Model 20
THE 'SPRINGTWIN' 498 c.c. O.H.V. With Full Teledraulic Suspension
Easy starting, smooth running and a sparkling performance place the 'Springtwin' in a class of its own.
Model 16M
347 с.c. O.H.V.
A new headlamp, front mudguards and fullwidth hubs have further improved one of the most popular and economical motorcycles on the road.
Model 18 498 с.с. O.H.V.
Similar in specification to the Model 16M but better suited to exceptionally heavy solo, pillion or sidecar work because of the greater power developed by the larger engine.
Model 16MS 347 с.с. O.H.V.
With Full Teledraulic Suspension A quickly detachable rear wheel, 32-gallon fuel tank and improved silencer are new refinements on an immensely popular three-fifty.
Model 18S 498 с.с. O.H.V.
With Full Teledraulic Suspension
When comfort, economy and performance are of paramount importance, this powerful single-cylinder model is the obvious choice.
The Competition Models
THE rigid and spring frame Competition Models, that have proved to be so outstandingly successful during the past few seasons, are continued for 1955 but in an improved form.
Numerous modifications have been incorporated with the object of still further improving their reliability, handling and performance.
As these models vary in several major respects from the General Specification on pages 12 and 13, the differences are detailed below.
MODELS 16MCS and 18CS are fitted with a strengthened spring frame of normal construction and wheelbase; special rear suspension units and stronger fork springs; racing cams; high compression piston; Amal T.Т.10 carburettor; a new competition Twinseat and special footrests.
MODELS 16MC and 18C are fitted with a rigid frame of low weight and all welded construction, and designed to provide a short wheelbase; adjustable waterproof saddle; cylindrical toolbox; and a very wide ratio gearbox.
All Competition Models have polished light alloy mudguards; light alloy number plates; Dunlop 'Trials' tyres; a high ground clearance; high level exhaust system: a folding kick starter; steel crankcase shield; 24-gallon light-alloy petrol tank; Lucas waterproof magneto with manually-operated ignition control, and a light-alloy cylinder barrel.
OPTIONAL EQUIPMENT
Standard or wide ratio gears, standard rear wheel, 3-gallon steel petrol tank.
OPTIONAL EXTRAS
Exhaust pipe extension; Dunlop 'Sports' tyres; quickly detachable electric lighting.
MODEL 7R
The phenomenally successful 348 c.c. Racing Model 7R with a single over-head camshaft is dealt with in a separate publication. Full details will be supplied on application.
Models 16MC 18C
347 с.с. O.H.V. 498 с.c. O.H.V.
Each machine is hand-built and will enable the average rider to compete in the stiffest events with every chance of success.
Models 16MCS 18CS
347 с.с. O.H.V. 498 с.с. O.H.V.
Highly developed spring-frame Competition Models which have proved outstandingly successful in National and International cross-country speed events.
SINGLE-CYLINDER ENGINES
High efficiency engines of A·J·S design, and manufactured in two capacities: 347 c.c., bore 69 mm., stroke 93 mm.; 498 c.c., bore 82.5 mm., stroke 93 mm.
Die-cast aluminium alloy cylinder heads with cast-in valve seats, and cast-iron barrels with deep fins ensure adequate cooling. Noisy valve operation has been eliminated by fully enclosing the operating gear and providing adequate lubrication of the moving parts. The valves, fitted with hairpin springs, have Stellite tips on the chromium-plated stems and are operated by Duralumin push rods enclosed within tubes.
The timing gear is enclosed within an oil-flooded case. Separate camshafts are used for inlet and exhaust, and the gear wheel and associated cam are in one piece.
A built-up crankshaft, with high-grade iron discs, individually balanced, and a forged connecting rod of high tensile steel, is carried on two ball races on the driving side, and a plain bronze bush on the timing side. The connecting rod is strengthened by a rib encircling the big end; the crankpin is of the two-piece type and the big-end bearing has three rows of rollers and a Duralumin cage.
