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Year by year changes for twins.

The AMC Twins

The first assembled machines, a Matchless G9 and an AJS model 30, were secretly shipped into Earls Court for the Motorcycle Show in October 1948. Production got under way during 1949 and all the early machines went to export to earn the mighty dollar. A few AJS models - probably less than 30 - trickled out to Australia and New Zealand. Has anyone any details of the whereabouts of some of these first models ? Does anyone know what the engine numbers were on those two machines in the 1948 Show - better yet, does anyone know where they are now ? Kindly speak up if you can help with information.

Features at introduction in 1949 were:

• One piece cast iron (Mehanite) crankshaft (stroke 72.8mm).
• Roller main bearing in each crankcase.
• Central plain main bearing that supplied oil to big ends.
• Polished forged aluminium (Hiduminium) conrods with no little end bush and plain big end shells.
• Separate barrels (bore 66mm), cast iron, and cylinder heads, alloy, with internal push rod passages and oil ways.
• Wire wound pistons with a compression ratio of 7:l .
• Tappet adjustment by rockers on eccentric spindles.
• Individual caps covering the rockers.
• Camshafts, inlet and exhaust, placed behind and in front of cylinders in the crankcase and driven through a fixed position intermediate gear (The cam profile appears skew since it is symmetrical about an arc centred on the cam follower spindle).
• Gear oil pumps driven from the timing side ends of the cam shafts with the pressure relief valve in the crankcase below the exhaust camshaft drive. Oil feed to the rockers from delivery pump (unlike most other British twins which had the feed from the return pipe to the oil tank).
• Gauze oil filter located in the crankcases below and in front of the exhaust camshaft.
• This was clamped between the timing side case and end cap containing the oil non-return valve.
• Crankcase breather at drive side end of the inlet camshaft tunnel.
• Transmission shock absorber on the crankshaft drive side axle.
• Dynamo mounted in front of the cylinders and driven from the exhaust camshaft gear.
• Magneto mounted from the timing side crankcase behind the cylinders and driven from inlet camshaft gear

1950

• 1950 saw a few minor changes. The steering crown lug incorporates the steering stops and is a steel stamping, with the fork-leg clamp pinned and brazed in position. This replaces the former malleable casting, which was much heavier.
• The rear brake pedal is of a slightly different, and more directional, shape. The front and rear mudguards have been redesigned and the circumferential rib is intended to provide greater stiffness.
• The footrest hanger boss has twelve internal splines which make a greater range of adjustment possible.
• The rear hubs are slightly wider and the tapered roller bearings are spaced further apart to give more support. The bearings have separate races, which may be detached, complete, from the hollow spindle. The diameter of the solid spindle has been increased to 1/2".
• Detail changes include the use of Amal combined clutch and ignition levers and front brake and air levers.
• There is an additional fabric filter in the oil tank and a sludge trap is incorporated in the crankshaft.
• Slightly modified pistons are fitted and the compression plates, used in certain models, are discarded.
• A minor change is made in the oil tank where the vent pipe was bent away from the return pipe spout.

1951

• 1951 season models included the rear suspension change to the famous Jampot unit. Nicknamed "Jampot" because of its shape in the 28th September issue of the "Motor Cycle". It is a nickname that really hit the nail on the head.
• The magneto cut-out was fitted on a new metal end cap, instead of on the handlebar.
• Synthetic rubber inserts were used on the oil pipes and synthetic rubber was also chosen for the new primary chaincase mushroom-section seal.
• Flexible horn mountings are introduced and a new Lucas horn-push which screws into the handlebar.
• The centre stand legs are increased by 1".
• A new medallion-type AJS badge replaces the previously used transfer.
• 'Vynide' instead of hide is used for the dual seat of the Matchless twin.
• A new lug for the front petrol tank mounting replaces the two tubes formerly used on the front down tube.
• The hinged tail of the mudguard on the rear-sprung models is moved closer to the wheel, making less gap between the two.
• The cheese-headed screws on the front forks are shrouded with light alloy (drain screws).
• The rear seat pillar contains a circular section through which passes a rubber sleeve to the new Vokes air cleaner.
• Front fork shuttle damping was replaced with rod and damper-type.

