I was thinking about this for awhile and wondered what is the best bearings? Roller, APEE, Friction bearings? I think I'm missing some others? I want to know what are the best.

I know that Friction bearings are metal on metal

Roller bearings are bearings on cushion of rollers

APEE?

The short story:

Exposed end cap roller bearings of which Timken AP are one brand of several available. EE is one size of many. All exposed end cap bearings are NFL - no field lube. All are acceptable in interchange.

Grease or oil bath rollers are good but require a periodic maintenance schedule. Timken and Hyatt are what you see the most. Some roads may balk at accepting them in interchange since they aren’t exposed. Trucks with these are usually easy to change over to exposed end cap when wheel sets are replaced.

Bronze/Babbitt are fine with proper maintenance but they are maintenance intensive. Also banned in interchange. Trucks can no longer be converted to rollers and would still be banned if you did. You may get a waiver on a conversion in extremely limited circumstances.

Best in what circumstances?

Actually all properly maintained rotating bearings are "metal on oil on metal". Once they degrade to a "metal on metal" state they are no longer a "bearing".

Old school "friction" bearings (brass on steel with oil) work quite well as long as they have lots of oil available. These bearing use one "hard" metal (steel) in contact with one "soft" metal (brass) with lots of oil to provide a "layer" between the metal surfaces which reduces friction and of course wear.

Roller bearings work by running two "hard" metals in contact with the smaller diameter of one rolling part acting to create a hydro-static "wave" of oil in front of the metal to metal contact area (very much like a surfboard riding a wave). When properly designed with "semi-permanent" lubrication they can run a lot longer than a "hard" shaft / "soft" bearing design.

Dirt is the bearing "killer".. The old school steel axle / brass bearing was hard to "seal" against dirt and that made them more maintenance intensive.

Babbitt as a bearing material is very insensitive to "dirt", but it wears quickly (relative to modern train cars that travel 10's of thousands of miles with minimal maintenance).

Modern roller bearing are well sealed and so very little lubrication leaks out over time and they are very long lasting. But they are very unforgiving, when they fail from lack of oil they fail in a spectacular fashion leading to lots of flying "Bits". But, with modern "hot box" detectors roller bearing with a high temperature are detected before they fail (in theory).

Another roller bearing was the Timken “Quad”. It was a four row roller bearing used on some passenger cars. I always considered it the best railway roller bearing, but it was dropped by railroads when the AP bearing was interdicted. The A P bearing was inexpensive and the “Quad” could not compete.

The AAR insisted that the design of the AP bearing allow conversion of plain bearing axles to roller bearings. This resulted in the AP bearing being longer than necessary resulting in axle deflection causing problems maintaining the proper lateral clearance. In recent years Timken introduced a narrow row bearing for use in high mileage captured cars to address this problem.

In railway preservation the plain bearing is the most suitable bearing. It is low tech and can be rebuilt with common machines and tools. Plain bearing cars will be running years after the roller bearing cars have been set aside due to non repairable defects. Eight and nine inch AP bearings are unavailable and have been for many years. Ten inch bearings cannot be far behind. Ask any museum that has been flooded how the bearing recovery went.

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Coming up on next week's episode:

What's a better truck, Ford, Chevy, GMC, Dodge?

There is another issue with roller bearings in railroad service: fretting corrosion. Even if the lubrication in a bearing is maintained, if it does not get regular turning the lubricant leaks down from the point of contact, and even small vibrations over a long period of time cause wear between rollers and races. This aside from the issue if the rollers take a 'set' and become oval from long static loading.

There have been some amusing horror stories about clever people deciding to convert plain to rolling-element bearings. One advantage of a good plain bearing is that it can be split (including by freeze-fracturing) with little loss of hydrodynamic performance -- that is NOT generally true for many types of roller, where there is essentially a repetitive line contact. What sometimes happens is that journals are machined down to take a fixed inner race ... which weakens them with the usual range of predictable consequences.

Not all plain bearings have to be waste-lubricated, or even total-loss lubricated: most internal-combustion motors wouldn't work well with roller bearings on their drank or camshaft bearings -- but wouldn't work long with waste or splash lubrication, either. They are pressure-lubricated, usually with lube-temperature 'conditioning' and there were experiments in the '50s with recirculating pressure lubrication of locomotive rod bearings. A different construction of plain bearing with theoretically better lubricant circulation is the Isothermos bearing, which has channels cut (usually in a spiral pattern) in the brass, so there is a larger volume available for hydrodynamic lift and absorbing shear heat. I am not altogether convinced these work 'as advertised' but a number of rail applications used them.

Note the detail design of the Union Pacific rod bearings designed for the high-speed 800s, which are plain bearings doing the job of 100mph Timken rollers.

I don't think this has been mentioned here yet, but a common misconception is that rolling-element bearings have lower rolling resistance than good plain bearings. While this is true for starting (when only the static oil film is available for plain-bearing lubrication) a number of historical sources agreed that above about 3mph the rolling resistance was comparable -- the great advantage of roller bearings being their grease-lubricated extreme longevity, and their ability to run 'unserviced' far longer than the wear life of the wheels in the sets they're installed on.

