Honda CB160 - CLASSICS REMEMBERED

In the 125-cc CB92 'Benly' of 1959 we saw that Honda had absorbed the lessons of European practice – the NSU-like leading-link front suspension (BMW and Guzzi used leading-link in the 1950s too) , the Horex-like SOHC rocker-arm two-valve cylinder-head, and the cost-cutting pressed-steel chassis and swingarm – but intended to innovate; Honda's addition of electric starting transformed the motorcycle from a fairly athletic undertaking (ever kick-start a 500 single?)into a no-sweat certainty. Bob Fink at Harley-Davidson told me in spring, 1966, "Everything Honda has done has helped our sales." Harley adopted electric-start in 1965.

CB160 developed out of the Benly, retaining the basic backbone chassis, but putting a tubular swingarm in place of the former pressed-steel one, and a telescopic fork in place of the leading-link. For me, the CB160 style defined the ‘Honda look’ for a decade. In particular, the resemblance of the front fender to those of the company’s GP winners brought the bike into the present.

Honda CB160 Road Test from the May 1965 issue of Cycle World.Cycle World

From the standpoint of performance, the 44 x 41-mm bore & stroke of the CB92 were enlarged to 50 x 41, raising peak power very little (from 15 to 16.5 @ 10,000) but with a very mild cam that gave the bike wide-range pull. At the large checking clearance of 1.1-mm, cam timing was 5/30, its modest overlap of 10-degrees putting it almost in Harley territory. CB160 was designed to carry the owner and a friend (the long bench seat leaves no doubt of this), to pull away easily from stoplights, to have usable torque everywhere. Given decent maintenance, such a mildly tuned engine could last a long time. Former American Honda racing manager Gary Mathers once referred to a 2500-hour all-conditions test that every Honda street model had to pass.

The existence of such a test is no surprise, for Honda knew that without high-level reliability his products could not make headway in world markets. In this way, products would sell themselves.

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The CB160’s backbone chassis, into which the engine bolted by its head and the back of its gearbox, was like that raced by Honda in their early 1960s 250-fours. This chassis was perfectly adequate on the street, but for 1962 Honda upgraded the racing four to a better-braced chassis. 1969 250 World Champion Kel Carruthers told me why. Lent an RC-161 for Australian races, he found that it oscillated during leaned-over acceleration – unless he made a deliberate effort to push the machine upward, holding himself down on the inside. Honda referred to this oscillation in the classic book, “Race for Leadership”, which described the machines in the 1961 GP championship. Kel attributed the oscillation to the backbone frame’s less-than-substantial support of the swingarm.

The Honda 160 engine was a two-valve hemi with the rather large valve included angle common at the time Honda evolution began – 78-degrees. This was also the case with the 160’s big brother, the CB450. During Honda’s intensive involvement in 1960s GP racing, engineer Shoichiro Irimajiri understood from the very early ignition timing required by these engines (As in 65-degrees BTDC! Compare with a contemporary Triumph at 36 BTDC) that they suffered from slow combustion and rapid heat loss. He gradually reduced valve included angle and increased bore/stroke ratio, such that the final 1967 version of the RC-166 250-6 was given a 58-degree valve angle and a bore/stroke ratio of 41/31.5 = 1.3. He introduced such changes first on the 50-cc twin, then on the 125-5.

Honda CB160 Road Test from the May 1965 issue of Cycle World.Cycle World

It might be supposed that the need of the ultra-high-revving GP engines for early ignition timing was because rpm was outrunning combustion flame speed. But Honda’s own research, conducted in that time and published as an SAE paper, told another story – that flame speed tends to rise pretty much in step with rpm.

When Irimajiri designed the CBX, he started out with progressive numbers close to what he had learned from his development of Honda’s GP engines. The CB160, hitting the market in 1965, was derived from earlier Honda practice and so even with its low 8.5-to-one compression, its combustion was none too fast; at full advance (achieved at 4200-rpm), spark timing was 45 BTDC.

The remaining population of CB160s has supplied the basis for a vigorous vintage racing class.

All that tech stuff aside, I remember the CB160 as a pleasant presence in the later 1970s. It provided stylish transportation without imposing an identity on its users.

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