A two-stroke engine completes its power cycle in two strokes of the piston (one crankshaft revolution), which typically makes it rev quickly and produce strong power for its size. In the segment, the hosts contrast two-stroke behavior with four-stroke engine constraints when discussing racing on rough surfaces.
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Yamaha RD 350
The Yamaha RD 350 is a liquid-cooled two-stroke road/production model that serves as the “base engine” in the host’s swap example. The discussion highlights how RD 350 cases can accept a TZ 350 cylinder, illustrating the modular nature of Yamaha’s two-stroke racing/production parts ecosystem.
“Liquid cooled” means the engine uses coolant circulated through passages to remove heat, usually via a radiator. The host mentions liquid cooling while describing fitting a TZ 350 cylinder onto RD 350 cases, implying cooling system compatibility matters when swapping racing parts.
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Yamaha TZ 350
The Yamaha TZ 350 is a well-known Yamaha racing bike with a 350cc two-stroke engine. The host is using it as an example of parts that racers would mix-and-match to build something faster.
A water pump circulates coolant through the engine’s cooling passages. In this segment, the host says adding a TZ 350 cylinder on RD 350 cases would require adding a water pump in the oil-pump area, emphasizing that cooling hardware can be part of the fitment when mixing racing and production components.
An oil pump moves lubricating oil to critical engine parts to reduce friction and prevent wear. The host’s “water pump in the oil pump arena” comment highlights packaging constraints—when you change cylinder setups, you may need to rework where pumps and related hardware fit.
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Yamaha TZ750
The Yamaha TZ750 refers to Yamaha’s 750cc two-stroke racing machine, a step up in displacement from the smaller TZ 350. The host’s point is that their RD 350 had a parts/engineering connection to the larger TZ750 platform, showing how Yamaha’s racing lineage ties together across sizes.
Grand Prix refers to top-level, factory-style motorcycle racing events and series. The segment says Yamaha engineers were tasked with developing 125 and 250 Grand Prix bikes for European FIM Grand Prix racing, tying the production-racer idea to the higher-tier racing ladder.
FIM stands for Fédération Internationale de Motocyclisme, the international governing body for motorcycle sport. Mentioning FIM Grand Prix racing signals the bikes were developed to meet the rules and competition level of the sport’s top sanctioning organization.
“Four valves” means the engine uses two intake and two exhaust valves per cylinder (a common performance configuration). The host links this to Honda’s four-stroke approach and RPM tolerance, arguing that valve control matters when the bike is bouncing on loose or rough surfaces.
Most engines have one main rotating shaft. “Two crankshafts” means this design uses two, which changes how the engine’s internal timing and layout work.
“Parallel twin” means an engine with two cylinders next to each other. It’s a common layout because it’s compact and can be tuned to rev quickly.
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radial hearth type splines
Splines are like interlocking ridges that help two parts spin together without slipping. The “radial” and “type” details describe the exact shape of those interlocks.
The FSO 125 is a small car made by FSO. In the podcast, it’s mentioned because the engine design was being developed, including plans to use a twin-cylinder setup. That’s why it shows up in a conversation about how cars’ engines evolved.
“Press fit” means parts are pushed together so tightly they stay in place without extra hardware. It can be faster to build, but it can be harder to fix if something isn’t aligned.
The crankcase is the engine’s main housing for the crankshaft. “Vertically split” means it’s split into two halves along a vertical line, which can make assembly more finicky.
The Pontiac Catalina is a car model from Pontiac. In the podcast, “Catalina” is mentioned because racing events happened there, and people sent vehicles to those annual competitions. So it’s part of the story about where the events took place.
Top dead center is when the piston is at its highest point in the cylinder. The closer the piston is to that point, the more heat builds up during combustion.
Most motorcycle engines use a “four-stroke” cycle. The piston moves through four steps—sucking in fuel, compressing it, burning it to make power, and then pushing exhaust out. The speaker is comparing how this affects heat in the engine.
The piston is the part that moves up and down inside the cylinder. It’s what gets pushed by combustion and turns into motion for the bike. Here they’re talking about how tight the piston-to-cylinder fit needs to be so temperatures don’t cause problems.
Cast iron is a metal that used to be common in engine cylinders. It’s tough, but it doesn’t move heat around as well as aluminum. That heat behavior changes how the engine runs and how the piston and cylinder expand.
Different engine parts heat up and expand by different amounts. The “expansion coefficient” is a way to describe how strongly a material expands when it gets hot. If the piston and cylinder expand differently, the engine can start rubbing or not seal properly.
“Hyper eutectic” is a fancy way of describing a metal alloy recipe. In this case, Yamaha used extra silicon in aluminum to make the cylinder material behave better under heat and wear.
Anodizing is a surface treatment that makes aluminum tougher by building a thin hard layer on it. The idea is to help the cylinder resist wear from the rings.
This is a coating applied to the inside of the cylinder. The “porous” chromium helps the surface hold onto oil, which reduces friction and wear when the engine is running hard.
On a two-stroke, the engine needs to “open” and “close” the air/fuel path at the right time. A disc valve intake uses a spinning disc to control that timing more precisely, helping the bike make stronger power.
Chrome cylinders means the inside of the cylinder is coated with hard chrome. That coating is meant to resist wear, but if it’s not right, it can cause problems like poor sealing or fit issues.
This is a special type of aluminum alloy with a lot of silicon. The idea is to make the cylinder resist wear and stay stable even when it gets very hot during racing.
Spa is a famous race track in Belgium known for long, fast straight sections. Bikes that do well there usually need strong top-end power and consistent fuel delivery.
A float bowl is the carb’s small fuel tank. It keeps the carb supplied with fuel at the right level, and on race bikes it may need more capacity so fuel doesn’t run low during hard riding.
A piston ring helps seal the combustion area and control oil use. A two-piece ring uses two segments, and if they don’t fit or seat properly, the engine can run poorly.
This means the engine cylinder is laid sideways instead of standing up. The orientation can affect how the engine is packaged and how it sounds and runs.
This describes a drum brake design where the brake pads are shaped so they grab the drum as the wheel spins. Having two “leading” pads on the front helps the front wheel slow down harder and more predictably.
A “single leading shoe” drum brake has only one shoe that is pulled into the drum during rotation. Compared with a two-leading-shoe design, it generally provides less front-to-rear braking bias and is often used where the rear brake is expected to contribute differently.
Bronze bushings are sliding bearing parts inside the fork that help the suspension move smoothly. They also play a role here because the fork’s damping fluid is controlled around them.
Damping is what slows the suspension’s movement so it doesn’t bounce uncontrollably. The speaker is describing how this fork’s damping was set up to behave differently when compressing versus rebounding.
The fork tube is coated with chrome to make it tougher and smoother where parts slide. In this design, the damping fluid interacts with that inner surface.
This is a nickname for a motorcycle front suspension fork that tends to damage its seals. The way it resists movement makes the seals get stressed, so after a few races they wear out or fail.
A one-way valve lets fluid move more easily in one direction than the other. In a fork, that means the suspension can feel different when it’s compressing versus when it’s rebounding.
“Rebound” is when the fork springs back after it compresses. Here, the bike’s design made rebound forces hard on the seals, so they failed after repeated racing.
“Bump” means the front suspension compressing when the bike hits something like a pothole or curb. The speaker says this fork didn’t slow that compression much.
