The legendary Yamaha TZ750 two-stroke racer was a bike three-time world champ Kenny Roberts said had "too much of everything." Technical Editor Kevin Cameron knows a lot of things about a lot of things, but he might know the most about Yamaha's world-conquering road racer. Kevin and Editor-in-Chief Mark Hoyer talk about the impact and evolution of this affordable production machine that leveled the playing field with factory racing machines.
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00:00Welcome to the Cycle World Podcast. I'm Mark Hoyer, Editor-in-Chief. I'm with Kevin Cameron, our Technical Editor.
00:06This week we're talking about the legendary Yamaha TZ700s, TZ750s.
00:14Kevin knows a lot of things about a lot of things.
00:19TZ750s, he might know more about those than all the other things that he knows.
00:24I mean, deeply, deeply intimate. Already tuning, already at road racing tracks, coming up with TD1Bs and all the Yamaha two-strokes that were running before that and working with Kawasaki's, Kawasaki two-strokes.
00:38My question to you, Kevin, is the TZ750, you know, when I look back at it, I feel like the TZ750 was the motorcycle that actually changed everything in road racing.
00:49Like, it was the first motorcycle that had ridiculously abundant horsepower.
00:54Maybe there were some Suzuki's and Kawasaki's a little bit before that, but the TZ kind of took it everywhere and pushed the technology.
01:05Is that fair to say?
01:06Sure it is.
01:07Because what had happened was that when Suzuki brought their 100-horsepower water buffalo in 1972, there was no tire that would stay on it.
01:22And the same thing with the H2R Kawasaki, quite a bit lighter than the Suzuki, therefore more easily able to spin its tire.
01:33But what a difference between then and now, because they couldn't deliver 100-horsepower to the pavement in 1972.
01:43And today, a whole grid full of riders are talking about how they make the tire last with 300 horsepower.
01:52So that is one of the dimensions of the progress that has been achieved.
01:57But so many riders, see, you could buy a TZ750A in 1974, and there were a lot of them at Daytona that year.
02:07Whereas the Suzuki and the Kawasaki were factory-only motorcycles that were not sold as production racers.
02:15And when Yamaha built this thing, they based it on the TZ250 and 350 twins, or the air-cooled predecessors, that had existed for a long time and which everyone knew how to work on.
02:34They knew how to rebuild the cranks.
02:35They knew how to get the aluminum off the cylinders if they seized and all that sort of thing.
02:40So what Yamaha did was, this is a TZ350 cylinder, but they basically put two of these on a common crankcase.
02:52I'm going to need that cylinder for my RD.
02:55Side by side.
02:56It would pep it right up.
02:58Yes.
02:59Indeed.
02:59They put two of these side by side, and underneath them, they put two crankshafts that were made from the same forgings as the street twin RDs.
03:11And so it was not a factory exotic in the sense of you need to go to school to learn to service this and so forth.
03:22It was a Yamaha.
03:24And what it did was, it put all that power in the hands of so many people that everyone instantly knew what the troubles were.
03:36Oh, the suspension is this.
03:38Oh, going out onto the banking at turn five.
03:42The thing jumps in the air and all these things that were happening in those early days.
03:47And, of course, the 750 was designed for Dunlop Triangular Tires, the legacy of the previous decade.
03:56So they got busy.
03:5874 was the year of the Goodyear Slick Tire.
04:04They began to adopt long-travel suspension from motocross, who are always the pioneers in suspension,
04:14because they need so much of it.
04:17They measure their suspension in feet, not inches.
04:21Yep, feet and the shaft speeds are supersonic on landing.
04:25Yes, indeed.
04:26So it took a while to solve the problems.
04:33But the big 750 won its first Daytona that it was ever entered for.
04:41And it won every Daytona 200 after that until and including 1982.
04:49And 82 was the year that Honda brought the fabled FWS, which was a V4,000cc four-stroke.
04:58And the things were fast.
05:00They had Freddie Spencer and Mike Baldwin on them, but they spent too much time in the pits.
05:06And guess who won the race?
05:09Graham Crosby circulating in a normal way on...
05:15It was actually a 0W31, but basically a TZ750 that had been made from the parts room.
05:24Oh, Graham's here.
05:26We don't have a bike.
05:27Go build him one.
05:30And it was designed to win the Daytona 200.
05:34So the TZ750 exerted steady pressure on chassis suspension and tires,
05:43such that when the second generation of superbikes was designed in Japan not to need to have the whole chassis reinforced with all kinds of welded-in gussets and tubes
05:57and throw away all the suspension and all of the wheels and brakes and tires.
06:03The second generation, which arrived in 83, were raceable street motorcycles.
06:15And the reason for that is that unrelenting two-stroke pressure on 1960s technology.
06:23Hey, we brought the horsepower.
06:26We can't get it to the road.
06:27And gradually, they became able to do it.
06:31So that pressure came from availability.
06:35It's like the GSXR750 in the sense that you could buy a TZ750, you said, for $3,500.
06:43$3,500.
06:44$3,500.
06:45You could buy a bike that was amazingly high performance.
06:49Right up there.
06:50Nothing higher.
06:51And compete with factory bikes.
06:54Yep.
06:54And that drove a lot of people to do that.
06:58It was the great equalizer.
