King Bearing discussion on MOFT

[RDY4WAR]

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.

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My only complaint about this article is they don't state the specs of the specific oils used. Is the 0W-20 a group III with a load of VII and PPD or an overkill PAO/POE/AN oil? Same for the 10W-60 and other oils. Different base oils have different friction/traction coefficients, pressure-viscosity coefficients, specific heat capacity, etc... Just some variables we could've used the answers for in this testing.

The description for the 2nd graph states the (fluid) turbulence increases at wider clearances which contributes to power loss. This is one reason why many top racing organizations aim for tighter clearances and thinner oil. Whether the oil film between the journal and bearing is 1 uinch (above surface roughness) or 100 uinch, no contact is no contact.

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!

I think that power loss is per bearing.

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.

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Conclusions from the article:

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I go by the old standard of .001" clearance for every 1" of journal diameter. That's a pretty safe and balanced clearance. Once you get tighter than that, the machine work becomes more critical and tolerances tighten. You have little room for error, but can reap rewards in power. Going wider increases eccentricity and peak load on the oil film, increasing hydrodynamic friction and thus robbing power. However, with the higher viscosity oil, it can take a higher load. Hence Pro Mods and such will have .004" clearance with an SAE 60 oil to withstand 3,000 hp.

This is a good article though. I love the graphs and how the conclusions are broken down.

 

[Vermess]

Meh....IMHO, I don't think coating offers a big benefit in bearings. Bottom end design to reduce deflection and engine design as a whole has more of a benefit than any coating, as @OVERKILL said.

You can use any coating you want, if the film fails and that crank touches those bearings at that speed and load, coatings going bye bye. One example is the ej25. You can use a coated crank, coated bearings, that thing has so much deflection, nothing will help it.

Coatings have so much more benefit to offer if used where combustion takes place. Pistons, valves, chamber itself can highly benefit from coatings to help heat transfer.

Another thing that can help is better head/valvetrain design. Too many moving parts. Idk why the idea if a rotary valve has not been implemented for the past 40 years. It would reduce so much friction, valve train weight, etc.