- 9 months ago
Kevin will start with atmospheric intake valves and someone from the 1800s, but for real we are talking about Overhead Cams here. Why has OHC become the standard for four-stroke-engine valve operation and what are its advantages. Also, you won't believe how old the technology is. Join Kevin and Mark for the bumpy world of cams above the head.
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SportsTranscript
00:00:00Welcome back to the Cycle World Podcast. I'm Mark Hoyer, Editor-in-Chief.
00:00:03Kevin Cameron, our technical editor, is here with us.
00:00:07We're going to talk about getting to overhead camshafts. How did we get there?
00:00:13Why do we use overhead camshafts? Why don't we all drive flatheads or big old
00:00:17crossed-over pushrods or parallel pushrods?
00:00:23You know, why do we do it, Kevin? Why?
00:00:26Well, at the beginning of any new enterprise, some new technology, there can be a million ideas.
00:00:40And the reason for this is no one has yet established the relative value of those ideas.
00:00:48It won't be long, though, two years, maybe, before it's clear that you can't make any money doing
00:00:56this category. And you might break even with this category. And everyone's jumping on doing it this
00:01:04way because it works, and it's affordable, and it's reliable enough for sale. So the thing is,
00:01:16it's easy to sort of try to focus on who invented something. But in fact, invention does not occur
00:01:27because someone invents. That is, awakens at four o'clock in the morning, shouts Eureka in a
00:01:35penetrating voice, and runs out into the winter, declaiming the new era. New inventions arise from
00:01:46need for them. I don't, I didn't like history in school, because it seemed to be an endless
00:01:56series of dates, kings, and battles to be memorized for the hour exam, giving no understanding whatsoever.
00:02:08So we could say that Boris Lutsky, in 1888, invented overhead valve, because he wrote about it
00:02:21then. And he wrote about it, presumably to an audience who understood what he was talking about. So
00:02:29the ideas were already in the air. People were thinking and talking about a thousand ways to do
00:02:37internal combustion. Now, terrible fuel was the rule in the early days, because nobody knew what
00:02:50destructive combustion was caused by. So as a result, when you bought gasoline, it was about,
00:02:57had an octane number of about 30. And it knocked so easily that engines had to be given
00:03:07very low compression ratios around three to one, like the Ford's Model T. And that meant that with
00:03:16the piston at top dead center, the volume of the combustion chamber was half the displacement of the
00:03:23cylinder. Wow. And that gave you a huge amount of real estate, which you could squash and squeeze
00:03:30into any shape you liked. You could put, poke valves into it. You could put the valves next. Here's the
00:03:36piston rising and fall. And you could put the valves next to it on one side, on both sides, on four sides.
00:03:44This era from 1900 to 1912, saw rapid fire changes. I mean, year by year, ideas would be discovered,
00:04:00discarded, discarded, replaced. And there were tremendous number of combinations that were tried.
00:04:13One of my favorites had, I believe it had eight exhaust valves, little tiny ones located
00:04:20on the two sides of the cylinder with the gigantic intake valve directly over the piston.
00:04:28Was that cam operated or atmospheric?
00:04:31That was atmospheric. That was sucked open by a light, against the light spring by the descending
00:04:37piston. Or as...
00:04:39Yeah, no cam, no overhead cam, no underhead cam.
00:04:42No cam. No mechanical cam. And it seems logical. It seems, you know, if you're just standing there
00:04:49going like, well, that makes sense because the piston's going to ask for it. But no,
00:04:53it doesn't make sense at all once we figured that out.
00:04:55But reed valves are still with us, which operate in the same fashion.
00:04:59That's so true.
00:05:02So reed valves have even been tried on four strokes as a way of being able to run really long,
00:05:09racy valve timings and still be retained drivability at, uh, away from the stoplight speeds.
00:05:18So here's this problem. We're going to build internal combustion engines in those early days,
00:05:25that low compression, you could build them any way you liked, but the simplest way, which was defined
00:05:33by the Count de Dion and his man, Georges Bouton, was to cast the cylinder and the head of a four-stroke
00:05:46engine in one piece with a side pocket that had the exhaust valve in it with its stem pointing down.
00:05:56This was rational because down is where the crankcase was, where the lubrication was.
00:06:03So it was possible to operate the exhaust valve by means of a cam that was lubricated reliably
00:06:10down in the crankcase. The intake valve would be on the same axis, but with its stem up. And it was
00:06:18in a little lighthouse that screwed into the hole through which the exhaust valve seat and the exhaust valve
00:06:28guide were machined. These people were thinking in terms of manufacturing costs. By 1900, these clever
00:06:38lads had sold 20,000 engines of this type.
00:06:42Yeah, they were in everything. They were used all over. Everybody around the world suddenly had a power plant
00:06:48that had some modicum of reliability and repeatability and the way they went building things to carry it.
00:06:54If you go to the Hammonsport, New York Curtis Museum, you'll see a bunch of these. Intake over exhaust,
00:07:02I-O-E, sometimes given as suction over exhaust, S-O-E. And Harley's name for this was pocket valve
00:07:11because there's this pocket that is sticking sideways out of the main combustion chamber
00:07:18with the exhaust valve on the bottom and the automatic suction operated intake directly above it.
00:07:25Well, your point about the lubrication of the cam, it's not just the lubrication, right? It's the oil
00:07:29splashing around keeping the exhaust cool and then intake air is keeping the intake valve cool.
00:07:35Yeah. So there's another thing here that's an accidental point is that the fresh
00:07:42charge coming in through the intake valve flowed over the exhaust valve, thereby cooling it. So
00:07:51De Dion and Bouton were both clever and lucky. And they had a viable business that went on for years.
