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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00:00 Welcome to the Cycleworld podcast. I'm Mark Hoyer, Editor-in-Chief. I'm with Kevin Cameron, our Technical Editor.
00:06 This week we're talking about the legendary Yamaha TZ700s, TZ750.
00:13 Kevin knows a lot of things about a lot of things.
00:18 TZ750s, he might know more about those than all the other things that he knows.
00:24 I mean, deeply, deeply intimate. Already tuning, already at road racing tracks,
00:30 coming up with TD1Bs and all the Yamaha two-strokes that were running before that,
00:35 and working with Kawasaki two-strokes.
00:39 My question to you, Kevin, is the TZ750, when I look back at it,
00:44 I feel like the TZ750 was the motorcycle that actually changed everything in road racing.
00:50 It was the first motorcycle that had ridiculously abundant horsepower.
00:54 Maybe there were some Suzuki's and Kawasaki's a little bit before that,
00:59 but the TZ kind of took it everywhere and pushed the technology.
01:05 Is that fair to say?
01:07 Sure it is.
01:10 Because what had happened was that when Suzuki brought their 100-horsepower water buffalo in 1972,
01:20 there was no tire that would stay on it.
01:23 Same thing with the H2R Kawasaki, quite a bit lighter than the Suzuki,
01:30 therefore more easily able to spin its tire.
01:36 But what a difference between then and now, because they couldn't deliver 100 horsepower to the pavement in 1972.
01:44 And today, a whole grid full of riders are talking about how they make the tire last with 300 horsepower.
01:53 So that is one of the dimensions of the progress that has been achieved.
01:58 But so many riders... See, you could buy a TZ750A in 1974, and there were a lot of them at Daytona that year.
02:08 Whereas the Suzuki and the Kawasaki were factory-only motorcycles that were not sold as production racers.
02:16 And when Yamaha built this thing, they based it on the TZ250 and 350 twins, or the air-cooled predecessors,
02:30 that had existed for a long time, in which everyone knew how to work on them,
02:34 they knew how to rebuild the cranks, they knew how to get the aluminum off the cylinders if they seized, and all that sort of thing.
02:42 So what Yamaha did was... This is a TZ350 cylinder, but they basically put two of these on a common crankcase.
02:52 I'm going to need that cylinder for my RD.
02:55 Side by side, it would pep it right up.
02:58 Yes, indeed.
02:59 They 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.
03:10 And 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.
03:22 It was a Yamaha.
03:24 And what it did was, it put all that power in the hands of so many people that everyone instantly knew what the troubles were.
03:36 "Oh, the suspension is this. Oh, going out onto the banking at turn five, the thing jumps in the air," and all these things that were happening in those early days.
03:47 And of course, the 750 was designed for Dunlop triangular tires, the legacy of the previous decade.
03:56 So they got busy. '74 was the year of the Goodyear slick tire.
04:03 They began to adopt long travel suspension from Motocross, who are always the pioneers in suspension because they need so much of it.
04:18 They measure their suspension in feet, not inches.
04:21 Yes, feet and the shaft speeds are supersonic on landing.
04:25 Yes, indeed.
04:27 So it took a while to solve the problems, but the big 750 won its first Daytona that it was ever entered for.
04:42 And it won every Daytona 200 after that until, and including, 1982.
04:50 And '82 was the year that Honda brought the fabled FWS, which is a V4,000cc four-stroke, and the things were fast.
05:00 They had Freddy Spencer and Mike Baldwin on them, but they spent too much time in the pits.
05:06 And guess who won the race?
05:09 Graham Crosby circulating in a normal way on, it was actually a 0W31, but basically a TZ750 that had been made from the parts room.
05:25 "Oh, Graham's here. We don't have a bike. Go build him one."
05:30 And it was designed to win the Daytona 200.
05:35 So the TZ750 exerted steady pressure on chassis, suspension, and tires, such that when the second generation of superbikes was designed in Japan,
05:51 not to need to have the whole chassis reinforced with all kinds of welded in gussets and tubes,
05:58 and throw away all the suspension and all of the wheels and brakes and tires.
06:05 The second generation, which arrived in '83, were raceable street motorcycles.
06:15 And the reason for that is that unrelenting two-stroke pressure on 1960s technology.
06:23 "Hey, we brought the horsepower. We can't get it to the road."
06:28 And gradually, they became able to do it.
06:32 So that pressure came from availability. It's like the GSX-R750 in the sense that you could buy a TZ750, you said, for $3,500.
06:43 $3,500.
06:44 $3,500. You could buy a bike that was amazingly high performance.
06:49 Right up there. Nothing higher.
06:51 And compete with factory bikes.
06:54 Yep.
06:55 And that drove a lot of people to do that.
06:59 It was the great equalizer. Let's slap leather.
07:02 And then you have this entire army of development people that would slowly feed back and develop.
07:12 It would change the product, and it would have to change the tires, and it would have to change the suspension.