Rigid mounted exhaust is bolted on without flexible isolation. If the engine vibrates a lot, that vibration can stress the exhaust and make it crack where it’s attached.
Term
180 degree parallel
This describes how the two pistons in a parallel-twin engine are timed to move. Because they move opposite each other, it changes the vibration you feel through the bike.
Carburetors are what mix fuel and air. Here, the host is pointing out that these carburetors were made with zinc, which can affect how tough and consistent they are under race conditions.
Term
inline Ford
They’re talking about an engine layout where cylinders are in a straight line. The point is that this layout can feel smoother than the harsh vibration you get from older race engines.
Some engines are mounted with rubber to soak up vibration. If the engine isn’t rubber-mounted, the vibrations can travel more into the bike and make the handlebars feel harsher.
RPM means how fast the engine is spinning. The host is saying that around a certain RPM range, the bike’s vibration and feel became very noticeable and matched what the engine was doing.
A “production racer” is a racing bike you can buy that’s already set up to race, instead of having to build it from scratch. The point here is that you can get it, fuel it, and go—without hunting down lots of special parts.
Here “crate” means the bike was shipped like a packaged kit—so you could unbox it and get it running. It’s being used to show how much easier it was to start racing.
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Triumph twins
“Triumph twins” means older Triumph motorcycles that use two cylinders. The host is saying that with these bikes, you often had to be more hands-on to get them race-ready.
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gold star
“Gold Star” is a famous name for certain older Triumph racing motorcycles. The host is using it to explain that some classic race bikes required more effort to get parts and build them up.
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AJS 7Rs
The AJS 7R is a specific older British racing motorcycle. It’s mentioned as an example of a bike you could buy ready to race, even though it wasn’t affordable for everyone.
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crat case
This looks like a transcription slip for the engine’s case area (the crankcase). The point is whether the race bike used the same basic engine-case design as a production bike.
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TD1B
TD1B is a Yamaha model name the host mentions while talking about buying pistons. It’s part of the story about how costly parts were for these race bikes.
Horsepower is a way to describe how much power the engine makes. The host is saying dirt-track riders heard it made about 35 horsepower and wanted to try it.
Dirt trackers are bikes built for racing on dirt tracks. The host is saying people adapted the Yamaha idea for dirt racing, and it ended up chewing through tires.
Andres Laschutes is the rider the host talks about. He bought the Yamaha and tried it at practice, and his comments are used to explain how easy it felt to go faster by just using the throttle.
A drum brake uses brake shoes that press outward against the inside surface of a rotating drum. The drum’s condition matters because cracking, rust, or uneven wear can reduce braking performance and accelerate wear.
Shock cooling means rapidly cooling a hot part, often with a big temperature drop. Cooling too fast—especially only on the outside—can lock in internal stresses and increase the chance of cracking.
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TD-1C
The Yamaha TD-1C is a two-stroke racing bike model. In this story, it’s mentioned as the next version that improved a problem they found in earlier front-wheel hardware.
Ring travel is the range of motion the piston rings move through as the piston cycles. Wear at the top of ring travel can indicate the ring material and cylinder surface are not holding up under heat and friction, which is critical for long-race durability.
Compression is the pressure the engine builds inside the cylinder. If you have “no compression,” it means the engine isn’t sealing well, so it won’t make power or run correctly.
The gas tank is where the fuel is stored, but on race bikes its shape can also change how the bike feels and how long it can run. Here they’re comparing tank shapes across versions.
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RD-48 tank
The RD-48 tank is a particular fuel-tank design used on an earlier version of the bike. The host is using it as a reference point to describe how later tanks looked and were shaped differently.
The swingarm is the part that holds the rear wheel and lets it move up and down. Making it stronger or changing its shape can change how the bike handles.
Ducati is a well-known Italian motorcycle maker. In this segment, they’re mentioned because people were using and modifying Ducati 250 single-cylinder bikes for racing.
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Ducati 250 singles
These are Ducati motorcycles with a 250cc engine that has just one cylinder. The segment is saying that in Canada, people stopped relying on those modified single-cylinder bikes for racing.
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Yamaha 350 twin
This is a Yamaha two-cylinder (a “twin”) engine around 350cc. The hosts are talking about how Yamaha designed it to be easier and faster to build, using a special crankcase layout.
This is how the engine’s outer housing is made to come apart. Splitting it horizontally can make it faster to build because you can set parts in place and then close it up.
Term
shimming ride
Shimming means adding tiny thin spacers to get the exact spacing between parts. The point here is that Yamaha’s design aimed to reduce the need for that fussy, tool-heavy setup.
This describes how the engine housing is split into two halves. Splitting it vertically changes how the parts are accessed and assembled, while still keeping the engine easier to build than a one-piece design.
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TD2
“TD2” is Yamaha’s updated 250 two-stroke race bike/engine from around 1969. The hosts point out it’s different from the earlier version, especially in how the cylinder ports are arranged.
Transfers are the channels that move the fuel-air mixture into the cylinder in a two-stroke engine. More (and better-shaped) transfer passages can help the engine breathe and make power more effectively.
Bottom dead center is the point in the engine cycle where the piston is at its lowest position. It’s important because two-stroke engines use piston timing to push fresh fuel-air mixture into the cylinder.
Transfer windows are openings that let the fresh fuel-air mixture move from the crankcase into the cylinder. When the piston uncovers them at the right time, the engine can clear out exhaust and refill with fresh charge.
The exhaust port is the opening where the used gases leave the cylinder. In a two-stroke, it opens and closes based on the piston position, so it affects how much fresh mixture escapes too.
Term
claimed horsepower
“Claimed horsepower” is the power number someone says the engine makes. It may differ from real-world dyno results, but it’s still useful for comparing versions.
Stroke is how far the piston moves up and down inside the engine. Keeping the stroke the same while changing bore helps make different engine sizes using many shared parts.
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TZ250
The Yamaha TZ250 is a Yamaha two-stroke race bike. In this segment, it’s mentioned because the engine parts could be swapped to compete in different classes.
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TA250
The Yamaha TA250 is a Yamaha two-stroke race bike. Here it’s mentioned because the engine parts could be swapped to compete in different displacement classes.
A modular engine means you can change the bike’s setup by swapping parts. The idea is to quickly adapt the same engine family to different racing classes.
Bore is the width of the cylinder. Changing bore changes how the engine breathes and can affect how well the exhaust port works.
LIVE
Hey, welcome to the Cycle World podcast. I'm Mark Hoyer, the editor in chief. I'm with Kevin
Cameron, our technical editor. We're going to talk about, I don't know, it's near and dear to
our hearts. Yamaha 250 production racers. Now Kevin's spanning 1961 to 2009. I have a narrower
band and I would say I don't have experience with production racers, except that I have experience
with Yamaha 70s two strokes, which were like the production racers, everything would swap over.
If I wanted to put a TZ 350 cylinder on top of my RD 350 engine cases, liquid cooled, I could do that,
but I'd have to put a water pump in the oil pump arena, correct? Yes. But see it's all slide right
on the stud. So Kevin's going to obviously add a lot here, but I was always delighted that somehow
my, exactly there it is, that somehow my RD 350 had anything to do with a TZ750 was spectacular.
I felt connected, you know? Take a spot, Kevin. Well,
when Yamaha got out of the phase of can we succeed in Japanese business and realized that
we have to get into export because in business, if you're not growing, you're slowing,
you're shrinking. And so it was decided, of course, to use racing as a promotional tool.