00:07:59And you didn't need much else. Harley-Davidson continued with the pocket valve engine,
00:08:11intake over exhaust, until replaced it with a side valve exhaust and intake beside the cylinder,
00:08:20stems pointing down, in 1929. So this is why I say that the history of invention is a history of necessity.
00:08:37So next, we're going to talk about the difference between the driving force behind automotive,
00:08:46automobile technology and that of motorcycle technology. Automobiles were at first sold to Vanderbilts
00:08:58and Rothschilds, extremely wealthy people. This was a new way to enjoy themselves. They might race their
00:09:08their speedboats on Monaco Harbor, the bottom of which is presumably littered with early hardware.
00:09:17Maybe it's been dredged. But these wealthy people were highly competitive with one another and
00:09:29And gigantic and extremely dangerous long distance city to city races were the first form of motorsport.
00:09:41And what those races did was they showed the motor car to millions, literally millions of people
00:09:50across Europe. The motor car is practical. Look, it's still going. Amazing.
00:09:58And consequently, when the new idea came along, a way of doing it better, more safely,
00:10:10getting greater performance, the money was there to support its exploration.
00:10:17The motorcycle was a huge contrast. It was the cheapest way that a person could become a motorist.
00:10:25You could taste internal combustion engine power. The British journalist who called himself Ixion,
00:10:34writing in 1950, said that his early motorcycle, built in 1898, typically caught on fire every time
00:10:45it fell over because its ignition system was hot tube.
00:10:49A platinum tube passed through an insulating thimble into the combustion chamber where its closed end
00:11:00was exposed to the fresh charge. The outer end was kept hot by a flame.
00:11:06The heat of the flame. The heat of the flame was conducted into the combustion chamber to create a primitive glow plug.
00:11:16So the piston comes up on compression. And if you've got the mixture right,
00:11:20and if a lot of other things are right, the glow plug ignites the charge and off you go.
00:11:29But it's easy to see why you would, your bike would catch fire when you fell over because
00:11:35the, there had to be fuel and there was flame.
00:11:40Combustion, external combustion.
00:11:45Well, external combustion, you knock, you know, you knock over carbureted bike, you get fuel a lot of
00:11:50times anyway, even on, you know, a good old modern Makuni or something, you get fuel everywhere. And
00:11:56imagine that carburetor, surface carburetor, you know, because the carburetor, even the modern carburetor has
00:12:04float bowl vents. If the, if the motorcycle falls over, there will be some gurgling of fuel through
00:12:11those vents. Anyway, um, those early motorcycles were kept simple, one speed. They had pedals.
00:12:25They, they talked about light pedal assistance, but Ixion said, in fact, you pedaled until you
00:12:34could taste blood because the weak little engine constantly needed the riders heaviest possible
00:12:43assistance. Anyway, that was the basis of early motorcycling. And those people were super
00:12:50enthusiasts because if your bike caught fire today, every time it fell over, how long would your
00:12:56enthusiasm last? That's hard to say. But in those days, they were madmen and women. So,
00:13:06meanwhile, an avalanche of progress is taking place in motor cars. And one of the things that was
00:13:16adopted fairly early was the T-head. Anyone who's had an old Gravely tractor will remember
00:13:23that it had a side exhaust on one side of the cylinder and a side intake on the other.
00:13:30So the cylinder head was in effect T-shaped.
00:13:34And there were all kinds of engines that were built this way with valves pointing stem downward
00:13:42toward a camshaft that was located in the upper crankcase half where the oil was splashing.
00:13:48This kept everything happy. And T-head was the hot setup for a long time.
00:13:58And
00:13:58The next step was overhead valve. Now, why would anyone put valves in the cylinder head operated
00:14:11by machinery that was out in the open? Push rods, rocker arm valve and at the stem of the valve,
00:14:18you could look through the coils of the spring and see it there.
00:14:21It meant that you had to stop every little while, get out your oil can and lubricate the parts that needed it.
00:14:30Who would want such a thing?
00:14:33Well, these, the side valve engines, particularly those that had the exhaust on one side and the intakes on the other.
00:14:42Those side pockets could hide little pockets of very hot combustion gas so that when the next intake stroke took place,
00:14:59it's in there swirling around in its little pocket, but not being flushed out.
00:15:04The piston comes up, piston comes up, some form of ignition, ignites it, and
00:15:14or the hot gas in the pocket ignites it. And you get premature high pressure in the cylinder, overheating, and an engine wreck.
00:15:23So Harley Davidson gave another reason for needing to replace the pocket valve because as time passed,
00:15:37there were fewer and fewer pattern makers who were willing to accept the going rate for a working person,
00:15:45a factory worker, for doing a really arcane piece of work,
00:15:51positioning all the core so that this one piece head and cylinder could be made accurately.
00:16:00So they wanted to cut costs.
00:16:03One of the things that Boris Lutsky talked about in 1888 was
00:16:09that the chamber is like a round bottomed cup with short straight sides.
00:16:18And that's what he built. He put one valve at the top and one valve sticking out the side.
00:16:26It was convenient. The way he was doing it, it was convenient for him.
00:16:32And it worked well enough, no better than anything else, because on three to one compression, how would you know?
00:16:40So all these ideas being tried.
00:16:47But what was the killer was that it's very difficult for air flowing up from a carburetor
00:16:53to an intake valve at the side of the engine, making all these twists and turns to finally get into the cylinder
00:17:03and follow the piston on a suction stroke.
00:17:06The early?
00:17:07Yes.
00:17:09Or...
00:17:10The pocket valve, the intake valve at the top of its little cage,
00:17:20the whole cage was sealed and there was a pipe running from it to the carburetor.