07:00Let's slap leather.
07:02And then you have this entire army of development people that would slowly feed back and develop.
07:12It would change the product.
07:14And it would have to change the tires.
07:16And it would have to change the suspension.
07:18Because all you had to do was, like, what?
07:20Raise the exhaust port and do this and do that and get your transfers.
07:23All those things.
07:23All the things you'd learned with the twins worked on the 750s.
07:26Right.
07:27And so you're making more power than anything else can handle.
07:31What was your Kenny Roberts quote?
07:33I mean, Kenny spent some time on this thing.
07:35Kenny said that he didn't like the TZ750 at all because it had too much of everything.
07:41Yeah.
07:42And what he meant was, you couldn't feed power with it.
07:48Whereas the 500s, which were a generation further on, Yamaha got interested in 500 about the same time they did in 750.
07:57But they saw that the 500 class in Europe was a, they needed to go win that thing.
08:06And so it was hotting up just as MV were deciding, well, our business is helicopters.
08:13And what is this?
08:15Move that aside.
08:17So they needed to have this race winning product and they put it together very quickly.
08:33They called Kel over to Japan to ride it.
08:36And he found that it weaved at high speed.
08:39You couldn't use all the speed that it had.
08:41But so he comes into the pit, takes off his helmet, and he tells them, you got a swing arm that's three inches longer?
08:49Let's try it.
08:51So they either had one or they whipped one up and it made the thing stable.
08:59And they went with that.
09:01It was just like with SR-71.
09:04One, those, those fellows looked at the stress from the wing beams and they said, whoa, these forward spars are doing more than their share.
09:12Let's, let's kind of curve that down.
09:16None of this partial systems of partial differential equations.
09:20Just bend it down.
09:21And that kind of ad hoc engineering is always present at the leading edge because there are the people who are working with this stuff every day and they're, they're rubbing shoulders with these fairly high level problems, but they're just problems like all the others that we have to deal with.
09:43So, uh, well, and in the racing, yeah, the racing context, you're dealing with a deadline all the time.
09:53You got to make, you have to make practice.
09:55So we got to go out and we got to try this.
09:57And then you try that and you're like, well, we have X amount of time before the next practice or qualifying.
10:01And then we only have X amount of time before the race and you do all the things and you suffer or you win and you have victory or you barely make it all the things.
10:10And then you get back in the van and you got time to think about it.
10:12Cause it's going to be, you know, 19 hours to get home.
10:16And then you, you do your stuff in the shop.
10:18You think about what you did and you try it.
10:20And that's that constant.
10:22We're in the field.
10:23That's the farmer farmer slash engineer.
10:25We got to, we got to get that hay in, get the hay in before the rain.
10:29Yeah.
10:30So at Talladega in 1974 on Friday, Kel's boys all had high speed weave past start finish.
10:39And it was scary.
10:40It threw Don Castro's feet right off the pegs so that he was holding on presumably with his hands and with the degree of prehensile ability that one can summon elsewhere.
10:56Harvesting seat foam with his.
10:59Yes, that was it.
11:01And those bikes came in.
11:04They had a hurried conference.
11:05The bikes went on the table and they were still on the table Saturday morning.
11:11And Kel found what I had also found.
11:18He was real busy doing dirt track and every other thing.
11:21And I, there I was in the winter.
11:23I will take this thing apart.
11:24Oh, why aren't these little wire clips in their groove?
11:27I'll make each groove five thousandths of an inch deeper.
11:31No more trouble again.
11:32So on the Monday after the race, people were having breakfast and standing around in this hotel.
11:42And Kel said something that was wonderfully true.
11:47He said, well, we learned one thing here.
11:50And that is that in future, we're going to have to work on the chassis almost as much as we do on the engines.
11:58Maybe more.
12:02And of course, now an engine is something that comes in a box like Kleenex.
12:07You know what's in there.
12:10Put in another one.
12:12And the chassis is the problem.
12:15Because the problem is to get whatever horsepower you have to the racetrack to accelerate and break and turn the motorcycle.
12:26And that's a technology that.
12:28Is still evolving.
12:30Not that engines aren't.
12:31But more power in an engine usually makes you lap slower nowadays.
12:36Because the chassis hasn't been developed to the point where it can transmit that.
12:43So the problem of riding the TZ750.
12:46At first, the A model had twin shocks in the back.
12:49And normal suspension travel is three and a half inches or so.
12:55And they were a handful.
12:57They were terrible.
12:58There were a number of riders who went back to their TZ350s.
13:05Because there were a lot of people at that time saying, well, it takes a special kind of craziness to ride the 750.
13:13And I don't have it.
13:14And some of those guys were really quite good riders on twins.
13:20But when they got on that dynamite package that blew you from one corner to the next, it got more attention than they could give.
13:31So, Kel built one with the monoshock.
13:41And he also came up with the idea of a better packaging for the exhaust pipes.
13:48Originally, what Yamaha had done was they squashed the round pipes until they were almost flat.
13:54And they could put four of them together under the engine.
13:59And when you send pressure pulses into an oval pipe, it tries to inflate to become round.
14:10And soon they crack.
14:16And in 74, the racetrack was covered with pieces of those flat pipes.
14:21Which is why a set of factory fresh ones still commands a fair price.
