Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/128317
The V is for Victory tarting with the 1969 season, the AMA rulebook underwent a considera ble change with regar d to the equipment specifications for the Gra nd Nati onal C ha m pionship series. Up until that time, the rules had given a displacement advantage to the sid e -valve Harley-Davidson KR racing engine , wh ich was allowed 750cc vers us the 500cc overhead valve Triumphs, BSAs and the like. For '69, all dirt -track equipment would be allowed to displace 750cc, with the roa d racing specification be ing bumped to 750cc by 1970. Despite winning the 1969 cham pions hip, thanks to the capabilities of its ta lented young fact ory star, Mert Lawwill, the Harley-Davidso n Moto r Co mpany saw the handwri ting o n the wall for the venerable KR, wh ich had bee n in use since the 1953 racing seas on, winning several cha mpions hips along the way. The company knew that it needed to make the switch to overhead valves for racing just as it had done with its range of street motorcycles years before. Thus the deci sion was made to build a new racing engine based on the popular XL883 engine used in the HarleyDavidson Sportster. Destroked to 7SOcc and with slightly lowered barrels, the XR750 was born. It would prove to be a milestone disaster in the company's otherwise rich racing history. Fast enough, but very unreliable beca use its cast -iron material failed to dissipate enough heat to keep internal com ponents from cooking, XR750 failures were all to o common . "T hose (iron ba rrels) just br oke, broke, broke, and spewed oil all ove r us and our co mpe titors," for me r Harley facto ry racer Mark Brelsford to ld Cycle News during an inte rview in 1998 (Issue #SO, January 6, 1999). "You can ta lk to anyone who raced w ith us, and if they were behind a Harley, they were cove red in S oil ." The company tried everything to make the Iron XR a winner, fro m chang ing internals to reconfiguring the cast-iron cylinder heads [AMArules forbade casting new ones without resubmitting them for homologation] so that the machine could run two carburetors instead of just one. It was an involved process, according to factory tuner Bill Werner, then just a young apprentice mechanic in the Harley race shop . 98 "To run two car bs, we co uld take tw o front head s and ge t the intake po rts in alignment, similar to wha t came out on the alloy XR later," Werner says. "We just had to reconfigure the exhau st ports on the back head because the exhaust port came out on the right-hand side. We had to close off the ex haust port and then machine and braze in a spigot to rec reate an exhaust port on the left side. Then we filled it in with brass, and on the intake side we had to weld in little stubs similar to the alloy XR. We also had to relocate the spark plugs to the cen ter of the heads. It took the be tte r part of the year just to make e ight or 10 sets of heads." And not under the healthies t of working conditions, as We rner reca lls. "We had to pack the head fins full of asbes tos and then pack the m in 55-gallon drums of asbestos to keep them from cracking when we welded on them," Werner says. "We literally had 55-gallon drums of the stuff. Hey, it was the '70s . There was no OSHA back then. Nobody knew." Harley-Davidson soldiered on through the 1970 and 1971 seasons, with factory riders Lawwill, Bart Markel, Dave Sehl and young star of the future Brelsford all managing wins on the iron XR750 before the "Mark II" version was released. MARCH 31 , 2004 • C YC LE N EWS Released for the 1972 racing season, the new XR75 0 featured re desig ned cylinde r hea ds that bo rro wed heavily from the experiences lea rned by the facto ry race team on the iron motor. It was twin-carbed right out of t he box, and it featured narrower valve angles, bigger valves and a shallower combustion chambe r. Be low the heads, th e bo re was increased and the stroke was dec reased to make more powe r at higher rpm . But pe rhaps most importantly, the new XR was an all-alloy motor, making it lighter and giving it the ability to dissipate much more heat than its cast -iron pre decessor. The alloy XR made its Grand Nat io nal dirt-track deb ut on the mile at Co lorado Springs, Colorado , on April 30, 1972. BSA factory rider Jim Rice won the race , spoiling Harle y' s chances for a de but victory, but Brels fo rd did finish second with the new motor. Victory was not far behind, though. Brelsford gave the new XR750 its first win on the Louisville, Kentucky, Half Mile on June 3, 1972, a race that saw Harley-Davidson XR750s finish in five of the first six places . Harley's dominance that day was not the end for the competition, but it may have been the beginning of the end . With the exception of Kenny Robe rts ' two-year championship run for Yamaha in 1973-74, the factory Honda RS750 assault from 1984-87, and Ricky Graham's miraculous comeback title aboard a privateer Honda in 1993, Harley-Davidson XR750s have take n ho me the Grand Nationa l Championship . That's 25 times in 32 seasons, ranking the venerable XR750 with the Offen hauser auto racing e ngine as one of the longest-lived racing engines ever produced . As we have turned the corner on the last century, it remains to be seen if the handwriting is indeed on the wall for Harley-Davidson again. Both Suzuki and KTM have taken advantage of new rules that allow a IOOOcc displacement for product ion-based four-valve engines to produce machines that could soon threaten Harley 's dominance. Time will tell, but time has been very kind to the HarleyeN Davidson XR750. 40th Anniversary SCOTT ROU SSEAU The annual Apri l Fool Issue featured former 500cc GP racer Russ Darnell riding the new Husky 400 across the cover of Issue # 12. We foundthe new Huskyto be amazingly stable and extremely powerful. It retailed for $1589... We also tested the new Suzuki TM400. One of the biggest attention-getters on Roger's Ride,accordingto our article, was the breather hose that extended from the gas cap... Over 1600 riders signed up for the OC Me Great Bear Gra nd Prix at Riverside Raceway. Jim Fishback won the 175 and 500cc classes, while Larry Roese ler won the IOOcc event... Harley's Gary Scott won the Ascot Ioo-IapTT for the second straight year. ~O YEARS AliO.• _ April 4, 1984 TeamHonda's David Bailey and Johnny O'Mara each won a nightat the ParisSupercross. O'Mara won Wednesday's final over Bailey and Rick Johnson (yam), while Bailey won Thursday's final over Johnsonand O'Mara. Bailey won $14,000, while O'Mara received $10,000... Bailey also bagged the Housto n '~troCroS5" win over teammate Ro n Lechie n . Yamaha's Broc Glover, and O'Mara. O'Mara took over the InSportSupercross Series points lead, 198-189over Ricky Johnson... Scott and Kurt Pfeiffer (Hus) dominated the SCORE San Felipe250 on a 250. Dans Smith and Ashcraft finished second, first open bike... Terry Van ce took out Ch arlie G ressman in the final to win the Gainesville NMRA National's Pro Stock class. 10 YEARS AliO.. _ March 30, 1994 The Indy 250cc m a in gets under way for the cover of Issue # 12 right above an imageof Jere my McGrat h (Hon), who scored his sixth mai n-event win in the eight-race-old series. W ith seven races left, he led the points by 47, 184-137 over Mike Kiedrowsk i. Jeff Emig (Yam) finished second in the main over Mike laRocco (Kaw), Mike Cra ig (Yam) and Kiedrowski. Ezra Lusk (Suz) won the I25cc main, his fifth in the sixrace-old series, over Jimmy Bu tton (Suz) and Robbi e Reynard (Kaw)... Fre d And re ws (Yam) won round two of the GNCC series over Scott Summers (Hon), switchingtheir finishingorder from round one. The 1990 125cc Western Regional Supercross Champion Ty Davis (Ka was aggressive, ramming w) Summers in a comer on the way to aDNF.