Honda RC70F
Seminal scrambler
Given that Honda and Yamaha’s earliest attempts at racing machinery were designed to be used on the rugged dirt surfaced courses in Japan like Asama Mountain, they were off-roaders as much as road racers – street scramblers if you like, and often shod with knobbly tyres. It was not until the early ‘sixties that the designs became slightly more refined (coincidentally with the increased popularity of motocross in Japan as a result of Aussie Tim Gibbes’ Racing Schools conducted there from 1963). But back in 1957 what Honda offered the budding racer was what the factory termed the RC70F; a 250cc twin using the C70 (and later C71) engine, which had the ‘rotary’ gearbox favoured by several of the Japanese manufacturers. This had first gear at the bottom of the shift pattern, followed by neutral, followed (if the rider kept pressing downwards) top gear and so on. The RC70 was offered for sale in Japan as early as 1958, and one school of thought has it that the overall look was influenced by the German Adler Cross scrambler. The two certainly shared many similarities, notably the long travel leading link front suspension and the wide cradle tubular steel frame. The frame itself is remarkably similar to the Adler. The RC70 was available with or without lighting.
Of course, the late ‘fifties was also the period when Honda was keenly eyeing the US market, taking the significant step of setting up their own distribution centre in California – American Honda – in early 1960. However prior to that, at least four examples of the production RC70 found their way to USA. Two went to Herb Uhl, who had a motorcycle dealership in Boise, Idaho, and who had competed in the International Six Days Trial in Europe on two occasions, riding with his brother Bill who was an Expert class flat track rider. Herb noted later “I imported a couple of RC70 offroad bikes from Honda Japan in early 1959 and they had excellent leading arm forks.” About the same time, another pair of RC70s was sent to Allan D’Alo in California. D’Alo was an amateur racer from Norwalk, California, who annually competed in the Catalina Island “Grand Prix” on an MV Agusta. The Hondas were imported ostensibly to test the market, and came with basic C70 250cc Dream engines, complete with rotary gearboxes.
Local racers were still wrestling with the “left side shift” gear levers on these early Hondas, because many of the European racing bikes came with “right side shift” transmission selectors. Having to remember which side of the engine to change gears with, as well as coping with the “rotary” gearbox function was more than most riders wanted to deal with, back then. The “fix” for the RC70 riders was to commandeer engine assemblies from the 1959 CE71s, once they were released for sale through the fledgling AHMC distributorship. The electric-start CE71 was Honda’s U.S.-spec “Dream Super Sport” model, which featured a conventional return-shift transmission, a larger 24mm carburettor (vs. 22mm carburettors that were stock on Dream engines) and a horsepower
upgrade due to higher compression pistons and more aggressive camshaft timing. One of the RC70s was assigned to budding scrambles rider Preston Petty, who later founded the plastic mudguard revolution that found a ready market in the booming off-road scene. Petty won several local Southern California dirt races on the RC70F, which later had a CE71 engine fitted. As the Honda was developed, some reports say Petty trimmed off the factory-installed leading-link suspension front end and machined up a new steering head which could hold AJS telescopic front forks and a wider, smaller 18 inch front wheel in place of the standard 2.75 x 19 front tyre.
The RC70F varied slightly in specification during the period of its catalogued existence, some being fitted with a high level exhaust pipe with a substantial muffler on the right hand side, others with straight through pipes exiting in front of the right hand rear shock absorber, and others with low road-style pipes and muffler. There were also dry-sump versions available. The 1960-61 pre-production Honda 250 Scrambler prototypes also came with single-carb Dream engines, but with return shift transmissions. When the 1961 CB72 Hawk sport bikes were released, the first thing that happened to the “next generation” 250 Scrambler was again a motor transplant, but this time from a CB72, which had dual carbs, even higher compression pistons and a 10,000 rpm redline. In fairness to Honda, they were not the only ones who offered “rotary gearboxes” to the public. Early Yamahas, the Bridgestone 175s and Lilac motorcycles also had this feature for a few years, among other now-extinct manufactured models. Honda continued to offer the rotary-gearbox option on domestic 250-305cc Dreams and CYP77 Police bikes into the mid-1960s, but no other “large” models were so equipped after that.
Resurrecting an RC70F
The subject of this remarkable restoration was discovered in Spain. Although it is thought to possibly be the ex-Preston Petty bike, this may not be the case given the substantial modifications Petty was said to have carried out, because this one, as found, was in basically standard condition. It had been ridden to near destruction, with oil baked on everything and many parts missing or semi-destroyed. However it was the chance to give a new life to a very rare motorcycle – Honda’s first production motocrosser – and the RC70 was soon on its way to its new owner, Mike Buttinger (founder of Consolidated Motor Spares, or CMS, the world’s largest independent supplier of parts for Japanese bikes) in Holland. It arrived mid-2014 and once ensconced in The Netherlands, the RC70 was entrusted to Marnix Deibert and Sebas van de Broek, who have done many restorations for CMS, including the C71Z featured in OBA 76. It turned out to be a big job.
Once dismantled, the task of identifying what could be saved and what needed to be recreated began. The seat had been incorrectly recovered but the base was usable, so that became an item for the upholsterer, in the correct red and black with white piping. As to be expected on a motorcycle that has spent its life bashing and crashing over jumps and bumps, the suspension needed serious attention. New bushes were made for both the front forks and rear swinging arm, and a new brake pedal spindle made to replace the missing one. Footrests were remade in the correct style, and the rocking pedal gear lever was refurbished. One item that was beyond saving was the exhaust system, so a new set of pipes were bent and a heat shield made from scratch to exactly match the original. Front brake and clutch levers are unique to the model and had to be remade, along with the handlebars which were still on the bike but in poor shape after being straightened numerous times. The friction steering damper was also still in place but in need of a complete rebuild. Likewise, the front and rear suspension units, also unique, were internally worn out but reclaimable after much precision machining. The outer covers were first panel beaten, then built up with copper before being chrome plated. The side covers for the fuel tank were also copper and chrome plated.
Fortunately the engine, with its 180º crank, is substantially similar to the early C70 and C71 types (without the C71’s electric starter) and CMS hold vast stocks of spares for these, so most of the parts needed came straight off the shelves. Cycle parts including the mudguards were able to be saved after much work, and finished, along with the frame, swinging arm and fuel tank, in the rich red common to many early Hondas. The result is an absolutely stunning rescue of a very tired old paddock basher that could well have ended up as scrap. Marnix and Sebas have gone to the finest detail to ensure every component is now exactly as it left the factory – recreated as necessary or painfully restored. The RC70 now forms another historic link in Honda’s history as part of the amazing CMS collection.