14:27But Kel was doing this work himself, basically.
14:32And then in 77, Yamaha made the TZ750, D as in David, with the monoshock and with the one-over, three-under exhaust system.
14:46And this was the great big long monoshock, right?
14:49This was the big shock that went from the triangulation on the swing arm.
14:53And it went like basically straight in line with the, you know, going up the frame to the steering head.
14:57And the bracket for the front of it, back of the swing arm, or back of the steering head.
15:01And so it was a real Louisville slugger, that monoshock.
15:06And it had a 20-millimeter shaft.
15:08So when you got your extra preload for Daytona by putting more air pressure in it.
15:15And that monoshock was designed before the revelations of Mr. Fox,
15:25who was the one who put suspension units on the shock dyno that could actually replicate the rapid rod movement that was present in motocross.
15:40And when they came up with a compression valving system that did not turn that turn five transition at Daytona into an impact that just pounded you up into the air, people went much faster.
15:58V-squared damping.
16:00Yeah, you got it.
16:01Got to kill that business.
16:03But these were some of the lessons that this motorcycle presented.
16:13Think about this this morning.
16:15I realized that had there been a rider training scheme in the US that was something like what they have in particularly in Spain and also in Italy.
16:29They could have come close to what is present in MotoGP now.
16:34Unlike any other racing series in the world, every rider is on a factory engineered factory race bike.
16:42Every rider has been through the ladder of training from mini bikes when they're five years old up through the Moto3, Moto2 ladder and then to MotoGP.
16:59And I remember reading without much surprise that Mark Marquez had a professional manager from age 12.
17:12And it wasn't because his family were in the oil business.
17:20Talent scouts had said, we want to buy into this program early.
17:28And so what was lacking in the case of the US was here were all these motorcycles with essentially identical performance.
17:37They all had too much.
17:39Only a very few people could ride them.
17:42So if you were watching the race, the factory bikes would come by, then the most talented of the privateers, and then the rest were mysteriously slow.
17:56And I think I once rode one of these things back to the paddock from Victory Circle at Loudoun.
18:08And I didn't go over 6,000.
18:11And I thought, there's a whiff of eternity.
18:17Two strokes, like a hot two-stroke will do that to you, even when they're small.
18:21And no power valves, so that you're really, the vibration, you know, as you always put it, it's an organ.
18:29It has one pipe, or in this case, four pipes, but they're playing the same note.
18:34They're playing the same note.
18:35And that's, this is the thing that people didn't get.
18:39When motocross bikes began to be given reed valves, same year as TZ750A, 1974, and hats off to Dale Herbranson, who probably gave Yamaha some helpful advice along the way.
18:57People had the idea that, oh man, you put a reed valve on that thing, and it'll pull like a bear from way down.
19:08Well, TZ750A, the torque curve went along, rising sort of slowly, and then it got to the 9,300 RPM.
19:18It doubled, and then it went on to another 1,000 or 1,300 RPM.
19:28That 1,000 or 1,300 RPM was the usable power band.
19:32If you tried to accelerate off a corner with that 9,300 in the middle of your acceleration,
19:40when it hit, you were either going to be carefully with the throttle more closed than open, or you're going on your posterior.
19:52Yeah.
19:52Well, all the 500 guys, you know, when I was growing up and watching, you know, Kevin Schwartz on the Pepsi Suzuki and Wayne Rainey and all those guys,
20:02you know, they would be, they would be coming out, and then they would be on the exit of the corner trying to moderate the torque
20:10because the spike was so big as they were coming into it, if you weren't already into it.
20:14I called that the Schwartz roll, rolling it back as you continue to accelerate harder.
20:20Yeah.
20:21And it makes perfect sense because when the exhaust pipe is not pumping the air, the crankcase is pumping it, and that has limits.
20:37And when the pipes, when the engine speed gets up to the point where the pipes are resonating,
20:43then the torque really starts to talk because suddenly the cylinders are getting that much more air.
20:51So, what Mike Baldwin did, oh, well, I'll back up a minute.
20:57There was one race at Loudoun, it was a club race, where my rider, Richard Schlachter, managed to beat Mike Baldwin.
21:05And Mike went away, and I think sat silently somewhere, thinking about all this.
21:13And the next race weekend, he just disappeared.
21:17And I had a conversation with him that weekend.
21:23He said, well, I've learned something.
21:26He said, don't ever let the engine turn less than 9,300.
21:33He said, stay in the linear zone, and it won't hurt you.
21:38And McDoin came to the same conclusion about Honda's NSR 500.
21:44Ride it in the linear zone.
21:47The Don Cane taught me, when I was riding a Hayabusa race bike, which you can imagine was a monster, a built Hayabusa motor on the track.
21:57And I was trying to ride it lower in the RPM range, thinking like, well, I want to keep this thing out of its power.
22:02But it was all power.
22:04And he said, no, it's the opposite of that.
22:06What do you want to do with this bike?
22:08It's the same theory.
22:08What you want to do with this bike is ride it on the downslope of the torque curve.
22:13So you want to take the RPM higher, because as you're rolling it on, it's not building torque.
22:19It's declining.
22:20Wonderful.
22:21And it was, that was, he had a lot of, Don Cane has a lot of thoughts, man.
22:25Oh, yeah.