00:17:27That valve was small because a big, heavy valve,
00:17:32atmospheric pressure differences caused by the piston suction stroke
00:17:38weren't going to move it against the spring that it needed to keep it closed.
00:17:42So those valves were small and they were restrictive.
00:17:45So when they began to put valves in the cylinder head, there was a big performance increase
00:17:52because the breathing was so much better.
00:17:55And Harley Davidson, again, discovered this.
00:17:59They knew it was happening because they were developing it.
00:18:02When the 61E was put on the market in what, 37, 36, somewhere thereabouts.
00:18:11At some point where the US economy was recovering a little bit and recovering more because a lot of
00:18:21companies were getting military orders from abroad.
00:18:26So there was a, there was optimism.
00:18:29And Harley was willing to gamble on a completely new product, replacing not only their pocket valve,
00:18:35which came to an end in 1929, but also the expensive Ricardo license they bought to build their flatheads.
00:18:46The flatheads had not turned out to be good at steady, high duty.
00:18:53And they tried all kinds of things.
00:18:55They, they began to make progress by casting steel struts inside the piston that physically stopped it from expanding and seizing.
00:19:06So, Harley put the two valves in the cylinder head.
00:19:13On the 61 inch, that's one liter, thousand cc's V-twin at the sacred 45 degree cylinder V angle.
00:19:24And it doubled the power.
00:19:27So that was the big attraction of overhead valve.
00:19:31It doubled the power.
00:19:33These early automobile racing engines, the, the simplest way to increase power was to make the thing huge.
00:19:43And you've probably seen the film of the 28 liter Fiat, uh, with flames shooting out of its exhaust ports.
00:19:56The beast of Turin.
00:19:57The beast of Turin, whose stroke was so long, it made the bonnet of the engine too tall for the driver and riding mechanic to see over it.
00:20:08So they had to look past it.
00:20:12Sort of like trying to land a, an F4U Corsair on a carrier.
00:20:17That big radial engine is up there.
00:20:20There's what carrier?
00:20:21There's no carrier here.
00:20:22They have a fuel tank between the pilot and the engine also.
00:20:26So, yeah.
00:20:27So, yeah.
00:20:27And then they, they ran the big one.
00:20:29They ran the 4360 on the end.
00:20:30That was the super Corsair.
00:20:32I don't know if that saw combat or not.
00:20:34Do you?
00:20:34It did not.
00:20:35F, F2G.
00:20:36Yeah.
00:20:37Yeah.
00:20:37They put the big, the big honker on the end of it there.
00:20:40That's pretty cool.
00:20:41That was an early one.
00:20:433000 horsepower.
00:20:45Um, anyway, um, the strokes were tremendously long.
00:20:51They could be eight or 10 inches.
00:20:54The stroke.
00:20:55So these engines were tall, which meant that if the camshaft is in the upper crankcase and there's tappets at each cam lobe, the push rods are a mile long.
00:21:10And this was okay when they first began building these things.
00:21:15They're running 1,000, 1,100, sometimes 1,200 RPM.
00:21:21Uh, World War I aircraft battles were fought at 1,200 RPM because the means to operate faster didn't exist yet.
00:21:34Uh, and if you let the propeller tip move so fast that it moved faster than sound, there were great losses.
00:21:42So, uh, what I saw in looking at photographs from this era is that over time, these overhead valve engines, tappet guides got taller and taller until they were more than one third the length of the push rod.
00:22:03And it made me suspect that they were having trouble with not only longitudinal vibration of the push rods, but lateral.
00:22:13Well, and they were trying to push open the valves through a stack of springs, the push rod was a spring, the rocker arm was a spring, and the valve springs are a springs.
00:22:27And as the RPM level was rising, turning higher RPM means that you're performing more power strokes per second, and that's more power.
00:22:41So, they made them huge.
00:22:4415 liters, 14, 15 liters was the size of a race car engine, four cylinders.
00:22:51Why not six?
00:22:53Because the early sixes that they built, the crankshaft was so long that it's torsional vibration, rattled the valve gear and broke the crankshaft.
00:23:03Good reason not to do it.
00:23:06Well, the early explorations.
00:23:08Yeah, the earlier explorations of crank damping that I've observed, like in late 30s, Rolls engines, for example.
00:23:18There's a monograph on this that Rolls put out.
00:23:20Oh, gosh, the crankshaft, the crankshaft damper is a multi-piece sandwiched.
00:23:27It's like a clutch.
00:23:28Clutch with a, yeah, with like a cotton canvas sheet in it.
00:23:33And then you torque, you build the thing up with all these stacks and layers, and then you put the damper in your vice, and then you take a torque wrench or a fish scale, and you measure the breakaway torque of the damper mechanism.
00:23:51And if it isn't right, you tear it all back down, and you shim it again, which is England, in a nutshell.
00:23:59That same car, it reminded me earlier of that same car that I was looking at, the updraft carburetor.
00:24:05And then the intake, it was on the opposite side of the intake valves, the carburetor was.
00:24:13It would come up the carburetor.
00:24:14It would go through the engine block, I'm assuming for heating, to heat it.
00:24:20To if that breaks the fuel, yeah.
00:24:21Right, so it's coming updraft, it's turning horizontally to go through the engine to, I think, warm the mixture, and then it does another 90 degrees to go up again, and then it goes down each direction to the cylinders in the distribution of inlet fuel mixture.
00:24:39I mean, what a journey.
00:24:40We're not revving high.
00:24:41Yes, no.
00:24:42You know, it's fascinating that, you know, high-performance cars of the 50s and the 60s started getting overhead cams, but like a Rover, you know, the Rover P5 with the 3-liter inline-6 was an inlet-over-exhaust that they made, I think, until 1967.
