AN O.H.V. BIG TWIN.
OF several engines which made their debut at the recent five hundred miles race at Brooklands, the British Anzani, mounted in a Zenith motor bicycle, gave a very promising performance.
We recently inspected this engine, which had not been interfered with since the event, and we were at once impressed by its condition. Externally, it had kept remarkably clean, whilst internally all the bearing surfaces were as new.
Two cast iron cylinders, which have a bore and stroke of 83x92 mm: (998 c.c), are provided with detachable heads, which accommodate the overhead valves, the rocker arms for these being pivoted in brackets mounted on twin lugs. The rocker bearings are lubricated by wicks fed from a cup filled with grease, which liquefies when the engine gets hot. The engine, it is claimed, has developed 24.5 b.h.p. on the bench at a speed of 5,500 r.p.m.
Lubrication is carried out by means of a plunger pump located in the base of the crank case sump. The plunger has a lore and stroke of 6x5 mm., and delivers oil at the rate of just under half a pint per minute at 3,000 r.p.m. engine speed.
The plunger is driven from an eccentric located outside the two cam wheels on the crankshaft. The oil is led first to the timing side, and thence, by a Y-shaped connection, to the flywheel side mainshaft bearings.
The drilled crankshaft is built up from the flywheel side, and feeds the cams via a small hole in the crank case casting, and the magneto bevel spindle through another channel. The flywheel side of the crankshaft is drilled, and conveys the oil to Ihe white metal big end bearing.
An additional oil lead to the front cylinder is regulated by a sight feed drip lubricator fixed on the tank.
Aluminium pistons carry three rings of the deep and narrow variety, the lowest acting as a scraper and distributing the oil in the cylinder. The little end of the connecting rod floats on a hollow gudgeon pin, which is retained in position by brass discs at each end.
Tappet adjustment is effected in the usual manner, by nuts on the push rods, whilst a long guide is afforded by the use of a brass casting fitted on the top of the crank case.
A quart of oil is contained in the sump, which may be drained by removing a small plug at the base of the pump. The rocker arms, riding over the cams, are provided with Hoifmann rollers - a very effective fitting - whilst the efficiency of the engine relies to a large degree on the special form of cam.
The crank case is held in the frame by four bolts located in shoulders cast at the front and, back, while additional support to the engine is also given by two frame tube clips fitted lower down on the casting. A 1,100 c.c. cycle car engine is also made, and, but for the provision of two belt-driven fans in front of each cylinder, and aluminium cases for the overhead valve gear, is identical with this unit. To meet the special requirements of cycle car transmission, the heavy flywheel is arranged to receive a clutch cone.
These engines, which are designed by Mr. Hubert Hagens, are made by the British Anzani Engine Co., Ltd., 30, Scrubbs Lane, Willesden, London, N.W.IO.
The MotorCycle, August 25th, 1921. p247
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