Member Contributer ShipFixer Posted June 21, 2021 Member Contributer Share Posted June 21, 2021 On 6/18/2021 at 9:38 PM, BusyLittleShop said: Always enjoy your learned responses Patrick and I agree... in fact water is doubly bad... it has the viscosity of 1 so it will pump and it might flow fast enough to lift 5,000 lb vehicle off the ground or float a 59,000 lb Granite Ball but it will rust our engines whereas Molasses with the viscosity of 5000 ain't even a player because it will hardly move... I think Honda will continue to recommend the viscosity of 10 or 30 grades for our bikes... The power of flow... Water has the viscosity of 1 yet water flowing between the sphere and its shaped holder lifts a 9 ton ball slightly where rotation can be accelerated by your hand and feels friction less... Okay, I don't know why I try... You are misinterpreting the first half of the foil video you reviewed, and did not comprehend the second part where he brings it back to "but why does the foil turn the flow of air down?" No, the answer is not "flow" in some mystical, abstract sense. The answer is viscosity. The air is not doing work on the foil, the air is being worked on by the foil. Just like a propeller is working on air, or in the internal lubrication sense, the bearing and journal surfaces are working on motor oil and that's what creates lift inside of the bearing. Air and motor oil are the working fluid, and the surfaces are doing the work, not the other way around as you seem to believe. Viscosity is a fluid's resistance to deformation. In immersed flow conditions where the working fluid is assumed to be "sticking," v=0 relative to the surface of a solid. As the surface moves, it applies force to the arbitrarily small layer of fluid attached to it, which applies shear force to the layer next to it, etc. We can think of it in piece-wise linear terms this way, in steps away from the surface. In the foil video, he walks you through this in the unbounded sense, where distance goes to infinity. But what happens when instead of a solid foil in an unbounded theoretical space, we have two surfaces parallel to each other, where one is fixed and the other is moving, and a Newtonian fluid with linear viscosity completely fills the space between them? The exact same thing. The surface that is moving is applying force while it moves, and the viscous fluid resists that deformation. Or, you know... (Force * Distance) = Work. In the bits and pieces that you cherry pick, they mention the bearing "pulling along" the oil. Well...duh, that's viscosity. It will pull the fluid wedge along with it, because it is performing work. If we try to angle the back end of the moving surface down, what would happen? Just like the foil example, the fluid will resist the deformation (because...viscosity) and push back against the surface, perpendicular to the direction of flow, as pressure...or lift. It gets better inside a bearing. In the 2D sense, so long as we can keep the space between them filled and stay in immersed flow, as the bearing works on the fluid, the fluid will resist deformation as it goes around and...voila, create lift. What matters in the space in between these two circles? Viscosity and the relative angular speed of the two circles. That determines how much counterforce will be applied to gravity, impulses from vibrations or pistons or whatever, etc. In bearing design, the balance between RPM and viscosity vs. those imbalances results in the eccentricity of the bearing. We design the bearing spacing to go with the viscosity of the lubricant and speed range of the application. The equations get a little sticky and involve things like the Sommerfeld number, but the general principle is easy to understand. If angular speed/RPM drops...eccentricity goes up and the journal gets further away from centerline, closer to the bearing surface. But the same occurs if viscosity drops too. So we want an adequate combination of speed and viscosity to keep them separated with lift while not creating too much heat. Because what is that temperature difference? That is heat created from work done on the fluid by the bearing. That (Force * Distance) part that we all know and love. It's not, and this is important, not from the fluid working on the surface, it's from the surface working on the fluid. It is definitely not just from your oil pump and pipes (which by the way...is working on the fluid through viscosity!) Its viscosity is its resistance to deformation, and the higher the resistance, the more work is required over time. And work over time gets us to...power out, including waste heat. This is where your Googling up a mechanic's "engine builder" view breaks down. He understands the fluid wedge, but not why it's there and not what creates it, or what matters. This is the point where if it's just "flow into" the bearing, then why not step down oil further and increase this flow? Why not substitute water? I'm asking you a reductio ad absurdam question here. Your engine builders can correctly tell you the trade offs to go to the bottom end of the range, but not why there is a bottom of the range through their logic. By their logic, and yours...why not SAE 0? So if the "flow" inside the bearings comes from the journals and bearings themselves, why do we have pumps and why do they matter? Because a.) the oil is getting hot and it is Newtonian within a given temperature range, so it's nice to cool it elsewhere, and b.) we need to keep that immersed flow condition, and c.) seals are draggy. There are large bearings out there which are in fact 100% sealed and remain lubricated, but they're not that common. You also see that in your engine builder references. What is the "flow" we