Two programs were initiated. One with engineers Hata and Naito were charged with
developing a 125 and a 250 Grand Prix bike for European FIM Grand Prix racing.
And another group were to invade the US racing scene in conformity with the AMAs.
It has to be sort of production. And like the wonderful distinction, yes,
the racing parts are listed in the parts book that the AMA did not tell us we have to sell in.
And we're not. So. Well, that was the secret handshake, right? You could only get them if you
were the chosen. Already in, yes, absolutely. So Yamaha and Honda and Suzuki had been going at it
in the volcano races, the Mount Osama and so forth, and which were cinder surface.
And we've talked before about how Honda, with their four strokes, had absolutely to have RPM
tolerance in their engines, had to go to four valves, because what happens on a loose surface,
your tack is always banging on the pin. But with a two stroke, it's, there's no power
above peak revs. And so it's not an issue. So they had built
a variety of machines initially that were that were based on their examination of the German
Adler, which was a parallel twin. The Adler had some German features like the two crankshafts.
How do we join them together? So they, they used radial hearth type splines with the whole thing
drawn together by a draw bolt, access to which was tricky in itself. But that's how they did it.
And when Yamaha decided that they were going to build a twin YD1,
they had already built the YA singles 125s for a while. But YD1 was going to be
a twin and they decided that it would be an all press fit crankshaft. There would be no
maniacal machine shop techniques used. It was just going to be banging together in the press,
knocking straight, like you're playing a xylophone with big hammers. And then
just pushing all together. These early engines had vertically split split crack cases, which
meant that the, to get a decently close fit of the bearings and the
seal on the center block and all these different parts, there had to be special tools for
laboriously drawing it all together. And if it didn't shift once you've got it all together,
you had to take it all apart again. So this was a built in set of drawbacks.
But they decided they were going to compete in US races and they sent some bikes to Catalina,
where there were annual events. And I believe somebody won the 250 class on a scooter once.
So it was possibly MIC, KEY, etc. But they wanted to get in and start playing. So there was a variety
of sort of fits and starts. The early engines had iron cylinders. The carburetors mounted on the
crankcase and half of the cylinder was set down into the case. So it was, the cylinders were only
about halfway finned. That had to go. So they made cylinders with the carburetors bolted to the back
of them and the exhaust coming out the front. And four studs for each cylinder, slide the cylinder on,
head gasket, cylinder head, four nuts, you're done. And this was the wonderful thing about
two strokes was you could change a piston. If you were hot, you could have it running again
15 minutes. And I think that many did because the problem with the early engines was piston
temperature with a two stroke, two stroke fires every time the piston comes near top dead center,
which means double the heating of a four stroke, not quite double, but a lot. And this meant that
they wanted you to fit the piston closely so that it could have intimate thermal contact with the
cooler cylinder, cast iron, I don't know if it's cooler. But it just took time for this sort of
thing to shake out. And meanwhile, the European race department is having its problems. And
as we know separately, Suzuki had gained some information from Germany
through an episode of Daring Dew, people stealing out of East Germany in the space between the trunk
and the rear seat. It was terribly dramatic. And the upshot there was iron liners.
But Yamaha proceeded in the direction of how can we reduce the expansion coefficient
of an aluminum cylinder.
They, and of course, the piston so that they didn't end up with a situation where
the piston grew, but the cylinder didn't or vice versa. And they developed what were called
hyper eutectic, meaning a greater content of the alloying element, in this case, silicon,
then the mixture of aluminum and silicon that would have the minimum melting point.
So they ended up with 20 odd percent silicon. And they started out with anodizing the cylinder wall.
Once they got rid of cast iron, of course, they had relative thermal advancement because iron is
heavy. It conducts heat only like one third as well as aluminum. And it's good for something
that's going to operate at moderate power for a long time. And so they switched to aluminum.
They tried the anodized surface to make the cylinder walls hard enough for the rings and
to slide against. It sort of worked. Don Vesco said an 89 mile per hour one lap record at Daytona,
not in an AMA race, outlaw. He was riding outlaw. That's the way they talked about it in those
days, as though it were some kind of hereditary defect of personality. If you're not with the AMA,
you're outlaw. So they switched to porous chromium plating directly on the aluminum.
And the anodized domestic racer, based on YDS2 crankcase, was TD1A.
And TD1A had a dreadful gearbox like most street bikes need to have a very low first.
Yourself, your girlfriend, the stuff you're taking to the Cape, uphill stoplight. How am I
going to get going? Just make the gear on the front shaft real small and big one on the back
shaft, which meant on the track it was a four speed because you would never shift into that
gear. So TD1A and the yellow tanker and the YDS1R and the other things that went before it
were sort of trial balloons. I think I saw one of the bikes with the early style gas tank,
which had knee notches with black rubber grips there so that you could hang on to the motorcycle
with your knees as well as with your feet and your hands. So by the time they got to TD1A,
they had decided we're going to use the chassis from the European race team
RD48, which was a rotary, a disc valve intake, parallel twin, which
was their first try in GP racing. And in 62, they took a year off because there were economic
reverses and what have you. But in 63, they came back with chrome cylinders. Now this is in Europe,
chrome cylinders, hyper-utectic aluminum alloy, and they, in the follow on to the RD48, which the RD56,
and in 63, two Japanese riders competed at Spa, which has long straightaways. And once they got
enough float bowl on there, they had to put four float bowls on it before they could get enough fuel
to the carburetors. It just motored away from the Honda 4 of the official team. So two-stroke,
maybe not so shabby because up to this point, people had acted as though, well, MZ in East
Germany, a thing is fast until it sticks. And they're really weird bikes. They come out with
all this prototype stuff and they never put any points together. So you just don't have to think
about those guys. But when these two Japanese riders blitzed Spa on a disc valve twin, it was
sort of like, what happens next? What happened next was, Phil Reid won the 250 championship the
next two years. So the chassis that preceded that chassis, the one from RD48 was brought
to the US race department, where they put a YDS2 based racing engine in there. That was the anodized
cylinder one. And the next year, 1964, they built the TB1B. The B model had the chrome cylinders.
The chrome wasn't all that great yet. Sometimes it would shift around the exhaust port. And the
rings were cast iron, sometimes trying ever so gently to ease them over the piston.
You know, riddle as hell. Two-piece ring, not so good.
Maybe big problem. Lose your spring that way.
Was not very springy. But Vesco's good performance on the A model. And the fact that when the B models
ran, they just blitzed away from the Air Maki 250 single, which was a pushrod four stroke
with the horizontal cylinder, and so loud. It was really noisy. Not that the two strokes were quiet,
but the chassis that was given to A and B models and later to the C model had a 200 millimeter
dedicated front brake. This was not some street stuff, warm no-bur. It had a
lightweight aluminum gas tank in such thin gauge material and the engine vibrating so terribly
that if you didn't mount the tank right and it touched the frame, it would crack at the point of contact.
And this is soft aluminum. This is not some kind of brittle alloy.
Yeah, it's usually, those days it was 1100 probably.
Yeah.
3003 maybe, I don't know, pure aluminum.
So it had a two leading shoe front brake and a single leading shoe rear brake that were both
dedicated for the purpose. They had cooling holes, they had fins. It was very racy looking.