07:18 Because all you had to do was raise the exhaust port and do this and do that and get your transfers.
07:23 All those things. All the things you'd learned with the twins worked on the 750s.
07:27 Right. And so you're making more power than anything else can handle.
07:31 What was your Kenny Roberts quote? I mean, Kenny spent some time on this.
07:35 Kenny said that he didn't like the TZ750 at all because it had too much of everything.
07:42 And what he meant was you couldn't feed power with it.
07:48 Whereas the 500s, which were a generation further on, Yamaha got interested in 500 about the same time they did in 750.
07:58 But they saw that the 500 class in Europe, they needed to go win that thing.
08:06 And so it was hotting up just as MV were deciding, well, our business is helicopters.
08:14 And what is this? Move that aside.
08:18 So they needed to have this race winning product and they put it together very quickly.
08:33 They called Cal over to Japan to ride it. And he found that it weaved at high speed.
08:39 You couldn't use all the speed that it had.
08:42 So he comes into the pit, takes off his helmet and he tells them, you got a swing arm that's three inches longer.
08:49 Let's try it. So they either had one or they whipped one up and it made the thing stable.
08:59 And they went with that. It was just like with SR-71.
09:05 Those fellows looked at the stress from the wing beams and they said, whoa, these forward spars are doing more than their share.
09:12 Let's kind of curve that down.
09:16 None of this partial systems of partial differential equations. Just bend it down.
09:22 And 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.
09:34 And 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.
09:44 So, uh, well, and in the racing context, you're dealing with a deadline all the time.
09:53 You got to make, you have to make practice. So we got to go out and we got to try this.
09:57 And then you try that and you're like, well, we have X amount of time before the next practice or qualifying.
10:01 And then we only have X amount of time before the race.
10:04 And you do all the things and you suffer or you win and you have victory or you barely make it all the things and you get back in the van and you got time to think about it.
10:12 Cause it's going to be, you know, 19 hours to get home.
10:15 And then you, you do your stuff in the shop. You think about what you did and you try it.
10:20 And that's that constant we're in the field. That's the farmer, farmer slash engineer.
10:25 We got to, we got to get that hay in, get the hay in before the rain.
10:29 Yeah. So at Talladega in 1974 on Friday, Kel's boys all had high speed weave past start finish.
10:39 And it was scary. It 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.
10:56 Harvesting seed from with his.
10:58 That was it. And those bikes came in, they had a hurried conference. The bikes went on the table and they were still on the table Saturday morning.
11:10 And Kel found what I had also found.
11:16 He was real busy doing dirt track and every other thing. And I, there I was in the winter. I'll take this thing apart.
11:24 Oh, why aren't these little wire clips on their groove? I'll make each groove five thousandths of an inch deeper.
11:31 No more trouble again. So.
11:35 On the Monday after the race, people were having breakfast and standing around in this hotel and Kel said something that was wonderfully true.
11:47 He said, well, we learned one thing here, and that is that in future, we're going to have to work on the chassis almost as much.
11:57 As we do on the engines. Maybe more.
12:02 And of course, now an engine is something that comes in a box like Kleenex.
12:08 You know what's in there. Put in another one.
12:13 And the chassis is the problem because.
12:17 The problem is to get whatever horsepower you have to the racetrack to accelerate and brake and turn the motorcycle.
12:26 And that's a technology that is still evolving.
12:30 Not that engines aren't, but more power in an engine usually makes you lap slower nowadays.
12:36 Because the chassis hasn't been developed to the point where it can transmit that.
12:43 So the problem of riding the TZ750, at first, the A model had twin shocks in the back and normal suspension travels three and a half inches or so.
12:55 And they were a handful. They were they were terrible.
12:58 There were a number of riders who went back to their TZ350s because.
13:06 There were a lot of people at that time saying, well, it takes a special kind of craziness to ride 750 and I don't have it.
13:15 And some of those guys were really quite, quite good riders on twins.
13:20 But when they got on that dynamite package, blew you from one corner to the next, it got more attention than they could give.
13:31 So.
13:34 It.
13:37 Kel built one with the monoshock.
13:41 And he also came up with the idea of a better packaging for the exhaust pipes.
13:48 Originally, what Yamaha had done was they squashed the round pipes until they were almost flat and they could put four of them together under the engine.
13:59 And.
14:01 When you send pressure pulses into an oval pipe.
14:07 It tries to inflate to become round.
14:11 And.
14:14 Soon they crack and in '74, the racetrack was covered with pieces of those flat pipes, which is why a set of factory fresh ones still commands a fair price.
14:27 But.
14:29 Kel was doing this work himself, basically.
14:33 And then in '77, Yamaha made the TZ750 Diaz and David with the monoshock and with the one over three under exhaust system.
14:46 And this is the great, big, long monoshock, right?
14:49 This was the big shock that went from the triangulation on the swing arm and it went like basically straight in line with the, you know, going up the frame.
