So much of great-working motorcycle comes down to precise heat management of the engine, tires, gears, brakes, and more. Technical Editor Kevin Cameron takes a deep dive with Editor-in-Chief Mark Hoyer on the many effects of heat and the cascading influence it has on overall motorcycle performance.
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Read more from Cycle World: https://www.cycleworld.com/
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SportsTranscript
00:00:00This is the CycleWorld Podcast. Welcome back if you're a listener already and
00:00:04welcome to any new listeners if you're new. We got more than 30 episodes behind
00:00:10us so go check them out. We try to hit a wide variety of topics from
00:00:15classic epic motorcycles like GSX-Rs and R1s and why Harley sold millions of
00:00:22motorcycles to pretty far out stuff like what are the great books of
00:00:28motorcycling and combustion and stuff like that. For some reason you guys love
00:00:33the TZ750 Podcast. We're thinking about a whole TZ750 channel, just kidding.
00:00:38Today it's another sort of fundamental or theoretical a little bit
00:00:45but it's also quite real and that is heat management. How do you manage the
00:00:49heat in your motorcycle? How do we keep them cool enough, keep them hot enough, do
00:00:54all the things that make the motorcycle perform in the way we want it to and
00:00:58really when I think about heat I think well it's quite relative. We think about
00:01:02the universe and we think about the Sun. Well the Sun's pretty hot. The Sun is
00:01:07very very hot. We're talking about on earth a small little window of heat
00:01:11management that works in our beautiful temperature range that we love and enjoy
00:01:15and when it gets really cold apparently the molecules stop moving. We've never
00:01:22tried that. I haven't anyway but yeah heat management from engines to brakes
00:01:29all of that. Of course the principal problem is combustion heat and I think
00:01:37that's a great place to launch. Sure and of course that's where the desperation
00:01:45of the early engine builders arose because although metal parts have a
00:01:53really high melting point, particularly iron, if you keep putting heat
00:02:01into metal which an internal combustion engine does every time the spark fires
00:02:06the charge its temperature jumps up 2600 K and some of that heat is transmitted
00:02:18directly into the material of the combustion chamber inner surface and the
00:02:22piston crown. If that heat is not removed as fast as it is gained the temperature
00:02:30of the parts will rise until the pieces lose their strength and fail.
00:02:38Yes so some of the early engine builders sort of I remember reading
00:02:48that Glenn Curtis asked about one of his early engines. He said it's the
00:02:57greatest engine in the world for about three minutes because it soon got hot
00:03:05and wouldn't do no more. So the heat has to be taken away somehow and in the
00:03:13early days and a direct way of doing that was to surround the cylinder with
00:03:19the jug and keep water in it and when the engine got hot enough the water
00:03:25began to steam and for every gram of water that was boiled away it took 540
00:03:35calories of energy. So those early farm engines that sit there going pack pack
00:03:42pack chup chup chup pack pack pack chup chup. Don't you just want to collect stationary
00:03:48engines? I do. I just want to go kapang kapang kapang and run a pump I don't know
00:03:53Circulating water and you presumably had some lad who was charged with pouring some more water
00:04:01and when it began to show signs of distress. Well it reminds me of an engine that was used
00:04:09in British motorcycles. There was one called a Matador. It was sort of circa 1907 or 1903.
00:04:17Way back it was called a Bradshaw oil boiler. Now how would it have gotten that name?
00:04:25Granville Bradshaw genius or charlatan but he was in the game. So people began to put
00:04:38so-called secondary surface onto the cylinder head and the cylinder. Secondary surface we call
00:04:47it fins. It's just a way of extending of adding more surface area to parts that cannot rid
00:04:56themselves of heat fast enough through their own natural surface area. So we're putting very
00:05:05intense heat from combustion into the inside of the combustion chamber so we're going to have to
00:05:10take extraordinary measures to pull that heat out from the outside surface and transmit it to the
00:05:17merry little breezes that are blowing through our lab or other enterprise. So cooling fins
00:05:27became a way you could tell an engine's point in time because they kept getting deeper and more
00:05:38numerous and when overhead valves came to be the rocker boxes were mounted above the cylinder head
00:05:48on little standoffs allowing cooling air to pass over fore and aft oriented fins on the cylinder
00:05:56head without obstruction. I just cornered our shop guy and tester and Evan Allen
00:06:05recently about cooling and about 90 degree cams or 120 degree you know included angle and
00:06:16tipping it forward to get all that air. We'd like them a lot closer but it gets too
00:06:21hot on a race engine so like the you know the Gileras and all those really wide cam boxes for
00:06:27the same reason as the standoffs. Yes absolutely and when Mr. Chorichiro Irimajiri was asked about
00:06:42why the cam boxes on early Honda racers were so far apart he said because it allows you to place
00:06:49cooling fins directly over the hot combustion chamber. Now we know that those deep hemi
00:06:58combustion chambers were much admired in the early days when a six to one compression ratio
00:07:04meant that you had a flat top piston with a hemisphere chamber above it and that worked
00:07:12acceptably but as compression rose the easy way to get more compression was to put a similar dome
00:07:20on the piston and then people began to take thought about this. Well the surface area of
00:07:28a true hemisphere is double that of a flat disc of the same diameter. Hmm we've built a heat trap
00:07:38here and the taller the piston domes became the more piston clearance was required because it
00:07:45made the pistons run hotter. So the place where you could see the growth of cylinder cooling fins
00:07:53best was in aircraft engines air-cooled ones and they started out with a sort of a sprinkling of
00:08:01fins the way some people put salt on their food hardly at all and they became more and more dense
00:08:10so that for a long time they were maybe a third of an inch apart and then they became a quarter of
00:08:18an inch apart. During World War II BMW built this 801 radials with fins spaced five millimeters
00:08:28200 thousandths apart. That's about as close as they could cast them in those days and they made
00:08:34them really deep. Also there was the problem of material. The first cylinders for motorcycle
00:08:42engines as well as for aircraft engines was cast iron. Cast iron heads, cast iron cylinders.