Engine changes after engine No. 7000:-

• A changed crankshaft incorporates a new narrow centre bearing with separate thrust washers and a reduced centre web. A groove is machined in the face of the crankshaft to enable the use of a wedge-shaped extractor for pulling off the main bearings.
• Cylindrical central cam tunnels fitted.
• Oil deflector plates deleted from crankcase.
• Oil pump had improved gears.
• Crankcases modified to suit the above.
• The pressure relief valve in the oil system, which was a spring loaded ball, is replaced with a plunger-type unit.
• The non-return valve, which was a spring and ball, retained in the cap for the filter housing, by a circlip, is now fitted with a detachable cap to enable easy dismantling and also enables fitting of a pressure gauge.
• The small timing pinion is reduced from 15/16" to 23/32" but given a spacing washer between it and the crankshaft.
• 1951 was the first year in which limited numbers of the twins were made available to the UK market, hence the lack of early numbers for English members in the Machine Register.

1952

• For the 1952 season the appearance of the machines had to be changed due to the restrictions on chrome-plating. Wheel rims were 'Argenised' - a baked matt-aluminium finish and all the petrol tanks were painted in black enamel.
• Both tank motifs are changed, the big metal 'M' becomes a smaller light alloy die casting. The AJS medallion becomes the letters AJS neatly bracketed by a metal cross piece, in light alloy.
• A small detail change is that the silver tank lining on the Matchless tank has a red line superimposed on the main silver line and a thinner inner line added.
• The light alloy fork sliders, previously enamelled are now polished and buffed.
• The steel front brake plate is superseded by a polished light alloy plate.
• The biggest single change is the employment of the new Burman B52 gearbox, which has shorter, more rigid shafts and stouter engagement dogs. The box itself is lighter. An improved gear change is claimed and clutch adjustment made easier.
• The primary chaincase has been modified by the fitting of an inspection plate to give access to the clutch thrust-rod.
• Outer cover members of the teledraulic forks are slightly increased in length.
• Two carriers are available, rear-mounted or centre-mounted.
• New Lucas headlamp with square patterning of the lens and an underslung Gondola which houses the pilot light is introduced.
• A newly designed handlebar head-lug clamp/top steering crown is introduced which enables a neater speedo mounting. The handlebar clamp is retained by three recessed Allen screws.

• The drain plug on the Jampot units is deleted.
• The automatic voltage control regulator is flexibly mounted on the rearward side of the battery carrier.

• The electrical wiring is neater and coloured cables are used throughout for easier cable identification. The new circuit is positive earth.
• The angle of the petrol pipes is altered to give greater accessibility to the throttle stop and pilot air screws.
• An entirely new crankcase pressure relief valve is used on the drive end of the crankshaft, which breathes into the primary chaincase, with a diaphragm in the engine sprocket nut and the crankcase modified to suit. This eliminates the rotary valve driven by the inlet camshaft which exhausted into the oil tank.
• Washers between crankshaft and roller main bearing deleted.

1953

• 1953 saw the standardisation of the twin seat, which was now slightly narrower, on both AJS and Matchless twins. Blue piping was used on AJS and red on Matchless.
• A simple thief-proof locking bar could be attached to the lower steering head and was available for 1s 6d.
• Chrome-plated wheel rims and petrol tanks were available on export models only and at an extra charge.
• A new-type front brake was introduced with the shoe-plate moved anti-clockwise a number of degrees and the cam lever turned relative to the camshaft. The lever projected forward instead of to the rear. The anchor stay also projected forward, to suit the brake cable.
• This year also saw the change of the four-bolt fixed rocker cover to the two-stud design, with the use of two Allen screws.
• The two cylinder head steady tubes were replaced by a 1/8" mild steel plate.
• An important motor modification was the provision of longer cam followers.
• The inlet manifold now had a rubber sealing ring recessed in its joint face.
• The top piston ring was chrome plated.
• A new chaincase sealing band made of an endless synthetic rubber moulding, wider than previously, and of greater resilience was used.
• A new type Lucas rear light was fitted, made of moulded plastic material; it could incorporate a stop light (as an extra).
• Short lengths of flexible tubing were incorporated in the petrol pipe.
• The top covers of the fork tubes were altered so that they were free to pivot, a soft rubber washer ensured a tight fit. The slider extension tube was also lengthened.
• Allen screws were used (instead of studs) to clamp the fork stanchions in the lower steering-head lug.
• The back portion of the rear mudguard became fully detachable, the tail being held by four 5/16" bolts screwed into captive nuts in welded pockets underneath the guard.
• Rear lifting handles on the spring frame were simplified
• Sturdier centre stands standardised.
• Motor modifications included a new cam follower spindle location, to suit the longer cam followers, and a new camshaft of a higher lift contour.
• The oil pressure release valve was changed from the plunger type to the spring and piston type and located in the timing side crankcase, adjacent to the body of the oil feed pump.
• Four plugs were used to plug the oil passages into the cylinder heads, replacing the three plugs used previously.
• A drain hole was incorporated in the timing side crankcase to drain the timing chest.
• The crankshaft and big end shells were changed as was the pushrod assembly.