14:56 And the bracket for the front of it, back of the swing arm, back of the steering head.
15:01 So it was a real Louisville slugger, that monoshock.
15:06 And it had a 20 millimeter shaft.
15:08 So when you got your extra preload for Daytona by putting more air pressure in it.
15:16 And that monoshock was designed before the revelations of Mr. Fox, who was the one who put.
15:31 Suspension units on the shock dyno that could actually replicate the rapid rod movement that was present in motocross.
15:41 And 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.
15:56 People went much faster.
15:58 V squared damping.
16:00 Yeah, you got it.
16:01 Got to kill that business.
16:04 But these were some of the lessons that this motorcycle presented.
16:13 Thinking about this this morning, I 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.
16:29 They could have come close to what is present in MotoGP now, unlike any other racing series in the world.
16:37 Every rider is on a factory engineered.
16:41 Factory race bike.
16:43 Every rider has been through the ladder of training from many bikes when they're five years old up through.
16:55 The Moto3, Moto2 ladder and then to MotoGP.
17:00 And I remember reading without much surprise that Mark Marquez had a professional manager from age 12.
17:13 And it wasn't because his family were in the oil business.
17:19 It.
17:21 Talent scouts had said, we want to buy into this program early.
17:27 And.
17:30 So.
17:31 What was lacking in the case of the US was here were all these motorcycles with essentially identical performance.
17:38 They all had too much.
17:40 Only a very few people could ride them.
17:42 So 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.
17:58 And I think I once rode one of these things back to the paddock from Victory Circle at Loudoun and I didn't go over 6000 and I thought, there's a whiff of eternity.
18:15 It's like a hot two stroke will do that to you, even when they're small.
18:22 And no power valve so that you're really the vibration, you know, as you always put it, it's an organ.
18:30 It has one pipe or in this case, four pipes, but they're playing the same note.
18:34 They're playing the same note.
18:36 And this is the thing that people didn't get when motocross bikes began to be given reed valves, same year as TZ 750A, 1974.
18:51 And hats off to Dale Herbranson, who probably gave Yamaha some helpful advice along the way.
19:00 People had the idea that, oh man, you put a reed valve on that thing and it'll pull like a bear from way down.
19:07 Well, TZ 750A, the torque curve went along, rising sort of slowly, and then it got to the 9300 RPM.
19:18 It doubled.
19:21 And then it went on to another 1000 or 1300 RPM.
19:28 That 1000 or 1300 RPM was the usable power band.
19:32 If you tried to accelerate off a corner with that 9300 in the middle of your acceleration, when it hit,
19:42 you were either going to be carefully with the throttle more closed than open, or you're going on your posterior.
19:52 Yeah. Well, all the 500 guys, you know, when I was growing up and watching, you know, Kevin Schwantz on the Pepsi Suzuki and Wayne Raney and all those guys,
20:02 you 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 because the spike was so big as they were coming into it.
20:13 If you weren't already into it.
20:14 I called that the Schwantz rule.
20:17 Rolling it back as you continue to accelerate harder.
20:21 And it makes perfect sense because when the exhaust pipe is not pumping the air, the crankcase is pumping it and that has limits.
20:36 And when the pipes, when the engine speed gets up to the point where the pipes are resonating, then the torque really starts to talk because suddenly the cylinders are getting that much more air.
20:51 So what Mike Baldwin did.
20:55 Oh, well, I'll back up a minute.
20:57 There was one race at Loudoun.
20:59 It was a club race where my writer, Richard Schlechter managed to beat Mike Baldwin.
21:04 And Mike went away and I think sat silently somewhere.
21:09 Thinking about all this.
21:12 And the next race weekend, he just disappeared.
21:17 And I had a conversation with him that weekend.
21:23 He said, well, I've learned something.
21:26 He said.
21:27 Don't ever let the engine turn less than 9300.
21:33 He said, stay in the linear zone.
21:36 And it won't hurt you.
21:38 And Mick Doohan came to the same conclusion about Honda's NSR 500.
21:45 Ride it in the linear zone.
21:47 The Don Kine taught me when I was riding a Hayabusa race bike, which you can imagine was a monster.
21:55 I built a Hayabusa motor on the track.
21:57 And I was trying to ride it lower in the RPM range thinking like, well, I want to keep this thing out of its power.
22:03 But it was all power.
22:04 And he said, no, it's the opposite of that.
22:06 What do you want to do with this bike?
22:08 It's the same theory.
22:09 What you want to do with this bike is ride it on the downslope of the torque curve.
22:13 So you want to take the RPM higher.
22:16 Because as you're rolling it on, it's not building torque.
22:19 It's declining.
22:20 Wonderful.
22:21 And it was.
22:22 He had a lot of.
22:24 Don Kine has a lot of thoughts, man.
22:26 Oh, yeah.
22:27 Well, Mike Baldwin said, here's my advice to people who want to ride this motorcycle.