00:08:50But if you put a bunch of material rods of different materials with their inner end on
00:08:56the gas ring radiating out you'll find that a copper rod gets really hot even at the far end
00:09:04but a cast iron rod takes forever to get even warm at the end and you can imagine that
00:09:12a warm rod doesn't lose heat as fast as a very hot one so it became important at a point to
00:09:20improve the cooling by changing the cylinder and head material. They switched from cast iron
00:09:26to bronze and you will see references to bronze headed Vincent TT replicas and
00:09:35variety companies made the bronze heads. Yeah, pre-war triumphs like Speed Twins.
00:09:40There's a beautiful available. Transmitted heat about twice as well as cast iron so it was a step
00:09:46forward. Also just as you could seat valves on cast iron you didn't need a hard insert
00:09:55seat. You could do the same with bronze but it didn't take long for the rise in horsepower
00:10:03of sports and racing engines to outrun the heat conductivity of bronze and people began to play
00:10:10with aluminum and they found that you couldn't seat valves on it very well although it was done
00:10:18on occasion and if you shrunk, screwed, or cast in place hard valve seat rings they would come loose
00:10:31in service and that's bad for motorcycling. So at one point Velocet, somebody there was
00:10:43riffling through the digest of metal alloys and oh here's a new high hot strength aluminum
00:10:54and it's not Y-alloy which is so difficult to cast. Let's try this and shrunken seat rings stayed
00:11:05in this modified Y-alloy and called alloy 142. Millions of aircraft engine cylinder heads were
00:11:15made out of it and after the war was over Harley-Davidson adopted it for the aluminum heads
00:11:22on the panhead bike. So this has been the progression from low heat conductivity but
00:11:29high practicality. Iron wears like iron. To medium practicality bronze, well it's a little bit better
00:11:40but man that stuff is heavy. And finally aluminum, a little tricky. You have to take care you can't
00:11:50just use melted down pots and pans but it can be made to work and it was. And in aircraft engines
00:12:00the fin pitch kept on getting smaller and smaller and the reason was they needed more
00:12:06and more cooling surface area as those engines were supercharged, turbocharged, squeezed in
00:12:13every way to get power from them. And finally when they were machining the fins out of solid
00:12:21forging they got down to 0.132 inch fin pitch and that's all she wrote. People who tried such
00:12:33close pitches on motorcycles found they cooled worse than fins pitched at a quarter inch. Why?
00:12:40Well it takes more pressure to push air through those tiny fin spaces than it does through
00:12:50more generous fin spaces. On aircraft engines the cylinder fins and the head fins were all
00:12:58baffled so that you could enter the fin space at the front but nothing could escape out the sides
00:13:06and the only way out of that fin space was a vertical, a tapered vertical slot in the back
00:13:13of the cylinder that let the air out. Had to go all the way around, cool the whole thing and then
00:13:19be dumped out the back of the nacelle. With a motorcycle fortunately there are obstacles to
00:13:29the continuous use of full throttle. There are things to bump into and there are officers of
00:13:37public safety who are waiting to tax you for your enjoyment. So
00:13:45what happens with the motorcycle air-cooled engine is when you gas it
00:13:52most of the heat is not immediately transferred to the fins and then dissipated to the air. It
00:13:58goes into making the cylinder head as a whole hotter. In other words the mass of the cylinder
00:14:04head is a heat sink just like you have in electronics. So when Harley's great racing
00:14:14director Dick O'Brien was working with Pete Zylstra, his draftsman, on the XR750
00:14:25aluminum engine, he said I want an inch of goddamn aluminum on top of that cylinder head.
00:14:32Zylstra, who knew that people were going to come back to him afterwards, said why is this
00:14:36thing so heavy? He said well how about a half inch? So they settled at three quarters. But there's a
00:14:44lot of metal on top of the cylinder head. Now there's more to this. I once had in my shop at the
00:14:51same time a head from an FZ750 Yamaha which was liquid cooled and a GS750 head, a four valve
00:15:00Suzuki head. So both were four valves, both were aluminum, but the one that was really light
00:15:11was water cooled. And water weighs only one third as much as aluminum. So filling up the
00:15:21water jackets did not make the cylinder head weights all that more similar. So the reason
00:15:28for the weight in the air-cooled cylinder is that need for a heat sink. You gas it,
00:15:34cylinder head temperature goes up, oh there's a corner, oh there's a policeman, we slow down.
00:15:40And so duty cycle saves the air-cooled engine in motorcycling, or it did save it for a long time.
00:15:50But then at a point the hottest parts of the cylinder head began to give trouble.
00:15:58The area around the valve seats, exhaust valve seats, is really hot because
00:16:04hot combustion gas, even though it's been expanded through the power stroke,
00:16:09goes rushing out through the valve at supersonic speed, scouring away any insulating boundary
00:16:16layer on the inside of the exhaust port, so that the conditions for heat transfer in the exhaust
00:16:22port are excellent. Even though the gas in the port is not as hot as combustion gas
00:16:30at peak pressure. So about half the heat energy taken up by the cylinder head comes from combustion
00:16:42in the combustion chamber, and the other half from the inside of the exhaust port.
00:16:49Which is why you will find recent designs have the shortest possible exhaust port,
00:16:56and it's made as small as possible. The goals in this case are to reduce its surface area.
00:17:05Now you may have noticed that some of the recent parallel twins no longer have tremendous bores,
00:17:13and wee little short strokes. They're moving back towards square. Bore and stroke are equal.
00:17:19The reason for this is that in a world of concern over emissions and fuel consumption,
00:17:29you want to expose the minimum surface area to combustion, which means making the bore smaller.
