Benefits of roller bearings

[John in Leeds]

Does an engine that has roller and needle roller bearings for mains, big end and camshafts have any advantage over one with plain bearing only.

 

Comments on longevity, friction, and expense would be welcome.

 

Simple language please.

[Ryland3210]

Does an engine that has roller and needle roller bearings for mains, big end and camshafts have any advantage over one with plain bearing only.

 

Comments on longevity, friction, and expense would be welcome.

 

Simple language please.

 

Roller bearings have considerably lower friction, and are able to live with much lower oil pressure. They cost more than plain bearings both because of the cost of the bearing itself, plus tighter tolerances required to mount them. Oil cleanliness is more important for long life.

 

Harley Davidsons, famous for being able to idle at subsonic RPM's are able to live with minimal oil pressure because of the use of roller bearings. Some say that all that is needed is to deliver oil to roller bearings. Guzzi's, in contrast, need 1100 or more RPM to ensure adequate oil pressure to prevent metal to metal contact in its plain bearings. When my bike was delivered, it idled at 600 RPM. That sounded cool, until I installed a pressure gauge. When hot, it made practically zero oil pressure at that idle speed. I immediately started using the so-called "choke" (actually a fast idle) to keep it up at 1100-1300 RPM.

[richard100t]

I agree with Ryland about keeping the idle speed at no less than 1100rpm. There have been several posts by other members that confirm the low oil pressure at reduced idle speed. Fwiw in the winter I keep the idle closer to 1300 & in the summer I turn it back close to 1100. When the temperature drops below 35f I recomend warming the oil in the sump before starting the motor as a good safety measure.

 

I use an electric space heater against the oil pan for 15 minutes or so to heat things up. There have been many other suggestions on how to do it but thats the easiest way that I know.

[John in Leeds]

Roller bearings have considerably lower friction, and are able to live with much lower oil pressure. They cost more than plain bearings both because of the cost of the bearing itself, plus tighter tolerances required to mount them. Oil cleanliness is more important for long life.

 

The reason I ask is that I have just had a catastrophic failure with my Highland. Just put the Rosso Corsa away for the winter, blocked up, cleaned, lubed, battery stored and SORNed. No salt for my beauty. Then the following day on a wet and windy motorway north of Blackburn doing a steady 80 - 85 the Highland big end collapsed.

 

The bike has been well cared for, never thrashed - (it is very fast) and I just don't understand it. Taking it down I see there are roller and needle bearings throughout and it seems really well built.

 

 

This in contrast to the KTM LC8 that is similar in design yet with all plain bearings. Haven't heard of bearing failure with those.

 

The Highland is such a top machine for me that when this problem is sorted I need to ensure it never happens again. Constructive advice would be really welcome.

[Paul Minnaert]

you are shure there was oil pressure?

[DVH]

This is bad news John, If you need any help give me a ring.

possible a bad bearing, any blueing of the crank or bearings to show possible oil pressure loss

Dave

[John in Leeds]

you are shure there was oil pressure?

 

No Paul - nothing to show loss of pressure yet. Waiting to see what happens when it is fully stripped. Rock and Road, where I bought it are always really helpful and it is in their hands now.

[John in Leeds]

This is bad news John, If you need any help give me a ring.

possible a bad bearing, any blueing of the crank or bearings to show possible oil pressure loss

Dave

 

Thanks for that Dave

 

Will keep you up to date

[Ryland3210]

Notice what I said about oil cleanliness being more important for roller bearings? They are more sensitive to hard particles, such as even very tiny bits of steel, because of the high contact pressures of the rollers. Even soft aluminum particles can cause rapid failure. If a roller skids, instead of rolling, it's quickly destroyed.

 

Obviously lack of oil is a killer, but also it would be a good idea to examine the failed bearing carefully to determine cause of failure.

 

If the pressure relief valve is connected before the filter instead of after, there is the additional risk that a particle sucked in by the pump, or from the pump itself sticks the relief valve open, thereby reducing oil pressure. Guzzi's have the relief valve after the filter. Have a real good look at the pump internals for any sign of failure.

[Lex]

Rollers are heavy, noisy, bulky, expensive, weaker and less stiff then plain bearings. Plain bearing are light, quiet, compact, cheap, strong and stiff.

 

The myth that roller bearings have less friction comes from people spinning an engine by hand and seeing how much more easily the roller bearing engine spins. What these people are missing is that when the oil system is supplying the high pressure oil that allows the two bearing surfaces of plain bearings to "float" over each other without contact the plain bearing engines spins just as easily as a roller engine.

 

Rolling element bearings are less, not more, sensitive to particulates in the oil. Rolling element bearings do need less oil pressure. The ability to live with low oil pressure and tolerance for "dirt" is why they were used for decades in motorcycles after they stopped being used in cars. The oiling system in bikes were poor and often unfiltered so the rollers gave better service. The first Japanese four-strokes and Ducati twins started with roller bearings and slowly converted to plain bearings over time. The same pattern happened on race bikes so the change was not entirely due to noise or cost reduction.