22:33 He said.
22:35 Get some tape, put it on your tachometer so you can't see anything below 9300.
22:41 Go out on the racetrack and do your stuff.
22:46 If at any time you cannot see the tach needle, pull into the pits, park the bike, take off your helmet.
22:55 Get the newspaper.
22:57 Turn to the help wanted and look for other work.
23:02 And yet Kenny Roberts says this.
23:06 I don't I hate this bike because it has too much of everything.
23:09 Yeah.
23:10 And, you know, I mean, Kenny's talented, right?
23:13 Kenny.
23:14 Yeah, no question.
23:15 Well, there were a couple of occasions where Kenny and Mike Baldwin were in the wrong order.
23:23 It didn't happen often, but it did happen.
23:26 So I think that there's no one rider who discovers everything.
23:33 But I do insist that in any given era, the top rider is likely to be the one who best exploits what is new.
23:44 In the motorcycle.
23:46 And I think when when Kenny came along, he realized that.
23:53 You could steer the thing with the throttle just like you do in dirt track.
23:58 And when he got to Europe in 1978, the Europeans just were.
24:05 Open mouth that this and that there they're sporting newspapers were full of all this talk about how American dirt track is the font of
24:15 future ability.
24:18 And so approved for a few years.
24:20 Yeah.
24:21 Well, and, you know, on that subject, Indy mile, I mean, too much of everything.
24:25 And 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.
24:32 And of course, it would have been I'm sure Kelker others would have tuned that bike to operate in more of a dirt track range.
24:40 But I mean, as you say, you know, time to cut wood, you hit whatever that time is where it's resonating.
24:46 It's just coming and it's just there.
24:48 And, you know, the famous quote was, they don't pay me enough to ride that thing.
24:54 Kenny Roberts, they don't pay me enough to ride that thing.
24:57 And we had a writer for us, Joe Scalzo, who was he was he was very good.
25:04 Joe, Joe did some beautiful work for us.
25:06 It's in the archive and it's fantastic.
25:08 But one of the things one of the ways he portrayed it was like, you know, it's like Jay Springsteen and I forget who else.
25:13 And they're riding XRs and they're like, oh, la dee da, Jay ain't life grand at the front of the pack.
25:19 Gasp, what's that horrible sound?
25:22 And then, yeah, then he would come.
25:25 Kenny comes smoking by and and then re redoing, you know, doing that.
25:30 I think it was oh nine when they got the bike back together at Indy and, you know, the famous video of Kenny going out and riding it again.
25:37 And Kel's there with the bike and, you know, the facial expression of Valentino Rossi of seeing that bike go by.
25:45 And then the way Kenny wrote it, you know, here's Kenny like throwing it in.
25:50 I mean, he really rode the bike.
25:52 He had it sideways in the sounds.
25:53 I mean, you got to find that find that video on the interwebs after you finish with this podcast.
25:59 Because, yeah, it's just absolutely remarkable.
26:03 And actually, the funny story is seeing Kevin Schwantz after that, because Kevin was going to do a lap on his Suzuki 500 Grand Prix bike at Indy for the MotoGP.
26:16 And he was going to do a parade lap.
26:17 And he's like, oh, bleep.
26:19 Now I got to really like ride.
26:21 He was like, yeah, I was just going to circulate.
26:23 But Kenny did that.
26:24 So now I've got to, you know, I've got to actually do something out there.
26:27 I can't just wobble around.
26:29 And he did.
26:31 Yeah, well, there were some things about the 750 that were unappreciated at the time.
26:39 One of them was reverse engine rotation.
26:42 Because each of the two separate cranks, which were end to end, had on its inner end a thin gear.
26:52 And that gear meshed with a double width gear on a jack shaft that went over to the right to drive the clutch.
27:00 And so that reversed the engine rotation so that it was the opposite of the wheels, which gave that motorcycle some advantages in direction changing.
27:15 Why is that?
27:16 Because the gyro resistance of the crank shaft rotating one way opposes the gyro resistance or cancels the gyro resistance of the wheels revolving the other way.
27:30 And what do we do in MotoGP?
27:32 In MotoGP, everybody has a reverse rotator.
27:36 Everybody reverses the crank rotation to allow the bike, you know, if you put a bit more.
27:43 Yeah, I talked to Mick Doohan about this and he said, well, we finally did that.
27:51 And while it was better, he said, it didn't fix everything.
27:55 Well, 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, there are always going to be problems.
28:12 Unless, of course, the tire and the track have cure teeth, which they don't.
28:18 Funicular road racing.
28:20 Funicular road racing, yes, sir.
28:23 So that was one of the little things.
28:26 Another little thing was that in 1961, Yamaha hired an engineer to design their Grand Prix bikes.
28:39 He designed a 125 and a 250.
28:42 And he gave each one a little gyro rotor pump.
28:49 He lowered the oil level in the gearbox down until no gear could touch it.