00:17:36So that's what everyone has done. I would like to take that notion to an extreme and say,
00:17:44would not the perfect internal combustion chamber cylinder be coated in such a way as that no heat
00:17:52was transferred or minimal, very little heat was transferred? I mean, what we're trying to do is
00:17:58keep all the heat. Ideally, you would keep all the heat energy in the charge and not transfer much
00:18:05heat to the engine. Absolutely, and the U.S. Army spent hundreds of millions trying to do exactly that
00:18:12with diesel engines. Why not do it in spark ignition engines? One of the
00:18:21speakers at an SAE small engine meeting, when grilled by attendees
00:18:34as to why he didn't use coatings on pistons, and he said, well, old Swain ain't going to like this
00:18:41much, but the reason is detonation. Now, detonation or engine knock is a form of combustion that can
00:18:53occur when the last parts of the charge to burn have a thermal history of their temperature just
00:19:02rising and rising and rising, and when it gets to be about 950 degrees Fahrenheit,
00:19:08it becomes chemically altered. It turns into a sensitive explosive, which can auto-ignite
00:19:16and then burn at supersonic speed. Is that active radicals? Yes, those OH- active radicals are
00:19:24rattling around in there, not to be confused with Marxists, mind you. They're another kind of active
00:19:33radical, but when the population of those guys rises to X level, then auto-ignition and
00:19:41supersonic combustion become possible, and that's the rattling or pinking or tinkling sound that
00:19:49you hear when you're lugging an engine at low RPM and large throttle, and that tinkling tells you,
00:19:57please don't, no, no, don't do that. Let up, we're going to start dusting aluminum off the
00:20:02cylinder. Or shift down. Pinch some rings. Racers used to, in the words of Joe Craig, who was
00:20:10Norton's legendary racing engineer, he said, the racer has to live on detonation's doorstep,
00:20:19because you want to push the compression as high as possible, you want to have ignition at the
00:20:25ideal point to reach peak pressure where you want it, and you want the best power mixture in the
00:20:32cylinder, and the tuner used to be responsible for all of this, actually having to make decisions.
00:20:39Nowadays, we have the engine computer, we have the oxy sensor, we have all sorts of
00:20:45temperature and barometric pressure sensors, and it's like having a crew of engine tuners
00:20:53working just for you. It doesn't matter whether you like this, it's winter or summer,
00:21:02spring or fall, high in the Himalayas or down in Death Valley, that system
00:21:10is going to deliver good, solid performance. But detonation was this horror
00:21:20which could arise when your engine ran too hot, when the compression ratio was too high,
00:21:28when the ignition was overly advanced. Anything that raised the temperature of those last bits
00:21:35of charge to burn out at the cylinder wall is likely to provoke abnormal combustion.
00:21:44So could you just explain, we've explained this before, but normal combustion is not an explosion.
00:21:51Normally we say like, oh it lights off and lights the charge. It's really controlled, and I think
00:21:56that's an important point to remember. I mean we're really trying to light a fire
00:22:02that has a flame front of a certain speed. Combustion happens faster in a compact chamber
00:22:08where essentially you're looking at a tiny little cookie, you squish, and you have a little kernel,
00:22:13and that lights off, and it lights off in a beautiful way, and the pressure rises. It's what you want.
00:22:17And when you have a hemispherical chamber, much like this microphone, if you light the charge way
00:22:22over here, sorry spotifiers, but imagine lighting the charge on one side of a mountain and the flame
00:22:27has to travel over the mountain to get to the rest of the chamber. So if you have a plug on the side
00:22:32or even on the top, it still has to go all the way down, whereas if it's nice and compact and flat
00:22:37and it's a nice straight line, it can happen very quickly. And that goes, that speaks to
00:22:42Norton ignition timing, 28 degrees of commando, 28 degrees of max advanced. What that means is
00:22:48combustion happens fast, even at the highest load and the highest RPM. You don't have to light the
00:22:55fire 40 degrees before the angle of the crank gets to where you want the most pressure to make the
00:23:02most of it. It's what a beautifully complex, fun system. And having all those sensors talking
00:23:09and sniffing out and knowing everything that's going on, rather than Joe Craig,
00:23:13building a structure in his mind over and over again and the witnessing or, or Irv Kanemoto,
00:23:19as you had told that story before in the pits, warming up in the morning going, Oh, we're going
00:23:24to have to switch to those other needles. Just hearing what it's burning like he was the sensor,
00:23:29you know, I mean, they, I'm sure that they had some, you know, engine telemetry type things.
00:23:35Well, that's the way our society streamlines itself. The wisdom of the ages is put into an ECU
00:23:45and the tuners retire and sit on their porches and watch the sunshine.
00:23:51And once that process has fully matured, we'll all be there on the porch watching the sunset.
00:23:58In the meantime, we, we have this, we have this podcast to do. And the thing is,
00:24:04Mark just talked a moment ago about heat leaving the combustion gas by being conducted into metal.
00:24:12That's a loss of power. So the longer that combustion gas is held in the chamber,
00:24:19that is the longer combustion takes, the more heat is lost from the charge.
00:24:24And the less power is delivered to the rear wheel. So it reminds me of an important point that you
00:24:33made about, uh, drag racing at the time where they were switching from iron heads to aluminum heads
00:24:41and the iron headed cars actually had a lower ET for a while until we figured out how to take
00:24:47advantage of aluminum's advantages. Because iron didn't conduct the heat out of the chamber as fast
00:24:54in this window of running a... For a few seconds. For a few seconds, it worked fine. And then it had
00:25:02the rest of the afternoon to... To cool. To cool off. Until the next round anyway. Yeah. So Mark
00:25:08had spoken of, why don't we insulate the piston crown with some material such as zirconium oxide?
00:25:14Zirc oxide, for a long time, was used to... As an insulation on turbine blades.
00:25:22And here, the argument that was given by the NASCAR team manager, which I gave in written form,
00:25:33calling it, oh no, not the blanket analogy again, works like this. We lie down on the bed and sit
00:25:43we lie down on the bed and soon we've chilled out. In fact, we're cold.
00:25:48I can't sleep. So I get a blanket. I get a comforter and I pull it over me.
00:25:55The heat that is being emitted from my body heats the inside face of the comforter,
00:26:02but it doesn't heat the outside face very much because the comforter is an insulator.
00:26:07So now we turn that around and we put the comforter on top of the piston.
00:26:14And combustion gas is heating the outside of the layer of insulation.
00:26:20It gets very hot because the heat can't travel through the insulator. That's the principle of
00:26:25an insulator. Transmits heat poorly. The vacuum is a great insulator, hence the thermos bottle.
00:26:31So the outside of the coating becomes very hot.
00:26:39On the next intake stroke, that heat is heating the fresh charge so that not as much of it can
00:26:46enter the cylinder. It expands. And while the piston is rising on compression, the heat that's
00:26:53still in that outer layer of insulation is heating more. It's making detonation more likely.
