The interesting thing to note about this Honda CB500R is that it was the product of the company’s Research & Development department, not the Racing department (RSC).
Based in Saitama, the R&D’s first design was built in 1971 and used the road-going CB500’s frame. It was raced by Morio Sumiya in that year’s All Japan Championship. For 1972 this much more focused bike was constructed and was ridden by Kengo Kiyama in the Open Class, winning several races.
It used a CB500 motor as its base with the capacity increased to 651 cc (64 x 50.5 mm). Numerous modifications from the stock motor included the following – the crankshaft was machined from solid; high-compression pistons with only two rings; dry-sump lubrication; larger, magnesium oil pump; magnesium sump and (smaller) oil filter housing; dry clutch; sand-cast cylinder head with magnesium valve cover; larger valves with stiffer springs and hardened seats; close-ratio five-speed gearbox; Kokusan electronic ignition. The Keihin 31mm carburettors were the same as used on the CR750.
The frame was made from chrome-moly steel, using 25mm diameter tubes, while the forks were also from the CR750. Power is 80 hp at 10,700rpm, with a dry weight of 138kg.
This bike was first displayed at the 1971 Tokyo Show and after it was retired kept in storage until Italian mechanic Carlo Murelli was offered his choice from Honda’s race bike collection as a retirement present after many years of working in Japan for Honda RSC (then HRC) on the NR500 and NS500 projects, amongst others.
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