King Bearing discussion on MOFT

[Bill_W]

I found this informative about the goldilocks location of where the MOFT should be.

https://kingbearings.com/wp-content/uploads/2014/10/Geometry-and-dimensional-tolerances-of-engine-bearings.pdf

There is truth to MOFT at a given value is a optimum point... Read oil clearances.

 

[Silver]

Check out this statement:

"Lower oil clearance results in a more uniform oil film pressure distribution and a greater oil film thickness".

I see what he's saying - I think. Less eccentricity, less of a sort of lobe digging into the film?

 

[Bill_W]

Check out this statement:

"Lower oil clearance results in a more uniform oil film pressure distribution and a greater oil film thickness".

I see what he's saying - I think. Less eccentricity, less of a sort of lobe digging into the film?

That goes with tighter bearing tolerance also.

 

[OVERKILL]

That goes with tighter bearing tolerance also.

*Clearances.

 

[ZeeOSix]

People here are just starting to realize this science of journal bearing Tribology after how many years? This stuff has been discussed over and over here for years.

Too tight of bearing clearance also makes the oil temperature inside the bearing go sky high and makes the bearing flow less oil, which in turn makes the viscosity and MOFT even more thin in the bearing when it has a high temperature rise. Too tight of clearance is the best way to smoke bearings regardless of what oil viscosity is used. And besides, it has been said many times that journal bearing clearances have not really changed in the last 50+ years. Why would they if the design has already been optimized many decades ago.

 

[4WD]

*Clearances.

Yup - tolerance is what engineers give the machinist/inspector - as in +/- 0.00xx…

 

[SubieRubyRoo]

Wow… 700W of heat generation. No wonder oil temps skyrocket during racing, and you’re only gaining 0.5HP by running a 20wt vs a 50wt!

 

[ZeeOSix]

From: https://www.substech.com/dokuwiki/d...y_on_hydrodynamic_friction_of_engine_bearings

"Effect on oil pressure distribution
The load is applied to a bearing through the oil film separating the bearing and the journal surfaces. The oil film is pressurized by the load but the pressure generated in the film is not uniformly distributed over the bearing surface. It reaches a maximum value close to the area where the oil film thickness has its minimal value. The ratio of the peak pressure to the average value of pressure (Pmax/Pav) characterizes non-uniformity of pressure distribution. Too high value of pressure non-uniformity may cause failure of the bearing due to fatigue of its material [5]."

This means the pressure distribution (Pmax/Pav ratio) is more uneven at the same bearing clearance as the oil viscosity decrease.

Thicker oil works better in bearings with higher clearance than thinner oil does in higher clearance for both the MOFT and the pressure distribution across the bearing.

Conclusions from the article:

 

[Silver]

journal bearing clearances have not really changed in the last 50+ years. Why would they if the design has already been optimized many decades ago.

So honest question, you don't think any of the changes in mfg process, metal coatings, types of oil, etc have changed enough to make any of the specific mechanics demonstrated in these articles obsolete in the tiniest bit? I'm not leading with this question, I honestly don't know.

 

[Slow Car Sport Mode]

I found this informative about the goldilocks location of where the MOFT should be.

https://kingbearings.com/wp-content/uploads/2014/10/Geometry-and-dimensional-tolerances-of-engine-bearings.pdf

There is truth to MOFT at a given value is a optimum point... Read oil clearances.

That paper used the term "tolerances".. I can only hope we don't go down the slippery slope of scientism.

That said, liking this article. Reading it now.

Touches on the basics of motor oil and hydrodynamic lubrication.

 

[OVERKILL]

That paper used the term "tolerances".. I can only hope we don't go down the slippery slope of scientism.

That said, liking this article. Reading it now.

Touches on the basics of motor oil and hydrodynamic lubrication.

Yes, it uses both tolerances and clearances, they are two different things. Clearances are the distance between parts, tolerances are the allowed variations in those clearances.

There's no "slippery slope of scientism" here. It's critical to understand the difference between the two terms because they are fundamental.

 

[DirectRejection]

So honest question, you don't think any of the changes in mfg process, metal coatings, types of oil, etc have changed enough to make any of the specific mechanics demonstrated in these articles obsolete in the tiniest bit? I'm not leading with this question, I honestly don't know.

Double fist pump.
Polymers.
It's the future.

 

[OVERKILL]

So honest question, you don't think any of the changes in mfg process, metal coatings, types of oil, etc have changed enough to make any of the specific mechanics demonstrated in these articles obsolete in the tiniest bit? I'm not leading with this question, I honestly don't know.

