Benefits of roller bearings

[canada goose]

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

 

Hubert

 

Then, why not an assembled crank with plain bearings? Although, delivery of oil to plain bearings through an assembled crank could present some challenges, it might be possible. There may already be one out there.

 

Ken

[Guest george in vancouver]

Just as an aside .............. I discovered recently that the Guzzi Falcone has a one piece crank and split connecting rod with un-caged roller bearings. It's the only bike I've ever seen with this set-up.

[John in Leeds]

Just as an aside .............. I discovered recently that the Guzzi Falcone has a one piece crank and split connecting rod with un-caged roller bearings. It's the only bike I've ever seen with this set-up.

 

The Nuovo Falcone went on to a plain bearing.

[Ryland3210]

Then, why not an assembled crank with plain bearings? Although, delivery of oil to plain bearings through an assembled crank could present some challenges, it might be possible. There may already be one out there.

 

Ken

 

The joint between mating parts of an assembled crank requires tight machining tolerances and an additional assembly operation, so it is hard to say whether an assembly of parts smaller than a cast or forged crank would cost less. My gut tells me it would cost more in parts as well as assembly labor. When I rebuilt my '64 Harley engine, it was quite a job to reassemble the crank pin to the adjacent crankshaft components. It used tapered ends to maintain concentricity, but the challenge was to prevent the two adjacent flywheels concentric with each other. It takes a lot less time to fasten a plain bearing connecting rod with its bearing cap to a single piece crankshaft, I can assure you, and no worries about crankshaft alignment.

 

The crankshaft was supported in roller bearings at both ends. Good thing, because the weight of the crankshaft was enormous. It would have taken quite a high oil pressure to maintain hydrodynamic lubrication on the beast, which it didn't have, especially at the design idle RPM, about as slow as a heartbeat!

 

As far as oil delivery is concerned, I don't see any major problem with drilling the holes in the individual components required for supplying oil to a plain bearing.

[Steve G.]

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'm questioning some of your points. Regarding the widespread use of plain bearings in cars today, it has more to do with the cost savings than you would aim to point out. As for race engines and roller bearings, it's simply a weight saving issue. This application has nothing to do with the apparent lack of strength of rollers, they are just too heavy. You should have separated longevity with strength of rollers, they are not one and the same. Yes, if given a proper lubrication atmosphere, plain shell bearings last longer. But rollers definitely do not take a back seat to plain shell bearings, in fact they will handle a much worse operating situation than plain shell bearings. Is it any wonder that in the worst motorcycle motorsport environment, nitro methane drag racing, the 28 yr old Suzuki in line 4 engine is still the favourite. Factory equipped with roller bearings throughout. You may note that car v8 dragsters are using plain shell, BUT, they change ALL plain shell bearings ever race!

 

Ciao, Steve

[luhbo]

Then, why not an assembled crank with plain bearings? ....

 

Funny how stunning ideas can be the moment you see them the first time, isn't it?

[luhbo]

..It would have taken quite a high oil pressure to maintain hydrodynamic lubrication on the beast....

 

It'S not necessarily so. Oilpressure is only needed to press the oil from the pump to the bearings. These average 3 bars never would be enough to keep the parts in an engine apart from each other. On the other hand - a glowing pressure light at idle is not really a bad thing. This low pressure might easily be enough to make the hydrdynamic principles work.

 

Why not look here:

 

http://en.wikipedia.org/wiki/Bearing_%28mechanical%29

 

http://en.wikipedia.org/wiki/Fluid_bearing

 

Hubert

[Ryland3210]

It'S not necessarily so. Oilpressure is only needed to press the oil from the pump to the bearings. These average 3 bars never would be enough to keep the parts in an engine apart from each other. On the other hand - a glowing pressure light at idle is not really a bad thing. This low pressure might easily be enough to make the hydrdynamic principles work.

 

Why not look here:

 

http://en.wikipedia.org/wiki/Bearing_%28mechanical%29

 

http://en.wikipedia.org/wiki/Fluid_bearing

 

Hubert

 

Good basic summary consistent with my trusty college textbooks of yesteryear. Nothing new there, but numbers are absent. My "high" pressure is relative, as is your "press the oil", and "This low pressure ..,"

 

The hydroplaning referred to in the article depends on the relative surface velocity of the bearing surfaces, and the rate at which oil can flow out of the bearing, and viscosity as well as other factors. Bottom line is that RPM and the ability of the pump to supply enough pressure to feed oil to the bearing are vital factors.