00:25:03Yeah.
00:25:03And I also, I think the 2.25-liter Land Rover engine was similarly hanging on to an inlet-over-exhaust.
00:25:11Wonderful.
00:25:12For a long time.
00:25:14So, I'm theorizing that the reason they made the tappet guides taller every year is to make the bouncy, longitudinally compressible pushrod smaller.
00:25:30And the ultimate goal of such a maneuver would be to make it smaller until it disappeared.
00:25:35So, everybody, everywhere knew about overhead camshaft.
00:25:44Overhead camshaft engines had been built in numbers.
00:25:48In 1905, George Widely, of the premier motor company here in the good old USA, built this gigantic air-cooled four-cylinder overhead cam, hemi-head engine.
00:26:05It was never raced for various administrative and financial reasons.
00:26:10Widely himself went on to become a Cadillac engineer.
00:26:13He worked there for years.
00:26:151905.
00:26:17And I think that Hans Ledwinke built an overhead cam engine for the Prince Henry trials in Germany.
00:26:27That was an important event at one time.
00:26:30So, here we are with this vibrating valve gear, which is making a problem.
00:26:42And they're trying to make the tappet guides taller because the tappet itself is a steel rod with a roller follower, usually, at the bottom of it.
00:26:55And it's inside of a cast bronze tappet guide, so it can't vibrate laterally, and it's too thick to vibrate much longitudinally.
00:27:07And here is this little lunchroom straw of a pushrod that is bouncing and doing all kinds of terrible things.
00:27:19Well, at a point, three experienced racing drivers, men who had driven every kind of car and taken a technical interest in what they were driving
00:27:35and knew all about the mechanical, three racing drivers, and a talented draftsman engineer from Switzerland, Ernest Henry, went to Peugeot, and they said,
00:27:51we think all these highfalutin people are doing it all wrong, and we'd like you to give us money to do it right.
00:28:02Who's going to believe them?
00:28:05Peugeot.
00:28:07And the thing was built.
00:28:10This was in preparation for 1912.
00:28:13What did it have?
00:28:14Four valves per cylinder, double overhead camshaft, and the valve stems, instead of being vertical, as they were in the Fiat of just one year previous,
00:28:28we're inclined to part in a way that allowed room as you make the combustion chamber into a pyramid, this distance here becomes greater than half of the bore.
00:28:45So you have room for bigger valves, should you need them at the higher RPM, you expect to be turning next year.
00:28:53This wonderful machine, 7.6 liters, entered for the French Grand Prix in 1912.
00:29:04The opposition, the opposition, the leading opposition was a 15 liter Fiat.
00:29:11And it was nearly a dead heat, but the Peugeot prevailed.
00:29:19It won the race.
00:29:20Two years later, there were no French Grand Prix's in the intervening.
00:29:30But in 1914, almost every car on the starting grid had an engine that was a dead copy of the Peugeot.
00:29:45I liked what you said earlier, closely resembled.
00:29:51Yes.
00:29:53And in 1913, a Peugeot of this type was imported into the United States, and it was wrecked.
00:30:00And I believe the driver was a fatality.
00:30:05There's a famous photograph of the car on three wheels with one wheel broken off and everything is smashed.
00:30:12Harry Miller, whose construction of engines would ring down throughout American racing history as the Offenhauser,
00:30:25was called upon to reconstitute the Peugeot engine.
00:30:31Hmm.
00:30:32I wonder why they did it that way.
00:30:34This is interesting.
00:30:35Guys, have a look at this.
00:30:37The seed was planted.
00:30:40This was a system of made up of parts that everybody knew about, but they had never been,
00:30:50this particular synthesis had not been tried in public.
00:30:56And when it was, it prevailed over a car whose displacement was twice as great.
00:31:03That was the end for the giant racers.
00:31:05Now we get back to motorcycles.
00:31:11Motorcycles, as they do today, rely on the auto industry to bring new ideas into production so that they can have access to them at lower prices.
00:31:26Let the big, rich automakers pay the R&D.
00:31:32This is why we don't have direct injected two strokes now on motorcycles is because the whole industry decided we're going to go with whatever the auto industry finds saves them the most money.
00:31:47And it turned out to be the catalytic converter and the oxygen sensor with the closed loop mixture control.
00:31:58Just wonderful technology.
00:32:01Compare a 1977 U.S. automobile, its engine covered with cracking black hoses, any one of which could be leaking air and creating the dreadful symptoms that are keeping you from getting your car inspected.
00:32:16Well, the 1979 Lincoln Town Car that my dad bought new Cartier edition.
00:32:23I think the horsepower rating, it was a 460 V8 and the rated horsepower was 160 or 180 horsepower.
00:32:32And it was pretty torquey, but it was pretty sad.
00:32:35I mean, for what it is, I mean, a 460.
00:32:37That's barely more power than the starter.
00:32:41Yeah, a 460, my gosh, you know, like an unregulated 460 with a good intake and a cam on it is a 500 horse, 500 pound foot.
00:32:50No problem.
00:32:51I mean, just loafing.
00:32:53The bottom ends are worth like a stock bottom end on a 460 is something like 700 or 800 horsepower.
00:32:59Don't change anything.
00:33:00Just start building her up.
00:33:01So they were sad times.
00:33:04When you open the hood, there's a famous picture of, I think it's a Honda.
00:33:08It's gone viral various times in social media, but it shows this Honda engine compartment.
00:33:14And it's a vacuum hose map.
00:33:18And it's just a thousand miles of tubes going everywhere.
00:33:21And that's what they were using to control EGR and you have your map sensor and bleeding air into the, oh, clearing out the canister, you know, the revap can.