And they had a terrible fork, which was the sliders were steel, the tubes were steel. It had
two bronze bushings in there and the damping was, the pumped fluid was what was caught between
those two bushings and on the inside the chrome plated fork tube. And there was a one way valve
and an orifice so that there was very little damping on bump and most all that was on rebound,
but the pressure of the rebound fluid bore against the seals. So you ride a few races,
blew your seals are gone. So this was called the seal blower fork when everybody
had mixed feelings towards it. And it had a racy looking seat with a rounded seat back just like
all those European bikes and pipes came out the front of the engine and swept under toward the back,
but they were rigid mounted, which meant they cracked constantly. They cracked at the mounts.
And at the front, they were held on in street bike fashion by big steel rings with threads that
held the pipes tightly against the vibrating cylinders. Now this engine is doing this because
it's a 180 degree parallel to it. So it's rocking basically. It's rocking horribly. It's rocking
and it's sort of a row, it's a rowing emotion almost, right? Like a kayak, like a double bladed
kayak paddle. Yes. And this is a violent motion such that if you got a year out of one of these frames,
you were either fortunate or slow. And the the rear lower left engine mount would break first
and it would break right off of the frame. And then the right one would break after you'd fixed
the left one. And then it would start in on the front ones after a couple years. And it would
break those two if you didn't constantly look for cracks, look for them, stop them. And it had
horrible zinc carburetors, 27 millimeters, a big step up from the 20s of the first
race engines. They were licensed reproductions of the Amel 276, which had a remote float bowl.
And the float bowl mount was fabricated from sheet steel and there was thick rubber between
the mounting bracket and the float bowl. And then the whole thing was bolted to the back of the
gearbox. So it reproduced every nuance of engine motion. I have to talk about vibration, Kevin,
because the times before when all this was happening, vibration was really something,
it was so much to the point that things were cracking and flying off. And it's just not like
that. And, you know, I had a friend who hadn't ridden a motorcycle in a really long time and I
put him on an inline Ford, he was blown away with the serenity of it, you know, like it's
serenity, what a word couldn't couldn't believe it. And it's, you know, you get on anything now,
even the the parallel twins where they're, you know, they're, they can make it 100% smooth,
they can, but they don't, they want to give you something, but they don't want to give you frame
cracking, teeth chattering, eye blurring, metal eating. Yes, it's just the strides here are
wonderful. We can kind of design anything we want and balance it. First time I rode a B model,
it turned my hands so numb that they were like pieces of meat that were separate from me.
It was terrible. Oh gosh, Norton, Norton, sorry, but very quickly that I rode an unbalanced Norton
650 cafe bike, a rigid mouse in a feather bed. And it was stroked to 750 and then, you know,
one of my friends said it might have used a commando crank, which has a different balance factor.
And you don't want it in a non rubber mount engine because it could be, it could have been
the case. I just never ridden anything quite like it because the handlebar grips, they went from
grips at like at 2800 RPM or 3000, they went from something that you just held on to and they felt
like they were this big. They vibrated. They just sang in sympathy so much with what was happening
in the engine. It was impossible. And a vision, vision, yes. Here's the great thing about production
racer. It comes in a crate. You open the crate, you gas up, you air up, start up and go. You're not
trying to get race parts from outside suppliers in Britain for your gold star. Fear was so much
wonderful stuff for a gold star and for Triumph twins, you could build your own. But you needed to
be a competent mechanic and possibly something of a machinist. But the idea of a production racer
did not start with the Omaha because we know there were Max Norton's that you could buy. There were
G50s and AJS 7Rs, VeloSets that you could buy ready to race. Even though they did not
share a crat case or live apart with a production model. But they were not cheap. When I went to the
dealer to buy pistons for my TD1B, two pistons, dealer discount, $12, $6, $6. When Matt McConnie,
a veteran dealer, Triumph dealer north of Boston, bought a piston for his G50 that he was running,
$90 in 1962 dollars, that is. Imagine what it would be today. So
America has been sort of the land that democratizes a lot of things. The Model T's put cars.
Thousand bucks, sorry. People, they got them down to the price of a C100 at one point.
Max Piston was a thousand bucks, Kevin. I'm sorry to railroad you. I looked it up,
but in 1962 dollars, it was $1,000 today. Yeah. Well, so the idea that Yamaha was selling a production
racing was just wonderful. And of course, the dirt track people, oh, the thing makes 35 horsepower.
Let's give it a try. They built some twin powered dirt trackers. And instead of eating the frame,
they ate the tires. But when our local Boston hero rider, Andres Laschutes,
bought his B model from Boston Cycles and went out and ran a couple of practices, he was just,
he was so happy because he'd been running souped up street bikes. And he said, this thing,
he said, when I want to go faster, I just turn the throttle more. When I want to stop more,
I just pull the lever harder and there's more. And this is the thing about a production racer. It's
more or less ready to race. And of course, by the end of the year, he was noticing that
when he pulled the backing plate out of his front wheel and looked inside to, you know,
kind of blow the dust out, friction material dust, asbestos. He noticed that the the iron ring
that the shoes bore against inside the drum was cracking.
And I thought I could fix this. So I put one in the lathe,
had to take this rim off because the lathe wouldn't wouldn't take a spoke wheel.
And I machined the thing until it was paper thin and then long slivers began to pour off
of the tool. And I saw the awful truth. These iron rings had been aged outdoors in the weather
and they were rusty as you would expect. Does rust transmit heat well?
So it's an insert. It's an iron insert in the an aluminum hub, correct? Is that what we're
talking about? Okay, so just like an iron liner and a cylinder. Yeah, so they just took the thing.
There's so many production stories about like, oh, the cylinders or crankcases come out of the
foundry and it's the winner. And they're on a cart and they're going from the foundry and they're
hot as hell. Because they just were poured, they were just cast. And they've cooled for a while,
but they're hot as hell. And then they walk them out and it's 29 degrees or 14 degrees.
And they're walking to the next step and the thing is shock cooled, only on the outside,
setting up tremendous tension in the part or crack. Yes. And thermal stress, thermal stress.
I mean, so anyway, yeah, so these are tossed outside, and they're rusty, and then they're not
cleaning it up. They're just pressing it in. So all this granulate into the mold and oxide.
And then away goes the yikes.
It's the awful truth discovered on the lathe.
Covered on the lathe and a pile of pile of iron, curvy, bendy iron pieces. So
in one year, a good rider had shown that he needed a new front hub. So the next year came the TD-1C.
TD-1C had so much improvement in it. The chrome process for making the chrome stick to the
aluminum cylinder was much better, such that you could wear it through at the top of the ring
travel. And that would be around 1,000 miles. And what I did to test this was I went to my third
drawer and got out a scriber with a nice sharp point on it. The scriber just glides along on
the hard chrome that doesn't dig in. But when I drew a line up toward the top of the ring travel,
suddenly, ugh, oh, that's aluminum right there. So it had worn out without seizing. This is a step
forward. And the piston rings, you could take them, here's the piston ring, and bend it around like
this. And it would not break. Of course, you couldn't use it then. It didn't spring back.
But it didn't break when you put it on the piston. It didn't break at random while you were racing.
Oh, no compression on number two. So they were going after the durability problems that were
preventing the B model from finishing longer races. And they fitted the B model.
Late B models had a gas tank that was long and pointed instead of the early ones,
which had the RD-48 tank, which I thought looked like a big old watermelon. And
the C model had a longer gusset on the swing arm. Somebody had complained. Test riders, maybe.
Still the same old horrible fork, but now with the beautifully
buffed fork crown in aluminum.