 

So I think it is fair to say we are on the same page, except glowing low pressure warning lights always make me nervous, especially with the 2-5 psi threshholds of many pressure switches today.

[luhbo]

...

So I think it is fair to say we are on the same page, except glowing low pressure warning lights always make me nervous, especially with the 2-5 psi threshholds of many pressure switches today.

 

Fair, ok, we are forum friends Let me repeat it anyway: it's not the oil pump that keeps the parts separated. Hovercrafts are another nice example. The relatively small vents could never keep the boat hovering, being a good lot heavier as the biggest helicopter is. It's the hydroplaning effect - not the pump or in this case the vent.

 

For the flickering oil lights - I know that for some a flickering oil light is a reason to nearly jump off the bike, and taking an oil light serious is of course a good idea. On the other hand, all my VW beetles had the light ON, not flickering, at idle, making good vibs at 400 rpm. All these engines made more than 300.000 kms, always giving all of their brute 34 hp

 

Hubert

[Ryland3210]

Fair, ok, we are forum friends Let me repeat it anyway: it's not the oil pump that keeps the parts separated. Hovercrafts are another nice example. The relatively small vents could never keep the boat hovering, being a good lot heavier as the biggest helicopter is. It's the hydroplaning effect - not the pump or in this case the vent.

 

For the flickering oil lights - I know that for some a flickering oil light is a reason to nearly jump off the bike, and taking an oil light serious is of course a good idea. On the other hand, all my VW beetles had the light ON, not flickering, at idle, making good vibs at 400 rpm. All these engines made more than 300.000 kms, always giving all of their brute 34 hp

 

Hubert

Hovercraft do not lift themselves up off the ground as a result of hydroplaning. They rise because of the static air pressure created under them. The fans used have sufficient flow rates to maintain that pressure even when they rise above the ground or water. A balance is achieved between the weight of the craft and the pressure times the area of the "footprint" of the Hovercraft. As it rises, the gap between the cushion and the ground or water under it increases. The larger the gap is, the higher the flow rate. As flow rate increases, the static pressure developed by the fans decreases until a balance is achieved. This is an example of the effect of static pressure, not hydroplaning.

 

I have also driven many an automobile with flickering warning lamps that would glow when the pressure dropped below about 1.3 bar. I wonder what the pressure switch threshhold on your VW was?

 

I remember when that was making many drivers worry back in the 1960's. Detroit's answer at the time was to lower the pressure switch threshhold to around 0.5 bar! My answer was to install high volume oil pumps in my cars.

 

For quite a few years, now, the cars I have been driving, some up to the 300 km and more with oil pressure gauges, have maintained oil pressure at idle of at least 2 bar, most maintain 3.5 bar until they reach about 200 km. The implication, at least in my opinion, is that the automakers have decided that pressures of 0.3 bar are unhealthy for the long term life of engines made these days.

[GuzziMoto]

I wish I had some valuable insight on this, as it is one of the more entertaining threads I have seen on this site in a while. But sadly, my knowledge is not well versed enough to be of use to others on this subject. I know enough of bearings to have my own opinion, but not enough that I expect others to want to hear my opinion.

[raz]

Great reading, thanks to all contributors!

 

I know enough of bearings to have my own opinion, but not enough that I expect others to want to hear my opinion.

Was that a teaser? Let it out! Don't be shy. Forums are always a lesson in source evaluation anyway.

[GuzziMoto]

Just remember, you asked. I've always heard that each had it's advantages. Plain bearings are cheap, quiet, and as long as oil pressure is high enough, low friction. Ball,roller, and needle bearing are low friction all the time(oil pressure be damned), handle higher loads(that's why they're used in twins and singles), and longer lasting. When I raced Ducati's with Gotham Racing in the 90's we blew up top ends, but never lost a bottom end. I'm told they use expensive Timkin bearings(a type of caged ball bearing I believe)

[Skeeve]

I'm told they use expensive Timkin bearings(a type of caged ball bearing I believe)

 

Timkins are a type of caged roller bearing, actually. More expensive than ball bearings, but better able to absorb shock-induced loads normal to the axis of rotation. AKA "tapered roller bearings."

 

Ride on!

[GuzziMoto]

Most of the "spun bearing" stories I've heard involve a plain bearing. If a plain bearing spins, among other things the hole that it's oil is pumped in thru no longer lines up so it loses it's oil pressure and fails. I'm sure any type of bearing can spin, and most if not all will have problems as a result. But plain bearings pretty much instantly fail when they spin.