00:33:32It's just, oh, gosh.
00:33:35And running it through combustion to do away.
00:33:38Yeah, and we've made a lot of progress.
00:33:41EGR, you see it on diesels, but not so much on a modern car.
00:33:46Now, the 1912 Peugeot, that was such a revolution, drove its overhead camshafts by means of shaft and bevels, shaft and bevel gears.
00:34:00They discovered what everyone who uses shaft and bevels on a multi-cylinder engine discovers, that the shaft is so torsionally flexible that you can't trust anything.
00:34:12The very next year, the very next year, a train of spur gears.
00:34:17So these people were doing things quickly out of necessity.
00:34:23Now let's go look at what's going on in motorcycling.
00:34:27After World War I ended in 1918, racing resumed and overhead valve asserted itself directly.
00:34:43There were still some side valve engines racing in those years, but overhead valve soon became dominant.
00:34:51In 1927, AJS decided, okay, we're going to try overhead cam.
00:35:00They built an overhead cam, single-cylinder 350, and it was slower than the pushrod engine.
00:35:08So their first response was, okay, back to pushrods for 1928.
00:35:13But in the meantime, they are studying.
00:35:18And over at Velocet, what is this, 1924 or 1925, they had made two strokes mostly.
00:35:28And Eugene Goodman decided that they must switch to four strokes.
00:35:34And since he was aware that there were all these sort of amateur builders who were showing up at the Great Brooklands Speedway, south of London, with overhead cam, homemade overhead cam engines, he decided, that's the future.
00:35:52I'm going with going with that.
00:35:54And the story is told of his using strobe attack-like devices, that is, a timed strobe light whose timing could be adjusted so that you could produce a slow-motion visualization of the valve train.
00:36:14And you could sit there while the thing is screeching away on the dyno, staring at this new world of vibrating parts.
00:36:26We have to calm these parts down.
00:36:31And then we'll have something great.
00:36:34So they are, a fellow came up with an overhead cam.
00:36:42They had the usual troubles that everyone had with an overhead cam because how are we going to lubricate it?
00:36:48How are we going to get the oil back to the sump?
00:36:50At one point, they had a little scavenge pump, a little tiny one up in the head that was sending the surplus oil down.
00:36:59But they designed around it.
00:37:01They came up with something that, that was perfectly workable.
00:37:04And it's obvious from the fact that he had to use a strobe that they had some problems of interest.
00:37:13Meanwhile, back at AGIS, they're realizing, wait a minute.
00:37:18We used the same cam profile for the overhead cam motor that we used for the OHV push rod and rocker motor.
00:37:29Why wasn't the power exactly the same?
00:37:34Because of valve float.
00:37:37The extra mass of push rod and rocker arm made it harder for the springs, even if they were much stronger than in the case of overhead cam,
00:37:48made it harder for them to return everything to its proper place, to make the valve train follow the cam profile.
00:37:59So it was lofting.
00:38:01Those of you who follow NASCAR will remember that lofting came in during qualifying.
00:38:09Namely, they would accelerate the valve so fast that it sailed right over the nose of the cam and landed on the closing flank.
00:38:23It's quite difficult to get this to work at one single RPM, much less across the range.
00:38:31But they understood the problem.
00:38:34Oh, well, let's give the overhead cam higher lift and see if we can make it follow the contour.
00:38:44Because the problem with the overhead cam they tried in 27 was it actually followed the cam profile.
00:38:52That is, it produced less valve lift and less power.
00:38:56Yeah, it was fascinating to think about that for the first time for me learning is that the tappet in an overhead valve engine, you know, push rod,
00:39:07the tappet is part of the weight.
00:39:09You're lifting that weight.
00:39:11The tappet is going up and it's lifting the push rod.
00:39:13And then it's pushing the rocker arm, which has some mass, which is then opening the valve against the valve spring pressure.
00:39:19And then the spring has to push the entire mechanism, all of that mass closed again.
00:39:26And that was the beauty of overhead cam.
00:39:28And, you know, this is all very romper room compared, which is a very old reference, by the way, to what Kevin is saying.
00:39:34But you take all of that stuff out and the cam is, you know, presumably working on a tappet or even better, a finger follower,
00:39:42which is what half the mass, essentially, you're only moving half.
00:39:45Oh, less than half.
00:39:46Less than half the mass.
00:39:47Yeah, it's eight grams in the latest version of the BMW Superbike.
00:39:54Eight grams.
00:39:55So you're removing the weight between the action cam and the actionable valve.
00:40:01It's beautiful.
00:40:03Finger followers were in use before 1910.
00:40:06This is why I say that everything is tried.
00:40:10And only what succeeds, what gets attention, what gets funding is remembered.
00:40:17In other words, make it work and make it sell.
00:40:23Then you're in with a chance.
00:40:26So AJS went back with their new understanding.
00:40:32They went back the following year with overhead cam.
00:40:34They stayed with it until the end of their days.
00:40:38Because they learned the big lesson.
00:40:41You can make the valve lift higher by eliminating all that extra weight.
00:40:48So the rule of thumb that was discovered was that a push rod and rocker arm engine needs roughly double the valve spring pressure of an overhead cam using the same cam profile.
00:41:03So just to move all those parts that you just mentioned.
00:41:09So I think that's just wonderfully fascinating.
00:41:15So now comes the big question.
00:41:18Why didn't an overhead cam take the place of overhead valve?
00:41:26Why didn't it push push rods and roller tappets and all heavy steel stuff?
00:41:32Dumpster, dumpster fodder.
00:41:35Get it out of here.
00:41:36It didn't happen.