Engines were much more reliable, and they wasted no time
cleaning the four strokes out of the lightweight class. They were finished.
In Canada, no more Ducati 250 singles, the ones that
were souped up by people with money in hopes of attaining European flair.
Even a B model, I remember pulling up on guys on my B model and hearing that
thudding sound of four stroke combustion and being able to just motor around them.
They're tucked in. They're looking good. And as one, as a friend of mine from that time said,
said, when you pass them, you want to sit up and pretend to adjust your goggles, as if
they and their four stroke are not just another mote of dust in your eye,
another blink, and they'll be gone. So that wasn't very popular, but
we'll have to put up with it. Well, the teeny one C was produced for
66 and 67 and 68. Well, Yamaha had designed a 350 twin to take the place of their
oversized 250s, which were 305s, YM1. And they had horizontally split cases.
And think of the time that was saved in assembling when the thing comes along the line.
There's the case. You set the crank here, the gearbox input shaft next, the gearbox output
shaft next, and then the kickstart shaft. Yeah, as you shared, it's just this wonderful tray.
It's this spectacular, this tray. And it has all the half rounds where all the shafts go.
And you just take your thing and go clunk. And then, you know, crank, as you said, crank
gearbox pieces and then slap the top. And you're away you go. None of this,
drawing it together and with special tools, tools and is the shimming ride and whatever,
you know, just. And so in 68, they offered a speed kit for this TR engine.
And it was cylinders, heads, pistons, carburetors, pipes, and an ignition.
And lo and behold, in the 200 mile race at Daytona, tell Raidman 1, as you would expect
in that time, on the KR750 Harley Flathead. And in second and third, where is long DML, and
oh, what's this name? I never can remember this guy's name. Well, it'll come to me in a minute.
Uh, they were two and three. So any thought that the AMA planners might have had of
the future 350 class, that just had to be scrubbed because four strokes were going to need to be
750 ccs to compete with these horrible two strokes. And it just, they just kept running.
Everyone's waiting for them to cease. It'll seize up any lap now. Just kept going
because Yamaha, we're getting the hand and hang of it.
Now in 69, Yamaha
built a definitively different, but still vertically split case,
250, the TD2. Now here's the difference.
This is a TD1B cylinder and you'll see that it has 12 transfers. That's it. Just two.
Tell them what the transfers do, Kevin. The transfers are the ducts on the sides of the cylinder,
which when the piston descends toward bottom dead center, raising the pressure in the crankcase,
fresh mixture goes up through those ducts, through the transfer windows into the cylinder,
squirts toward the back wall, goes up it, across the cylinder head and down to the exhaust port.
Here is the TD2 cylinder. Four transfers. None, two.
The four. What this does is it slows the mixture traveling through the transfer
port so that it doesn't reach the exhaust port as soon. 16% power increase. C model,
38, claimed horsepower, TD2, 44. And they went fast.
So, TD2 and TD2B, 69, 70, and 71.
Somewhat lighter than a KR750 also, we might point out.
Yes. These bikes weighed about 230 pounds. So,
they were now making 250s that were vertically split and 350s that were horizontally split.
They decided that didn't make any sense. They made a plan to build
both displacements with the same 54 millimeter stroke in a new horizontally split. Easy to
assemble. Easy to work on. Crankcase. And this was the modular engine that came out in 72.
And they solved so many problems this way for private-tier racers. Because if you bought a
TZ250 or a TA250 or 350 motorcycle, you could buy the other displacement cylinders, heads,
pipes, carburetors, and you could switch from one to the other in an hour.
So, you could ride two classes. You could have more of your favorite beverage.
Well, yeah, yeah. And you could make an extra buck if you're really trying to do it.
You can get out there because you cut more laps and you had a better chance of getting
surprise money. Yep. So, this modular engine was a strange thing because
it ended up that the 350 with its larger bore, it was 64 by 54,
was a little short in the exhaust port department. And the problem is that, of course,
with the four stroke, the valves go in the cylinder head. So, the larger the bore,
the larger the more room there is for valves. But with a two stroke, it turns out that port area
increases faster with longer strokes than it does with big divorce. So, the 350 was a little bit
handicapped. But despite that, in 1972 and 1973, the Daytona 200 was won by 350 Yamaha Twins.
Little dinky motorcycles hardly weighed anything. And the thundering four strokes,
tri though they might, were left behind. And, of course, the British were about to throw in the
towel because their business practices had led to a condition that businessmen fear no profit.
They had changed, they had mergered and they had, they had changed things. They had
changed models. They had the oil in the frame model.
They thought they were Honda. They put on dealer shows as though this is a huge enterprise and
just get behind it. And then they couldn't produce the bikes. And it just all fizzled out and it was
so sad. But, meanwhile, people are racing these things. The TV2, souped up TV2's returning 12,000
RPM. And they had stepped crankpins. See, this part in the middle is where the big end of the rod
with its roller, needle roller assembly, runs against that. And these smaller diameter parts
are pressed into the fly wheels. There's a step here. Good design. Good designers know that
anywhere there's a change in cross-section, it has to be very gradual. It needs a radius.
Kevin means if it's square. So if you, like you said, you have a horizontal part of the pin to a
vertical part of the pin, if that is a very sharp edge, if that is a pure 90-degree transition,
propagation of cracks. And not only that, but even when they made the smooth radius,
this could happen. Look, it's a broken part. There's a crankpin with steps
that failed. And so they decided to fix that in the modular engine that they brought out in 72.
And so they said to themselves, we'll make a straight crankpin. And I've never seen one break,
not ever. There's no stress raisers in it. They had a hole through it. They thought this
hole would help them with engine balance. The press fit wasn't tight enough with the hole.
Oh man, you should talk about that a little bit. They made the hole smaller. Now, when
Bull Taco did the same thing, made hollow crankpins, and they found that the press fit wasn't strong
enough to keep it from shifting. They drove expander plugs into the end in the press to
increase the fit, the interference. And they stuck with that plan for quite a while. But Yamaha didn't.
Yamaha's solution was a solid pin. I was going to say that's a lot of trouble to go
to to make a hollow pin and then drive something into it and make it unhollow.
This is the RD-400 pin, and they put them in the race bikes too, the 250s. And of course,
this is the equivalent of a roll of quarters. So if you want to be involved in risky illegal
bar fighting, consider a crankpin rather than a roll of quarters. It's roll of quarters is paper.
It doesn't have the strength to stay together through thick and thin. Well,
those straight crankpins with no hole still slipped a bit. So now they put little striations in them
in hopes that that would work. The people welded the pins. The welds cracked because
it's high carbon steel. And of course, the heat from welding reduced the grip of the press fit
somewhat. Anyway, just little details, but the company was constantly at work on all this stuff.
The years from 72 to 1980 were years of steady advance using the production crankcase from the
RD-350. R5, right? It started with R5, then RD-CS. Yeah. So R73 was the R5. That was where the
first modular was. And then R5. That's correct. R5 has the gas tank you want because it doesn't
have that flip up. The R5 has that nice gas cap you can just put in. Then in 74. More transfers.
Water cooling for the 250. And they put two cylinders in one block because with water cooling,
seizing became less likely. So it was acceptable. But now here's a problem with it all to win.
You need to explain that because the reason they were separate before, Kevin is saying you might
have a seizure on the air cooled more often and you could just maybe you could change one piston.
