the factory spec? I'm sure the designers had spent many hours testing to arrive at the spec. I see no reasons to increase the clearance.

Not necessarily saying I agree with increasing the clearance, but I imagine the rationale would be these engines blow up regardless of whatever testing the factory did.

[sapote]

Not necessarily saying I agree with increasing the clearance, but I imagine the rationale would be these engines blow up regardless of whatever testing the factory did.

I understand the so-called weak rod bearings for these cars, but I personally don't think it was a bad design or mistake. I think it's a compromise of having high rev engine and bearing longevity. Factory used narrow bearing and this is the reason for their relatively "short" life, but they had to do this way for high rev and stronger crank, I think.
Do people think by having more clearance will help to cool the bearing and less wear? People think the spec clearance doesn't provide enough oil film? I think M3 bearing clearance is not tight compared to other modern engines out there.

The only way to improve is to use wider bearings and a machined crank to widen the bearing journals, but keep the bearing clearance the same. But wider journal mod could lead to weak and cracked crank (I don't think this has happened yet).

[Pavlo]

I understand the so-called weak rod bearings for these cars, but I personally don't think it was a bad design or mistake. I think it's a compromise of having high rev engine and bearing longevity. Factory used narrow bearing and this is the reason for their relatively "short" life, but they had to do this way for high rev and stronger crank, I think.
Do people think by having more clearance will help to cool the bearing and less wear? People think the spec clearance doesn't provide enough oil film? I think M3 bearing clearance is not tight compared to other modern engines out there.

The only way to improve is to use wider bearings and a machined crank to widen the bearing journals, but keep the bearing clearance the same. But wider journal mod could lead to weak and cracked crank (I don't think this has happened yet).

You are spot on with everything. S54 has some of the highest piston speeds of any production engine ever built, so the fact that we can get 100k miles on them is very impressive. Its the nature of owning a car with a racing engine, it comes with racing engine maintenance (because physics).

There isn't a magic oil clearance or bearing to "fix" anything, just a small window of right and a big window of wrong. The lowest stock clearance that I've measured was about 0.0017", with a larger clearance bearing you end up at the high side of what will work (0.0027"). I've put together engines with high clearances before (0.0028") and had hot idle oil pressure flicker, ended up taking it apart and using half and half bearings to get it down to about 0.0023" (which has been great in my current engine). Some S54s are at about 0.0023" stock, in which case that extra 0.001" will take you way out of a usable range and you will absolutely have low oil pressure issues.
I'd recommend taking it apart and inspecting the oil pickup O-ring, but also measure your clearances (at least on several rods). Plastigauge isn't the most accurate, but pretty decent at checking things on the car. You can also mix the bearing shells to get the right clearance. This is all way cheaper and easier than replacing or building a new engine.

[George Hill]

Also note the oil pressure light turns off above .5bar (7.4psi). Which means if you have .6bar (9psi) then the light is off. If its on at idle that is not normal and maybe it only gets slightly better off idle, I wound't want to be driving around with .6bar oil psi.

*Also note the oil psi light coming on at idle on M54 engines is common and the fix for those cars is to bump the idle speed as they hover .5bar +/- at idle and flicker the lights as those engines get "loose" with age. That is not the same as this situation IMO.

[R1pilot]

On the e36 M3s the oil light will turn on at around 7 psig. So let’s say that this car is the same and you are getting 5.5-6 psig at idle, thats a 10-20% potential loss of pressure AT idle.

What happens at 3500 rpms on the highway? Are you running 10-20% lower oil pressure as well? ... I would be concerned more so at higher RPMs than at idle.

I would remove the pan and inspect the o-ring. Possibly run a thicker oil like 20w50 with the engine cold and see if there is any difference vs 10w60.

[Thoglan]

Pavlo yep exactly as I did with my motor. Best way to build them is to measure every bore and mix and match bearings to get the perfect clearance for each rod. Half and half is what ended up working best for my motor in terms of clearances (haven't run it yet, still finishing up the rebuild so take with a grain of salt). I can't believe people just buy a standard set of bearings and call it a day. Definitely need to be measured to be sure.

[Pavlo]

On the e36 M3s the oil light will turn on at around 7 psig. So let’s say that this car is the same and you are getting 5.5-6 psig at idle, thats a 10-20% potential loss of pressure AT idle.

What happens at 3500 rpms on the highway? Are you running 10-20% lower oil pressure as well? ... I would be concerned more so at higher RPMs than at idle.

I would remove the pan and inspect the o-ring. Possibly run a thicker oil like 20w50 with the engine cold and see if there is any difference vs 10w60.

Nah, it doesn't really work the same as volume flow changes. Plenty of racing engines that can't make oil pressure at idle (lower temperature build up and less power consumption). At low volume of oil flow, the amount that escapes the bearing becomes a big portion of the total oil being fed to the engine; at high oil flow rate this ratio becomes way more reasonable. Assuming the bearings are at the high side of clearance that I mentioned, the pressure at high RPM is probably just fine as the stock pump flows way more than needed at reasonable oil temps (that's why there is a pressure bypass). Oil pressure itself doesn't fix a poorly selected rod bearing clearance though, but in this case thicker oil will help as it is more suitable for the rod (but still just a band-aid).

[Pavlo]

Pavlo yep exactly as I did with my motor. Best way to build them is to measure every bore and mix and match bearings to get the perfect clearance for each rod. Half and half is what ended up working best for my motor in terms of clearances (haven't run it yet, still finishing up the rebuild so take with a grain of salt). I can't believe people just buy a standard set of bearings and call it a day. Definitely need to be measured to be sure.

It is genuinely scary! So many local shops plop in VAC coated bearings with ARP bolts and deem the car "fixed." This is straight up gambling.