22:26Well, Mike Baldwin said, here's my advice to people who want to ride this motorcycle.
22:33He said, get some tape, put it on your tachometer so you can't see anything below 9300.
22:41Go out on the racetrack and do your stuff.
22:45If, if at any time, you cannot see the tach needle, pull into the pits, park the bike, take off your helmet, get the newspaper, turn to the help wanted, and look for other work.
23:03And yet, Kenny Roberts says, I hate this bike because it has too much of everything.
23:09Yeah.
23:10And, you know, I mean, Kenny's talented, right?
23:13Yeah, no question.
23:15Well, there were a couple of occasions where Kenny and Mike Baldwin were in the wrong order.
23:24It didn't happen often, but it did happen.
23:27So I think that there's no one rider who discovers everything.
23:34But I do insist that in any given era, the top rider is likely to be the one who best exploits what is new.
23:43In the motorcycle.
23:45In the motorcycle.
23:46And I think when Kenny came along, he realized that you could steer the thing with the throttle, just like you do in dirt track.
23:57And when he got to Europe in 1978, the Europeans just were open mouth at this and that their, their sporting newspapers were full of all this talk about how American dirt track is the font of future ability.
24:17And so it proved for a few years.
24:20Yeah.
24:20Well, and you know, on that subject, Indy Mile, I mean, too much of everything.
24:25And then the quote from Kenny Roberts was, I mean, if it's too much of everything on a road race course, imagine that on a, on a flat track.
24:32And, and of course it would have been, I'm sure Calc or others would have tuned that bike to operate in more of a dirt track range.
24:40But I mean, as you say, you know, time to cut wood, you hit whatever that time is where it's resonating.
24:45It's just coming and it's just there.
24:47And, uh, you know, the famous quote was, uh, they don't pay me enough to ride that thing.
24:54Kenny Roberts, they don't pay me enough to ride that thing.
24:56And we had a, a writer for us, Joe Scalzo, who was, uh, he was, he was very good.
25:04Joe, Joe did some beautiful work for us.
25:06It's in the archive and it's, it's fantastic.
25:08But one of the things, one of the ways he portrayed, it was like, you know, it was like Jay Springsteen and I forget who else.
25:13And they're riding XRs and they're like, Oh, la de da, Jay, ain't life grand at the front of the pack.
25:20Gasp, what's that horrible sound?
25:23And then Kenny would come, Kenny comes smoking by and, uh, and then redoing, you know, doing that.
25:30I think it was 09 when, uh, they got the bike back together at Indy and, you know, the famous video of, of Kenny going out and riding it again.
25:37And Kel's there with the bike and, uh, you know, the facial expression of Valentino Rossi.
25:43Of seeing that bike go by and then the way Kenny wrote it, you know, here's Kenny, like throwing it in.
25:50I mean, he really rode the bike.
25:51He had it sideways and the sounds, I mean, you got to find that, find that video on the, uh, interwebs after you, uh, finish with this podcast.
25:59Cause it's just absolutely remarkable.
26:03And actually the funny story is seeing Kevin Schwantz after that, because Kevin was going to do a lap on his, uh, Suzuki 500 Grand Prix bike at Indy for the MotoGP.
26:15And he was going to do a parade lap and he's like, Oh bleep.
26:18Now I got to really like, right.
26:20Like he was like, yeah, I was just going to circulate.
26:23But Kenny did that.
26:24So now I've got to, you know, I've got to actually do something out there.
26:27I can't just wobble around and he did and he did.
26:31Yeah.
26:32Well, uh, there were some things about the 750 that were unappreciated at the time.
26:39One of them was reverse engine rotation because each of the two separate cranks, which were end to end, had on its inner end, a thin gear.
26:52And that gear meshed with a double width gear on a, on a jack shaft that went over to the right to drive the clutch.
27:00And so, uh, that reversed the engine rotation so that it was the opposite of the wheels, which gave that motorcycle some advantages in direction changing.
27:14Why is that?
27:15Every, every, because the gyro resistance of the crankshaft rotating one way opposes the gyro resistance or cancels the gyro resistance of the wheels revolving the other way.
27:30And what do we do in MotoGP?
27:33In MotoGP, everybody has a reverse rotator.
27:36Everybody reverses the crank rotation to allow the bike, you know, if you put a bit more.
27:43Yeah.
27:43And I, I talked to Mick doing about this and he said, uh, well, we, we finally did that.
27:51And while it was better, he said it didn't fix everything.
27:55Well, I think if you're trying to send 200 or 300 horsepower through one tire that only uses one third of its width at any given moment, uh, there are always going to be problems.
28:11Unless, unless, of course, the tire and the track have cure teeth, so, which they don't.
28:18Funicular road racing.
28:20Funicular road racing.
28:21Yes, sir.
28:22So, uh, that was one of the little things.
28:26Another little thing was that in 1961, Yamaha hired, um,
28:32an engineer to design their Grand Prix bikes.
28:39He designed a 125 and a 250.
28:41And he gave each one a little, uh, girotor pump.
28:49He lowered the oil level in the gearbox down until no gear could touch it.
28:54Um, and he had six or eight or however many gears pairs there were oil squirts across the top of the gearbox.
29:02Um, Kevin Schwantz's Suzuki has them too.