00:41:37When Edward Turner drew the 500cc Triumph Speed Twin for about the same time as Harley's overhead, it had a practical valve train.
00:41:54It could rev to 6,500 RPM.
00:41:57What had changed?
00:41:57Previously, we've made the vibrating push rod and rocker arm and all that other, that stack of springs, we've made them into a demon, stopping progress.
00:42:10Well, wonderful things had happened in the meantime.
00:42:15In 1920, Duesenberg, to participate in a new three liter formula, built a straight eight three liter race car engine.
00:42:28And it was breaking valve springs.
00:42:30And they tried this and they tried that overhead cam engine, breaking valve springs.
00:42:36Oh, dear.
00:42:38So they got in touch with this fellow Hall who lived up in Berkeley.
00:42:44And they said, here's our problem, doc.
00:42:50Where's the medicine?
00:42:52And he said, can you send me an engine?
00:42:55So they got one of their riding mechanics, a fellow named Ernie Olson, and said, drive this race car over public roads up to Berkeley and deliver it to this man.
00:43:10Well, Hall was one of the two men who, in 1916, were put into a hotel room in the District of Columbia, where they worked day and night with constant deliveries of food from the hotel kitchens.
00:43:31Until they had designed the Liberty aircraft engine, of which just over 20,000 were built.
00:43:40None saw combat for a variety of reasons.
00:43:44But it was a famous aircraft engine because it held back aircraft engine design through sheer numbers.
00:43:55When the war ended, you could buy liberties for pennies on the dollar.
00:44:01Rum runners used them to power their speedboats.
00:44:04So this fellow Hall up in Berkeley understood R&D.
00:44:14The car gets there.
00:44:16I think it must have spent some time there.
00:44:18He graphed out the travel of the valve train, its velocity, and its acceleration.
00:44:32And the acceleration was infinite.
00:44:38It was applied at infinite speed so that it was like the famous case of the fellow that said, my car won't start.
00:44:47Can you give me a push?
00:44:49Fellow backs up, accelerates to 30 or 40 miles per hour, and crashes into the back bumper of the inert car.
00:44:57Parts fly everywhere.
00:44:59Impact breaks things.
00:45:01It's not the fall that kills you.
00:45:03It's the landing.
00:45:04Yes.
00:45:05So you look at those early cam profiles, and they look no different from a modern cam profile.
00:45:13They were defined by three arcs.
00:45:15One is the base circle, which is the part of the cam that is close to the lifter when the valve is closed.
00:45:23There are the flank radii leading to the nose, where there's a nose radius.
00:45:30That's all it was.
00:45:31And when you graph this thing out, the acceleration goes up vertically, stays there for a while, and then suddenly drops to zero.
00:45:40Well, all those parts have been accelerated, like the back bumper of the car I just described, to orbital velocity.
00:45:51And they are going to next expand once they're released from this, and they're going to send the valve train off the flank of the lift sides into the air.
00:46:06And in the meantime, the spring has been compressed at such a violent rate that the compression did not occur to all coils simultaneously, but rather as a crashing together.
00:46:20The wave.
00:46:21And the coils on the moving end, which then expanded and came running back and forth, multiplying the number of fatigue cycles by a very large number.
00:46:33Valve spring breakage.
00:46:36So what does Mr. Hall do?
00:46:40He comes up with a modified cam profile, which has been described as a four arc or a five arc.
00:46:50And what they did was to moderate the decrease of this acceleration so that it didn't flick the valve train off of the opening flank.
00:47:02And later on, they would come up with what has been called generated cam profiles, in which you would say,
00:47:10let's draw as a graceful curve, how we would like the acceleration to begin, to rise, reach a peak, and then decrease.
00:47:22Because by gentling these impacts, they became mechanically tolerable.
00:47:31And indeed, around 1953, somebody with a mathematical turn of mind said,
00:47:40well, if we're going to build pushrod and rocker engines,
00:47:45then let's write into the control expression the frequency and the stiffness of all of the parts.
00:47:57And then let's design a cam form, which was called polydyne,
00:48:04that essentially anti-jiggles the parts so that their own natural jiggling is not excited.
00:48:15And when I first asked about polydyne, I thought, it's a lot of nonsense.
00:48:21It's within the tolerance, the manufacturing tolerance.
00:48:25You can't make something that's that.
00:48:29It's tenths of a thousandth, the difference.
00:48:33Well, however that may be,
00:48:37Ed Iskandarian got hold of the idea and seemed to do well with it.
00:48:40I don't know if he made polydyne cams or if he just made cams that worked.
00:48:49But that's all that anyone wanted.
00:48:52And that is why, because all over the world,
00:48:55people were doing analysis like that of Hall up in Berkeley.
00:48:59And they were discovering the same thing.
00:49:02Hey, the rate of change of acceleration is infinite.
00:49:05And no mechanical part can survive that.
00:49:10Duh.
00:49:11We've got baskets full of them to prove that.
00:49:14We already knew that.
00:49:17And that is why that Triumph, designed by good old Edward Turner,
00:49:23could operate at 6,500 RPM and not break springs and shoot push rods off.
00:49:29And incidentally, the push rod part of the story in the TT races in the Isle of Man
00:49:36during the overhead valve era, that is push rods and rockers in the 1920s,
00:49:45riders carried two spare push rods down one boot top
00:49:49and a valve spring compressor down the other boot top.
00:49:53Oh, push rods went flying and stopped by the roadside.
00:50:00Compress the valve, drop in another push rod, position it so that as you let the valve spring
00:50:06take over, the ball end and the rocker come together.
00:50:13Push off, you're racing.
00:50:15Away you go.
00:50:16Well, it's a good time to point out Harley-Davidson's Big Twin versus the Sportster.