28:54 And he had six or eight or however many gears pairs there were oil squirts across the top of the gearbox.
29:02 Kevin Schwantz's Suzuki has them too.
29:07 So each mesh got its own little oil squirt, and then the shafts were hollow and they got oil sent through them to lubricate the free spinning gears so that they couldn't seize on the shaft.
29:20 And in some engines, getting rid of that oil churning is several horsepower.
29:27 And I talked to...
29:29 And heat. I mean, heat.
29:30 Yeah, heat.
29:31 Which is going to go to your oil cooler, which then has to be bigger, which means that you have more drag.
29:37 You know, 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.
29:48 And then we want to put in more fuel and we want to do this.
29:51 We want to... Oh, well, we need a new engine."
29:53 Well, the engine update's coming in a year and a half.
29:56 And that's life, is that you're always chasing these problems and trying to achieve a net improvement is not guaranteed.
30:09 F-22s are pretty big.
30:13 Yeah, they're big.
30:14 I mean, they're big.
30:15 I mean, you think about a B-17 and how large a B-17 looks in flight and on the ground.
30:21 Man, you roll an F-22 up next to it and it's like, holy moly, you know, it's like taking a traditional Mini or a traditional Porsche 911 and putting it next to their modern counterparts.
30:32 And it's like this diminutive little toy car compared to the big thing.
30:37 Monster.
30:38 It is.
30:39 Mission repeat.
30:40 Yeah.
30:41 So T-750 got one of those little gerotor pumps.
30:45 And of course, it was liquid cooled too and had on the jack shaft, there were a couple of cross-axis gears.
30:53 One of them drove the water pump.
30:56 And it was a pretty easy engine to work with because you knew how long the cranks would last.
31:08 It lasts about 900 miles and the factory guys changed them at 450 or so, just to be sure, because they had them stacked like cordwood in the back.
31:22 When you encounter the stories that Robert Iannucci tells about getting replacement crankshafts made for the Honda 6 250 racer.
31:35 When I heard them warming those things up at Mosport in 1967, it sounded like they had those crankshafts stacked like cordwood in the van.
31:45 They were just barking.
31:48 Yeah, Robert Iannucci is the team principal and grand old man of team obsolete racing.
31:54 And he had bought out the MV Agusta racing department.
31:57 And he had a real penchant for the very finest, most exotic racing motorcycles of this very classic era.
32:05 And man, does he have a collection and does he run them too?
32:10 He's active getting them on the track and all that still to this day.
32:14 He has more than 80 bikes.
32:19 Many of them are AJS 7Rs and Matchless G50s, but he also has exotic Harleys, Benelli, MV, all those things.
32:32 But let's not get started in that direction.
32:36 No, no, it's fine.
32:37 We drop names a lot in this.
32:40 Yeah, they do need to be explained.
32:42 We got to have our Rob out there and talk about our physics.
32:47 Here's another little tidbit about the TZ750.
32:51 The reed valve, there are four of them, one for each cylinder.
32:56 Or I should say two for each cylinder pair because they're in blocks of two.
33:01 Is the same part number as the reed valve on the YZ80 Charles motocrosser.
33:07 Yes, sir.
33:09 Oh, they'd be so weak.
33:11 Okay.
33:13 Well, they were, Irv Canemoto always referred to them as the obstruction.
33:21 Because if you pry those reed valves open as far as they would go, you could get about a cross-sectional area of about 600 square millimeters.
33:31 But the cross-sectional area of the carburetor was 900 and something, 50% more.
33:39 But I think that thing was thrown together at the last minute.
33:43 It was sort of like, "Okay, what do we got here?"
33:45 Hey, we got a bunch of these.
33:48 Seems to run.
33:49 Yeah.
33:51 And so the first year, the bike was 64 by 54 bore and stroke, same as a TZ350.
33:59 And they had the blue cylinder nuts made of aluminum, which occasionally broke.
34:09 And they also had the cylinder stud breakage problem.
34:12 That got overcome the following year, 750B.
34:18 And they also manufactured what they called the full kit, which provided you with cylinders and pistons and heads for 66.4 millimeter bore, which brought it out to a full 750.
34:34 And that's why we talk about the TZ700 was really what it was.
34:39 It wasn't a 750 at the outset.
34:41 A 693 or something like that.
34:43 Yeah.
34:44 Little.
34:46 Little, he says.
34:49 To me, the -- why did Yamaha -- sorry, go ahead.
34:53 No, what were you going to say about Yamaha?
34:55 I was going to say, why did Yamaha choose reed valves?
34:57 There's all kinds of different ways.
34:58 I think we're talking about fire-breathing, two-strokes, and so forth.
35:02 Maybe we can talk about how reed valves work and why Yamaha would choose them versus other types of induction and location of carburetors and what are the advantages and disadvantages.
35:12 Because 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.
35:20 Yeah, it did.
35:21 And, in fact, with the 500, they dropped the reed valves.
