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

[digger]

The F20 is smaller, lighter, lower displacement and, I think critically, has a shorter crank. The S54 also has to deal with a heavier car and makes more power. It is just not comparable and without being the engineer that worked on the S54, I don't think anyone can say it was poorly designed. Any poor design would be an artifact of MBA's and accountants driving the decisions.

Also for what it's worth, plenty of S54's make it near or over the 200k mark, I have also read the F20 is not immune to bearing failure/replacement.

The F22 has essentially the same stroke and redline as s54.
The F20 with shorter stroke sees higher acceleration loads due to rpm^2 factor.
F20/22 and S54 make about same power per cylinder.
F20/22 bearing are 1mm smaller diameter but 3.4mm wider and thus 20% more projected area.

So they are fairly comparable yet they came up with fairly different designs.

note that BMW reduced bearing area from S50B30euro-->S50B32-->S54B32 obviously chasing less friction.
IMO the trend for narrower but slightly larger diameter rod bearings hasn't worked well for them as that's what they did with the S65/S85 as it has bigger problems than s54 and the loading is measurably lower on S65/85 due to the small stroke

obviously other factors at play to like actual delivery of oil to the bearing not just the loads

[Icecream]

I have an S2000 with 200k miles that I bought brand new ... at around 30k miles I supercharged it ... never touched the bearings. Check those piston speeds.

The bearings on my M3 at 97k miles were toast.

I don't know if BMW got it right or no, Honda did.

The F20 is smaller, lighter, lower displacement and, I think critically, has a shorter crank. The S54 also has to deal with a heavier car and makes more power. It is just not comparable and without being the engineer that worked on the S54, I don't think anyone can say it was poorly designed. Any poor design would be an artifact of MBA's and accountants driving the decisions.

Also for what it's worth, plenty of S54's make it near or over the 200k mark, I have also read the F20 is not immune to bearing failure/replacement.

[R1pilot]

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).

I have an S2000 with 200k miles that I bought brand new ... at around 30k miles I supercharged it ... never touched the bearings. Check those piston speeds.

The bearings on my M3 at 97k miles were toast.

I don't know if BMW got it right or no, Honda did.

[yhp2009]

For something with such critical clearance as rod bearings, at least one should double check the dimension of the bearing shells out of the box. Parts do mix up accidentally and you don't want to find out after everything was buttoned up. We're talking 0.001" or less could cause a major problem. It doesn't take much times to do this with a caliper.

If BMW Tis did not say to check the new bearings before install, it probably assumed the bearings they used had passed Quality Control department.

Agreed, definitely will check when i get mine done

[sapote]

I agree that to get perfect clearances everything must be measured, but the procedure that BMW specified for the rod bearing service bulletin did not include this. It just says to do what most people end up doing, which is to take the bearings out of the box and put them in the engine. I would imagine that if the bearing clearances varied enough to cause problems, we would be seeing a lot more 01-03 cars with engine failures, especially considered the replacements first started to be done like 15 years ago.

For something with such critical clearance as rod bearings, at least one should double check the dimension of the bearing shells out of the box. Parts do mix up accidentally and you don't want to find out after everything was buttoned up. We're talking 0.001" or less could cause a major problem. It doesn't take much times to do this with a caliper.

If BMW Tis did not say to check the new bearings before install, it probably assumed the bearings they used had passed Quality Control department.

[heinzboehmer]

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.

I agree that to get perfect clearances everything must be measured, but the procedure that BMW specified for the rod bearing service bulletin did not include this. It just says to do what most people end up doing, which is to take the bearings out of the box and put them in the engine. I would imagine that if the bearing clearances varied enough to cause problems, we would be seeing a lot more 01-03 cars with engine failures, especially considered the replacements first started to be done like 15 years ago.

[yhp2009]

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.

Thats an interesting point. But, why do we not have more cases like the OP if many owners are doing it the "wrong" way. I doubt many people actually measure the clearance, yet most have success replacing their bearings with no problems.

[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.

[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).

[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.

[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.

[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.

[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.

[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).

[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.