Is that? Sure. Yeah. Right. It was just easier to take it apart, put it back together. But once it
was reliable, they let you just put it on as a big cylinder block. Just like today,
they nick a cylinder that are cast in one piece with the upper crankcase. And of course, people who
looked at this said, oh, you can't re-bore it. It's going to be terrible. Oh, what a bad idea.
But it turned out that, of course, now that engines are controlled by computers and their
mixture is constantly responding to changes in the atmosphere and altitude. And there's rev
limiters and there's all kinds of protections that engines did not have in the Horry old times.
Engines don't wreck themselves like they used to. Yeah. I got that old Chevy Colorado with 200 and
I don't know, 212,000 on it. It doesn't burn a lick of oil. Bottom end is just tight as can be.
I did have to do the cylinder head, burn it out. But just it's remarkable. The bottom end,
I mean, even Norton commandos, if you were kind of gentle with them and the bottom end of a Norton
commando could go a long time. But you were definitely replacing cylinders. Yeah. So during
that eight-year period, they added water cooling. They added monoshock. They kept increasing the
size of the intake port because these are piston-controlled inlet engines. When the piston
goes up and expose the skirt, it exposes a big hole in the back of the cylinder like
yes, big, big hole. And in the cylinder, you won't be able to see it too well, but
there's a gigantic intake port. When they got to 1980, the pistons weren't lasting very long
and they needed a new engine. So they built, instead of the $105 dealer net production crankcase,
there were some modifications, by the way, but a lot of people used production crankcases when
they needed one. They made a new engine with sandcast cases, so instead of $105 for a new
case set was $1,000. And this was a giant piston port, but they gave it a jack shaft. So now the
rod angularity during the part of the cycle when the intake skirt of the piston is looking at that
huge port and thinking, I could go out here. People were getting 80 mile life out of pistons,
with little cracks, all kinds of trouble with it. So we got one of these H-Model TZ250H
and it was a monoshock and it had all modern stuff. And I kept looking at the pistons and they
looked fine. And I kept looking at them until we had like 365 miles on them. And I replaced them out
of a sense of impropriety. You know, you're supposed to change your pistons.
Fear.
Yes, fears. But it was so much kinder to pistons with the engine revolving the other way.
And so began a move toward a more expensive motorcycle. We're talking 7 or 8,000 now,
where the TD1B had been the 1147 retail plus destination and set up 847 to the dealer.
Hundreds, not thousands of dollars to buy the early production racer.
It was wonderful. And so many people rode TZ250s and TDs. And many great talents in racing got
their start on these available, easy to maintain and potentially very fast motorcycles.
Well, I liked your story about opening the dealership and joining your friends with
Triumph and Kawasaki to open a Triumph and Kawasaki dealership on April Fool's Day in 1969
and that you wanted to go racing. So you phoned the Triumph importers and asked them about
special parts to build Triumph. So they actually laughed.
You know, come on. And so for Yamaha to just lay it out there and just like, yeah, here it is.
Here and six bucks for a piston. Let's go. Whatever. Amazing.
So by 1973, I think you're paying 1,800 bucks for a 250 road racer. And
during that eight year period, they got disc brakes, monoshock, all mod cons, and they're
playing around with the engine. They in the F model, which I think was 78 or 79,
they went to a big exhaust pipes with big 108 millimeter center sections
that accelerated really well. And then that whole era came to an end. Basically, forget low price.
Because now these bikes were, if not competitive in GP racing, they weren't advancing.
And Yamaha was developing simultaneously a YZF 250, YZR 250.
And they weren't getting anywhere. Honda had switched to a V-twin. Now imagine this.
When you build a V-twin with a 90 degree angle like Ducati do, it becomes possible to completely
balance primary shaking force. But it does leave a little rocking couple. And in a parallel twin,
which has been turned into a 90 degree V-twin, in a two stroke, there has to be a seal between
the two crankcase halves. And there's a bearing there too. So the cylinder axes are offset.
So the engine is doing some of this. So the wider that offset goes, the more that rocking couple
more rocking roll. Yeah. And so this was a very bad problem for these engines,
because the transfer ports are so close together. And yet they're not really,
the ideal transfer ports are like cup handles. They curves out and they come back in and they
enter the cylinder at a small angle, a small up angle. They may even be zero. But Jan Teel,
who has now sadly died, which is what people do when they get really old,
he said his motor began to really make power when he adopted this style of transfer port,
rather than the kind that is squeezed together by close cylinder spacing. So if the port has to go
up and then turn at right angles to enter the cylinder, of course, the flow is thrown to the
outside and the lower one third or even one half of the port doesn't flow at all. So the poor old
350, which had the same cylinder spacing as a 250 because it melt on the same crankcase,
its transfer ports were in effect a two thirds rather. When TZ350 signed off in GP racing,
they did so at about 80 horsepower. And the production, last production racer,
250 from Yamaha was in 2009. It was the last season in FIM racing. The year after that it was
Moto2 four strokes. That bike was 27,000. And then you needed the FIM kit and a bunch of other
tricks stuff to make it into a Grand Prix contender. Who knows how much that stuff was.
And they claimed 93 horsepower for that engine. Honda in 94 for their NSR 250 program factory bike
had set 100 horsepower as their goal for that year. So these engines, the production racer started
out at 31 horsepower and signed off at three times that much and costing 30 times as much.
But that's truly racing math. It really is. That's exactly how it costs. That's how it goes.
When the H model was introduced, it received the variable height exhaust port technology called
PowerValve. And Kenny got a PowerValve inline four 500 in 78. At first they sort of thought, oh,
it's a big operation in California. They want this kid, Roberts, riding one of our bikes. So
okay, but we know that Johnny Saccato is the real thing because his name ends in ORA. And wait a
minute. Didn't Kenny become world champion that year? And in 79 and in 80 on a bike with
this type of piston port cylinder. This right here is where the eyelid mechanism goes inside.
And that made it so much easier. You know that two strokes have a hit when they when the exhaust
pipes start to tune in, they start to resonate and they pump air. That's what the hit is. All that
extra air going in mixture going into the engine. And the exhaust device did not turn the bike into
a farm oil tractor the way people like to think that Reed valves gives you all this broad power.
But it enabled Kenny to beat
the Suzuki's. Suzuki produced a production racer RG500 in 1975. And here it is. It has
four transfers and another one up the back wall. Then it's a disc valve motor.
I think that year the factory was making like 114 horsepower. So if they'd made a 250 out of this
thing, it would have been pretty strong. I was gonna say, yeah, it's spicy.
The H model might was getting close to 60 horsepower. During the module era, it was sort of 51, 53,
was, you know, struggling along. And H model was a step forward.
And finally, Yamaha decided, well, we have the TZR V-Twin street bike. Why don't we use that crank
case to build a private tier 250 V-Twin? Well, the great thing about the V-Twin is when the
vibration is gone, so is the best, the top reason for not using an aluminum chassis.
And there's been all sorts of talk about vibration. There's no big deal or it's
actually good for you. But it's not good for machinery. So why should it be good for humans?
Anyway, Yamaha went to a V-Twin. What is another thing that can happen when you have a V-Twin?
And what happens is that suddenly, the cylinders can have as wide transfers as they like,
because they're nowhere near each other. Wonderful. These are V-Twin cylinders. There's
no one to join the party. Let's rush up there. Looks great. Get into the combustion chamber
and boogie. Well, I like the contour on the edge of the cylinder as well.
Which is very nice. Yeah. Smoothly curved, getting towards a cup handle transfer port.