00:50:20That is a coping width of RPM.
00:50:23So the Big Twin has crossed over push rods, so they're kind of at an angle.
00:50:27And if you imagine getting lifted violently, you would unleash a wave through that push rod.
00:50:35You know, that's what's going to happen.
00:50:36And the reason the Sportster had straight ones in all those cams was a nice straight push.
00:50:41You didn't get a wave.
00:50:43It's still going to vibrate and it's still going to compress, but it's going to do it probably less so.
00:50:47There were various schemes to shorten push rods.
00:50:50I've always been a big fan of the Perilla, which they call the 250 of the late 1950s, mid-50s.
00:50:58And they just moved the cam way up high.
00:51:01They drove the cam very close to the head so that your push rods were just like tiny little
00:51:06things.
00:51:07And it's a gorgeous engine.
00:51:09And the two fills.
00:51:10The two fills over at Vincent.
00:51:12They did the same thing.
00:51:13They moved the cam way up for the same reason.
00:51:17Velocets were like that.
00:51:19Even the push rod, you know, the 500 MSS like I have is relatively high in the engine.
00:51:24And the push rod is relatively short.
00:51:27And they did all kinds of things with materials and taper, you know, steel caps on an alloy,
00:51:33hollow alloy tube, all kinds of things.
00:51:37It's really cool.
00:51:38What it teaches, among other things, what it teaches is that subject to similar problems,
00:51:47the humans working on these problems in widely different places will come up with remarkably
00:51:52similar solutions because they're all working against the same resistances.
00:52:02Cost, time.
00:52:02Beauty is truth and truth is beauty.
00:52:05Oh, well, there's that.
00:52:08But, yeah, you are working toward, you know, we have physical constraints, lots of different
00:52:14solutions, but we're all working with the same physical constraints here, aren't we?
00:52:18Yep.
00:52:19So, in 1959, here came the Honda Bentley, the CB92, with an overhead, single overhead camshaft.
00:52:29Oh, wow, this thing's really modern, huh?
00:52:31Yeah, 1912.
00:52:33Yeah, 1912.
00:52:36But nobody thought at that time that overhead cam was going to be the norm for all four-stroke
00:52:43motorcycles in a short time, 10 years.
00:52:49Here came CB750 with a single overhead cam.
00:52:53And three or four years later, the 903cc Z1 Kawasaki with double overhead cam.
00:53:04And who was going to dare to go against such engines with pushrods and rockers?
00:53:12Pushrods and rockers, however, have persisted in V8 automobile engines, and they have persisted
00:53:21in American racing because they were a kind of engine from which tremendous power could
00:53:27be had, provided that you could cope with the valve train.
00:53:31And they have coped.
00:53:33The early way, the early formula for all of this was, and I've got a Triumph Soup Up book
00:53:41that shows you how to grind your rocker arms away until you can practically see through the
00:53:46beam.
00:53:48No, wrong.
00:53:50It turns out the way to make the valve train successful is to make it extremely stiff so
00:53:56that its vibratory frequency is too high for the engine singing its heart out to break
00:54:04that particular wine glass.
00:54:06And make the parts stiff enough that they don't ring, and you have a recipe for success.
00:54:16And that's what they've done.
00:54:17The rocker arms, rocker arms on a Ducati MotoGP engine look like they should be good and stiff.
00:54:29The production stuff is just an L-shaped part.
00:54:35The race stuff has carefully shaped beams.
00:54:41They're shaped derived from finite element analysis, as you would hope.
00:54:47Kevin's talking about the Desmo follower arms.
00:54:50The closer, yeah.
00:54:52The Ducati's valve spring, in effect, because it is loaded in bending.
00:55:01But it's also, I mean, the cam profile, the closer, and the arm ratio and all that is setting
00:55:10the valve down as gently as practical.
00:55:14Yes.
00:55:16To reduce the amount of impact, which is what the cam profiles are meant to be doing also.
00:55:23Well, for years and years, the late Kenny Augustine would tell me,
00:55:31in one of his many phone calls, how deeply he yearned for a Spintron.
00:55:39The Spintron is the modern embodiment of the test rig that Mr. Hall built in Berkeley in 1920.
00:55:49In other words, let's simulate valve train conditions under circumstances in which we can measure everything that's happening.
00:55:59And the Spintron, instead of using a solenoid, which was the method of measuring valve travel in flight in the 1940s,
00:56:11it uses laser interferometry, which means that it can measure the distance traveled by the valve
00:56:21to less than one wavelength of visible light.
00:56:27And what a wonderful thing, because you can see on a screen
00:56:33the degree to which the valve is or is not following the cam contour.
00:56:42And when the valve is deposited on its seat, is it deposited like two men wearing
00:56:51abdominal braces, unloading a washing machine, crash, or is it landing gently?
00:57:03And at S&S, one of the fellows running the Spintron said, NASCAR used to accept five bounces after closure.
00:57:16Now it's down to three.
00:57:20Well, 500 miles is a long way.
00:57:22But what this has done, it has allowed valve control to, well, Honda's test engine for ultra-high-speed valve operation.
00:57:38By 1964, they had tested at 27,000 RPM.
00:57:45So we have a lot of help from instrumentation.
00:57:49Well, if you can't measure it, you can troubleshoot, but it's blind troubleshooting,
00:57:55or it's what the veritable and legendary parts cannon would be.
00:57:59You're having a problem, and you think in your head, like, oh, it's maybe EFI.
00:58:04Maybe it's the map sensor.
00:58:05Yeah, those map sensors.
00:58:06You can't measure them.
00:58:08I don't own an oscilloscope.
00:58:10It's probably the map.
