1969 Yamaha TR2 350 Production Racer—Classics Remembered

Yamaha, after producing some overbored 305cc models (YM-1 of 1965) based on its original Adler-influenced 250 parallel twin, decided for 1967 to manufacture a full 350 with all modern conveniences: an easy-to-assemble horizontally split crankcase in place of the more complicated vertical split of the 250; a drum-shifted five-speed gearbox; and a conventional crankshaft lacking the strange "centerblock" construction of the 250/305 twins, with its large molded seal. This new engine would begin with a large countershaft-mounted multi-plate clutch rather than the problem-ridden "exploder" crank-mounted clutch of the previous twins. Bore and stroke were 61 x 59.6mm = 348.4cc and the cylinders were given square finning to clearly distinguish the new model from the old round-fin twins.

Racing versions of this new bike were prepared for the Daytona 200, in which they would run against the dominant Triumph 500s (Gary Nixon won that year on one and the entire top 10 consisted only of Triumph 500s and 750 Harley-Davidson KRs). Tony Murphy and Mike Duff finished 18th and 19th on the new Yamahas, clearly a "fact-finding mission."

CHECK OUT MORE CLASSIC MOTORCYCLES

The next year, US racing was hit by a double shock:

The winner was the great Calvin Rayborn on one of the revitalized Harleys (whose new horsepower had come from a casual experiment with “quarter-inch head gaskets,” performed at C.R. Axtell’s shop the previous winter by Neil Keen and associates).

This was scary stuff, shaking the very foundations of masculinity. If Rayborn’s lone Harley had stopped, then the winner’s bike might have said “ding” instead of the proper “brumble.”

Yamaha claimed 36-hp for the street R2 and 54-hp at 9500 rpm for the race engine. This equaled the power of the new Harleys, but without the KR’s pulling range (especially since the AMA had wisely compelled Yamaha to race with just four of its five speeds.

That fall the AMA held its competition congress, which was understandably bursting with conflicting viewpoints and corporate ambitions. Triumph badly wanted back in to racing, which would require raising the OHV four-stroke displacement limit from 500, now shown to be too feeble; its proposal was 650cc, for which they had a model in production, the Triumph Bonneville. Harley, not relishing the specter of drowning in a sea of fast Yamahas, also desperately needed to raise its game; H-D countered with a 750cc OHV limit. Meanwhile, the two-stroke displacement cap would stay at 500. The new limits passed, with effect beginning in 1970.

The Harley KR would win the 200 one more time in 1969, but meanwhile the race department, up at the end of Juneau Ave (it was a hike up that black metal outdoor stairway) got busy seeing what it could contrive in the way of an OHV 750 out of iron Sportster parts.

Yamaha now scrapped the obsolete RD48 chassis and running gear which had served TD1-A, B, and C 250 production racers, originally designed by Takashi Matsui for 1961. In its place, it put a chassis based on that of the championship-winning RD56 of engineer Kuromori, with a giant four-leading-shoe double-sided front brake, a fork with proper inside piston-type dampers (rather than the old "seal-blower" damping system previously used), and rectangular-styled tank and seat. There would now be two US-market production road racers, the 250 TD2 and the 350 TR2.

Bear in mind that the old way to go racing in the AMA Expert Heavyweight class was to build yourself a Harley or Triumph, using a combination of factory and aftermarket tuning parts, and coming up with brakes, suspension, fairing, etc. from the limited list of what was “AMA approved.” There were no race-ready four-stroke production racers. Stirred into this thick batter like marble cake was a rich layer of politics. Were you a good guy? (That is, were you subservient to your brand’s race boss? You were a good guy if you promptly handed over any “speed secret” you might discover, for then your parts orders would be picked and shipped. If not, there could be “delays.”)

Yamaha cut through that like a hot wire through Styrofoam. The beauty of the production racer concept was that word: production. Because the engines were built on essentially production crankcases (under $100 to the dealer), it was possible to crank out a run of 200 bikes quite easily and cheaply. Yes, their crank bearings, gearbox ratios, ignition systems, etc. were different from standard, but not so different as to require hand assembly by “wizards of tune.” Yamaha production racers were the Colt six-gun of roadracing. Their sale prices were a small fraction of what it would cost to hand-craft a Triumph or Harley that was even close to factory level.

