Humber Motorcycles

Today in Motorcycle History

Humber 1914 Flat Twins

A 6 h.p. Horizontal Twin Humber.

A Water-cooled Sidecar Machine; Three-speed Box; Enclosed Chain Drive.

ONE of the most striking designs for 1915 which we have had the pleasure of inspecting is the 5 h.p. horizontal twin-cylinder water-cooled Humber. Apart from the fact that the principle of a horizontal twin has been adopted for the first time by the Humber Co., the engine itself possesses many new features and practical points of real interest. For instance, the cylinders are not in line, which allows of big end bearings of exceptionally large dimensions. The crank is a plain one of nickel steel, and the big end bearing measures 35 X 30 mm.

Above the crankshaft and driven by a train of gears is a case-hardened steel camshaft formed from the solid and running in ball bearings, the cams operating direct on to adjustable tappets. The valves themselves are practically horizontal and arranged above the engine. The starting handle engages with the camshaft, thus giving a 2 to 1 gear, and making the starting comparatively easy.

Detachable Valve Pockets.

A practical feature of the engine is the detachable valve pockets, each pair of which are held in position by a yoke and a stout nut and bolt. By removing this single nut the yoke may be detached and each valve withdrawn separately, complete with its seating. It is almost unnecessary for us to emphasise the advantage of such a system, in view of the fact that the condition of the seating. may be inspected with the greatest ease, and, moreover, the valves may be ground into their seatings in the clear view of the operator; but this is not all. An expedient which will undoubtedly be followed by users of horizontal twin Humbers will be to carry a spare seating and valve complete, so that, should the compression show signs of weakening after prolonged running, it will be the work of but three or four minutes to fit a new valve and new seating, and thus restore compression.

The fact that the valve ports are not water-cooled, although the remaining part of the cylinder is liberally water jacketed, may cause surprise at first, but the experiments which the Humber Co. have made include a test of the design in an air-cooled form, and it has been found that the valves and their seatings have stood up wonderfully well. It is, therefore, practically certain that, working under the much more favourable conditions provided by a water-cooling system, the life of the valves and their seatings will be greatly prolonged. A Hallite washer is used for the joint, which is found to be superior to the copper and asbestos type of washer for this purpose. The sparking plugs are in a most accessible position. The cylinders can be removed without disturbing the crank case.

As regards the lubrication .system, the splash feed is relied upon. The pistons have flat tops and a pair of rings. The crankshaft revolves on ball bearings, a double row of bearings being arranged on the flywheel side and a single bearing on the timing gear side. The oil retainer on the flywheel side is of interesting design, as it has phosphor bronze rings, which are kept in contact by the pressure in the crank case. We are -told that this system works perfectly. The engine is secured to the frame, top and bottom, the top connection being affixed to the lower tank tube.

The cooling is on the thermo-syphon system, pannier radiators of one gallon capacity being arranged immediately behind the steering head and connected to the petrol tank. The circular oil tank is fitted into a recess of the petrol tank in the usual Humber manner.

Gear Box and Clutch

The gear box has three speeds, the shafts revolving on ball bearings, and the operations being effected by a single sliding wheel on a double dog clutch system. The gear ratios provided are 4.76, 7.33, and 13.8 to 1. The chain transmission is enclosed in oiltight cases.

A multiple-disc clutch is mounted on the main gearshaft, and is designed to stand any amount of slipping. Four rings of Ferodo are utilised as the slipping medium. The chain wheel, besides being sandwiched between Ferodo rings, has another member clawed to it again working between Ferodo rings. It is controlled by a foot clutch, a quick thread screw on the right-hand side operating a rod in the hollow shaft. A gate change lever is provided, two free engine positions being obtained.

A detachable rear wheel, made under the Lea-Francis patent, is another feature, and mounted within the hub is a slipping clutch device which is very efficient in practice, the snatch of the engine being first taken up by the spiral springs and the recoil by the rubber buffers.

The detail work of this new Humber has received careful attention. We noticed that the links of the Druid spring forks - a source of wear, especially with sidecar outfits - are designed so that each wearing face in contact is of hardened steel. Moreover, each securing nut is of the castellated type with split pins. A Rotherham petrol filter gauge and filler cap has been adopted as standard, whilst a sight feed drip lubricator is mounted in a convenient position at the forward end of the tank.

The silencing is well carried out, a separate pipe leading to a large expansion chamber in the front, an extension pipe being carried to the rear, near the end of which is other chamber is formed.

The Running of the Engine.

With the Claudel-Hobson carburetter the engine is one of the most controllable we have seen, and another good point that impressed us was the comparative silence of the valve gear. No doubt some of this silence may be put down to the water-jacketed cylinders, which are devoid of that ring which is so noticeable in an air-cooled casting. The engine would tick over so slowly that it was possible to count the explosions, and it will at once roar away on the throttle being swept open. The note of the exhaust is particularly pleasing.

The new 6 h.p. Humber is bound to make a strong appeal to that growing section who favour the moderate-powered twin-cylinder sidecar outfit, especially as the Humber will be sold complete with a handsome coachbuilt sidecar. The 6 h.p. twin and the 3½ h.p. air-cooled models - close upon four hundred of which, as we have mentioned, have been supplied to the Russian Government - will form the two patterns of Humber motor cycles which the company have decided to market in 1915.

The Motor Cycle, November 12th, 1914. pp529, 530.