00:27:01Well, don't worry about it. We'll lower the compression two points. Look what it did to
00:27:06our lap time. Yeah, well, reality is tiresome that way. And so people began to use the coating
00:27:17more as a very thin coating. This was told to me by Don Tilley, who lived down there in Statesville,
00:27:25which is NASCAR land. He said, you put on a very thin coating of that, just like anodizing,
00:27:32and it sort of discourages the first chewings of detonation. So it gives you a little more margin
00:27:41against detonation. If you're tuning right onto detonation's doorstep, you're going to need some
00:27:46margin. What was Don Tilley running is the question. For those who don't know, what was
00:27:52Don Tilley running? Don Tilley was running 883 Harley V-twins. And gigantic Buells. All those
00:28:00things. He blew so many head gaskets in his Buell 1340s that he went to half inch cylinder studs.
00:28:12Now, those are getting to the point that they're more like bats than they are like studs. Half
00:28:19inch, that's hefty stuff. He said, I think we got her this time. And I heard...
00:28:25Imagine the clamping force to get that.
00:28:28Just imagine the distortion. But when you hear one of them go, one of those bikes came past start,
00:28:35finish one time at Daytona, and I heard this squeaking. It's just a kind of an eep. That's
00:28:42the engine farting. That's the difficulty of forcing high peak pressure out through the gasket,
00:28:54blowing it. And so that's another piece of meaning with regard to life on detonation's
00:29:02doorstep. You have to go to the highest compression ratio that you can make reliable.
00:29:08And he wasn't shedding heat with water cooling. That's the other point there is he's limited by
00:29:15his fans. Now, in the design and development of large air-cooled radial piston aircraft engine,
00:29:26how's that for an adjective string? People reasoned, well, the engine's not actually
00:29:34overheating, but the oil is so hot that we're starting to get scoring between the piston and
00:29:40the cylinder. So let's cool the oil. Benelli patented an oil cooler in 1933 because motorcycle
00:29:49engines had hot oil on race day.
00:29:53Coking would happen.
00:29:55Yeah. Coking, that's the decoking was a process by which you took the cylinder head off your motor
00:30:03every couple of months and scraped all that carbon out of there. Because if you left it in
00:30:09there, it would retain heat and glow red. And any oxygen and fuel molecules who needed a minister
00:30:19to marry them would find it in the form of that hot glowing carbon deposit.
00:30:26And the British, up until they went out of business in the motorcycle business in the 70s,
00:30:32were really big fans of like, oh, it's time to take off the cylinder head for a decoke.
00:30:37Like it was not as often as changing the oil, but it was darn frequent.
00:30:42Yeah. So the whole business of trying to insulate piston crowns and combustion chambers was driven
00:30:58by the U.S. Army because they wanted to approach an ideal, which they called the adiabatic engine.
00:31:07Adiabatic roughly means without heat transfer. You know that if you're going to compress air
00:31:15in an air compressor, the air compressor cylinder is hot. It's not as hot as in a
00:31:21combustion engine, but it gets good and hot when it's running.
00:31:25But ideal compression is what is called adiabatic. And so they thought to themselves,
00:31:32hmm, our diesel tank engines are, say, 38% efficient. And if we could increase that to 50%
00:31:42or 55%, the range, the operational range of our tanks would be greater.
00:31:49And so they put a lot of money into trying to come up with piston materials,
00:31:56cylinder wall materials, and so forth that did not require cooling.
00:32:02Because if the closer heat transfer depends on the temperature difference between the hot object
00:32:09and the cooler coolant, and the closer those two come together, the less the heat transfer.
00:32:17So they reasoned if we have this extremely hot piston, cylinder wall, and combustion
00:32:24chamber inner surface, we won't have nearly as much heat loss and we'll get this great effect.
00:32:31But they found that not very much air was going into the cylinder because when it encountered
00:32:36all those hot parts, it expanded and not as much of it would fit. The charge density dropped.
00:32:46What did you say? Life is tiresome in this way?
00:32:48That's right. You're trying to do good. You've got an idea that theoretically should work.
00:32:59But in practice, they found that it was so difficult to cram fresh air,
00:33:05diesels take in nothing but air and the fuel is injected later.
00:33:09It was so hard to get the fresh air into the diesel and it took so much work to compress
00:33:16it, the piston, because the diesel compression ratio in a large engine is 16 or 17 to one,
00:33:23that they were losing in compression work pretty much all that we were gaining by
00:33:31approaching the adiabatic ideal. So cooling, engine cooling is a compromise.
00:33:37We're going to cool it just enough that the parts could live through the experience,
00:33:43but we're not going to over cool it by throwing away the thermostat and running our engine so
00:33:50cold that not all the fuel vaporizes. This is something we used to encounter at the races.
00:33:57You'd gas up and air up and start the engine because your practice was next and it wouldn't
00:34:08happen. And you knew that the volatile part of the gasoline was the only part that was
00:34:15vaporizing. The rest of it was sort of saying, okay, Sarge, show us how it's done.
00:34:22And so the mixture was too lean to ignite. Well, heat influence on this is something,
00:34:30heat everywhere, heat working on your choked motorcycle and you're putting extra fuel in
00:34:36there so that there's enough of the volatile to get it to start from cold. It starts you
00:34:41immediately back if you're on a choke motorcycle, immediately back the choke into a range that it's
00:34:47allowing it to run. The velocities are increasing. Your throttle is still closed because you're just
00:34:53running fast idle. And say you're at 1800 RPM and you think, oh, this is pretty good.
00:34:58And you go to take off and you load the engine slightly and you open the throttle.
00:35:03And for the temperature, the pressure change in the intake tract goes from high vacuum pulling
00:35:11things apart and making vapor to close to atmosphere. And all the drops go back together
00:35:17and they don't light off and you bog, a bog away. You can light vapor, you can't light droplets.
00:35:24And it's heat, it's all heat related. Yeah. So when Suzuki set themselves a goal in the early
00:35:35eighties of building a hundred horsepower 750, they tried to accomplish it with air cooling.
00:35:43And they found, as we've just discussed that there were some complications. So
00:35:49this project was under the direction of Etsuo Yokouchi, whose name you may very well have heard.
00:35:57He was the GSXR guy. He was involved with the RG500 two-stroke Grand Prix racer. He was one of
00:36:06Suzuki's main men for years. He had an engineer on staff whose name was Masahisa Kamiya. And Mr.
