General Specification...
This specification gives full details of the 1938 A.J.S. Models illustrated on pages 9, 10 and 11 of this catalogue.
The three models are generally similar in design, but the Models 38/8 and 38/18 are fitted with overhead overhead valve engines, whereas the Model 38/9 is fitted with an engine of the side valve type. All three models have engines of 498 c.c. capacity.
ENGINE. Designed and manufactured throughout in the A.J.S. factory, the engines fitted in these three models incorporate every modern refinement. The design is generally similar to the models described in detail on page 2. All are of 498 c.c. capacity, the 38/8 and 38/18 being of the overhead valve type, while the 38/9 is of the side valve type. The Model 38/8 is fitted with two-port cylinder head and the Model 38/18 with a single-port head.
The side valve engine fitted in the Model 38/9 incorporates a car-type detachable cylinder head designed to promote turbulence combined with good cooling, so giving the highest possible power-output with smooth running and absence of "pinking." The design incorporates a dwarf tappet chest with the valve springs carried in steel cups which are entirely insulated from the heat of the cylinder. The handsome finned cover to the tappet chest is quickly removed to give access to the valve clearance adjustment.
The overhead valve engines fitted in the Model 38/8 and Model 38/18 produce nearly 25 B.H.P. but are exceptionally smooth running and flexible and are notable for an almost entire absence of mechanical noise in operation
All three engines have the following dimensions: Bore, 82.5 mm.; Stroke, 93 mm.; Capacity, 498 c.c.
LUBRICATION. Full dry sump system with cylinder feed pressure type fabric oil filter, as described on page 2. and
GEARBOX. Heavyweight four-speed gearbox with built-in automatic stop foot gear change. Hand gear-change not available. Gear ratios: All three models-38/8, 38/18 and 38/9-5.0, 6.4, 8.8, 13.3 to 1.
TRANSMISSION. By chain throughout. Front chain completely enclosed in pressed steel oil-bath chaincase of A.J.S. patent design with combined filling hole and oil level indicator. Rear chain completely protected by new design deep-section rear chainguard with front and back panels giving almost complete enclosure.
EXHAUST SYSTEM. Model 38/8 is fitted with twin exhaust pipes of large diameter, terminating in tubular silencers. Models 38/18 and 38/9 fitted with one large diameter exhaust pipe with tubular silencer.
FRAME. Heavy duplex loop frame with single front down tube, centering head bearings, forged rear fork-ends, and extended front engine lug providing efficient crankcase shield.
SPRING FORKS. Heavyweight locked-link fork girder assembly, fitted with double anchor plate pattern adjustable fork dampers. Model 38/18 is fitted with special competition type forks with rebound check springs exactly as used on A.J.S. racing and competition machines. Steering damper.
TANKS. A.J.S. deep contour petrol tank, made of pressed steel and welded throughout giving capacity of three gallons, fitted with flushfitting instrument panel carrying electric lighting switch, ammeter, detachable inspection lamp, and with provision for fitting of clock. Tank finished in chromium plate with black panels and gold lines in usual A.J.S. deluxe design. Large-area knee-grips. Oil tank: Pressed steel, welded throughout, carried below saddle, with quick-action filler-cap. Capacity, four pints.
HANDLEBARS. Carried on adjustable trailing links giving infinite adjustment for position and angle; all controls adjustable for position.
TYRES. 26 in. x 3.25 in. studded cord tyres on both wheels.
BRAKES. Large diameter internal expanding front and rear, fitted with hand adjusters, dust and water excluders. Cooling fins fitted to front brake drum. Both brakes very smooth and progressive in action. Quickly-detachable brake connections. Special high-friction brake linings.
WHEELS. Rims chromium plated with black centres and gold lines, taper roller bearings in hubs. Rear wheel is quickly detachable without disturbing chain or brake.
STANDS. Low-lift spring-up rear stand with separate tubular stand for front wheel.
MUDGUARDS. Models 38/8 and 38/9 fitted with valanced guards with centre rib giving handsome appearance and good weather protection. Model 38/18 fitted with wide dome-section guards of sports pattern. Back portion of rear mudguard detachable on 38/18, hinged on 38/8 and 38/9.
ELECTRICAL EQUIPMENT. Ignition by separate magneto, mounted front of engine and driven by chain in cast-aluminium chaincase. Lucas six-volt electric lighting set, with separate dynamo, with constant voltage control. Electric horn. either
SPECIAL NOTE. Models 38/8 and 38/18 can be fitted with high or low exhaust pipes to order. It is essential that when ordering, the type of exhaust system required is specified; otherwise we supply as the illustration of the corresponding model.
Unless specially ordered otherwise, all machines are supplied with speedometer at the extra charge shown on page 24.
PAGE 8
Source: AJS Factory Catalogue 1938