To reduce clearances and eliminate mechanical noise, wire-wound aluminium pistons are used. There are three rings, two compression (the top one is chromium plated) and an oil-scraper ring.
LUBRICATION
Dry sump. The oil is circulated through the engine and returned to the tank by a double-acting, reciprocating plunger pump. One side forces oil to the big end bearing and valve gear and the other returns the surplus oil, which has drained to the sump in the crankcase, to the tank. Fabric and metal gauze filters prevent foreign matter from being circulated with the oil.
TWIN-CYLINDER ENGINE
498 c.c., bore 66 mm., stroke 72.8 mm.
The 'Springtwin' is powered by a parallel twin cylinder engine designed to give a high safety factor even when the engine is run at high r.p.m.
The crankshaft is in one piece and manufactured from a high-grade alloy iron. It is housed in a spherical crankcase of die-cast aluminium alloy and supported on caged roller bearings on the drive and timing side, and a plain Vandervell shell bearing at the centre.
The rigidity of the crankcase ensures that the centre bearing is not heavily loaded. This bearing is carried by a separate light-alloy plate which is spigotted into both crankcase halves and bolted to the drive-side half.
The connecting rods are immensely strong and forged in light alloy. Split Vandervell shell bearings are fitted to the big-ends. The big-end cap studs are anchored in steel trunnions, a method which obviates a source of weakness at a vital point. This is an instance of the application of racing experience.
As on the single-cylinder models, wire-wound pistons with chromium-plated top ring and slotted oil control ring are fitted.
Each cylinder barrel and head is separate. The barrels are of a high-grade cast iron and the heads light-alloy die-castings. The barrels are deeply spigotted into the crankcase and the whole assembly of barrel, head and crankcase are bolted together to ensure rigidity.
The ends of the valve stems are Stellite tipped to resist wear. Inlet valves are Silchrome steel and the exhaust valves are of KE965 steel. The valve rockers-- one-piece forgings-are mounted on eccentric spindles to facilitate the adjustment of valve clearances. Reciprocating weight in the valve operating mechanism is reduced by eliminating tappets, the cams operating short single arm followers. Two camshafts are provided, one for the inlet valves and one for the exhaust valves, and are driven by spur gears. The camshaft levers and timing gear pinions operate in an oil bath, the oil level of which is controlled; surplus oil drains into the crankcase sump.
LUBRICATION
The engine is lubricated by a dry-sump system employing two separate gear pumps, each independently driven-at half-engine speed from the camshafts. The delivery pump feeds oil direct to the centre main bearing, and then via oilways to each big-end. The rocker boxes are supplied via oilways in the cylinder barrels and heads, and the overflow drains down the push-rod tunnels into the camshaft chambers.
The scavenge pump, which has twice the capacity of the delivery pump, collects oil from the sump in the crankcase and returns it to the tank. Filters, easily detached for cleaning, are placed in the delivery and return paths, and pressure relief valves are fitted as a precaution against excess pressure when the oil is thick during very cold weather.
CARBURETTOR
The latest Amal 'monobloc' instrument has been standardized for 1955. Float chambers and mixing chamber are a one-piece casting. The instrument incorporates a pilot jet and throttle stop and has a twist grip throttle control. The air control is by a handlebar mounted lever.
IGNITION
The single-cylinder models have a chain driven, rotating magnet Lucas magneto incorporating an automatically controlled advance and retard mechanism.
A gear-driven magneto is fitted to the twin-cylinder model, and the advance and retard is manually controlled by a lever mounted on the handlebars.
All models have KLG FE80 'Corundite' plugs.
GEARBOX
Heavy-weight, with four speeds, foot operated, positive-stop gear change, and kick starter.
CLUTCH
Multi-plate dry clutch hand controlled from the handlebars.
TRANSMISSION
The primary chain is enclosed within an oilbath chain case and the rear chain is covered by a deep section guard extending over the entire length of the top run. A spring-loaded cam type shock absorber is fitted on the engine shaft.