00:36:18And Mr. Kamiya raised his hand at some point and he said, in the war,
00:36:26we found that aircraft engines using oil coolers got one third
00:36:36of their cooling from the oil cooler. Because think of it, oil is lubricating
00:36:46all the moving parts. You have to have oil passing through the connecting rod bearings because
00:36:54the oil that's in there is only a thousandth of an inch thick and it will quickly boil away
00:36:59from friction if it isn't constantly replaced with fresh, filtered, cooled oil. And all through
00:37:08the valve train, the cam drive, the chain sprockets, all of that is generating heat
00:37:16and the oil is picking that heat up. So let's just run it through an oil cooler
00:37:21and everything will be hunky-dory. But Kamiya said, why don't we increase the circulation of
00:37:30oil enough that we can mostly cool the whole engine? We'll run big jets of oil down onto the
00:37:38tops of the combustion chambers. And instead of having to have two plumbing systems, one for water
00:37:44or engine cooling, and another one for oil, we'll simplify casting problems. The outside of the
00:37:51engine will still have fins and the inside will be entirely cooled by oil. And that was the genesis
00:37:58of the, pardon me, Yamaha, of the Suzuki GSX-R, which was oil cooled until what? 1992, I think.
00:38:09And it was very practical for a street bike because although oil has only about 40% of the
00:38:19heat capacity of water, water is a truly remarkable substance,
00:38:22if you use enough of it, you can get the cooling effect that you wanted.
00:38:27But what really hurt was in racing as 100 horsepower turned into 120 horsepower and 140 horsepower,
00:38:37oil was falling behind as a coolant and they were adding more and more coolers. I remember one
00:38:42race, they had coolers underneath the rider's forearms, there were coolers everywhere. And
00:38:51that had no future. So they switched to liquid coolant, namely, press stone and water.
00:39:02But what high-performance motorcycle today doesn't have a piston oil cooling jet
00:39:09skirting at the bottom of the piston, probably. Absolutely, absolutely. And this is something
00:39:16that bothers the people who own classic motorcycles. They see modern motorcycles with
00:39:24the little short skirted pistons and all these things that are so attractive to us. We look at
00:39:33them and say, I yearned for this, give me that thing. But if you put that type of piston into
00:39:41your classic Triumph BSA or Norton, how can they get their heat, lose their heat to the cylinder
00:39:48wall, which is the only way that pistons are cooled in such engines, is by touching the
00:39:54cylinder wall, which is cooler. We hope it's cooler. And if it isn't good enough, then we
00:40:01get scoring up and down the cylinder wall. Oh dear, oil failure. So we're obliged in the modern
00:40:12to have lightweight pistons because it reduces vibration or it reduces the amount of counter
00:40:18weighting or the amount of balance shaft that we have to use to smooth the thing out.
00:40:23Or the piston acceleration.
00:40:26Yes, yes, because the lighter the piston, the more difficult it is to yank the wrist pin.
00:40:34Because feet per second, your average piston speed is certainly important. If you're
00:40:38going to modify your WR250 and you want to bore and stroke it, as I have done the numbers on this
00:40:45piece of paper, I could add three millimeters of the stroke and at 11,000 I could still be
00:40:52under 5,000 feet average. But if I throw a really heavy piston in there, I might lose the rod anyway,
00:41:00because it's not necessarily the average velocity, it's like coming to a complete stop
00:41:05and yanking it in the opposite direction. The one reason that modern engines have such
00:41:10light pistons and get away with it, is that they no longer need a thick dome to act as a heat path
00:41:18carrying that combustion heat that's going in the top of the piston out to the cylinder wall.
00:41:24Yamaha went to a piston dome thickness of 11 millimeters when the FIM said no more leaded
00:41:32gasoline. And that meant you have to lower your compression ratio. Well, what if we could reduce
00:41:38the piston temperature? We'll make the piston really thick. Then they had to change the rod bearings
00:41:45as well. More rollers in there. So, once again, reality is so tiresome.
00:41:53But we don't have anything. What's the alternative? Alternative? Nope. So,
00:42:00modern engines are able to use thin crown pistons that are extremely light and which
00:42:07have minimum contact with the cylinder wall, which is what you want for low friction.
00:42:11Because they have oil cooling jets squirting up at the underside of the piston dome.
00:42:17And the benefit.
00:42:18Yes. You'll find them on Harley Davidson big twins. And there's even a precedent
00:42:27among the Harley faithful in the form of Tom Sifton, who when he had the traditional
00:42:36the traditional cylinder distortion problems with the racing flatheads of the time,
00:42:45he thought, well, aviation fellows uses piston cooling oil jets now.
00:42:51I think I better give that a try. Lo and behold, it worked.
00:42:58Because evidently, we all live in the same reality. Oil cooling works there. Probably work
00:43:05here. So, when I think of spraying oil at the bottom of the cylinder, we're gaining a great
00:43:10benefit. But it's also contributing to something else. Another heat generating phenomenon called
00:43:18windage. And so, this is another this is something you just don't think about. But the oil flinging
00:43:26around. My related story is rebuilding the transmission in my 1971 Triumph TR6 car.
00:43:33I put I did all I measured all my synchro clearances and I staked the bearing because
00:43:37the bearing staked the bearing housing because the bearing was a little hogged out. And I didn't
00:43:42know about green Loctite, but I put a new bearing in a state that fit pretty good. And I thought,
00:43:47man, I'd love to see what goes on inside there with this thing running. So, in a triumph, you
00:43:51can take off the tunnel, the tunnels, cardboard, I glassed fiberglass mine to make it so that I
00:43:57didn't die of asphyxiation from carbon monoxide poisoning. I made a good seal, but I took it off
00:44:03and the transmissions there and I left the top off and all the gears there. And I just stuck my
00:44:07finger in the selector and I said, well, I'll stick it in third gear. So, I stuck it in third
00:44:12gear, made sure that the selector was in a good position and it wouldn't move. It was on its
00:44:16detents, fired it up, let the clutch out. I'd wrapped the transmission with saran wrap so that
00:44:22I had a window and I'm like, I don't know what's going to happen, but there's a lot of oil in here.
00:44:28And I revved that thing up and I could not believe the violence of what was going on,
00:44:33of oil flinging everywhere and churning through the gears. And I was like,
00:44:37holy cow. I was like, how come a transmission can leak out the top? Well, that's why it can
00:44:41leak out the top because it's just flinging everywhere and inside the engine with oil
00:44:47flipping around and mist and everything. And every time a part contacts oil in space,
00:44:53it's making heat in the combustion or in the crankcase. Here comes the pitch, a blob of oil.