And at a point, Yamaha made a big decision. He said, let's just build one bike. We'll build
the Grand Prix bike and the Privateer bike off of the same basis. And then we'll provide FIM kits
for people who are going to race FIM and the people who are going to race AMA won't get it.
And one of the differences is that when you look at the standard cylinder at the transfer port
windows where the fresh charge enters the cylinder, the corners are quite rounded. You might almost
call those ports semi-old, like looking at Adonapolis track from high altitude.
They're four corners. And the FIM kits cylinders were right angles.
And the dividers between the ports are down towards a mill movement.
They were getting all the smoke hole that they could out of these states. Yamaha at a point had
decided on a big oval exhaust port, which they had always used, with two little booster ports,
one on either side. The idea of this was the wider the exhaust port is,
the later they can open it. Which means, oh, we can run more compression because if we're letting
the exhaust out of the cylinder later, the stuff that goes scouring at supersonic speed across the
piston crown is cooler now. But Axlund explained this to me. He said, this is what people are
working toward is crowding all of the exhaust action, the transfer action, into a smaller and
space near bottom dead center, so that the power stroke can be longer.
Well, in the meanwhile, all these terrible things are happening. They're making these
test engines to check on whether the cylinders are round.
And they're not. They're bulging out on the exhaust side because
this whole thing here is full of hot gas at 1700 degrees and that heat is going back into the
cylinder and it's causing the exhaust side to bulge out and the piston ring
does not conform to the bulge. This was the same problem that the rotary engines had in
World War One. The cylinders couldn't be round because they're whorling around furiously.
The leading edge of the cylinder is cool. The trailing edge is overheated. So the cylinder
is not round and the piston ring couldn't seal it. So then they decide let's
surround the whole exhaust valve business with these big water chambers.
They're trying to cool the exhaust side of the cylinder so that it doesn't bulge out.
At the same time, another research group is trying to find ways of finishing the cylinders
so that they are anti-bulged to begin with so that when they bulge, they'll be round.
Now, this is not the same as using a honing plate on a V8 engine. What's going on here is
the early engines had studs that went through so that the head
the force required to make the head gasket seal is crushing the cylinder.
But as soon as they could, they made flanges so that the cylinder was held down by little
flanges here. No more bulk force going through the cylinder which we don't want warping and
becoming square or triangular or whatever it chooses to do. And they found a bunch of power
this way. It had been leaking past the piston rings that were not able to seal anything but
round cylinder. And when that leakage blew into the crankcase, it added inert gas which we would
like to replace with fresh charge. And in the early days, people were filling the balance holes in
the crank shaft and adding plates to the flywheels because they thought this would make a better
pump out of the crankcase. But as they learned more about other aspects of the engine, this
became less and less important. Early engines had a crankcase compression ratio of 1.75.
Then about 68 Yamaha was at 1.5. Then 1972 it was 1.35. And when the read valve thing started,
Yamaha were initially not really willing to do this. They didn't approve of that.
But they saw Honda having a big success in 1983 when Freddy won two races, two 500 races on this
underpowered 500 triple and had these great big reeds in it. So Yamaha, we'll put some little
pedal reeds in the 250 and they got little performance too. So the next year they had to
put the big six pedal reed in. But I don't think Yamaha's heart was in the 250. I think they were
really paying attention in 500 because after Wayne Rainey had his terrible accident,
they weren't able to find someone comparably able to get the best out of their 500. And people were
saying during the reign of McDon, 93 to 97, if Yamaha could find somebody to ride the bike,
it would be more than competitive because it always had tremendous torque.
And the same thing played out on the 250s. But every year they added more stuff. For example,
the 250H of 1981 had a power valve, but it was controlled by a watt governor. You know those
pictures of the fly ball governor whirling around on a frame like this? That was used to make an
steam engine run at a constant speed. In the case of the 250H, it controlled the angle of the eyelids.
And people were actually saying, oh no, it's supposed to be like that. You get to
8,500, bang, they open and it just stays like that. So I took the mechanism apart and polished
everything. And guess what? When you rev the engine up, the eyelids would smoothly come up
in relation to RPM. And we had a good, strong engine. Well, that's sensible. It's just like
ignition timing. Nice smooth weights. Everything's lubricated properly. The weights fly open to RPM.
Yes. And you might even get an ignition curve out of that rather than a switch. Yes. But then
there were other things like the power jet in the carburetors was intended to correct
mixture problems that they had measured on the dyno. And sure enough, they needed to be able
to turn it on and off. So that, the computer handled that. And the electric power valve
in 1981, top riders in Europe were given the electric controlled one. The next year,
it was on the private-tier bike. And they kept adding more and more GP features to the motorcycles.
And they were wonderful bikes. But they cost so much. It would be nice just for a week or two to have
that unending flow of money that would enable a person not to think about such things.
But for most of us, it's not like that. So these motorcycles became less and less common in the
US. And finally, in 2003, I think it was, they decided that a 600 Supersport would be the lightweight
class and the 250 class would come to an end. And that was actually reasonable because at the
beginning, you could get into Supersport for about 2,500 bucks. Tires, brake pads, five-angle,
valve job, fork dampers, a different rear shock. And you're ready to go because you weren't allowed
to modify the engine just the valve seats. Of course, that caused lawyerly thinking to rise
to the surface. There's a lot of subtleties that we can find, don't you think? Hey, boss, look at
these rules. It says valve seats may be modified or replaced. Why don't we put some real tall ones
in there and push the compression right up? So it was done. And that's why John Ulrich said,
we don't race in 600. It's too extensively cheated. Because, of course, they did have the money
to follow through on their ideas. But I think the 250s, the 250 production racer started out
as a wonderful thing because it was available to so many people. It wasn't very good,
but it was better than the existing four strokes. And nobody else was making a 250 production racer.
There were some attempts. Air Maki made one. And I think that Eric Buell had one of those
Air Maki 250s. And Kawasaki
were active in 250 and 350, but they weren't production racers. So I think that Yamaha did
racing in the US a tremendous favor and elsewhere. Australia, UK, Europe.
By making a virtually race ready bike available, pay this amount, it will help you load it on your
truck. And it stayed that way for really quite a long time. And in the 90s, it really got out of
hand. The cost of buying one went up tremendously. I think there was one young man who bought an
Aprilia, which was not really a production racer because one of the things that he had to do with
this bike was make both pistons come to top dead center together. It was a V-twin with disc valves,
27,000. And it was understood that if you were serious about
racing, that you would learn Italian and you could afford frequent trips to Italy to get parts.
There was no program in the US and it was not successful. It could have been, the bikes were
really fast. So it's hard to imagine a production racer concept
with four strokes. So what they've done is they fixed it so that Moto two has a spec engine.
And Moto three may have a spec engine soon if they make a rules change. Because four strokes are
so much more complicated to work on and they are expensive. Let's try nine different camshafts.
Well, we'll need access to a dyno and a dyno operator and, then the systemic
nature of all of this lobe centers and opening ramps and how's the exhaust system? Not that
these things aren't happening in a two stroke, but boy does it, like when I talk to someone who
actually knows what they're doing, when I talk to you about building engines and we start getting
into the details of resonance and heat and this, there's, you know, it means physics, man. It seems
absolutely infinite. So it's just a, it's not just changing the cam. You just,
you can't just change the cam. What happens is, what's the actual compression ratio versus the
mechanical one? You know, the mathematical compression ratio is one thing, but if you have
some crazy camshaft, you could actually really reduce your compression ratio by having the
valves open too much. And then you go back to our friend, Kenny Augustine saying, well,
it's always important to remember that the only time the engine makes powers when the valves are
closed. Well, in fact, that the power stroke is the only real action. The rest of it is housekeeping.
