3 LEAF CLOVER
Dick Mann’s unlikely Daytona winner
During Dick Mann’s racing career, people said: “He sure is lucky. Just when you think someone’s got the race sewn up, he comes from nowhere to win it.”
The truth was that Mann understood what machines could and could not do. He managed his resources wisely. In 1970, he won the Daytona 200 on a Honda Cb750 based racer. Mike Hailwood on a BSA Triple was out on lap eight with center-piston failure. Cal Rayborn’s iron XR Harley-davidson failed a valve. Ron Grant’s Suzuki seized, and then Gary Nixon’s Triumph Triple failed, as Hailwood’s had. And there was Mann, first at the finish.
AMA racing’s rules had for years pitted 750cc Harley side-valve four-strokes against everyone else’s 500cc overhead valve (OHV) models and two-strokes. Then, in 1968, Harley-davidson brought innovations to Daytona that rubbed out the Triumphs that had won the 200 in 1966 and ’67, relegating them to sixth in 1968 and ninth a year later.
Crisis was the agenda that December for AMA’S first Competition Congress. Triumph proposed 650cc OHV for all comers (because 650 Bonnevilles were what they had on hand), then Harley raised the bid 100cc to 750—and the measure passed. For two-strokes, the limit would remain 500.
This unleashed new and potent market forces into AMA racing. American riders had demanded more-powerful bikes every year since the end of World War II, and in 1969, Honda and Triumph/bsa raised the ante with the CB750 Four and 750 Triples based on Triumph’s already proven 500. The history of this Triple was much older. In 1960, the designer of the original Speed Twin of 1937, Edward Turner, authored an ominous report on his trip to Japan: Ultramodern production techniques stood ready to dominate motorcycling’s future. As early as 1948, designer Bert Hopwood had explored modular design, a “means of producing a range of machines, from small to large, with as many common components as possible.”
Had this been adopted, the results might have been a 250 Single, 500 Twin, 750 Triple, and a 1,000cc Four. Britain instead stuck with steady growth, of displacement and vibration, in its existing Twins—until the Triple.
The Triple began with lessons learned from the 250-cylinder size of the refined 500 Twin. Like it, the Triple’s design would conserve cost and tooling by remaining a two-valve pushrods-and-rockers engine. Engineers separated the Twin’s two near-hemispherical case halves and placed between them a casting supporting the Triple crank’s center crank throw between two plain insert main bearings. The result was a bodge, and it was heavy. A single, separate finned aluminum cylinder casting carried aus tenitic iron liners, topped by a unit cylinder head whose top cooling fins were walled in by its two full-width rocker boxes. Their cooling was just adequate for the streetbike duty cycle.
Unleashed by the AMA, the four-stroke factories had little time to develop Daytona-eligible race bikes. In an intensive crash program, Harley designed and manufactured 200 new iron XR7 50S. The threatening spoiler was Yamaha, whose little 350cc air-cooled two-stroke twins had finished second and third in the Daytona 200 in 1968, and third, fifth, seventh, and eighth in 1969.
In late November 1969, Triumph contested the 1970 Daytona 200. What could it accomplish in three frantic months?
New AMA rules allowed approval of special racing chassis, suspension, and brakes, so the new Triple engine was modified in the usual ways and placed in a Rob North twin-loop steel-tube chassis. Front suspension was
telescopic, with a four-shoe 250mm Fontana drum brake and a small disc rear.
The cylinder head was ported, drawing mixture from triple 1-3/16-inch Amal GP carburetors with remote float chamber. Higher-lift cams were prepared with close-to stock timings. The stock 9.5-to-1 compression ratio was boosted to near 12-to-1. A 3-into-1 exhaust terminated in a megaphone. To satisfy AMA regulations, quantities of certain parts were shipped to the U.S. “to be counted,” but my dealership’s efforts to order such parts were met with condescending amusement. AMA tradition did not require such parts to actually be sold.
These were factory bikes, not production racers anyone could buy at a dealer. This 200 was a race of attrition: Only 16 of the 98 starters finished. Mann’s thoughtfully ridden CB750 Four was the only Honda running at the end. Of the six factory Triumph/bsa Triples entered, three finished second, third, and 12th. Gary Nixon had led on a Trident until 110 miles, but his No. 2 piston holed. Although there was talk of overheating caused by a too-small cooling air opening in the fairing, at least two other possible causes existed: 1) spark timing scatter caused by motions of the exhaust camshaft that carried the ignition breaker cam; or 2) fuel-feed irregularities causing the team to later replace Amal GP carbs and their remote float with integral-float Amal Concentric carbs (introduced in 1967).
Harley’s hot-running iron XRS detonated and failed pistons despite drastic lowering of compression ratio. Their best finish was nowhere—unless you count Walt Fulton Jr. in sixth on an “obsolete” KR side-valve.
The Triumphs in second (Gene Romero was closing on Mann) and third looked promising, but at their heels was Armageddon—the two-stroke threat of Yvon Duhamel’s tiny 350 Yamaha in fourth and the Suzuki 500 twin of New Zealander Geoff Perry fifth. Kawasaki was still a bit player.
Dick Mann did it again, staying with the lead group while conserving himself and his machine.
ABOVE: AMA rules allowed for a special chassis, suspension, and brakes to keep Triumph/bsa competitive. OPPOSITE: Feeding the Triple are 1-3/16-inch Amal GP carburetors.