00:45:01Click, you hear it connect. And windage and oil control inside has had some very
00:45:07exotic solutions. It got really worse for those big twins with the giant round flywheels.
00:45:16Harleys and Indians. And Dick O'Brien, that former Harley racing manager,
00:45:25said that they called it wet something or just something, which meant that instead of the
00:45:33scavenge pump picking up oil as it was flung off from the bearings and returning it to the oil
00:45:41tank, it was somehow accumulating until the close-fitting flywheels picked it up and it was
00:45:48dragged through the small clearance between the OD and the faces of the flywheels and the inside of
00:45:54the crankcase, which means it turned into a high RPM viscosity measuring apparatus.
00:46:02And O'Brien told me, he said, you could see it at Daytona. He said, it was like a big invisible
00:46:11hand came down and said, no, you don't because the motorcycle would just. And so he said, we had
00:46:22many innings of struggle to overcome that. And when Kawasaki in mid-seventies designed its
00:46:36KR250 Road Racer, it was a tandem twin. It had two crankshafts that were geared together
00:46:43and it did not. Sounds like trouble. Yeah, it did not have a, it wasn't built on a production model.
00:46:54So there was no kickstart. There was no extra bulge in the crankcase where the kickstart fit.
00:47:02Well, in prototyping, prototype running, those engines had black paint on the magnesium crankcase.
00:47:09They burnt the paint off the gearbox, off the crankcase. Well, the two cranks were joined
00:47:17together by four inch gears and the gears, the meshing speed was 12,000 feet per minute.
00:47:26And the classic idea of how to lubricate a gearbox is to fill it up to the shaft center line.
00:47:32So what was happening was that many horsepower, and each horsepower is 746 watts.
00:47:42Many horsepower was being transferred to the oil and then to the inside of the cases,
00:47:49which got so hot that they burnt the paint off. So their idea was to do what RD350 racers
00:47:59since time immemorial have done. Go out for first practice with 1700 cc's in the gearbox,
00:48:07because you want oil to be splashed everywhere if it's a fresh build. Then after first practice,
00:48:13drain it out, replace and rewire the drain plug and put a cord in.
00:48:20And that made the problem less severe.
00:48:26And I thought I should build a little weir around the phasing gears in my KR250.
00:48:34And I drilled a one millimeter hole in the bottom to let oil in. And just enough would be filling
00:48:41up all the time that the tips of the gear teeth would touch that and fling it about.
00:48:47And fling it about. But ideally, ultra high speed gearing should be lubricated with air oil mist.
00:48:58And short of that, a small oil jet into each mesh. And that's just what you'll find on Kevin Schwantz's
00:49:10RG based Suzuki racers. You look at the top of the gearbox and you'll see
00:49:17a ridge going across right to left. And they're plugged, six plugged holes there.
00:49:24The drill went through and then the tops where the drill came in were plugged. So now that
00:49:31oil gallery has six jets, one for each mesh. And you'll notice that many bikes have
00:49:39limited access to the primary gears. The gear oil or the engine oil can't reach the primary
00:49:47gears in large volume because they will just chew up horsepower like you wouldn't believe. So
00:49:54ideally, we'd like to have just this little piddly stream of oil going in there. That's all those
00:50:00things need. Strategic lubrication, oil jets on the piston, strategic cooling. You know, you would
00:50:08talk to me about the story of like, well, some water is good for water cooling. Let's make these
00:50:12water jackets huge and it'll work great. And in fact, there was no turbulence. There was nothing
00:50:17to take the water away from the heat source. And so when they made them compact and you were
00:50:23forcing water through, it tumbled around and it took a lot more. Much better. Yes, you want
00:50:30turbulent flow because if you have laminar flow, it means that the layer of water slowly drifting
00:50:36along the hot surface is not being replaced by cooler water from in the middle of the flow. So
00:50:44that thin layer gets very hot and cooling decreases because it decreases the temperature
00:50:52difference between the hot thing and the cool coolant. So early engines had these great big
00:50:59water jackets. They soon learned better. Oh, we need velocity in there. And well, maybe velocity
00:51:07isn't the end of the story either. So they made water jackets with plexiglass windows so that
00:51:14they could look in and, oh, look, nothing's happening here. Just whirling around in one place.
00:51:20So a lot of work goes into making a successful water cooling system. It's a lot more than just
00:51:27surrounding the hot parts with basically a pot of water. Well, I observed turbulence
00:51:35in college with a friend of mine who was disappointed by the warmth of his unopened beer.
00:51:42And he went to the cooler and stuck it in there and constantly rotated it.
00:51:46Yeah. So that it would cool faster and he can he can enjoy his. You bet. And of course, we all
00:51:53beverage. We all know intuitively the boundary layer because you run a hot bath and you think,
00:52:03man, that's going to be comfortable. What do I read? And got the bath ready. Yeah, that's
00:52:11that's almost too hot. Just what I want. And I put my cold self into it and you lower yourself
00:52:17into the water and you're delighted for about three minutes and then you feel.
00:52:26Something's happened here. I don't feel good anymore. So you stir around a little bit and
00:52:33now you feel better. Oh, OK. Now that's how it's supposed to be. Well, what's happened is
00:52:40there's very little water velocity in the bathtub and the water next to your skin.
00:52:47From colliding with your cooler skin, loses energy and forms a stagnant cool layer,
00:52:56which is no longer heating your skin. And now you're pretty unhappy about it.
00:53:02So finally, you have to turn on the hot water and paddle furiously to get that hot water in
00:53:08contact with yourself. Well, any vehicle that is moving through the air, an artillery shell
00:53:14or an airplane or what have you, this boundary layer gets thicker and thicker the farther the
00:53:21flow travels along the surface. And it's a very simple thing. The fact is that air colliding,
00:53:30air molecules colliding with the less energetic or actually it depends on whether you're traveling
00:53:38with the vehicle or standing next to it. But there's an energy exchange which causes the
00:53:45vehicle to drag a layer of air along with it. And it moves very slowly. And it was said that on the
00:53:53Great Zeppelins that there was a hatch, a companion way with a hatch at the top where you could
00:54:03emerge at the top of the aft end of the gas envelope and have a look around.