35:25 The original, the bike that Agostini won the 500 championship on in 1975 was a reed motor.
35:39 And when they needed more power, they dropped the reeds and had piston port induction.
35:48 And that's the type of engine that Kenny won three world championships on, no exotic disc valves and certainly no reed valves.
35:58 Well, the thing about the disc valve is that you can make the timing asymmetrical.
36:05 You can open it when the piston starts to move to draw air into the crankcase, because the crankcase is a pump in these two-strokes, air pump.
36:15 And you can close the valve fairly early after top center if you want a somewhat broader power band.
36:24 Or you can close it as late as 85 degrees if you want to.
36:29 And they carried, Aprilia carried stacks of these disc valves with all different timings.
36:35 But what Yamaha found out was when you finish your beer and you don't have another, what do we do now?
36:47 Well, you blow across the mouth of the bottle and it makes a [makes a noise] makes a tone.
36:53 Well, engine crankcase does the same thing.
36:58 And the piston is there moving up and down to excite vibration.
37:05 And Yamaha found that if they could make the timing open 100 degrees before top dead center or 102 and close it 102 after.
37:19 And if you were in the power band, it would develop wonderful power.
37:25 The intake system flowed a lot of air.
37:28 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.
37:41 And so the air would say, oh, my mistake.
37:43 I'm going back this way.
37:45 And so the reed valve stopped that reverse flow.
37:52 So instead of having.
37:55 So it's a check valve.
37:57 Yeah, that's all it is.
37:58 If you've never seen a reed valve, it's basically here's your carburetor.
38:02 The carburetor then has the reed valve, the block that goes into the cylinder block.
38:07 That's tapered.
38:08 And that air tapered.
38:09 And there are pedals on it.
38:12 So when the intake blows in and there's vacuum on the other side of the reed valves, they open and the air flows in air fuel flows in to the crankcase under the pistons.
38:23 The 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.
38:33 And but it's all connected.
38:34 There's nothing shutting off the exhaust pipe from any of this.
38:39 So the reed valves, when that pulse would come back, the reed valves would close and keep that from blowing back out your carburetor.
38:47 Another wonderful thing that could happen.
38:50 Another wonderful thing, though, is that.
38:54 You can imagine that.
38:57 The piston has come down and it's closed the reed valve.
39:01 And now the piston is it has a bottom center in the exhaust pipe is, if you will, sucking on the cylinder.
39:09 The pressure in the cylinder is dropping, dropping, dropping.
39:13 Now the reeds open again.
39:16 And the exhaust pipe pumping action is pulling air straight through from the atmosphere, through the carburetor, through the reed and into the crankcase.
39:25 So and this is something that that Dr. Blair documented.
39:32 Second opening.
39:34 And so that Blair, Dr.
39:39 Blair up there at Queen's University in Belfast, Northern Ireland, was a computer programmer and math modeler who took an interest in two stroke engines.
39:51 And when he came to visit me, he brought a bottle of old Bushmills.
39:58 And we drank that stuff and had a nice conversation that evening.
40:03 But he he was basically one of those math heavy.
40:09 Scientific types who whose attitude was, oh, I can calculate that.
40:14 And he sold a lot of services to the motor industries.
40:19 And I think he was all set to do the same with Detroit during the years when they were having a hmm.
40:28 I wonder if a two stroke engine would solve some of our problem because two strokes are are wonderfully compact and they're lightweight.
40:38 And if you could just stop them leaking mixture out the exhaust straight to Ann Arbor, where the EPA is, you you could have a hell of a low emissions engine.
40:53 So he was on that program.
40:55 But then he said they they were trying to reinvent the wheel as far as two strokes were concerned.
41:04 And he said what they really needed was somebody who already knew about two strokes, i.e. himself.
41:11 And but it was killed by the by the being being counters because they they spent a bunch of money and then they didn't get anywhere with it.
41:21 But the valve made engines rideable that had extraordinary.
41:33 Radical port timing, they they would just kind of burr along rather than constantly burping and farting mixture out back out of the intake.
41:48 But when Freddie began to win races in Europe on that three cylinder Honda, which had large area read valves, real read valves from motocross at that point.
42:01 People all thought, man, that thing's got some kind of lobe of bottom end must be those read valves.
42:09 And that really amused Erv Canemoto, who was working with Freddie at that time, because he said.
42:16 Freddie knew that that bike didn't have the power to accelerate with the four cylinder bike, so he was riding a corner speed style and he would be going so fast at the apex that his exit speed was high.
42:32 And it looked like, man, that thing really accelerates.
42:36 No, what it what it does is it doesn't have to decelerate as much to get through the corner.
42:43 But Freddie's engine came on at ninety eight hundred and was all finished at eleven thousand.
42:54 So like the TZ 750, a twelve hundred RPM power band.
42:59 So that drives me back to the the TZ and the evolution of road racing.
43:05 When did tires catch up or did they ever catch up with the TZ 750 power production?