The mechanisms aren't obsolete, what have been implemented are workarounds and mitigation schemes.

For example:
When Ford developed the Modular engine, the idea was to make it far more tolerant of thinner oils than the Windsor it replaced. One of the keys in achieving that was to make the bottom end FAR more rigid, this was achieved using a deep skirt and multi-bolt and cross-bolted main caps, making an extremely solid "unit" for the crankshaft to rotate within. This dramatically reduced potential for deflection, twist and distortion; it tightened up the tolerances for the main bearings, while the clearances remained roughly the same as the Windsor.

Another thing implemented was coated skirts, this was also to reduce friction. This was coupled with shorter skirts, to also reduce friction. GM did the same thing on the LSx engines, but didn't do the coating at first, and this is one of the reasons the early LSx engines were notorious for piston slap.

Coatings, things to reduce load (lighter valvetrain components, so you can run lighter springs...etc) and improved additives in the lubricants designed to provide better wear control in boundary and mixed lubrication regimes all work together to keep wear to acceptable levels with the use of thinner oils.

 

[kschachn]

A properly designed bearing

Double fist pump.
Polymers.
It's the future.

Or as a different view, yet another thing we have to pay for in order for the automaker to glean their CAFE credits and meet mandated fuel economy targets. All of this component redesign (along with the equally expensive oil redesign) has to be paid for by the consumer.

The automaker benefits but do you? Is the increased cost for a new vehicle offset by the individual fuel cost savings? I've never seen such a cost-benefit analysis.

 

[DirectRejection]

The mechanisms aren't obsolete, what have been implemented are workarounds and mitigation schemes.

For example:
When Ford developed the Modular engine, the idea was to make it far more tolerant of thinner oils than the Windsor it replaced. One of the keys in achieving that was to make the bottom end FAR more rigid, this was achieved using a deep skirt and multi-bolt and cross-bolted main caps, making an extremely solid "unit" for the crankshaft to rotate within. This dramatically reduced potential for deflection, twist and distortion; it tightened up the tolerances for the main bearings, while the clearances remained roughly the same as the Windsor.

Another thing implemented was coated skirts, this was also to reduce friction. This was coupled with shorter skirts, to also reduce friction. GM did the same thing on the LSx engines, but didn't do the coating at first, and this is one of the reasons the early LSx engines were notorious for piston slap.

Coatings, things to reduce load (lighter valvetrain components, so you can run lighter springs...etc) and improved additives in the lubricants designed to provide better wear control in boundary and mixed lubrication regimes all work together to keep wear to acceptable levels with the use of thinner oils.

At the HPL Open House, I tried to ask the panel about the interactions between novel coatings on the one hand, and oils with their chemistries, on the other hand..

They said "that's a good question."

We are getting into uncharted territory, my friends.

 

[Bill_W]

A properly designed bearing

Or as a different view, yet another thing we have to pay for in order for the automaker to glean their CAFE credits and meet mandated fuel economy targets. All of this component redesign (along with the equally expensive oil redesign) has to be paid for by the consumer.

The automaker benefits but do you? Is the increased cost for a new vehicle offset by the individual fuel cost savings? I've never seen such a cost-benefit analysis.

Thanks for your view. Everyone has a different view. Change for the better is inevitable.

 

[DirectRejection]

A properly designed bearing

Or as a different view, yet another thing we have to pay for in order for the automaker to glean their CAFE credits and meet mandated fuel economy targets. All of this component redesign (along with the equally expensive oil redesign) has to be paid for by the consumer.

The automaker benefits but do you? Is the increased cost for a new vehicle offset by the individual fuel cost savings? I've never seen such a cost-benefit analysis.

I am certainly no tree hugger, but better and better efficiency ultimately benefits everyone doesn't it ?

I am reminded of Milton Freidman, and The Parable of the Pencil.

 

[Jetronic]

What coatings on piston skirts are typically used? My cars engine has graphite coated skirts

 

[Astro14]

That paper used the term "tolerances".. I can only hope we don't go down the slippery slope of scientism technical accuracy.

That said, liking this article. Reading it now.

Touches on the basics of motor oil and hydrodynamic lubrication.

There, fixed it for you.

 

[4WD]

What coatings on piston skirts are typically used? My cars engine has graphite coated skirts

Last I knew GM was using a polymer - I know from owning the new gen L83/L84 engines - you don’t hear them like my older 5.3L powered vehicles … Very quiet engines …