An inspection cover is fitted on the primary chain case over the clutch.
FRAME
Duplex cradle type of brazed construction. Integral lugs are provided for the attachment of a sidecar and pillion footrests. The spring frame is of the swinging fork type controlled by two oil damped Teledraulic suspension units.
FORKS
Teledraulic forks telescopic with hydraulic damping are fitted to all models.
MUDGUARDS
The rear mudguards of the spring frame models are valanced; those on the rigid frame models are of domed section. Both have a detachable tail to facilitate removal of the rear wheel. The front mudguard is of a new design. The front stay has been eliminated and the guard is now held in place by an integral valance and attached to the front forks by bolts. The whole structure is sturdy and of pleasing appearance.
WHEELS
19-inch rims, full-width die-cast aluminium hubs front and rear, and straight spokes. The rear wheel of the spring frame machine is quickly detachable and can be removed in approximately 60 seconds. The rear brake, sprocket and chain are left undisturbed.
TYRES
Front: Dunlop ribbed 3-25 x 19 inch. Rear: Dunlop studded 3-25 x 19 inch on 350 c.c., 3.50 x 19 inch on 500 c.c. models.
BRAKES
Internal expanding 7-inch diameter front and rear. The front is hand-operated from a lever mounted on the handlebars, and the rear by a pedal. The position of both controls is adjustable.
TANKS
Steel with welded seams. Bonderized and finished in black enamel. The 'Springtwin' has a chromium plated petrol tank with black enameled panel. All petrol tanks carry an attractive round badge bearing the letters A·J·S and are rubber mounted. Chromium-plated quick-action filler caps are fitted and the petrol tank capacity is 3 gallons; oil tank capacity gallon.
STANDS
Rigid models: front, rear and prop stands. Spring frame models: front, central and prop stands.
SILENCER
Of new design with pleasing lines. It is finished in heavy chromium plate and held in position by a stay and clip.
SADDLE
A Twinseat of special design–Dunlopillo covered with black Vynide–is fitted to the spring frame models, and an adjustable sprung saddle to the rigid frame models.
HANDLEBARS
Chromium plated, 7/8-inch diameter, rigidly held in a substantial clip. The angle is adjustable to suit individual tastes. Mounted on the handlebars are the headlamp dipper switch and horn button.
FOOTRESTS
Adjustable and rubber covered. The frame has integral lugs for pillion footrests.
ELECTRICAL EQUIPMENT
7-inch headlamp of new design, the shell of which encloses the speedometer body, and mounted on either side of the lamp are streamlined pilot lights. The rear lamp is a plastic moulding with red and white windows.
Twin-cylinder models have a 45-watt dynamo, the singles 32-watt. All models have a separate voltage control unit, electric horn and 6-volt battery.
TOOL BOX
Sheet metal with hinged lid and finished in black enamel. Two deep boxes are mounted on either side of the spring frame models and one large box on the right-hand side of the rigid frame models.
FINISH
All enamelled parts are first Bonderized and then given three coats of high quality black enamel and stoved. Petrol tanks are hand lined, wheel rims chromium plated with enamelled centre, controls and certain other parts heavily chromium plated. Aluminium hubs, fork slides, etc., are polished.
EQUIPMENT
Illuminated speedometer, ammeter, red reflector, tyre pump, grease gun and tool kit.
Optional extra equipment includes stop light, pillion seat, folding pillion footrests, air cleaner, luggage panniers and luggage carrier.
New Features A·J·S 1955 Models
The automatic ignition control (single-cylinder models) is enclosed within the chain case
Front brakes are enclosed within the full-width light alloy hub
Deep and efficient chain guard is a feature of the spring-frame models
The new quickly detachable rear wheel and diecast light alloy hub
Ammeter, control switch and speedometer are grouped neatly within the headlamp shell
The new silencer fitted to all models
Oil-damped Teledraulic front forks
page 14
