Born under the success of the CB 750 Four, no one expected that Honda would have made the four-cylinder engines of smaller displacement, partly because it already produced some popular twin-cylinder models of 350 and 450 cc. But the appearance of the Honda CB 500 Four in the spring of 1971 was a real surprise in the two-wheeler market and marked the beginning of the production of an authentic myth.
Enjoyable in everyday use, the small Honda CB 500 Four proved agile in urban traffic, so that seemed a 125 cc, unlike the CB 750 which was instead a bit ‘heavy in city maneuvers and therefore less agile. With the 500 Honda spent an eye on the lightness and weight distribution. The frame was redesigned above all in the upper part. The CB 500 kept under the engine the classic closed-tube structure (characteristic of the Four) but in the tube-frame connection it was much simpler and made extensive use of the printed plate. Outside the city on fast and free roads, the engine could easily be entered in pairs with 7,500 rpm, abounding in the use of the clutch. Traveling in fifth to 9,000 rpm meant exceeding 180 km / h and this was a great result for a 500 cc heavy barely over 200 kg.
LA TECNICA DELLA CB500 FOUR
From a technical point of view the new Honda CB 500 Four was not a miniature version of the 750, with which it only shared the number and layout of the cylinders in addition to the single-shaft distribution with chain drive, the result of a totally new project.
The lubrication system was different; with the new CB 500, in fact, the dry crankcase model of the larger displacement was moved to a simpler one, with a wet casing.
The 750 engine was a long stroke, while the 500 was a superbox. As for the distribution, the two castles had been abolished, fixed above the head, which supported the camshaft and in which the rocker axles were inserted; the latter were now installed in the cover of the head itself (and the camshaft supports were half-formed in the head and half in the cover). The result was a greater compactness and a better constructive rationality, with a lower number of components and workings.
Completely different the primary transmission, which in this case was “mixed”, ie made with a scheme to which the Honda has remained faithful for a long time, even for other models appeared later. A silent chain started from the center of the crankshaft, and this was an interesting novelty for the motorcycle industry. This toothed chain (clearly more robust than a roller chain, with the same width) dragged in rotation an auxiliary shaft, which in turn transmitted the motion to the clutch bell by means of a pair of gears, as well as ensuring the connection with the starter motor and to operate the oil pump.
The camshaft was controlled by a centrally located roller chain, on which an anti-skid pad and a leaf tensioner, of the semi-automatic type operated.
Periodically it was necessary to loosen the locking nut of the adjusting screw; a calibrated spring therefore provided the correct lathing to be assumed by the tensioning sheet and thus imparted the correct tension to the chain. Holding the screw (located at the back of the cylinder block), the nut was tightened again and the operation was completed.
The camshaft pins rested directly on the aluminum of the head and the lid, and it amazed many fans of the time. Yet this solution, without rolling bearings and without bushings, was used for years in automotive engines such as the twin-shaft of the Alfa Romeo Giulietta and Giulia.
The angle between the two valves of each cylinder (the intake one was 27.5 mm and the exhaust one of 23 mm) was slightly lower than that used on the CB 750; from 58 ° it passed in fact to 56 °. The 56 mm bore was combined with a 50.6 mm stroke. The cylinder block was equipped with cast iron pipes installed with interference. The forged steel crankshaft rested on five bench supports and worked entirely on bushings.
The engine of the Honda Cb 500 Four was powered by a battery of four 22 mm Keihin carburettors and had a compression ratio of 9: 1, the house declared a maximum power of 50 horsepower at 9000 rpm.
LE VERSIONI DELLA HONDA CB 500 FOUR
Honda produced 4 series of the CB 500 Four: k0 (1971), k1 (1972-1973), k2 (1973-1974) and k3, known simply as “k” (1975-1979).
The first series was associated with the initials K0 and this, in the years following that of its presentation to the public, had remained basically unchanged: the only significant notes of the subsequent series K1 and K2 were limited to modest updates mainly aesthetic, such as: the shape of the instruments, the exhaust mufflers, the direction indicators, the difference in liveries and the addition of a further attachment for the second front disc brake.
The last of the successful series was the CB 500 Four K, which would have chronologically the acronym K6, if the K4 and K5 had been imported also in Italy. The K was the series that made more changes than the previous ones: the colors, in addition to the tank, the saddle, the instruments, the direction indicators: even the shape and size of the mufflers had changed.
Still new updates will lead to the models CB 550 Four and CB 650, which will not be able to maintain the same charm of the previous and famous “true” Four and not even bear the comparison with the competitors of the same displacement.
THE TECHNICAL SHEET OF THE HONDA CB 500 FOUR
|Dimension and weights|
|Dimension (lenght.×width.×height.)||2120 × 825 × 1115 mm|
|Height||Seat: 805 mm – Minimum from the ground : 165 mm|
|Interasse: 1405 mm||Massa a vuoto: da 183 a 191 kg||Serbatoio: 14 l|
|Engine type: 4 strokes, 4 cylinder||Cooling: air|
|Displacement||498,5 cm³ (Bore 56,0 x Stroke 50,6 mm)|
|Distribution:||Carburattors: 4 Keihin 627B 22 mm|
|Power: 46-50 hp a 8500/9000 rpm||Torque: 42 Nm a 7500 rpm||Compression ratio: 9 : 1|
|Clutch: multiplate in oil bath||Gearbox: 5 speed sequential (always in gear) Trasmission ratio 2.353 1.636 1.269 1.036 0.900:1|
|Start||Electric and pedal|
|Suspension||Front: Hydraulic shock absorber with telescopic fork /Rear: Hydraulic shock absorber with oscillating arm|
|Brakes||Front: 275 mm single disc / Rear: 180 mm Drum|
|Tires||Front 3.25-19 – Rear 3.50-18|
|Top Speed||180 km/h|
|Fuel Consumption||average 15 km-liter|