Rod Bearing brand options? - OEM, ACL, VAC, BE, King Race

[JakeM346]

so Mahle made original bearings and now we have Mahle MS saying they were good......lol

IMO you would need your head read to use anything near 0.001" clearance on a Sxx engine which is what is at the lowend of permissible. IMO the range provided is too large

there is obviously alot more to bearing life than simply the clearance but BMW's clearance spec is a joke, obviously its a tough thing to mass produce and control the tolerance band but Mahle's own guidelines say for 0.00075 to 0.001 per inch of shaft +0.0005 for a high performance engine which is roughly 0.0020 to 0.0025 so we as individuals would be much better to follow this than the "BMW" spec which is based on what they can achieve on 10's of thousands of engines in a mass production environment.

Well I’m using 0.001“ on my main bearings without a problem. Only thing that was important to consider was the crankshaft having wobble.
and this clearance is great because of in general lower heat on main bearings therefore reducing side leakage rate increased oiling to my conrods which easily prolongs their life.
i basically never use 0.002 or 0.0025 these clearances are way to big and as soon as your bearing wears they get unsustainably big.

ypur forgetting that clearances are a part of a system…..the oiling system. And rule of thumb is the stupidest thing to apply there since then you’d have to increase oil pump flow which would lead you to soooo many problems down the line.

basically from an engineering standpoint I’m saying that your talking ……. Crap

mahles Motorsport bearings have higher clearance since they are accounting for an contaminated environment which considering how many engine builder work….no clean rooms is just…..forward looking.

Mahle is saying the bearings are working how they suppesed too….which makes sense since your crank hasn’t seized or maybe it has because you didn’t change them (bearings are a consumable-they wear to protect the crank) ….. and actually cranks seize when the clearance and oil leakage gets to big leading to metal to metal contact which causes friction welding after a point…..

your running a marathon backwards……..

the problem in the s65 main bearings is definetly not the bearings but rather high chain tension and in comparison a not broad enough bearing Journal….which is a design problem of the engine….
main reason probably Hereford was bmw trying to reduce cost by not having a separate bearing only for the front.
actually bmw cost cutting can be seen in all s xx engines since the keep the first bearing the same size and just grind the crank journal a bit smaller to increase oil leadkage accounting for the missing rod bearing….all other mains lubricate one rod bearing…..

anyways a broader front journal should…..take that with a grain of salt (I’m guessing this one because I don’t have a book at hand) - increase counteracting force on the crank therefore compensating chain tension
Also it should be noted that the oiling gap in the main bearing decreases lad carrying capability. So bmw might have been better of decreasing the oiling gap in the bearing just as the oiling channel which would have reduced flow….that is anyways not needed…..and increased load carrying ability


ok if gotten carried away…..but what I’m saying is that more clearance is

stupiddddddddddd

[chris719]

VAC seems to be using Clevite bearings, does anyone know what their clearance specs are? I saw 2 examples where people pulled these out of S54s and they looked pristine and coating fully intact.

[JakeM346]

VAC seems to be using Clevite bearings, does anyone know what their clearance specs are? I saw 2 examples where people pulled these out of S54s and they looked pristine and coating fully intact.

well vac and be bearings both carry the mahle and 77 marking. Meaning they use the same clevite coating. Probably the VAC bearing is the BE bearing which have 0.002“ clearance if I’m right

[JakeM346]

VAC seems to be using Clevite bearings, does anyone know what their clearance specs are? I saw 2 examples where people pulled these out of S54s and they looked pristine and coating fully intact.

Also mind sharing pictures of these used vac bearings.
would be interested in the wear pattern or possible lack thereof

[digger]

Well I’m using 0.001“ on my main bearings without a problem. Only thing that was important to consider was the crankshaft having wobble.
and this clearance is great because of in general lower heat on main bearings therefore reducing side leakage rate increased oiling to my conrods which easily prolongs their life.
i basically never use 0.002 or 0.0025 these clearances are way to big and as soon as your bearing wears they get unsustainably big.

ypur forgetting that clearances are a part of a system…..the oiling system. And rule of thumb is the stupidest thing to apply there since then you’d have to increase oil pump flow which would lead you to soooo many problems down the line.

basically from an engineering standpoint I’m saying that your talking ……. Crap

mahles Motorsport bearings have higher clearance since they are accounting for an contaminated environment which considering how many engine builder work….no clean rooms is just…..forward looking.