00:54:11And it was like the thing's going 60 miles an hour and you don't feel a thing because you're
00:54:16in the boundary layer. The thing is 750 feet long. So it can accumulate a hell of a boundary layer.
00:54:25And that's also why when you see a P-51 Mustang, the intake to the cooler,
00:54:30which is under the fuselage and just behind the pilot, there's a gap between the entry and the
00:54:38bottom of the fuselage. That is there so that none of that slow moving boundary layer is going to go
00:54:44into the cooler and be wasted because it doesn't have the energy to carry its weight. You want
00:54:55full ram air pressure, not a low energy feeble boundary layer. So you'll see those gaps on a
00:55:03lot of vehicles that are trying to scoop high energy air. It sounds like the reason we have
00:55:09jets and hot tubs as well. You got it. Absolutely. That's why a hot tub has those jets because
00:55:16the water temperature, once you get it right, those jets are going to see to it that that
00:55:22boundary layer is scoured away. Just like I talked about the boundary layer in the exhaust
00:55:28port being scoured away by the sonic flow. Boundary layer is scoured away. Temperature
00:55:35difference between your skin and the warming liquid is high. And so is your delight.
00:55:42Delight, indeed.
00:55:49But there are all sorts of things that require dealing with heat. For example, brakes.
00:55:58It used to be when drum brakes were nearing their end that the drum would expand. Kawasaki had some
00:56:05experience with magnesium drums. The drum would expand and the spokes would get loose and the
00:56:11rider would say, this thing handles like poo-poo. And then the team manager would come over and say,
00:56:20nothing wrong with it. Spokes are all tight. Everything's fine. Get out there and do your job.
00:56:27And so the problem with drum brakes was that you're putting heat into this ring of material,
00:56:35which is restrained on one side by the structure of the wheel. And so the ring is going to open up
00:56:44like in a sort of bell mouth fashion. And pressure from the brake shoes is going to be more like
00:56:54edge contact. So they came up with disc brakes. The disc can't get away. There's a pad on either side.
00:57:01Well, I had a 1964 Cadillac with four-wheel disc brakes and it was really great for two stops,
00:57:11for two aggressive stops. And then I always described it as brake fade while you wait.
00:57:18It's just, you'd put it down and then it would get worse as the heat, you know, just had
00:57:23nowhere to go and everything did. They were great big drums. They must have weighed, god, they must
00:57:27have weighed 25 pounds each. Huge finned iron drums. It was a beautiful braking system.
00:57:35And obviously we're not braking at the end of the Mulsanne straight and we're not doing that over
00:57:40and over again in the 64 Cadillac. But in the late 30s, the German Grand Prix cars, the
00:57:46Auto Union and Mercedes, they had enormous aluminum drum brakes, very large in diameter.
00:57:53And the drivers took it for granted that at about 30% race distance, you would have to start
00:57:59using downshifting for more and more of your slowing down for corners because the brakes
00:58:07were sort of saying, well, I did all I can and I'd love to help you, but that's how it is.
00:58:14Yeah. That expansion of material, you know, the early kind of the fixed mount discs.
00:58:21Oh yeah.
00:58:24Going cone shaped. I always thought about RDs. You know, I came to your shop years ago with
00:58:28the RD 350 and you were porting away and I'm working, chasing threads and doing all that.
00:58:33And I'm looking at the cylinders and there's gaps in the fins all the way around. And there's no
00:58:40reason for the gaps except to say, I bet that's where it cracked because the depth of the fin is,
00:58:46you know, inches. And so, you know, it's not going to...
00:58:50They interrupt the fins so that you don't have a ring.
00:58:55Inside is closer to the heat, so it's expanding more. The outside of the fins is cooler,
00:59:02so it's expanding less. So it's going to crack. So let's make gaps there.
00:59:11Take care of that. Well, in 78 at Loudon, we had this terrible problem with the TZ750
00:59:17that Rich Schlachter was riding. It was, something was pushing the brake pads back. He came in and
00:59:24he's gesturing and showing the brake lever coming to the bar. And I got out my 12 inch straight edge
00:59:35that I carry, carried, and slapped it onto the disc and there was a gap. The disc was cone-shaped.
00:59:46Well, it was flat when it was installed, so how did it become cone-shaped?
00:59:52What it turns out is the brake pads on those Yamahas were about two inches in diameter.
01:00:00So the outer part of the friction track was experiencing high horsepower friction because
01:00:10the velocity was high, and the inside of the friction track, lower horsepower, lower velocity
01:00:17of force times distance. So the outside of the disc was becoming very hot, and as it expanded,
01:00:27the inside of the disc elastically resisted that until it reached its elastic limit, and then it
01:00:34yielded. The outside of the disc physically stretched the inside to a larger diameter.
01:00:42Then when the disc cooled, the inside was too big for the outside, and the only thing it could do
01:00:48was to pop into a cone shape. And so we got floating discs so they weren't anchored
01:00:55by firm bolts at their centers to hold them in place, and then what did we do? We made
01:01:01the friction area short, narrow from top to bottom. So that the velocity friction,
01:01:08rubbing velocity, was not so different between the ID and the OD of the friction track.
01:01:15And what I did that night, I rushed home in my silly old six-cylinder van,
01:01:26getting 17 miles per gallon, and I cut radial slots in the discs, and I terminated them in
01:01:32drilled holes so that there was a radius at the tip of each saw cut. Now don't try this at home,
01:01:41because if you're like me, you're worried to yourself, I've shown this disc a crack,
01:01:48what if it likes it? What if it propagates it inward until pieces come off? Well,
01:01:55all kinds of military aircraft have brakes that have separate segments to their brake rotors,
01:02:02so there's a tremendous clattering when they're taxiing, all these separate pieces. Anyway,
01:02:10it worked. The next morning, well, when I made the saw cuts, the disc flattened out
01:02:16very satisfactorily. And the next morning, first practice, no brake troubles. This is so wonderful,
01:02:24because in racing, so many things that you try just don't work. The race bike looks back at you
01:02:32like, did you want something? What are you trying now? And the rider comes in and says, well,
01:02:44maybe it was a little better, and you know, he's being polite.
