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Brough Motorcycles

Brough Flat Twins for 1921

Olympia Show 1920

Brough. (Stand 64.)

  • 5 h.p.; 70x90 mm. (690 c.c); twin-cylinder four-stroke; side-by-side valves; hand pump lubrication; Amac carburetter; Thomson-Bennett gear-driven magneto; three-speed Sturmey-Archer gear; chain drive; 650x55 mm. tyres.

E. Brough and Co., Basford, Nottingham.

On the Brough stand there is the overhead valve 3½ h.p. and the large 5 h.p. model G. Both machines are designed on very pleasing lines, so that they not only have a smart appearance, but also are essentially workmanlike, and a sound mechanical job - a point which is not without considerable value in the eyes of the possible purchaser.

The 5 h.p. flat twin engine has the two cylinders considerably staggered, and carried rather higher than is usual. On the 5 h.p. model there are a number of fairly thick fins, especially around the valve ports, which are placed on the upper side of the engine. The valves are above and horizontal, in which position they are accessible - the adjustment and tappet gear particularly so. From the ports short pipes are cast with the cylinders, and curve away to the main exhaust pipe below the engine. Either aluminium or steel pistons are optional, according to the work to which the purchaser desires to put the machine, but both are fitted with two piston rings at the top and a single keeper ring to secure the gudgeon pin from endwise movement.

An interesting point in the design is the aluminium inlet pipe, which is secured by a C spanner nut to the valve port at the outer end, but is socketed in a special packing washer at the crank case end, allowing for differences in expansion. The second model is a modification of the well-known 3½ h.p., which differs from its larger brother, in that there are fewer fins on the cylinder head, and that the valves are in the head itself, and are operated by rocking levers and long push rods, a small aluminium coverplate protecting the mechanism for each.

A part of the inlet pipe is cast in the crank case, but the mixture is conducted to the ports by a pipe constructed on the same lines as that on the 5 h.p. The engine has a bore of 70 mm. and a stroke of 64 mm., giving a cubical capacity of 495 c.c. The remainder of the specification follows that of the 5 h.p.

Olympia Show. The Motor Cycle, December 2nd, 1920. Page 716




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