29:05Uh, so each mesh got its own little oil squirt and then the shafts were hollow and they got oil sent through them.
29:13Um, uh, to lubricate the free spinning gears so that they couldn't seize on the shaft.
29:20And in some engines, getting rid of that oil churning is, is several horsepower.
29:27And I talked to heat.
29:29I mean, yeah, heat, which is going to go to your oil cooler, which then it has to be bigger, which means that you have more drag.
29:36You know, it's, it's like what always happens with fighter planes is that they say, oh, well, we've got this new gun and it carries 200 rounds, more ammunition.
29:47And then we want to put in more fuel and we want to do this.
29:51We want, oh, well, we need a new engine.
29:53Well, the engine updates coming in a year and a half.
29:55And it, it, that's life is that you're always chasing these problems and trying, trying to achieve a net improvement is not guaranteed.
30:08But F-22s are pretty big.
30:12Yeah, they're big.
30:13I mean, they're big.
30:14I mean, you think about a B-17 and how, uh, how large a B-17 looks and in flight and on the ground.
30:20And, man, you, you roll an F-22 up next to it and it's like, holy moly, you know, it's like taking a, it's like taking a traditional mini or a traditional Porsche 911 and putting it next to their modern counterparts.
30:32And it's like this diminutive little toy car compared to the big, the big thing.
30:37Monster.
30:38It is.
30:38Mission creep.
30:40Yeah.
30:41So T-750 got one of those little gerotor pumps.
30:44And, of course, uh, it was liquid cooled too and had, uh, on the jack shaft, there were a couple of cross-axis skiers.
30:53One of them drove the, uh, water pump.
30:56And it was pretty easy engine to, to work with because you knew how long the cranks would last.
31:07They'd last about 900 miles and the factory guys changed them at 450 or so, uh, just to be sure, because they had them stacked like cordwood in the back.
31:20Um, when you, when you, when you encounter the stories that Robert Iannucci tells about getting replacement crankshafts made for the Honda 6 250 racer, uh, when I heard them warming those things up at Mostport in 1967, it sounded like they had those crankshafts stacked like cordwood in the van.
31:45They were, they were just barking.
31:47Yeah, Robert Iannucci is, uh, is the, uh, you know, team principal and, and, uh, grand old man of team obsolete racing.
31:54And, and he had, you know, bought out the MV Augusta racing department and he had a real penchant for the very, uh, the very finest, most exotic racing motorcycles of this very classic era.
32:05And man, does he have a collection and does he run them too?
32:10He's really, you know, he's active getting them on the track and, and all that still.
32:13Yeah, he has like, he has like more than 80, 80 bikes.
32:18Um, many of them are, um, AJS 7Rs and matchless G50s, but he also has exotic Harleys, Benelli, MV, all those things.
32:31Uh, but let's not, let's not get started in that direction.
32:36No, no, it's fine.
32:37I just, you know, when we, uh, we drop names a lot in this and, and when you say something like Rob, we've got to have our, our Rob out there and, and talk about our physics.
32:46Here's another, here's another little tidbit about the TZ 750.
32:50The reed valve, there are four of them, one for each cylinder, um, or I should say two for each cylinder pair because they're in blocks of two.
33:00Uh, is the same part number as the reed valve on the YZ 80 child's motocrosser.
33:07Yes, sir.
33:09Oh, they'd be so wee.
33:10Uh, well, they were Irv Kanemoto, um, always referred to them as the obstruction because if you pride those reed valves open, as far as, as they would go, you could get about a cross-sectional area of about 600 square millimeters.
33:31But the cross-sectional area of the carburetor was 900 and something, 50% more.
33:38But I think that thing was thrown together at the last minute.
33:43It was sort of like, oh, okay, what do we got here?
33:45Hey, we got a bunch of these.
33:46Yeah.
33:48Seems to run.
33:49Yeah.
33:50And, uh, so the, the first year of the bike was 64 by 54 bore and stroke, same as a TZ 350.
33:57And, uh, they had the, the blue cylinder nuts made of aluminum, which occasionally broke.
34:08And they also had the cylinder stud breakage problem that got overcome the following year, 750B.
34:15Um, and they also manufactured a, what they called the full kit, which has provided you with cylinders and pistons and heads for, uh, 66.4 millimeter bore, which brought it out to a full, uh, 750.
34:34And that's why we talk about the TZ 700 was really what it was.
34:38It wasn't a 750.
34:40Yeah.
34:40It was a 693 or something like that.
34:42Yeah.
34:43Little, um, little, he says to me that why did Yamaha, sorry, go ahead.
34:52Yeah.
34:53No, what were you going to say about Yamaha?
34:54I was going to go, why did Yamaha choose reed valves?
34:56There's all kinds of different ways.
34:57I think, you know, we're talking about fire breathing, two strokes and, and so forth.
35:01Maybe we can talk about how reed valves work and why Yamaha would choose them versus other types of induction and location of carburetors.
35:09And what are the advantages and disadvantages?
35:11Because it's obviously a formula that worked that picking reed valves and doing the inline, the way they did it really worked for a long time.
35:20Yeah, it did.
35:20And in fact, with the 500, they dropped the reed valves, the original, the, the bike that, um, Agostini won the 500 championship on in 1975, uh, was a, a reed motor.
