BSA Motorcycles 1920s

The 3.49 h.p. O.H.V. Model.

Remarkable acceleration and high maximum speed are features of this machine with its high efficiency overhead valve engine. The valve gear, being enclosed and automatically lubricated, requires little attention. This model should particularly appeal to the sporting motor-cyclist who requires a light and tractable machine for high speed touring. Fitted with a B.S.A. No. 14 sidecar, it makes a light sporting combination outfit.

Single cylinder, 3.49 h.p., 72 x 85½ mm. bore and stroke (349 c.c.). Double row roller big-end bearing. The engine mainshaft is mounted on ball bearings. Accessible detachable head fitted with overhead valves and compound valve springs. Valves operated by phosphor bronze bushed rockers, equipped with felt oiling rings working on hardened steel pins. All valve gear is enclosed and automatically lubricated by oil mist from crankcase, forced up push-rod casings to rocker boxes by crankcase compression. Aluminium alloy piston and silent timing gear. Steel fly-wheels. Special plated exhaust system with large silencer giving mellow note without loss of efficiency.

Magneto and Carburettor.
Amac. A special carburettor fitted with air cleaner can be fitted as an extra. Magneto, driven by adjustable chain in aluminium dust-proof case.

Gravity feed to mechanical pump of improved type, then to sight feed on timing case, feeding to crankcase. A hand pump is also fitted for emergency use. Oil is supplied to the primary chain by depressing a spring bypass valve on sight feed. Hubs, fork links, etc., are fitted with grease-gun nipples.

Front drive, ½ x .305 in. roller chain enclosed in two-part chain case, and 5/8 x ¼ in. roller chain rear drive protected by an efficient guard. A cam-faced cush drive is fitted to the engine shaft. For gear ratios see page 69.[1]

Contained in large chain wheel, and is of the floating dry-plate type. Controlled by lever on left of handlebar with large diameter cable.

B.S.A. Three-speed. All gears constantly in mesh and increased in width to give additional strength. The kick-starter mechanism is enclosed in the gear-box. Inclined change-speed lever on right side of tank. Screw adjustment of box position for accurately setting chain tension.

Frame and Spring Fork.
The frame is designed to give low riding position, and is constructed of weldless steel tubing and forged steel lugs throughout. The head lug is of continuous type, giving great strength. Fitted with special lugs to take B.S.A. sidecars. Strong carrier fitted. The spring fork is of the strengthened B.S.A. type, fitted with taper compression spring and shock absorbers.

Adjustable, mounted behind steering head with forward bend at centre and back sweep at end. Reversible for sports use. Long rubber grips.

Tapered type specially reinforced, supported by brackets brazed on to the frame. Filler caps secured with bayonet joint and chain ; unleakable petrol tap. Capacity: petrol, 1½ gals. ; oil, 3½ pints. Adjustable rubber knee grips fixed to tank.

Wheels and Tyres.
Wheels: heavy gauge rims, 21 in. x 2¼ in. enamelled. Taper roller bearings to rear hub. Dunlop cord types, 27 in. x 2.75 in., wired-on, or 26 in. x 3.25 in., wired-on with special front mudguard extra.

Both of the internal expanding type. Front, 5½ in. diameter operated by lever on right handlebar. Rear, 7 in. diameter, operated by toe pedal on independent fulcrum on right side of machine. Grease-gun nipples fitted to the cam spindles.

Saddle and Mudguards.
Terry spring seat, De Luxe type saddle. Brooks supple seat B.190/2, if specified. Rear mudguards, 6 in. wide of plain section. Front fitted with side wings and splash attachment.

Footrests, Stands, and Tool Box.
Footrests are adjustable. Stands, back, kick-up ; front, rigidly secured to guard. Tool box, metal case. Complete set of' tools and grease gun in a neat roll. Special combination tools provided for easy removal of valve springs. Levers on this tool are detachable for use as tyre levers. An inflator is provided.


1. More pages from this book are available at Craig Howell's Flickr pages. Craig Howell

Source: Book of the BSA by Waysider. Pitmans, 1928.