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/127413
; TECH Honda NR750 e Arguably the most exotic street bike ever offered for sale to the public, the Honda NR750. Its limited production means you'll never see it homologated for racing. 'Never Ready'to 'New Road': The Honda NR story By Alan Cathcart Photos by B. Thiebault he evolution of Hon da 's ovalp iston NR p roj ect spa ns a period of 15 years, wh ich coinci den tally also parallels H on da 's resur gent participation in Grand Prix road racing. When the Japanese giant retired from the G P arena in 1967, they had transformed Western attitudes to Orien tal motorcycles from patronizing condescension to outright admiration, by virtue of their countless G P victories and World Championship titles with ultra-sophisticated mach ines the like of which the world had never seen before - or since. Bikes li ke the fabulous 250 six and its 297cc big bro ther, the five-cylinder 125, or 'th e 22,500 rp m, 8-valve 5Occ. twin, four strokes all and as brave and advent uro us in th eir design as any motorcycle ever built. Only the World Championsh ip titl e in the 500cc class eluded Honda's grasp; th e might of Ital y's MV Agu sta triple and G iacomo Agostini's riding talents were too much even for Mike "The Bike" Hai lwood and h is pow erful bu t unruly RCI81 Honda four . 50 when Honda announced th eir return to GP racing a decade later, after successfully establishing themselves as T 16 the world's major motorcycle manufacturer in the interim , it was wit h a sole objective: to secure victory' in the one class where a title had th us far escaped th em , bu t which was the grea test p rize of all: the 500cc World Championship crown. But typically, being Honda, they chose to try to do so not by developing their own versio n of the rotary-valve two-strokes which had by then come to dominate even the largest category of GP racing. Ins tead, fiercely wedded as ever to the four-stroke concept which has been the basis for the company 's product development on road and track since it was founded, H onda set about the seemingly im possible task of reversing the tru th of tim e by building a four-stroke that would battle the two-strokes on an eq ual basis, and beat them. H on da had don e it before and, so corporate reasoning went, the y could do it again by relyin g on ad vanced , materials, revolution ary desi gn , and lots of mon ey. Time would prove th is idea, fallacious, but instead Honda ended up acquiring a wealth of information and experience they cou ld never have obtained otherwise, which in turn led directly to the evolution of the most exotic street bike ever offered for sale to th e public, the NR750. From the nettle of failure, Honda would pluck the fiowerof success. The NR500 project actually began in 1975, under th e supervision of Honda's to p mo torcycle" designer, Soichiro Irimajiri, the ma n responsible for those fabu lous multi-cylinder GP racers of the 1960s, fives, sixes and the like. Honda 's traditional defense against the encroaching potential of their two-stroke riva ls had traditio n ally been to a ttai n th e greate r specific power avai lable at higher revs by multiplying the number of cylinders and reducing friction and inert ia to a minimum; if this also meant' narrowing powe r bands, th is could be circu mvented by simp ly adding mor e ratios to the gearbox - th e 22,500 rpm RC I16 50cc twin or 1966 had a ninespeed gearbox, for example, and the 21,500 rpm RC149 five-cylinder 125 eig ht. But new FIM regulations passed in 1969 limited cylinders to four for the 500cc class and gear rat ios to six , hampering this approach. However, in a two-clever-by-half wording to the regu la tion presumably designed to take account of the split-single two- strokes firms like Puch and DKW ran in the vin tage era, th e FIM regulations actua lly spo ke of a maximum or four combustion chambers, no t cylinders as suc h, wh ich left Honda a possible ch in k in the regulat ions. For this reaso n, the first NR (sta ndi ng for 'New Racing', not Never Ready as the British pr ess later unkindly dubbed the bike) was act ua lly a 500cc V-8 with each pair of p istons sharing a common combustion chamber. However, reluctant to risk criticism or possibl y even event ual ex cl usion caused by a too li teral read ing of the regulations, Irimajiri concl uded that the V-8 was not a viable solution, even if the need to produce a high-revving bike with eight valves p er cy li n de r wa s of p aramount 'importance. The result was the four-cylinder oval piston design, Honda's first (of more than 200 later) patents which were applied for in March 1978. Initial tests took place with a slave engine employing a humble XL250 trail bike crankcase, fitted with an oval piston using a single connecting rod, before the twin-conrod design was adopted to stop the piston rocking in the bore. Rather aptly, this early development