provide to lubricated bearings? The answer is enough to ensure they remain immersed. We design them so that the flow in = the flow out. We do not...repeat...do not design the bearings or something with "flow" to keep them centered, any more than "flow" is magically pushing up on wings. The journal itself does the work on the fluid to keep it centered, we just need to keep it immersed. Keep this in mind. In almost every large system, we may monitor oil pressure in many places, but we are really only watching one indicator, typically placed at the "most remote" spot served by the forced lubrication system. We do not care that each bearing and lubricated surface is often getting different amounts of "pressure" and therefore "flow in/flow out." We only care that they are getting a.) enough to remain immersed and b.) not too much to blow things. (Aside from other things, applying positive pressure to the bearing case would probably be a Bad Thing.) Every single lubricated surface inside your bike is getting a different "flow" than an identical surface nearby, but it's just fine. Think about that...if it was "flow," we would be bending over backwards on lubrication system design with exquisite piping solutions. Here's another thing to think about...in very large machinery like power plants, oil pressure is provided by an externally driven pump. It is more or less independent of RPM or load, sometimes completely...its control logic is exclusively set up to monitor whether the lubricated surfaces and bearings remain immersed or coated. There is no "flow" logic in there, or anything that looks like it. The only thing I needed to know for my first ship's propulsion plant lube system was two set points...and that's before I knew how this stuff was designed. We are providing pressure based on the design requirements of the bearings and other surfaces, where we know that X psi will ensure Flow In is roughly equivalent to Flow Out, and the bearing will stay lubricated. So what does it matter? Let's go back to the OP's question, with an informed answer. - Motorcycles share a sump with the transmission; this requires a high viscosity oil with very high resistance to destruction from shear deformation in between gear teeth. Your car has a gear oil designed for it...here we are hoping for the best in a lighter application with motor oil. So this means...the engine is stuck with a relatively high SAE viscosity oil. - The bearings are designed around these motor oils. But they are still going to get their teeth kicked in by the transmission. - It has a range, because...wait for it...the bearings and other lubricated surfaces have a design range across RPM for which a number of oils will work within tolerances for eccentricity, and because viscosity is temperature dependent in two ways in motor oils, and different climates may impact the oil temperature. All of the oils in the specified ranges for temperature will work, because the bearings and other surfaces were designed to work with them. However...higher viscosity will equal lower eccentricity, and keep your parts separated better. That's the math, that's how it works. It is specifically hotter because more "lift" work is being done, in addition to parasitic drag along the way. The lower viscosity oils will work just fine too, within the published limits. But... The always-immersed condition is an ideal, and there's cold starts, etc. There is also turbulence, cavitation, and all sorts of other conditions not covered here in the basics. So if you want arbitrarily better protection, a little higher viscosity will in fact protect the motor and the transmission a little better. This is also important...a race team is going to have a very different investment view than a vehicle owner. YMMV...but we don't randomly toss lubricants inside of bearings and wonder how it's all going to work out. An important caveat to that though...the car companies and others out there will kill for a minor reduction in their CAFE average, whether that's in shaved tires or less fluid drag from motor oil. So beware some of the specs for oil viscosity when they are reduced downwards in future model years. Some car companies have been caught making longevity vs. efficiency decisions for the consumer in the past. If you know your bearings and such were designed around a specific viscosity range, and then the viscosity range is pushed down in a later year with no part changes...well... Link to comment Share on other sites More sharing options...
Member Contributer Dutchy Posted June 21, 2021 Member Contributer Share Posted June 21, 2021 Many 😁 Link to comment Share on other sites More sharing options...
Member Contributer SirDoh Posted June 24, 2021 Author Member Contributer Share Posted June 24, 2021 Bringing it back........To restate the question in a different way.. The engine running in 15°C ambient will run between 85 and 104°. The engine running in 30°C ambient will run between 95 and 104° (assuming the same riding style) Surely that doesn't justify a different viscosity of oil. If so why? Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted June 24, 2021 Member Contributer Share Posted June 24, 2021 2 hours ago, SirDoh said: Bringing it back........To restate the question in a different way.. The engine running in 15°C ambient will run between 85 and 104°. The engine running in 30°C ambient will run between 95 and 104° (assuming the same riding style) Surely that doesn't justify a different viscosity of oil. If so why? Mate give it a break... Seriously, after all thats been discussed here! What more do you want? You're worring about nothing. Maybe, give Honda a call! Link to comment Share on other sites More sharing options...