35:37And when they needed more power, um, they dropped the reeds and had piston port induction.
35:47And that's the type of engine that Kenny won three world championships on.
35:52No, no exotic disc valves or, and certainly no reed valves.
35:57Well, the thing about the disc valve, uh, is that you can make the timing asymmetrical.
36:03You can open it, uh, when the piston starts to move to draw air into the crankcase because the crankcase is a pump in these two strokes, air pump.
36:14And you can close the valve fairly early after top center if you want a somewhat broader power band, or you can close it as late as 85 degrees if you want to.
36:28And they carried, Aprilia carried stacks of these disc valves with all different timings.
36:34But what Yamaha found out was, um, when you finish your beer and you don't have another, what do we do now?
36:46You know, well, you blow across the mouth of the bottle and it makes a, makes a, a tone.
36:51Um, well, engine crankcase does the same thing and the piston is there moving up and down to, uh, excite vibration.
37:04And Yamaha found that if they, they could make the timing, uh, a hundred, open a hundred degrees before top dead center or 102 and close at 102 after.
37:18And if you were in the power band, it would develop wonderful power.
37:25The intake system flowed a lot of air, but if the engine was at a lower RPM, of course, it would blow back a lot of the air because the air wouldn't be rushing in as fast as the piston came down and started to compress the crankcase.
37:40And so the air would say, Oh, my mistake.
37:43I'm going back this way.
37:45And so the read valve stopped that reverse flow.
37:52So instead of having.
37:55So it, it, it's a check valve.
37:57Yeah, that's all it is.
37:58If you've never seen a read valve, it's, you know, it's basically, here's your carburetor.
38:01The carburetor then has the read valve, the block that goes into the cylinder block and there are pedals on it.
38:11And so when the intake blows in and there's vacuum on the other side of the read valves, they open and the air flows in, air fuel flows in to the crankcase under the pistons.
38:23The pistons are then coming down and they're pushing the air through the transfer ports, which are just tubes in the cylinder to get fired into where the chamber is.
38:33And, but it's all connected.
38:34There's nothing shutting off the exhaust pipe from any of this.
38:39So the read valves, when that pulse would come back, the read valves would close and keep that from blowing back out your, your carbonator.
38:47Another wonderful thing that happened.
38:49Another wonderful thing though, is that you can imagine that, uh, the piston has come down and it's closed the read valve.
39:01And now the piston is, has it bottom center and the, the exhaust pipe is, if you will, sucking on the cylinder.
39:09The pressure in the cylinder is dropping, dropping, dropping.
39:12Now the reed's open again and the exhaust pipe pumping action is pulling air straight through from the atmosphere, through the carburetor, through the reed and into the crankcase.
39:25So, uh, and this is something that, that, um, Dr. Blair documented second opening.
39:33And so that, uh, Dr. Blair up there at Queens university in Belfast, Northern Ireland, uh, was a computer programmer and math modeler who took an interest in two stroke engines.
39:52And when he came to visit me, he brought a, a bottle of old Bush mills.
39:57And we drank that stuff and had a nice conversation that evening, but he, he was basically one of those math heavy scientific types who, whose attitude was, Oh, I can calculate that.
40:13And he sold a lot of services to the motor industries.
40:19And I think he was all set to do the same with, uh, Detroit during the years when they were having a, Hmm.
40:28I wonder if a two stroke engine would solve some of our problem because two strokes are, are wonderfully compact and they're lightweight.
40:37And if you could just stop them leaking mixture out the exhaust, uh, straight to Ann Arbor, where the EPA is, you, you could have a hell of a low emissions engine.
40:53So he was on that program, but then he said, they, they were trying to, uh, re invent the wheel as far as two strokes were concerned.
41:04And he said, what they really needed was somebody who already knew about two strokes, i.e. himself.
41:10And, uh, but it was killed by the, by the, uh, the bean, bean counters because they, they spent a bunch of money and then they didn't get anywhere with it.
41:20But the reed valve, uh, made engines rideable that had, um, extraordinary, uh, radical port timing.
41:36They, they would just kind of brrrr along rather than constantly burping and farting mixture out back out of the intake.
41:46But when, uh, Freddie began to win races in Europe on that three cylinder Honda, which had large area reed valves, real reed valves from motocross at that point, people all thought, man, that thing's got some kind of lope of bottom end must be those reed valves.
42:08And that really amused Irv Kanemoto, who was working with Freddie at that time, because he said, Freddie knew that that bike didn't have the power to accelerate with the four cylinder bike.
42:21So he was riding a corner speed style and he would be going so fast at the apex that his exit speed was high.
42:31And it looked like, man, that thing really accelerates.
42:36No, what it, what it does is it doesn't have to decelerate as much to get through the corner.
42:43But, um, Freddie's engine, uh, came on at 9,800 and was all finished at 11,000.
42:54So like the TZ 750, a 1200 RPM power band.
42:58So that drives me back to the, the TZ and the evolution of road racing.
43:05When did tires catch up or did they ever catch up with the TZ 750 power production?
43:11Well, I think TZ 750 became irrelevant and the tire people turned to the 500s.
43:21They turned to super bike and so forth.
43:23So, um, but there were, there were some, for instance, at the end of the 1976 Daytona race, um, the leaders' bikes were all weaving quite furiously.