43:11 Well, I think TZ 750 became irrelevant.
43:17 And the tire people turned to the five hundreds, they turned to super bike and so forth.
43:23 So but there were there were some, for instance, at the end of the nineteen seventy six Daytona race, the leaders bikes were all weaving quite furiously that their tires had had become fatty gay.
43:42 And so the 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.
43:58 He's making faces here for you audio people.
44:02 He Kevin grabbed his lips and moving them around.
44:04 It was good.
44:05 So those those tall sidewall tires were quite commonly used at Daytona in the in the later 70s.
44:17 But what happened next was that five hundred horsepower course started out around 90.
44:27 Actually, the M.V. four strokes were faster than the Yamaha's to begin with, just that the Yamaha's accelerated better and they didn't have engine braking problems.
44:37 But the five hundred started out around 90 horsepower.
44:40 And when Kenny was riding the zero W48 and so forth, they were making maybe one hundred and a quarter.
44:48 And then pretty soon they were making one hundred and fifty and then one hundred and seventy.
44:54 And when they got up to the one eighties and one nineties, it was time for tires were all finished.
45:02 The bias tire 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 you could do.
45:20 So you could race for 10 laps on those tires and then you had to be ahead far enough that you could.
45:29 I'm not going to look back, but I know those guys are sliding all over the place just like I am.
45:35 And that was something that Mick Doohan talked about later, although with the new radial tires that came in 84, that you're going to spend the last 10 laps of the race sliding around just trying to finish.
45:53 And in 81, the way Marco Lucanelli was able to win races was at the start, he would let everybody go, just like in this last race.
46:07 At Barcelona, MotoGP race, Bagnaglia 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.
46:21 And he said, a few laps later, their pace came back to me.
46:26 And then he was able to pass them.
46:29 And he said, when I got into the lead, after one lap, I had a lead of four tenths of a second.
46:34 And I knew all I had to do was wait for the finish line to come.
46:40 And what a luxury to have tire.
46:44 Somehow that all started with the TZ750, I'm sure.
46:47 It sure did.
46:48 It sure did.
46:49 Yeah.
46:50 And people who rode Michelins and Dunlops and Goodyears back in the biased tire days, the Goodyears were never more desirable than on extremely hot days.
47:05 When the other two companies would tell their contracted riders, go see the Goodyear guys, we don't have anything that'll work today.
47:13 Because their tires were optimized for dreary northern Europe.
47:21 So when the TZ750 was released and people started messing with it, what kind of horsepower was it making?
47:29 90.
47:30 90.
47:31 And then what were they doing at the end, you reckon?
47:34 Well, people who've done dyno work with them, and of course, dynos are also different.
47:41 But they said 120 for a well-tuned DEF model, which is the 1x2 part number prefix for the big late model engine.
47:58 We'll do an entire podcast on the part numbers that Kevin remembers.
48:03 So 120 for one of those, and they thought 140 for a successful modification.
48:17 Like Richard Schlechter had when in, what was it, '81, he looked like he had the race won.
48:24 He was pulling away from Singleton and all those French fellas.
48:29 And then his chain began to go...
48:34 And he thought, "Oh, I could fail to finish."
48:39 So he knocked it just enough to finish third, which I thought was a good performance.
48:46 Yeah. Talk to me about Talladega.
48:49 I mean, a big track like that, was that much different than Daytona?
48:55 What was Talladega like? I'd never been.
48:57 I think the times that I was there with the big motor, the riders' minds were elsewhere.
49:06 You know, it's running.
49:09 So I think what Goodyear had done, well, what they told me in 1978, I went to visit those guys.
49:20 And they said, "When we decided that we should get into motorcycle racing with Harley Davidson pushing them,
49:28 we were filled with pride at the wonderful, exotic new rubber compounds that we'd developed in sports car racing.
49:36 So we made motorcycle carcass with those lovely rubber compounds on, and they were terrible.
49:46 They just gave up immediately.
49:49 And we're having a meeting and we're drinking bad coffee and eating more donuts.
49:53 You know, our wives are saying, "You know, you're going to have to get some bigger shirts."
50:01 And somebody raised his hand and said, "How about we try some of our NASCAR compounds?"
50:08 They have that high specific loading, pounds of load per square inch of tire footprint, like a motorcycle.
50:18 Yeah, yeah, that's a good idea.
50:20 So they did that, and that worked.
50:23 They were on their way with that.
50:26 And because, like I said before, a motorcycle tire, not only is it small,
50:31 but you're only using one third of it at a time or one quarter,
50:34 because 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.
50:41 So it was a story of finally realizing that the tires with pattern, with rainwater drainage grooves in them,
50:59 the tread was just too flexible.
51:02 It heated up too much, and it lost its properties.
51:06 So they did what they were doing in sports cars and in the cars and went to a slick.
51:14 And they were handing out sort of half-hearted slicks for comments at the end of the '73 season.