Mahle is saying the bearings are working how they suppesed too….which makes sense since your crank hasn’t seized or maybe it has because you didn’t change them (bearings are a consumable-they wear to protect the crank) ….. and actually cranks seize when the clearance and oil leakage gets to big leading to metal to metal contact which causes friction welding after a point…..

your running a marathon backwards……..

the problem in the s65 main bearings is definetly not the bearings but rather high chain tension and in comparison a not broad enough bearing Journal….which is a design problem of the engine….
main reason probably Hereford was bmw trying to reduce cost by not having a separate bearing only for the front.
actually bmw cost cutting can be seen in all s xx engines since the keep the first bearing the same size and just grind the crank journal a bit smaller to increase oil leadkage accounting for the missing rod bearing….all other mains lubricate one rod bearing…..

anyways a broader front journal should…..take that with a grain of salt (I’m guessing this one because I don’t have a book at hand) - increase counteracting force on the crank therefore compensating chain tension
Also it should be noted that the oiling gap in the main bearing decreases lad carrying capability. So bmw might have been better of decreasing the oiling gap in the bearing just as the oiling channel which would have reduced flow….that is anyways not needed…..and increased load carrying ability


ok if gotten carried away…..but what I’m saying is that more clearance is

stupiddddddddddd

the clearance i recommended/quoted is Mahle's own recommend starting point maybe that is stupid but it is more forgiving and it is not considered large by any means and not even near the high side of BMW's own specs.

i dont think any professional engine builder would use 0.001 on rods let alone mains for the S series BMW engines especially the s54, there are more risks with this than there are benefits.

BMW only allow this because they cant control the tolerances any better without a order of magnitude increase in costs so they just accept that some small % are going to be at the extreme ends and deal with any consequences as this is the cheaper overall option

[JakeM346]

the clearance i recommended/quoted is Mahle's own recommend starting point maybe that is stupid but it is more forgiving and it is not considered large by any means and not even near the high side of BMW's own specs.

i dont think any professional engine builder would use 0.001 on rods let alone mains for the S series BMW engines especially the s54, there are more risks with this than there are benefits.

BMW only allow this because they cant control the tolerances any better without a order of magnitude increase in costs so they just accept that some small % are going to be at the extreme ends and deal with any consequences as this is the cheaper overall option

It’s funny that you think to know what bmw can and can not do…..have you worked in the construction Departement……study mates of mine do…..advantage of living in Munich…and if you think bmw can’t control their tolerances in a area of 0.03 mm then I don’t know where you have your knowledge from. Actually it’s controllable to 0.001 mm and lower. Just depends on the money. The green white and yellow all have 0.01mm step. And bmw Standard Factory Set it between 0.03 and 0.04mm……
the point with engine builders is…..they are builders…..not engineers

also if the crank turn when using 0.001“ when building the engine it’s gonna work perfectly fine when the engine is running the engine housing is cast iron and the crank crMo steel. Both have a similar coefficient of thermal expansion. So it won’t seize. The best thing that we aim to achieve for engines is close to 0 clearance but we can’t….due to technical limitations.

crank runout it the biggest, then there’s flex …the oil Film are partly only 0.0005mm thick…
then we have the point that our oil need to be exchanged for engine heat management….otherwise it would overheat due and viscosity would become to thin.
then there’s cavitation. If the differences of pressure in the bearing are to big our bearing would get eroded by air bubbles mixed in the oil bursting.

actually have a look at subs tech and see his charts….that the only stuff of this information I’m allowed to share without copyright infringement….
the sweet spot for many engines is gonna be more around 0,0017“

and technically I’m not running 0,001“ but around 0,0013“ inches

[chris719]

well vac and be bearings both carry the mahle and 77 marking. Meaning they use the same clevite coating. Probably the VAC bearing is the BE bearing which have 0.002“ clearance if I’m right

I’ll try to find them. They were in videos or at least one was.

[digger]

It’s funny that you think to know what bmw can and can not do…..have you worked in the construction Departement……study mates of mine do…..advantage of living in Munich…and if you think bmw can’t control their tolerances in a area of 0.03 mm then I don’t know where you have your knowledge from. Actually it’s controllable to 0.001 mm and lower. Just depends on the money. The green white and yellow all have 0.01mm step. And bmw Standard Factory Set it between 0.03 and 0.04mm……
the point with engine builders is…..they are builders…..not engineers

also if the crank turn when using 0.001“ when building the engine it’s gonna work perfectly fine when the engine is running the engine housing is cast iron and the crank crMo steel. Both have a similar coefficient of thermal expansion. So it won’t seize. The best thing that we aim to achieve for engines is close to 0 clearance but we can’t….due to technical limitations.

crank runout it the biggest, then there’s flex …the oil Film are partly only 0.0005mm thick…
then we have the point that our oil need to be exchanged for engine heat management….otherwise it would overheat due and viscosity would become to thin.
then there’s cavitation. If the differences of pressure in the bearing are to big our bearing would get eroded by air bubbles mixed in the oil bursting.

actually have a look at subs tech and see his charts….that the only stuff of this information I’m allowed to share without copyright infringement….
the sweet spot for many engines is gonna be more around 0,0017“

and technically I’m not running 0,001“ but around 0,0013“ inches

What is funny is that you think you know what you're talking about because of what your mates might or might not know

yeah keep back pedaling

[Obioban]

At least we can all see why I didn’t want to derail the s54 bearing chat with s65 bearing clearance discussion that isn’t at all relevant to the s54

[JakeM346]

What is funny is that you think you know what you're talking about because of what your mates might or might not know

yeah keep back pedaling

Well simple fact is my mates work at bmw Motorsports in Development. I only studied mechanical engineering with specialization in automotive drive systems and don’t work at bmw…..maybe somewhere else tho…..

you get the point or………..