43:36Their tires had, had become fatty gay.
43:42And so the, uh, Goodyear people did what Dunlop had done years before to stabilize that mode, make tire with a taller sidewall so that it had more wiggle to it.
43:58He's making faces here for you audio people.
44:01Well, he, Kevin grabbed his lips and moving them around.
44:04It was good.
44:05So, um, those, those tall sidewall tires were, uh, quite commonly used at Daytona in the, in the later seventies.
44:17But what happened next was that, uh, 500 horsepower, of course, started out around, uh, 90.
44:28Actually, the MV four strokes were faster than the Yamahas to begin with, just that the Yamahas accelerated better and they didn't have engine braking problems.
44:37But the 500 started out around 90 horsepower.
44:40And when Kenny was riding the Zero W 48 and so forth, they were making maybe a hundred and a quarter.
44:48And then pretty soon they were making 150 and then 170.
44:53And when they got up to the one eighties and one nineties, um, it was time for tires were all finished.
45:02The bias tire, uh, people would sometimes come to the line with their tires, shiny with mold release compound shiny because they didn't want to scuff them in because that might be one more good lap.
45:18You could do so you could race for 10 laps on those tires.
45:24And then you had to be ahead far enough that you could, I'm not going to look back, but I know those guys are sliding all over the place just like I am.
45:35And that was something that, uh, Mick Doohan talked about later.
45:39Although with, uh, the new radial tires that came in 84, that, um, you're going to spend the last 10 laps of the race sliding around just trying to finish.
45:52And in 81, the way Marco Lucanelli was able to win, uh, races was at the start, he would let everybody go just like in this last race, um, at Barcelona, MotoGP race, uh, Bagnaya, uh, didn't mind when two guys passed him in the middle of the race, because he said, I knew that the same things would happen to their tires.
46:20And he said, a few laps later, their pace came back to me.
46:26And then he was able to pass them.
46:28And he said, when I got into the lead, after one lap, I had a lead of four tenths of a second.
46:34And I knew all I had to do was wait for the finish line to come.
46:40And what a luxury to, to have tire.
46:44Somehow that all started with the TZ 750.
46:46I'm sure.
46:47It sure did.
46:48It sure did.
46:48It did.
46:49Yeah.
46:49And people who rode, um, Michelin's and Dunlop's and Goodyear's back in the bias tire days, the Goodyear's were never more desirable than on extremely hot days.
47:05When the other two companies would tell their contracted riders, go see the Goodyear guys.
47:10We don't have anything that'll work today because their tires were optimized for, um,
47:17dreary Northern Europe.
47:22So when the TZ 750 was, you know, released and people started messing with it, what kind of horsepower was it making?
47:2990.
47:3090.
47:30And then what, what, what were they doing at the end, you reckon?
47:33Uh, well, people who've done dyno work with them.
47:37And of course, dynos are also different, but they said 120 for a well-tuned, um, DEF model, uh, which is the 1x2, uh, part number prefix for the, uh, big, big, late model engine.
47:58The entire podcast on the, on the part numbers that Kevin remembers.
48:02So, uh, 120 for one of those.
48:09And they thought 140 for a successful modification.
48:15Like Richard Schlachter had when in, um, what was it, 81, he looked like he had the race one.
48:24He was pulling away from Singleton and all those, uh, French fellas.
48:29And then his chain began to go.
48:32And he thought, oh, I could fail to finish.
48:39So he, he knocked it just enough to finish third, which I thought was a good performance.
48:46Yeah.
48:47Talk to me about Talladega.
48:49I mean, you know, sort of a big track like that.
48:51I mean, I, you know, is that, was that much different than Daytona?
48:55What was Talladega like?
48:56I'd never been.
48:56I don't, I think the times that I was there with the big motor that riders at mines were elsewhere.
49:04Uh, you know, it's running.
49:09So I think what Goodyear had done, well, what they told me in 1978, I went to visit those guys.
49:20And they said, when, when we decided that we should get into motorcycle racing with Harley Davidson pushing them,
49:27um, we were filled with pride at the wonderful, exotic new rubber compounds that we'd developed in sports car racing.
49:36So we made motorcycle, uh, carcass with those lovely, uh, rubber compounds on.
49:45And they were terrible.
49:46They, they just gave up immediately.
49:48And we're having a meeting and we're drinking bad coffee and eating more donuts.
49:53You know, our wives are saying, uh, you know, you're going to have to get some bigger shirts.
49:57Um, and somebody raised his hand and said, how about we try some of our NASCAR compounds?
50:08They have that high specific loading pounds of, of load per square inch of tire footprint, uh, like a motorcycle.
50:18Yeah.
50:19Yeah.
50:19That's a good idea.
50:20So they did that and that worked.
50:23They were on their way with that.
50:25Um, and because like I said before, a motorcycle tire, not only is it small, but you're only using one third of it at a time or one quarter,
50:34because when you're upright, you're in that little center area and then you're on the shoulder and then you're on the edge.
50:40So it was a story of finally realizing that the tires with pattern with rainwater drainage grooves in them, the tread was just too flexible.
51:01It heated up too much and it lost its properties.
51:06So they did what they were doing in, uh, in sports cars and, and Indy cars and went to a slick and they were handing out, um, sort of half-hearted slicks for comments at the end of the 73 season.