When the new bikes arrived at the dealer in their crates, we busted them out, put on race tires in place of the furnished “rim protectors,” made bronze bushings for the swingarm in place of the stock plastic (which looked like it was made of compressed peach pits), and checked through engine tuning basics. Then gas/oil mix into the tank, air up the tires, and you’re ready to start up.

Paddocks were instantly more "ding" than "brumble." Harley and Cal Rayborn would win the 200 in 1969, Honda's new CB750 would take it (carefully managed by Dick Mann) in 1970, and Dick Mann would shepherd a BSA Triple to victory the year after that. That was the end for four-strokes, for in 1972 and 1973, the 200 would be won by little Yamaha 350 twins—not the TR2 and TR2-B of 1969-71, but the new modular 54mm-stroke engine that became a 250 with 54mm-bore cylinders, or a 350 with the bigger 64mm top end. Own one of each, they're cheap. Race in both classes.

Triumph and BSA, puffed up in Wizard-of-Oz fashion in 1971, were revealed a year or two later to be hollow and without force. Harley, who strove with might and main to crank 200 iron XR racers for 1970, then just as feverishly performed miracles of modification (as in eight-hour sessions of cylinder-head brazing) to come up with the much-improved 1971 bike on which Rayborn performed miracles in the Trans-Atlantic Match Races, were unable to push competitive horsepower through all that resisting iron. For 1972 the XR was redesigned with a much cooler-running aluminum top end. Only this past year, 2017, has Harley formally replaced the aluminum XR in dirt track with its "Street"-based XG750R, a lifetime of 44 years.

Despite its good power and reliability, the TR2 350 had its problems. Most basic was that, like the TD1-C of 1967-’68, each cylinder had two main transfer ports served by ducts originating in the crankcase and two much smaller "B" transfers, served by slot ports through two skirt holes in each piston. This limited the amount of flow through the B transfers. They looked promising but were only half effective. And they were dinky.

The wonderful step forward of the 1969 Yamaha production racers was their Mikuni VM integral-float-bowl carburetors. No more 1950s-vintage remote float bowls! And these new carbs (34mm on the 350, 30mm on the TD2 250) were clamped into flexible rubber flanges, to a useful degree isolating them from the highest-frequency engine vibes. Further, the VMs were tunable with a full range of available needles, jets, needle jets, idle, main, and air jets. Let the Bultaco TSS owners put their carb needles in the drill press, and while pinching the spinning needles with sandpaper, try to remember just how high the slides had been when the thing seized. Here, in the Sudco book, were all the needles and their measurements. This was a wonderful resource.

The two-coil rotating-magnet Hitachi magneto on the TD1-C had been an advance over previous, but folks had become tired of the whole syndrome of two-strokes fouling a plug mid-race because: 1) Pistons in air-cooled cylinders needed a cooler-burning overly rich mixture to survive; 2) Magnetos, while great at providing ignition energy, lacked the voltage and fast voltage rise time to jump a gap much over .014 inches, or to spark at all when offered the layer of conductive carbon being deposited on the plug’s insulator by #1.

Therefore, when Yamaha arrived at Daytona in 1969, its team bikes had two types of electronic ignition available to them (one of which used an RF trigger). And in Europe, the FEMSA electronic ignition was coming into being, soon to be followed by the Motoplat and German Krober. I would soon be mounting a lot of Krobers for Yamaha privateers.

The prototype FEMSAs produced mystery misfiring until the nature of two-stroke ignition was better understood. Initially, spark duration was extremely short. A two-stroke’s cylinder charge was an imperfect mixture of fresh fuel/air from the crankcase and leftover exhaust gas from the previous cycle. A very short spark could occur just as a blob of inert exhaust was blowing past the plug electrodes and no ignition would take place. When the arc duration of the ignition was increased, the misfiring was gone.

Yamaha would provide electronic magnetos on their modular-engined production racers from 1972-73 onward through the subsequent TZ range.

The other notable problem of these interim bikes was premature breakage of the needle bearing cages in their connecting-rod big ends. I have a modest collection of these. Getting the cages right was a matter of a succession of small changes. As an example, some needle rollers are made with fairly square ends, while others have rounded ends. Round-ended needles allow a larger radius to exist where the “rungs” of the cage join its “rings.” The larger the radius, the greater the fatigue strength. An acceptable lifetime for a racing two-stroke crank was 900-1000 miles, after which it would be rebuilt. But parts were cheap: a rod set (con rod, big-end bearing, and side washers) was $15-18 and ball main bearings $3-7. A new crankpin was a buck. A few hours at the press and parts washer and your crank was ready to go again.

