An Entirely New 692 c.c. Model, the Latest Production of the Brough Factory, the Outcome of Several Years' Experience with Horizontal Twins.
AT the present time, as will have been gathered from recent issues of The Motor Cycle, there is something akin to a boom in "flat twins," as we have styled these horizontally-opposed engines. Some twelve machines are already well known to the motor cycling public, and among them the productions of Messrs. W. E. Brough and Co., of Basford, Nottingham.
The 3 1/2 h.p. model of the firm, or, as they are pleased to call it, "The Pup," has proved its worth, not once, but many times, in competition, and it speaks well for the machine that it seldom appears in the second-hand market, and when it does, always commands a very high figure.
The larger machine now makes its appearance in an improved form, and, without overstating the case, we may say that it is a very fine product in every way, but, unfortunately, for the present, it is not obtainable, for the simple reason that Messrs. Brough are much too busy on important Admiralty work, which must not be delayed or interfered with in any way. The 5 h.p. flat twin must remain in being only, so far as two or three models are concerned, awaiting the termination of the war, when it will take its place as a standard model. Messrs. Brough are convinced of the superiority of flat twins over singles, and this after extensive experience over a period of twenty years of engine manufacture.
The specification of this outfit, for it is intended to be sold as a complete combination with a specially designed sidecar, may briefly be stated thus:
Cylinders. - Horizontally-opposed, each 70 X 90 mm. = 346 c.c.
Transmission. - 1/2 in. chain to counter-shaft, Sturmey-Archer three-speed gear, and l 1/8 in. belt to driving wheel.
Magneto- - Thomson-Bennett.
Carburetter. Claudel-Hobson, with hot air jacket.
Frame of special design, rendering removal of cylinders an easy matter, leaving the crank case in situ.
Splash lubrication by drip feed.
Features of the New Engine.
The cylinder casting of the new 5 h.p. engine is a fine piece of work, the fins being arranged horizontally on the cylinder itself and "herring boned" over the valve pockets. Between the pockets is an air passage to assist cooling. The cylinders are staggered to the extent of one inch, and bolted to a very cleverly designed crank case casting in aluminium. The latter is entirely in one piece, with a large cover plate forming the off side of the chamber and secured by twelve nuts. All corners and edges are rounded, and particular attention given to making the engine uiiit as clean and plain in its lines as possible. Absence of dust-collecting corners and general simplicity have always been the striking features of the smaller Brough machine. Lubrication is very efficient, the oil being fed directly over the big ends, and dropping into the crank case, to be utilised again on the splash system.
The valves are placed horizontally, side by side, above the cylinders, are of large diameter, and easily accessible in either cylinder. The whole power unit is held rigidly in the frame. The back part of the frame is carried underneath the crank case, and the front down tube carries the crank case at the top, which arrangement facilitates the ready removal of either cylinder. The crankshaft is well balanced and of substantial design, as also are the connecting rods, which latter have the usual car type big ends. The piston has two rings at the top and one at the bottom, with a keeper ring over the gudgeon pin.
The Thomson-Bennett magneto, placed above the crank case, is gear driven. It is interesting to note that Messrs. Brough have been fitting this magneto from the early days of the war in place of the Bosch, and it has given entire satisfaction. The usual outside flywheel is fitted, with the chain-sprocket on the outer side connecting the power via a half-inch chain to the standard Sturmey-Archer gear and clutch (handle-bar controlled).
The exhaust is carried by easy sweeping pipes into a cast aluminium box carried under the crank case. No baffle plates are used, but the engine runs very quietly.
The head of the frame is particularly strong, and has cast integral with it two lugs for sidecar attachment. The forks are specially made, the main blades being very wide. Two gallons of fuel may be carried in the tank, whilst the oil compartment is partitioned off in the centre of the right hand side, the control being by plunger pump and visible drip feed.
The sidecar is of special design, being roomy and having a capacious locker at the rear end. That the springing is efficient and well thought out we were able to prove later during a short run on the rough suburban roads of Nottingham. The sidecar is being made especially for this machine by the Derwent Sidecar Co., of Borrowash, Derby.
After a thorough examination of the machine we were invited to take a trial trip in the sidecar. The first noticeable feature was acceleration; as soon as the gear is changed from low to top the speed jumps to 25 m.p.h. in a few yards, and this speed can be maintained on a give-and-take road on a mere whiff of gas, whilst the quiet purr of the engine is very pleasant. But as the throttle is opened the big reserve of power is drawn upon, and very high speeds, for a sidecar combination, can be maintained whenever the road permits; 45 m.p.h. is easily reached on deserted stretches of road. No doubt 50 m.p.h. can be attained without undue effort, and this, with rider and passenger of normal weight, about 12 stone each. The engine can be throttled down to about 10 m.p.h. on top gear, and it pulled steadily at this speed up a gentle rising gradient without labouring in any way. AU horizontally-opposed engines show a marked reduction in vibration from that to which we have become accustomed on the single and V twin types; but this superiority is particularly noticeable in the Brough. It is excellently balanced, for even when revving fast on the stand the usual tremor was almost absent. Without doubt Messrs. Brough have perfected a splendid example of the horizontally-opposed engine, which will add greatly to the cult of the "flat twin."
The Motor Cycle, November 23rd, 1916.
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