51:20Um, so those tires were really flexible.
51:23And then by the time they were, um, in production with racing slicks for TZ 750s, uh, in the spring of 74, they were good for like three quarters of a second a lap.
51:36Amazing.
51:37Other people could just go home.
51:39Um, and Goodyear hung in there until 1984 and then they said, well, we're not doing that anymore.
51:47Goodbye.
51:48Hmm.
51:49And that was, that was the end of that.
51:52But everything comes to an end.
51:55Uh, TZ 750s came to an end.
51:57They dominated, uh, U.S. racing for that whole period.
52:01And then, uh, they were stopped at the stage door.
52:06You know, you guys have to pay admission, go around the front.
52:10And suddenly it was super bike.
52:14And it had to happen because four-stroke motorcycles are what they make.
52:19And commerce, you know, identify, identification.
52:21I mean, it was one thing to identify with the brand and yeah, you could get an RD 350 or an RD 400, but the world was certainly moving to big four strokes and it made sense for identification purposes and enthusiasm.
52:35It's such a, it's, it's such a, a contrast to think about a TZ 750 on one hand, which has a throttle, a brake, a rear brake.
52:49Uh, it has an enrichment lever for starting, which had little, little carburetors molded onto the side of each carburetor.
52:58It had a little piston valve and it provided starting mixture.
53:03And that was it.
53:06That was the extent of the rider's interaction.
53:09And what information did the motorcycle provide?
53:12RPM.
53:14And water temperature.
53:16Uh, but if you look at a modern MotoGP bike, it is just so much more sophisticated and just as is the case with carrier planes, the rider is given help where help is needed.
53:38Nobody wants a ramp strike.
53:40So they've got autothrottle and they've got radio beam guidance and all these things to help you.
53:50We're going to make night traps here.
53:52Are you scared?
53:54Were you scared already yesterday?
53:57Uh, so in order to allow the rider of today's motorcycle to concentrate on what the human is uniquely good at, which is how am I going to use the tires in such a way that my tire budget won't be negative at the end?
54:19Because I might have to maneuver, I might have to attack the guy ahead of me, or I might have to fend off the guy behind me.
54:27And if my tires are gone, I'm just going to have to put my hands up and say, I surrender.
54:32So all those electronic systems and all those, the sophistication of modern suspension units and the marvelous properties of modern tires are there to allow the rider to actually command the system.
54:52Because if you look at a manx Norton, it had a mixture control lever so that if you were thudding past the, the forest section at, uh, some of those European tracks where everyone believed that all this oxygen was rolling out from tree breathing, you could richen up a little bit.
55:17Oh yeah, I think I'm, I think I got 50 revs out of that.
55:21And so much in those early days, the rider was sort of like an engine manager and particularly so on the two strokes.
55:33Um, some of those people were, were really good at keeping their engines alive through a long, uh, TT event.
55:44And nowadays that's handled.
55:47Um, and the engine is something that comes in a, just like a, a modern jet engine comes in a can.
55:55It's filled with nitrogen so that nothing in there is going to deteriorate from exposure to oxygen.
56:02And you take out a new one when they tell you that you may.
56:06But I think, uh, it's a whole different game because now the rider is having to extract what the tire can give using his style of riding at the point that it is that day.
56:24Because all these guys are talking now about, uh, Mark Marquez was saying, oh, I looked at the data from the other riders and I see some of the things that they're doing and I decide I'll try that.
56:38But then for the race, he said, I go back to my own style because safest thing is what, you know.
56:45Well, it is a huge evolution of the sport, the technology in the days.
56:53Enough, it's evolution, it's evoluted away from $3,500 in a crate.
56:59Well, that was the great thing about TZ750 was you could have one.
57:04You could have one and then you could put the pipes wherever you want.
57:09You could take it apart, port it.
57:10You can get, you could get parts to redo something that you messed up.
57:14But you, you had, you know, you didn't like the steering head angle.
57:17It was made of steel.
57:19No one's changing steering head angles in MotoGP.
57:22They're not opening engines.
57:23They're not putting bearings in.
57:25No one's filing the edges of a crankcase in the back of a van.
57:28It is a much, much different place.
57:31But, you know, really the, you know, looking back at it, the TZ sort of laid all of this groundwork for this tire management that you're talking about.
57:42It really was the problem, yes, in a very forceful way.
57:46Of so much power.
57:50More, you know.
57:52How are we going to manage it?
57:53Too much of everything.
57:55Yep.
57:55Too much of everything.
57:57Too much of everything.
57:58Well, I think it's a good place to, we've had too much of everything today as well.
58:06We've done the job here.
58:08We thank you for listening to the TZ750 Cycle World Podcast.
58:13It's near and dear to Kevin's heart.
58:15And, of course, I'm an RD 350 enthusiast and owner that's a Kevin Cameron port job on it.
58:23Going to have to finish those pipes soon, I guess.
58:25When you put a 750D cylinder on an RD, it's called an OW15 1⁄2.
58:38I'll give you a call.
58:39Let's talk.
58:40Let's talk about cylinders then.
58:41Okay.
58:43All right.
58:44Thanks for listening, everybody.
58:46We'll catch you next time.
58:47We'll catch you next time.