Oh, this burn gas, what are we going to do with it? Let's push it out. Well, we'll need a whole
window. I'll open it. How are we going to refill it? Well, we'll suck in some fresh mixture.
We're going to need a window. I'll open it. Open the other window. Close that one quick.
I don't mean to make fun of four strokes because as Rob Muzzy said so memorably, said,
it's a funny thing. The more you tune on a four stroke, the more it comes to resemble a two-stroke.
And that's easy to understand because what's happening is you're making use of the helping
hand of intake and exhaust wave action. And just as in the case of a two stroke, the wave action has
one part of the wave helps you. And if you wave half a cycle, it's hurting you. So your power
band is going to be like that of a Norton Manx or a TZ250 or a TZ750. 12 to 1500 RPM. That's it.
And people talk about read valves. They don't change the pipe. The pipe defines the engine
and the exhaust system in the case of a four stroke also defines the engine.
The influence of the four into two into one exhaust system on four strokes,
it was such an improvement, such a vast improvement over a four into one
that the first year that they appeared, I couldn't find a single four into one pipe
in any of the garages in Daytona. And I looked. I went round and looked.
The word has got around. You've got to have this. It kills the flat spot.
Your bike just accelerates like mad. I mean, you're gaining the midrange that you didn't have
and you're essentially matching the peak where you're not with a four to one.
Yeah, that's, doesn't that sound like free money, folks? It does.
Well, you're not, you're not, the torque is not horizontal all the way across because it's
going to be, but it is. There isn't a dip at the usual flat spot. So in the early days of the air
cooled bikes, a lot of people just ran four thousands clearance. The book said 1.6 thousands.
And lots of people tried the process that was spelled out in the little handbook.
Lou and White, a cover that said, run your engine at 75, ride around the track at 7,500 RPM,
then tear down and file off hardest spots. Now 8,000 RPM and so forth until you're tired
and you've burned up a lot of gas and tires. And you're not. So basically you're trying to get
this perfect fit. We never could get that perfect fit. And the water cooled engines were such an
improvement because if you thought the water cooled engines cylinders went out of round,
try air cooled. Because you've got all that hot exhaust rushing through this piece of pipe.
And it's right on the front of the cylinder. The exhaust port and the force stroke is in the head.
It can't affect the cylinder very much on the flatheads it did. Because of course the exhaust
valve was next to the cylinder and so was the port. So it's kind of like flatheaditis. But
every year there were lots of little changes. And it was wonderful to open a crate and see
the new cylinders, see the new stuff. But then it got so expensive we couldn't afford it anymore
and we didn't open any crates. But it was a lot of fun while it lasted.
Yeah, my experience coming in at the end of the era, I was covering 250 class
at Cycle News in the like 94 to 99 era. And so they were racing 250 GP but also
you're getting 600 Super Sport. And then I was testing bikes and I got a little bit of seat time
on a 250. I'm a pretty big guy but I was made to fit. And what was shocking to me was how
well it was a race bike. It was really my first taste of a truly race only motorcycle. So you had
a tremendous amount of rigidity, communication, fabulous lightness. Because I'm riding
four-stroke street bikes essentially. I mean I rode some sort of race super sport bikes but
what a massive difference it was. The communication, the communication through the seat,
the response, everything about it was so serious and wonderful and it just was spectacularly awesome.
And it put this experience within financial reach of a large population. And it made racing
attractive. Well, it's 1,100 bucks. I can't not do it.
Yeah, you were telling the story about super hawks and four-stroke,
60s. Oh, that terrible 305. I rode one in an AAMRR race practice and the brakes would be
way terrible at the end of the practice even though they'd been sort of okay at the beginning.
So I put the bike on a box, take front wheel out, take the backing plate out and what is this
glassy stuff on the brake? The friction material. I'm going to get some sandpaper and have that
off there. Next practice. Good brakes for several laps, then bad brakes. It seemed like wax paper.
As soon as I got it hot, the wax would rise to the surface and it would like lubricate the brake
action. Well, I needed to get over to Aljo Brake and Muffler because they had ferroto green stuff
and all that. I can't even imagine where the name Aljo came from.
Imagination is a wonderful thing, isn't it? But they would fix you up with nice riveted on
friction material that actually had friction even when it was hot.
And when the modular engine came along for the first year or so, they had the big four-leaning
shoe drum brake which had been on the factory racer at some point or was inspired by it.
And it was a big heavy club and it was very powerful but it was the old technology.
And so disc brakes came and that was all over with, finished.
And the nice thing about disc brakes is that you can just replace stuff. You don't have to machine
things and arc the shoes and go through all this. Well, people who got good results that way will
remember it fondly. And I appreciate that. But the disc brakes, if the disc is damaged, unbolt it,
put another disc on. Oh, it runs too. Or if it doesn't, you can quickly fix it. New pads, click,
click. And these are, this is steady product development moving right along. Just like
the history of crankpins. I mean, it's a small thing. We used to pay $1 for the crankpin.
And as the 250 evolved and as their street two-strokes evolved, they reduced the number
of press fits by making the crankpin, forging the crankpin as part of the flywheel. And even
in the case of the TZ500, the two center flywheels and the main shaft were forged in one piece
and they put split-race bearing them. So it was a steady march toward no press joints.
And that's what we have today with four-strokes. Forge crankshaft, all in one piece, machined in
one piece. And if you wrecked it, you can get another just as good. And it'll fit, usually.
It's the nice part. Well, thanks for listening, folks. Kevin, I want to recommend that we do a
Patreon podcast on the various ways of controlling the two-stroke power valve because some of these
were very watch-like, terrible, tiny, horribly hard to make work right mechanisms.
Well, for the little subports, they had to have their own little twist-ums.
Yeah, so maybe we can do something over that on Patreon. So Ketch is on Patreon.
Subscribers get all the episodes for free, including, well, they don't get them for free,
but they get them without commercials. Commercial free. So that's one of the benefits. But I think
oh, I think a power valve, we can do a short form on a power valve. That'd be a lot of fun. So
thanks for listening, folks. We really appreciate it. Join us in the comments. We appreciate the
support. Love you guys on YouTube. It's so cool to see the comments and respond. And yeah,
I respond to everything on Patreon. I try to respond as much as possible on YouTube.
We just really enjoy our time. And thanks for listening. We'll catch you on the next show.
About this episode
Yamaha’s two-stroke production racers are traced from Grand Prix influence to the practical engineering that made them work on real tracks. Hosts dig into modular swap-ability—like fitting a “TZ 350 cylinder” onto “RD 350 engine cases”—and explain why two-strokes demand different heat and sealing solutions. They cover early crankcase assembly quirks, cylinder material/coating changes, and reliability fixes (from vibration damage to drum-brake and cylinder wear issues). The episode also highlights accessibility: “It comes in a crate… start up and go.”
Find us on Patreon! https://www.patreon.com/cw/CycleWorldPodcast
Yamaha democratized racing in the 1960s with affordable two-stroke production racers that were essentially ready for the track. How TDs, TZs and more made racing affordable and changed the paddock over two decades.