[chris719]

So what do we think about the harder overlays in the aftermarket bearings? Any risk to crank journals over time?

[JakeM346]

So what do we think about the harder overlays in the aftermarket bearings? Any risk to crank journals over time?

Well depends on which you’re talking about. S54 crankshaft is forged nitrocarburated 42CrMo4 Steel. That means approximated hardness will be between 550 to 750 HV.
I don’t think any bearing overlay gets close to this. Only thing I’d be really concerned about is embedibility.

the question is also what do you wanna achieve. A harder overlay will lead to higher fatigue strength of the bearing. So if you increase cylinder pressures by adding a turbo or supercharger definetly do it but I don’t think it‘ll have that big of an advantage concerning reliability/ longevity of the engine since much of the wear on the s54 bearings is gonna be corrosive wear. Could be tho that I’m missing something important ….open for suggestions

[chris719]

Well depends on which you’re talking about. S54 crankshaft is forged nitrocarburated 42CrMo4 Steel. That means approximated hardness will be between 550 to 750 HV.
I don’t think any bearing overlay gets close to this. Only thing I’d be really concerned about is embedibility.

the question is also what do you wanna achieve. A harder overlay will lead to higher fatigue strength of the bearing. So if you increase cylinder pressures by adding a turbo or supercharger definetly do it but I don’t think it‘ll have that big of an advantage concerning reliability/ longevity of the engine since much of the wear on the s54 bearings is gonna be corrosive wear. Could be tho that I’m missing something important ….open for suggestions

Some cranks show a bit of surface modification over time even when a bearing hasn't spun or knocked. I think Anri has posted a couple examples. Anyway, I don't think S54 bearings show corrosive wear at all. Even the conclusion on that Mahle Motorsport paper for S65 is dubious in my opinion. I'm not sure how corrosive wear explains the top shell, which experiences the highest loads, being worn considerably while the bottom shell looks nearly pristine.

My question was really about avoiding a potential bad tradeoff of journal damage in the pursuit of longer bearing life. Your point on the crank hardness is valid, but there seem to be cranks that have enough contact over time to cause some damage.

[JakeM346]

Some cranks show a bit of surface modification over time even when a bearing hasn't spun or knocked. I think Anri has posted a couple examples. Anyway, I don't think S54 bearings show corrosive wear at all. Even the conclusion on that Mahle Motorsport paper for S65 is dubious in my opinion. I'm not sure how corrosive wear explains the top shell, which experiences the highest loads, being worn considerably while the bottom shell looks nearly pristine.

My question was really about avoiding a potential bad tradeoff of journal damage in the pursuit of longer bearing life. Your point on the crank hardness is valid, but there seem to be cranks that have enough contact over time to cause some damage.

Yes you’re definetly right. I believe tho that most of the crank wear we see from s54 is 3 body abrasive wear/ adhesive wear(especially since the wear marks are not perfect matches on bearings and crank) and will therefore not be prevented or reduced by a harder bearing material. It will probably increase because of lower embedability as I wrote before.
corrosive wear alone doesn’t explain it but if you combine corrosive wear with the usual engine operation. Than the wear mechanism is similar to bearing overlay fatigue. Basically the corrosive wear weakens the overlay and then over time the overlay gets worn away by the usual abrasive wear (since it’s surface becomes rough/brittle and „attackable“). And after some time bearing clearances become to big leading to a breakdown of the hydrodynamic regime-which explains the quick transition from first wear to down to copper and possibly seizure.
Considering the shells I haven’t seen it but obviously the top shell being worn more would lead to the conclusion that inertia forces are lower than combustion forces. This might be explainable that when the engine operates at lower speeds it experiences lower inertia forces but still similar/ high combustion forces. In order to have a proper conclusion we’d basically need to look at a race engine that was constantly highly revved for the same wear interval and then check the wear in this engine.

also what can’t be consider without proper research would be chemical wear mechanisms. Things similar to dlc coatings and zddp …. I don’t recall anything like that for crMo stell and Aluminium or other overlay materials. But it could be…

ah and before o forget mahle does indicate that the corrosive wear is most likely due to overheating of the oil in the lubrication gap. Which will lead to a lower viscosity…..this could also lead to contact
awaiting your response…. Actually really nice conversation😁