Member Contributer St. Stephen Posted June 25, 2021 Member Contributer Share Posted June 25, 2021 1 hour ago, Grum said: Mate give it a break... Seriously, after all thats been discussed here! What more do you want? You're worring about nothing. Maybe, give Honda a call! C'mon Grum, a few more weeks of informed debate and we might achieve full factory power. 😎 Link to comment Share on other sites More sharing options...
Member Contributer ShipFixer Posted June 25, 2021 Member Contributer Share Posted June 25, 2021 6 hours ago, SirDoh said: Bringing it back........To restate the question in a different way.. The engine running in 15°C ambient will run between 85 and 104°. The engine running in 30°C ambient will run between 95 and 104° (assuming the same riding style) Surely that doesn't justify a different viscosity of oil. If so why? That's a relatively easy one. Your "engine temperature" is your coolant temperature, not your oil temperature, and the viscosity of the oil is of course based on its own temperature. The design of the lubricated surfaces is again based on a range of RPM and working viscosity (at temperature). We cannot infer what the oil temperature is solely through observing an interconnected system, especially since it has its own heat exchanger and other paths to shed heat, and the coolant is primarily shedding heat from combustion (the largest delta T in the engine). There is a related rates problem here but you can't solve for it looking at one point in one system that is partially related. Even in vehicles with integrated radiators and transmission or oil coolers like my Nissan, the coolant temperature is not directly related to my transmission fluid temperature in a straightforward way. Monitoring coolant is a "leading" indicator for other temperature problems, and the odds of catastrophic this or that from overheated coolant is much higher than overheated oil (which is relatively hard to do outside of wiped bearings, etc). In very large systems, we monitor coolant, oil, air, and exhaust temperatures at multiple points. There's not much to overthink here, beyond there is a large degree of overlap between two viscosities of oil., which at working temperature are not that far apart. So if you find yourself at one extreme or the other, go with that. If you are in the normal ambient temperature range, choose between a little more protection or a little lower operating temperature and a small loss to parasitic drag. Both are "adequate," as would be oils with viscosity in between. Link to comment Share on other sites More sharing options...
Member Contributer BusyLittleShop Posted June 25, 2021 Member Contributer Share Posted June 25, 2021 8 hours ago, SirDoh said: Surely that doesn't justify a different viscosity of oil. If so why? Surely it doesn't... according to the riders with 300,000 miles on the clocks either viscosity will meet and exceed your mileage expectations... what you might notice running the freer flowing 30 grades are quicker cold starts, faster acceleration, and lower coolant temps... Link to comment Share on other sites More sharing options...
Member Contributer ShipFixer Posted June 25, 2021 Member Contributer Share Posted June 25, 2021 7 hours ago, BusyLittleShop said: Surely it doesn't... according to the riders with 300,000 miles on the clocks either viscosity will meet and exceed your mileage expectations... what you might notice running the freer flowing 30 grades are quicker cold starts, faster acceleration, and lower coolant temps... None of that is what he asked. And like the OP, you are probably also not considering the difference between coolant temperature and oil temperature, which you cannot directly observe from the saddle. You know that there is increased temperature in the coolant from additional heat transfer in, but you do not have direct observation of oil temperature, and it is complicated by the oil system's independent heat transfer paths. They are partially linearly correlated and that is all we can confidently say. The original poster asked if ambient temperature was enough to justify a viscosity selection. Since the technical manual provided by Honda doesn't convince you, we reviewed the collective human knowledge on "How Lubricated Surfaces Work" as developed from ~350 years of fluid mechanics beginning with Newton, ~200 years of modern thermodynamics and mechanical engineering design, and ~50 years of tribology (the study of wear). You should, by now, know that the "flow" you believe lubricates the bearing, is created primarily by two characteristics: the RPM or relative angular speed of the wetted surfaces, and the viscosity of the lubricant. Ironically, we also covered how that increased temperature is evidence of the lubricant increasing distance between the lubricated surfaces (Force * Distance / Time = Work / Time = Power). You cannot believe that "flow" is what lubricates the bearing and ignore relatively simple hydrodynamic truth about where that "flow" actually comes from. Your sources curiously correctly state it's not "pressure" from the pump that lubricates, but they mysteriously don't really have a full reason for why oil flows around a lubricated bearing, or between piston rings and cylinder heads, etc. Cause, you know...those aren't engineering or science references you are using. Those are anecdotal references, rather than first principles arguments or statistically inferred proofs. I recommend a classic reference, like Shigley's Mechanical Design. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.