51:21 So those tires were really flexible.
51:23 And then by the time they were in production with racing slicks for TZ750s, in the spring of '74,
51:33 they were good for like three quarters of a second a lap.
51:36 Amazing.
51:37 Other people could just go home.
51:42 And Goodyear hung in there until 1984, and then they said, "Well, we're not doing that anymore.
51:47 Goodbye. Thank you."
51:49 And that was the end of that.
51:52 But everything comes to an end.
51:55 TZ750s came to an end.
51:57 They dominated U.S. racing for that whole period.
52:01 And then they were stopped at the stage door.
52:07 You know, you guys have to pay admission, go around the front.
52:10 And suddenly it was Superbike.
52:14 And it had to happen because four-stroke motorcycles are what they make.
52:19 And commerce, you know, identification.
52:21 I mean, it was one thing to identify with the brand.
52:23 And, yeah, you could get an RD350 or an RD400.
52:27 But the world was certainly moving to big four-strokes.
52:31 And it made sense for identification purposes and enthusiasm.
52:35 It's such a contrast to think about a TZ750 on one hand, which has a throttle, a brake, a rear brake.
52:50 It has an enrichment lever for starting, which had little carburetors molded onto the side of each carburetor.
52:58 It had a little piston valve.
53:00 And it provided starting mixture.
53:03 And that was it.
53:06 That was the extent of the riders' interaction.
53:09 And what information did the motorcycle provide?
53:12 RPM and water temperature.
53:17 But if you look at a modern MotoGP bike, it is just so much more sophisticated.
53:27 And just as is the case with carrier planes, the rider is given help where help is needed.
53:38 Nobody wants a ramp strike.
53:41 So, they've got auto throttle.
53:45 And they've got radio beam guidance and all these things to help you.
53:50 We're going to make night traps here.
53:53 Are you scared?
53:55 Were you scared already yesterday?
53:59 So, in order to allow the rider of today's motorcycle to concentrate on what the human is uniquely good at,
54:09 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?
54:20 Because I might have to maneuver.
54:22 I might have to attack the guy ahead of me.
54:25 Or I might have to fend off the guy behind me.
54:28 And if my tires are gone, I'm just going to have to put my hands up and say, "I surrender."
54:34 So, all those electronic systems and all the sophistication of modern suspension units,
54:43 and the marvelous properties of modern tires are there to allow the rider to actually command the system.
54:54 Because if you look at a Manx Norton, it had a mixture control lever.
55:00 So that if you were thudding past the forest section at some of those European tracks,
55:09 where everyone believed that all this oxygen was rolling out from tree breathing, you could richen up a little bit.
55:18 "Oh, yeah, I think I got 50 revs out of that."
55:22 And so much in those early days, the rider was sort of like an engine manager, and particularly so on the two strokes.
55:34 Some of those people were really good at keeping their engines alive through a long TT event.
55:44 And nowadays, that's handled.
55:48 And the engine is something that comes in a... just like a modern jet engine comes in a can.
55:55 It's filled with nitrogen so that nothing in there is going to deteriorate from exposure to oxygen.
56:02 And you take out a new one when they tell you that you may.
56:08 But I think 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.
56:25 Because all these guys are talking now about...
56:29 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."
56:38 But then for the race, he said, "I go back to my own style, because safest thing is what you know."
56:47 Well, it is a huge evolution of the sport, the technology in the days of...
56:54 It's evoluted away from $7,500 in a crate.
56:59 That was the great thing about TZ750 was you could have one.
57:04 You could have one, and then you could put the pipes wherever you want.
57:08 You could take it apart, port it.
57:10 You could get parts to redo something that you messed up.
57:14 You didn't like the steering head angle. It was made of steel.
57:18 No one's changing steering head angles in MotoGP.
57:21 They're not opening engines. They're not putting bearings in.
57:25 No one's filing the edges of a crankcase in the back of a van.
57:28 It is a much, much different place.
57:31 But really, looking back at it, the TZ sort of laid all of this groundwork for this tire management that you're talking about.
57:42 It posed the problem, yes, in a very forceful way.
57:45 It posed the problem of so much power, more...
57:52 How are we going to manage it?
57:54 Too much of everything.
57:55 Yep, too much of everything.
57:57 Too much of everything.
57:58 Well, I think it's a good place to...
58:04 We've had too much of everything today as well.
58:07 We've done the job here.
58:09 We thank you for listening to the TZ750 Cycleworld podcast.
58:14 It's near and dear to Kevin's heart.
58:16 And of course, I'm an RD350 enthusiast and owner.
58:20 It's a Kevin Cameron port job on it.
58:23 I'm going to have to finish those pipes soon, I guess.
58:26 When you put a 750D cylinder on an RD, it's called an OW15.5.
58:39 I'll give you a call. Let's talk about cylinders then.
58:42 Okay.
58:44 All right. Thanks for listening, everybody.
58:47 We'll catch you next time.