01:02:48But this was a case of something that actually worked, and I was delighted.
01:02:53Such a good feeling, such a good feeling, yeah.
01:02:55So the permanent solution, of course, was to make the friction track narrower, and to mount,
01:03:04to make the disc mounted in floating fashion on the carrier, so that it could expand however it
01:03:11liked, and without being hotter at the outer edge, cooler at the inner edge, to such an extent
01:03:19that it worked. So that was another. On another occasion, this is for the people who believe that
01:03:27they can gain eight horsepower by replacing all their ball bearings with ceramics.
01:03:38We had a cast iron disc on the back of a big Kawasaki, and it was mounted to the hub.
01:03:49And the rider went out and melted all the grease out of the wheel bearings with that brake.
01:03:56Melted it all out, gone. Now, normally, wheel bearings don't get hot enough to melt all their
01:04:05grease out, so I conclude that each wheel bearing is not consuming one horsepower. Undoubtedly,
01:04:10it's consuming something, because the bearings get warm. But 746 watts? I don't think so.
01:04:20Anyway, I made an insulating mount for the brake disc, and the grease stayed in the wheel bearings.
01:04:27And the modern motorcycle is the result of all these little steps with people like myself who
01:04:37said, I've got to come up with something for tomorrow. And that business of the radial slots,
01:04:44I took that from Norton clutch plates that I'd seen that had radial slots in them,
01:04:49for the same reason. You'll notice, by the way, that clutch plates...
01:04:56Some of you haven't ever seen a clutch plate, I'm sure, because this is the new century.
01:05:01But clutch plates, the friction surface is radially very small. It's just a narrow track,
01:05:08and that is done for the very same reason that I just described causing the coning of brake discs.
01:05:15So, every time that energy changes form, a tax is imposed on it, and it usually is paid in the
01:05:27form of heat. And that was the case with brake disc failures. In the case of rear suspension
01:05:38units, there was a mad craze for making everything possible out of aluminum. And what happened was,
01:05:46unwanted suspension energy is turned into heat as the damper piston forces oil back and forth
01:05:55through small orifices. Result, the damper fluid gets hotter and hotter.
01:06:03The body of the damper becomes hotter and hotter. Oh, a gap has appeared between the piston
01:06:10and its bore. The damping has gone away. Bumpity bump. So, people designing suspension dampers
01:06:21took steps to make sure that whatever form of seal was made between the piston and the cylinder,
01:06:27damper getting hot didn't leak. So, any place you look, you'll find
01:06:39this tax being imposed on transformations of energy. Oh, I'm charging my laptop.
01:06:45That's very comfortable. I'd like to have that on my lap. It's like having a pet cat.
01:06:52There is the charge-discharge efficiency, which can be as low as 70%. You're
01:06:59putting energy into the battery to charge it, but you're having to overcome
01:07:05electrical resistance in the various elements of the battery, and that resistance is turning the
01:07:12flow of current partly into heat. So, once again, reality has to be dealt with.
01:07:24The reason that I was originally very interested in racing cars, and I turned to
01:07:34motorcycles because they were in my scale and within my financial reach. I think that's
01:07:41true of a lot of people, and I think the motorcycle is a marvelous study in so many
01:07:49different subjects, and I've enjoyed that all my life. Same. Yeah. The dynamics, the working on
01:07:57them, the problem-solving. Solving that problem and getting what you came for, or more of what
01:08:04you came for, really. Yes, getting more, and of course, waste is offensive. It is.
01:08:11When Pratt & Whitney was developing their geared turbofan, an engine for large commercial aircraft,
01:08:21the fan provides most of the propulsion, and it has to turn slowly, but the power is coming from
01:08:29a turbine, which likes to turn much faster. So, they usually compromise. They make the turbine
01:08:36very large so that the gas has more leverage with which to turn the shaft, which is turning at a
01:08:43lower speed to drive the fan, but both are losing efficiency. So, they said, let's bite the bullet.
01:08:52We'll put a gearbox between the turbine and the fan, three-to-one ratio,
01:09:00and what they came up with was 13,000 horsepower is going to drive the fan during takeoff,
01:09:08and the power loss in the reduction gear is 100 horsepower, or seven-tenths of a percent.
01:09:19Very small loss, and I think that's wonderfully admirable. You know that the dyno people are
01:09:27always saying, well, it's a 15% loss between the crankshaft and the instrument in the office here.
01:09:36Well, that's vulgar. That's nasty. Primary gear, maybe 2%, transmission gears,
01:09:48maybe another 2%, chain, maybe another 2%. You know what I think? That 15% loss comes
01:09:55from tightly strapping down the back wheel of the motorcycle onto the roller.
01:10:01There's so much rubber flexing going on, most of that power loss is back there.
01:10:08We'll have a look at that. We don't overly tighten down our bikes on the Cycleworld dyno.
01:10:13We dyno almost everything that comes through. We're consistent about what the tire pressure is.
01:10:19Yeah, you have to be, because that's working with instruments.
01:10:22And we strap it down, I want to say, just right, because we're doing a chassis dyno,
01:10:28we can't have slip, so we have to balance slip versus overdoing it.
01:10:34Yeah. There's another one, which was when the British rubber industry began applying the
01:10:48wartime discovery of synthetic rubber to automobile tires, they found that butadiene styrene rubber
01:10:57could, if it were in the proper mixing ratio, give extraordinary grip, especially wet grip,
01:11:09but also increased dry grip, such that when they made race tires for cars out of it,
01:11:17the race car lost several miles per hour in top speed because that type of rubber has a lot of
01:11:23internal friction. That internal friction was acting to produce greater grip through the corners
01:11:32so that the lap times improved by seconds. So once again, you have to make a deal with Mother Nature
01:11:42in order to get what you want. Yeah, we like impressive top speeds, but
01:11:47we also want to be ahead at the end, so we're going to go for lap times.
01:11:54Well, thank you for listening, folks. We really appreciate it. This episode is graciously
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01:12:37We hope we have contributed to the terrible signal-to-noise ratio found on the internet
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01:12:55that as well. Get in the comments. This discussion and one that's forthcoming about fuel types and
01:13:03so forth have come from the comments in our podcast. Anyway, we love hearing from you and
01:13:09carrying on that conversation there. Thanks again for listening, everyone. We'll see you next week.