00:58:10Well, let's just try it.
00:58:11We'll swap it out.
00:58:12And a thousand bucks later, there you are.
00:58:17You know, it's just, it's great that we can measure that stuff.
00:58:22Yeah.
00:58:23I think, you know, the V8, the American V8 land, there's a guy I would like to talk to at some point named Billy Godmold.
00:58:33I guess he isn't directly working for CompCams anymore, but he did work for CompCams, which does all that V8 American stuff.
00:58:39And they are spinning V8s with one cam and push rods and rocker arms to astronomical RPM, like, I don't know, probably.
00:58:509, 10, 11.
00:58:51Yeah, and survivable.
00:58:53Big stuff.
00:58:54Yeah, survivable.
00:58:55Well, I mean, just fascinating that we would do that kind of poetry within the form, because it's a really solvable problem, like the 427 cammer that got outlawed.
00:59:06You know, they put, Ford put the cam in the head, you know, overhead cam on that thing, and everybody said, nope, that's illegal.
00:59:13Yeah.
00:59:15It's like, what if everybody did it?
00:59:18Sure, well, that was the story when Steve Whitelock was World Superbike Tech Chief.
00:59:26His way of working was not to insist that everyone absolutely obey every letter of the law, but rather to maintain a sane level of performance across the paddock.
00:59:43So guys would come and say, what are you going to do if we bring this technology?
00:59:49Well, I'm going to tell you that if you do that, Honda over here, I happen to know that they have something even better than that.
00:59:57So how much do you want to find out and how soon?
01:00:02Hmm.
01:00:03Yeah, well, we'll talk about it.
01:00:07Trying to just keep things down to a simmer.
01:00:11Not one of those deals like, let's weld the top on this tea kettle and see what happens.
01:00:18So it's just one of possible other approaches.
01:00:25But certainly overhead cam has simplified a lot of problems.
01:00:33And there are so many ways that overhead camshafts are driven.
01:00:38We'll talk about that another time.
01:00:41But there are numerous choices, depending on what your goals are.
01:00:46Well, the Honda 50 twin, I mean, if we look at what was happening in, say, 1952, 1948, circa 1950 and circa 1960 to 65, where the Honda 50cc four-stroke twin was turning, what, 23,000 RPM?
01:01:05Well, it could.
01:01:07But peaking at, like, 21.5, I think.
01:01:10Yeah.
01:01:12Lots.
01:01:1221.5.
01:01:13I mean, your street bikes were – I mean, we're still turning Harley big twins to 4,500 to, you know, the hot rod motors with the HO-121 turned to 59 for a period of time.
01:01:24And then the ECU will, like, dial you back.
01:01:26You can't just hold it pinned there forever and do your top speed run across the desert.
01:01:31But 21.5.
01:01:35I mean –
01:01:36Good stuff.
01:01:38And that was with simple, standard overhead cam hardware.
01:01:45That is, a cylindrical tappet sitting on top of the valve and the cam lobes bearing each one.
01:01:53Each lobe had its own cylindrical tappet.
01:01:56And Formula One decided to get rid of the extra mass of that type of tappet at one point, and they went to finger followers.
01:02:12And, of course, then pneumatic springs.
01:02:15The pneumatic springs never made it as a fuel economy booster.
01:02:26Why should you drive a car whose valve springs are exerting 6,500 RPM of force at 1,800 RPM up the freeway?
01:02:40That was a question that they wanted answered.
01:02:44And if you had a pneumatic system, you could vary the pressure.
01:02:49Well, Ducati's Desmos system at idle, there's hardly any inertia force, and there's no spring force at all.
01:03:01Whereas when you have valve springs, the worst possible condition for the friction taking place between the cam lobe and the tappet is at idle.
01:03:12And low RPM use.
01:03:14Because the layer of oil that you hope to wipe between those moving parts is saying, oh, I'm not going in there.
01:03:26Oil-o-plane.
01:03:28Right, it's a wedge of oil.
01:03:29You're trying to keep them from touching.
01:03:31When you slide your business card across the conference table to the curious person who may order from your company, you are studying flight and ground effect.
01:03:47Air is a lubrication provider.
01:03:50It's one of the beautiful things of the Desmo valve system is the cam, the opening cam that opens the valve, because it can be a little knife blade.
01:04:01It's far narrower than your standard spring cam, and it is a thing of beauty.
01:04:05They're very pretty, and you appreciate why it looks how it does.
01:04:10And if you look at the giant radials of World War II and the piston era, which ended in 1957 commercially, the pushrods look a lot like pushrods from a pro-stock auto, because they're barrel-shaped.
01:04:29To make them extremely stiff against lateral vibration, they are steel, they are hollow.
01:04:40Good design.
01:04:42The good design was not the result of saying, how can we improve this, but rather, how can we stop these suckers breaking?
01:04:50Yeah.
01:04:51And you keep working until you've got it under control.
01:04:54Next year, they come up with more power.
01:04:56They want to use a different cam profile.
01:04:58Now, the headaches come again, but you have a method.
01:05:03Well, it wouldn't be a banger of a podcast, according to our producer, but certainly, somewhere in there, there's frequency, because everything vibrates at a frequency, and that's where you get your problems.
01:05:15Yes.
01:05:17Propeller blades.
01:05:18Propeller blades.
01:05:19A flight from New York to Miami, an 18-inch piece, went through the cabin of the airplane.
01:05:25As my old friend, Sandy Ruby, liked to say, super grimness.
01:05:33Well, let us know if you want a podcast on frequency and vibration, because I'm sure that we can find it.
01:05:46That's it for now.
01:05:47Thanks for listening.
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01:05:54Thanks for joining us for another Cygworld podcast.