This machine is similar to the 3.49 h.p. O.H.V., but has special features that should appeal to the rider who requires a fast reliable machine for general competition work.
Engine.
Single cylinder, 3.49 h.p., 72 mm. x 85 mm. bore and stroke (349 c.c.). Double row roller big-end bearings. Engine mainshaft mounted on ball bearings. Steel fly-wheels. New type detachable head, fitted with overhead valves mounted at 90°, and compound valve springs. Inlet and exhaust ports carefully polished. Enclosed rockers mounted on roller bearings. Tubular alloy steel push-rods, working in dust-tight tubes, made telescopic to allow adjustment of return springs. Low compression piston fitted as standard. High compression piston can be fitted, if specified, or supplied as an extra with the tool kit. Two spare valve springs supplied. Special plated exhaust system giving mellow note of all speeds without loss of efficiency.
Carburettor.
Special Amac Lever or twist grip throttle control to order. A special carburettor fitted with air cleaner is an extra.
Lubrication.
Oil tank mounted on seat tube, capacity 5 pints. Gravity feed to mechanical pump, then to sight feed on timing case, feeding to crankcase. Oil is supplied to the primary chain by depressing a spring by-pass valve on sight feed. Foot-operated plunger pump mounted on tank supplying oil direct to big-end bearing. Hubs, fork links, etc., fitted with grease-gun nipples.
Gear-box.
B.S.A. three-speed, specially selected for freeness. All gears constantly in mesh and increased in width to give additional strength. Kick-starter mechanism enclosed in gear-box. Inclined change-speed lever on right side of tank. Screw adjustment of box position for accurately setting chain adjustment. A close, or specially wide, ratio gear-box can be fitted if specified, see page 69.[1]
Frame.
Specially designed to give a low riding position and low centre of gravity. Head fitted with B.S.A. steering damper. Constructed of weldless steel tubing and forged steel lugs throughout. Head lug is of continuous type, giving great strength. Strengthened and fitted with special lugs to take B.S.A. sidecars.
Handlebar.
Sporting, adjustable, mounted behind steering head, with forward bend at centre and back sweep at ends. Reversible for sidecar use. Long rubber grips.
Tank.
Tapered type petrol tank, capacity, 2 gals., specially reinforced and supported by brackets brazed on to the frame. Filler cap secured with bayonet joint and chain ; unleakable petrol tap. Adjustable rubber knee grips fixed to tank.
Saddle.
Special Terry racing spring seat. Brooks T.T. type, if specified.
Mudguards.
Rear: strong and wide, of plain section, with hand hold on stay. Front with side wings or plain blade, if specified. Detachable carrier extra.
Notes
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.