Like all successful racing two-stroke big-end cages, these were silver-plated. Silver makes a good low-friction sliding pair with steel. For example, when US Navy dive-bomber engines in WWII began to experience overspeed big-end seizures (plain bearings in this case, not rollers) the fix was P&W engineer Earl Ryder’s idea: “Put some silver on it."

The needle cages in two-stroke rod big ends are guided by the ID of the rod, so centrifugal force at high revs can result in some serious pressure between the two. This is compounded by the fact that little oil is present (just the typically 20:1 mixed into the fuel) so local bearing temperature can sometimes exceed 400 degrees Fahrenheit.

Early 350 race engines opened their exhausts at 83 degrees ATDC and transfers 31 degrees later, but later the exhausts were advanced to allow higher revs.

Kel Carruthers and Don Vesco in 1971 decided to try supplying the "B" transfers via ducts excavated all the way down to the crankcase. This wasn’t easy to do as the cylinder base on the crankcase left very little metal for this. Nevertheless it was done, with an evident power gain; at the VIR non-national that year my rider, Cliff Carr, on a Kawasaki 500 triple led for a time from a closely pursuing Carruthers, but once Kel got past he was able to pull away. Pretty strong 350. And I seem to recall its being speed-trapped at 163 mph that year.

A big departure from established two-stroke practice was Yamaha’s extremely long intake timing of 202 degrees open (101 degrees either side to top center). Prior to this, for engines with piston-controlled intake ports 75/75 timing had been considered radical. Yamaha engineers had ceased to look at the crankcase simply as an air pump and now considered it as a Helmholtz resonator (the tone you can generate by blowing across the open top of a bottle is an example; the mass of air in the bottle’s neck is the oscillating mass. The compressibility of the air in the bottle as a whole is the “spring” against which the mass oscillates, and the stream of air from your lips drives the oscillation by alternately entering the neck or blowing across it).

With this new understanding, and by correctly proportioning the intake tract in relation to crankcase volume, Yamaha engineers were able to flow a lot of air while the engine was "on the pipe." Our late and much-respected tech editor Gordon Jennings was at the time skeptical that 101/101 could actually work with so little crankcase compression (transfers closed at 66 ABDC and inlet opening began at 101 BTDC, leaving only 180 – (101+66) = 13 degrees of compression). Well, maybe it was just one of life’s little mysteries, like the oft-heard assertion that, “According to science, bees shouldn’t be able to fly.”

In the zone from 9,000-10,500 rpm it worked fabulously, with or without permission from science, supplying all the intake flow needed by 1972 Daytona 200 winner Don Emde and 1973 winner Jarno Saarinen, both on dinky little 350 twins, reaching over 160 mph on the bowl.

And before I hear you murmuring, “Yeah, those damn two-strokers; they had zip for powerband,” I must remind you that the fabled four-stroke Manx Norton of the 1950s came to the boil at 5,500 (below that lay “megaphonitis”) and was pretty much all done at 6800 (above which lay forbidden kissing between exhaust valve and piston crown).

The cycle parts which had seemed so wonderful when revealed by opening the crates in 1969 were soon to be sold off to street stylists in favor of disc brakes that actually worked. I loved the look of the twin front brake cables (a pair of shoes on either side of the double drum) and the balance device that mounted up close to the hand lever. But this year’s great brakes are next year’s linoleum faders; people got busy riveting short segments of friction materials of increasing grip onto each shoe, generating such self-servo action that some brakes became pretty much on/off only—not much modulation possible.

That’s the nature of obsolescence: When the Honda V4 RC30 first appeared, power started at 7,500, but when it reached its highest form, there was nothing below 10,500. Its powerband grew taller but narrower, eventually requiring a fresh design. So it was with drum brakes. As they were made more powerful, their degree of control diminished, requiring a fresh start with a new idea, disc brakes, which arrived on the modular TZ250/350 in 1976. As the jokesters said upon first laying eyes on really big drum brakes in 1969, “Why, it takes a brake that big…just to stop the brake.”

Yamaha production racers naturally made their way into European GP racing, with Giacomo Agostini taking the 350 championship on a twin in 1974. Yamahas would win the class only three more times before it was terminated after 1982. It had become much more difficult to win races with a production-based bike such as the TZ350.

All the same, the production racer idea had been a great success, populating starting grids, putting racing within reach for a larger population, and launching many championship careers.