WATER-COOLED V-TWIN

Press, 23 February 1978, Page 11

WATER-COOLED V-TWIN

Big changes are being made in the Honda range of r.oad machines and the new’ CXSOO V-twin is indicative of this. It is very different from anything previously produced by the Japanese motor-cycle industry and will probably be the forerunner of a whole new range of V-twin machines.

The 80deg V-twin enI gine of the CXSOO has a I big 78mm bore and an extremely short stroke of 52mm, it is water-cooled : which is unusual in a four- [ stroke, the cylinder heads ; have a 22deg twist, and ! the four-valve combustion j chambers have centrally , placed spark plugs. i There is nothing new ! about a V-twin layout. This

has been chosen too eliminate vibration and to reduce the height of the engine. But having the cylinder heads angled 22deg from the crankshaft is rather unusual. This allows the intake air flow to travel in a straight line through the carburettors, cylinder heads, and out the exhaust pipes. Because the air’s directional inertia is not altered, the power output is increased compared with the conventional Vtwin. Water-cooling, rare on a

four-stroke, has been used to improve thermal efficiency in the high compression (10 to 1) motor. This immediately produced a weight problem. This has been at least partially overcome by the inclusion of a compact, built-in radiator. At 20Okg, the CXSOO is only slightly heavier than other aircooled machines in its class.

This has prompted the manufacturers to describe it as a sports tourer. It seems that the long distance rider who also likes

a spirited performance will find it very appealing. The 22deg of twist also created a problem for the designers.. With this arrangement, it is virtually impossible to connect two camshafts, a necessity with an overhead camshaft engine. To overcome this, the engine has been equipped with four pushrods driving eight valves with the motion changed 22deg by a single camshaft. This allows it to rev up to 10,000 r.p.m. in perfect safety. The torque reaction

caused by the crankshaft’s revolutions has been eliminated by installing a massive clutch which counter-rotates at high speed. There is also a large flywheel. A new diamond frame, similar to that in the CBX, is used. The engine is bolted on the front and there is no down tube as on conventional frames.

Performance is always a strong selling point and the Honda fares well in this regard. It is claimed that the CXSOO can cover a standing 400 m in 13.4 sec. Economy is another impressive feature. Thirty kilometres a litre is claimed at 60km/h. Comstar wheels of the alloy variety but with separate spokes, are standard. These are more rigid than wire spoke wheels but can flex a little, which helps handling and suspension. TUBELESS TYRES An innovation is the introduction of tubeless tyres—the first to be fitted to a production road bike in the world. Not only does this reduce the possibility of tube blowouts, but it also reduces the weight. Braking is by hydraulic disc at the front and drum at the rear.

The gearbox has five speeds and drives through a shaft to the rear wheel. Starting is electric and ignition fully transistorised. Maximum speed is in the vicinity of 180km/h.