Incidentally, rollers depend on rolling contact. The earlier hydrodynamic explanation applies to needle bearings, a kind of cageless bearing (which I believe is more like a plain bearing with renewable hard polished surfaces spreading a large volume of the lubricant) -- see the famous Multirol bearings for examples. (You will find many people who say these rollers revolve under load, but my understanding is that is not the principal effect as loaded in the absence of a cage to prevent mutual interference).

Another problem with roller bearings is after a derailment, if the car ran over a certain umber of ties say 7, the wheelsets have to be replaced because the bearings are in danger of failing. Whereas plain bearings can be quickly inspected and repaired if necessary.

The September 6, 1943 derailment of PRR's Congressional Limited at Frankford Junction in Philadelphia with 79 fatalities was ascribed to a hotbox leading to axle failure.

PRR 152, motor 4930, was a nonstop from Washington to Newark NJ and Penn Station NY. The train was schedulled to go 225 miles without stopping and without a journal inspection. I understand 152 was supposed to have only roller bearing equipped cars.

Near North Philadelphia, a lineside shifter crewman saw flame coming from the 7th car, a P70 with conventional bearings. He had someone call "SHORE" tower from a lineside phone but the train had passed the home signal already. The bearing and axle failed in the curve and the 7th car derailed and struck a heavily-built signal bridge, tearing off the roof and one side. The 8th car struck the bridge and bent into a U-shape. All the fatalities were in these two cars.

Amtrak 188, motor 601, derailed in the same curve on May 12, 2015, with 8 fatalities. Cause was excess speed (100 mph) in the 4.00 degree curve.

Phil Mulligan

This is good info for people not exposed to this type of work on a regular basis. It has been preached by the class 1s regionals and some shortlines that roller bearings are a must and the best thing since sliced bread. That may be true for everyday interchange, but a few years back I had to do some heavy bearing, wheel and axle repair on an ex CN heavyweight and got an education from Kelly Anderson, HLX and Ohio Valley Railcar. The type of operation plays a huge factor into what is best in alot of cases, bearings or otherwise. Good question.

Agreed. I should have mentioned that we have equipment with all three styles of bearings mentioned in my earlier post. All are perfectly adequate for our type of operation - typically short jaunts at around 10 mph. At those speeds and overall usage, maintenance really isn’t a burden.

I don't post much, but this is an interesting topic that requires some thoughtful consideration. There is definitely a time and a place for each bearing design. Roller bearings have created efficiencies that have significantly contributed to the success of railroads in the modern world. The modern world is also a throw away world, which is a very different from the mindset during the time our treasures were designed and built. For museums and tourist railroads, check your needs carefully. As stated above, one should consider their repair capabilities in addition to their operating needs when considering which is best. I can say first hand that roller bearing conversions don't belong on steam locomotive drive axles. Leading and trailing trucks have more room for success, but not generally worth the trade offs in my opinion. This is especially true if you are considering sealed roller bearings located inboard of the wheels. Check your definition of "greased for life" against the bearing manufacturer's.

Something else to keep in mind is the lateral motion between the two designs. Sealed roller bearings have zero lateral motion. Non sealed have some. Plain bearings can have a half inch or more. One or the reasons 1702's bearings didn't last was that they couldn't handle the lateral forces required for a 2-8-0 after having lost all the lateral clearances. On that same railroad there are several heavy weight six axle cars. Many of those cars were built with plain bearings, and were converted to sealed roller bearings in the 80's or 90's. The maintenance on the bearings went down considerably. On a straight railroad they would have been fine. When you consider the mountain railroad they were working on, the reality is a little different. Including the wheel, rail, pedestal, equalizer, and journal box wear in the equation, it was a net loss. Six axle cars don't belong in those curves to begin with, but converted to sealed rollers they were even worse. We certainly never realized the benefit of the sealed for life aspect of the bearings, as we were sending the wheelsets out every 18-24 months for the wheels to be trued due to flange wear. The wheel companies rightfully refused to send the sets back without replacing the bearings so as to not jeopardize their AAR certifications. I would have converted the cars back to plain bearings if I had still had the boxes. We had a roller bearing failure on the Bryson City back in about 2007 or so. The cost of renting a crane from 2 hours away and changing a wheelset in the field would have paid for a lot of oil.

Choose wisely my friends. Your mileage will vary.

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Hi Kelly

To be honest I don't remember giving that idea much thought at the time, although it would be interesting to draw that out and see just what kind of margin it would have given us. At the time I was trying to convince the powers that be that we needed to transition to four axle cars. At least for the cars that were routinely running between Bryson City and Nantahala. I was also trying to keep the wayside greasers working and supplied. The greasers were somewhat effective in reducing the wheel and rail wear, but did nothing for the pedestals, boxes, and equalizers. There were many things requiring attention at the time, and some things were just out of reach.

The track charts showed the sharpest curve Just West of NOC. It had been softened some over the years, as much as the SRR could make fit. IIRC, the track charts showed it at 21 degrees, but it has been reduced to 18 or so. Somewhere I think I still have the summary of the curves on that RR. Those seven miles between NOC and Nantahala are rough.