3 LEAF CLOVER

Dick Mann’s un­likely Day­tona win­ner

Cycle World - - Contents - By Kevin Cameron

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.

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