 

The differences between two types of bearings are well known to any mechanical engineer, nothing above is controversial or new information. Rather than get into a discussion with anyone who believes the myths about low friction from rollers I'd ask them to explain why every modern engine uses plain bearings for main, rod and cam bearings. This runs from the cheapest Toyota to the engine in every MotoGP bike and Formula One car. Roller bearings are limited to places where oil flow is poor but low friction is required.

 

When you find an engine with roller bearings there is a reason. My Harley has rollers on the crankshaft and rods because weird pressed together "knife and fork" crankshaft design requires them; two strokes can't provide oil to the bearings; a few singles use pressed together crankshafts that require roller bearings, other bikes have poor lubrication (sounds like the Hyland may be one) and need rollers for survival.

 

Lex

[luhbo]

Rollers are heavy, noisy, bulky, expensive, weaker and less stiff then plain bearings. Plain bearing are light, quiet, compact, cheap, strong and stiff.

....

Lex

 

[canada goose]

a few singles use pressed together crankshafts that require roller bearings

 

Lex

 

I pretty much agree with your whole post, but I think you got this one backwards. The roller bearing requires the pressed-together crankshaft, otherwise it would be impossible to assemble. I think many old bikes stuck with roller bearings long past their time because the manufacturers couldn't or wouldn't produce castings and machined surfaces that were tight enough to contain the oil pressure required by plain bearings.

 

Ken

[luhbo]

... I think you got this one backwards. The roller bearing requires the pressed-together crankshaft....

 

If you keep in mind that an assembled crankshaft can be cheaper you're thinking forward again.

 

Hubert

[John in Leeds]

I'm certainly getting a lesson here, thank you gentlemen.

 

Just looking at it from a layman's point of view I suspect that the change to plain bearings also has something to do with the improvements in lubrication technologies - I notice the oil specifications are continually changing. I would guess that it would rarely be cost effective to change from a plain bearing to a roller because of poor lubrication, surely improving the oil flow would be a cheaper option. More metal to support a roller in the forging or casting would I suspect often require a major redesign, larger oil pump or improved galleries less so. Any thoughts?

 

[Ryland3210]

Rollers are heavy, noisy, bulky, expensive, weaker and less stiff then plain bearings. Plain bearing are light, quiet, compact, cheap, strong and stiff.

 

The myth that roller bearings have less friction comes from people spinning an engine by hand and seeing how much more easily the roller bearing engine spins. What these people are missing is that when the oil system is supplying the high pressure oil that allows the two bearing surfaces of plain bearings to "float" over each other without contact the plain bearing engines spins just as easily as a roller engine.

 

Rolling element bearings are less, not more, sensitive to particulates in the oil. Rolling element bearings do need less oil pressure. The ability to live with low oil pressure and tolerance for "dirt" is why they were used for decades in motorcycles after they stopped being used in cars. The oiling system in bikes were poor and often unfiltered so the rollers gave better service. The first Japanese four-strokes and Ducati twins started with roller bearings and slowly converted to plain bearings over time. The same pattern happened on race bikes so the change was not entirely due to noise or cost reduction.

 

The differences between two types of bearings are well known to any mechanical engineer, nothing above is controversial or new information. Rather than get into a discussion with anyone who believes the myths about low friction from rollers I'd ask them to explain why every modern engine uses plain bearings for main, rod and cam bearings. This runs from the cheapest Toyota to the engine in every MotoGP bike and Formula One car. Roller bearings are limited to places where oil flow is poor but low friction is required.

 

When you find an engine with roller bearings there is a reason. My Harley has rollers on the crankshaft and rods because weird pressed together "knife and fork" crankshaft design requires them; two strokes can't provide oil to the bearings; a few singles use pressed together crankshafts that require roller bearings, other bikes have poor lubrication (sounds like the Hyland may be one) and need rollers for survival.

 

Lex

 

I agree with some of your points, but not all. This mechanical engineer is familiar with bearing design and practice, but takes exception to some of your statements. It is an established fact that rolling friction is less than sliding friction, otherwise we would be still dragging sleds along on greased skids instead of wheels. The example given does not take into account the viscous friction of plain bearings, which remains even when hydrodynamics of a plain bearing with sufficient pressure and surface velocity prevent metal to metal contact.

 

In a subsequent paragraph, you reverse your own position, and give an example where rollers are used for lower friction.

 

Plain bearings have been used for hundreds of years, and long before roller bearings. The use of relatively soft bearing liners allowed them to live in unfiltered oil because particles could embed themselves in the soft liners, while the shafts were hardened. There's an interesting case involving Isambard Brunnel's Great Eastern of the early 1800's. It's original iron propellor shaft spun in a bronze bearing shell. Years later, a new owner tried using an iron bearing shell to reduce cost. It failed rapidly.

 

Your points are well taken on the need for rollers in 2 stroke engines and low pressure engines such as at least the older Harleys (I do not know whether the newer models have higher oil pressure at idle).

 

I agree that the reason why modern engines make extensive use of plain bearings requires no lengthy discussion, but do not agree with your conclusion. With such factors as today's adequate and dependable oil pressure, better oils, and anti friction additives, the substantially lower manufacturing cost offered by plain bearings is motivation enough for the high volume makers. Regarding cost no object race engines, there is the trade-off between the lower friction offered by roller bearings and the weight savings offered by the plain variety, especially in high velocity applications, such as crank pins, to explain the various decisions.