1954

• 550cc models were introduced, G9B/20B, these were essentially the same as the G9 but with a cylinder bore of 69.0mm.
• A full-width light alloy front hub was introduced.
• A new design of fuel tank was also standardised holding three & three quarter gallons.
• The oil holes in the big end journals were repositioned to eliminate the build-up of sludge in the oilways.
• Cam profiles were changed to give softer valve timings and 8:1 compression pistons were offered as an option.
• The bottom front engine mounting bolt, which also connects the cradle to the front down tube, was increased in size from 5/16" to 3/8" to gain more rigidity.
• A new cast alloy shoe plate was employed for the new front hub, with a grease nipple for the cam spindle.
• Chrome plating was reintroduced for the wheel rims, with black enamelled wells (red for Matchless with red panelled chrome tank) and silver lining for Matchless and gold lining for AJS.
• The front fork sliders were given a more round, uniform conformity.
• The front mudguard was given a flared end and rolled edges.
• The rear chain guard was extended rearwards and given a general clean up, to make it more efficient.
• The new petrol tank had its seams stitch-welded for the first time and the petrol pipes were ferruled PVC flexible lines.
• The oil filter was housed in the outer half of the oil tank, for ease of accessibility.
• The voltage regulator unit was moved to a location between the seat stays, under the dual seat.
• The front frame lug had been redesigned and now contained an extra attachment point from which to hang the horn, which was rubber mounted.
• The headlamp under slung "gondola" pilot light had been deleted in favour of two small lamps mounted on the outside of the headlamp supports.
• A new type dipper switch was used.
• The leads from the dynamo were enclosed in a rubber sheath.
• Petrol tanks were once more available with chromium plating.
• To give access to the clutch without removing the chaincase outer half, a domed cover held on by eight screws replaced the small inspection panel formerly employed.
• The clutches were lined with a new, more efficient, friction material which gives better grip. The number of clutch plates was reduced as a result of the new efficiency.
• The carburettor 76AG/lAU was superseded by 76AT/1EF with a new mixing chamber casting. This was redesigned to prevent distortion to the manifold studs caused by faulty tightening of the carb.
• The oil metering plugs in the heads, which formerly used a small flat on the side to pass the oil, now had a small hole drilled in the centre of the plug.

1955

• For 1955 both wheels were given full width hubs with the front one of a new design from the previous year. The width was reduced and the dishing was increased on the brake shoe plate and end cover. The diecast hub shell had a more barrel-like appearance. Brake linings were trued after the wheel was built, to obviate the chance of ovality from spoke tension.
• Engine modifications included improved lubrication to the pushrod end of the overhead rockers by means of a groove machined in the top of the rocker arm.
• The filter element in front of the crankcase had a shallower and more shapely cap nut.
• The former double-cranked brackets from exhaust pipe to front engine plate were replaced by tubular pillar nuts, which connected the pipe to the forward cradle bolt.
• Air cleaners on twin and single models were identical.
• Amal Monobloc carburettors were adopted.
• Silencers of greater capacity and improved appearance were fitted.
• Oil pipes were repositioned in the oil tank to lie one behind the other (formerly side by side).
• A new front mudguard with no front stays, but a stiffening bridge member to give adequate support was introduced. The rolling of the edges continued right round the new front guard.
• Front fork stanchion tube dimensions were increased from 1.1/8" to 1.1/4" for greater resistance to bending.
• The upper covers between the steering head crowns were tapered to mate up with the larger diameter spring covers.
• The welded-on headlamp covers had a horizontal top edge ( instead of the previous triangular shape fitment ).
• A new headlamp shell was introduced, basically a torpedo shape, and accommodated the speedo towards the rear. The under surface of the shell terminated at a vertical bulkhead just behind the light unit.
• Upper and lower steering head crowns were redesigned. The lower crown was a forging with a special hole for the speedo cable. The top crown, in malleable cast iron, had a cleaner shape and blended with the rear of the new headlamp unit. Overall height of the steering-head portion of the crown was reduced. The steering column was shorter and there was a long sleeve nut passing into the crown, whereby adjustment of the head bearings was effected.
• Handlebar shape was altered to provide increased tank clearance on full lock.
• The handlebar clamp had been cleaned up.
• There were deeply domed fork bolt caps, which pushed on to the stanchion bolt washers on the top fork clamp.
• The new full width rear hub did not contain the brake drum, which was still in unit with the rear sprocket. The wheel was quickly detachable by virtue of a pullout spindle and engagement of five large diameter pegs. The rear wheel, like the front wheel, had straight spokes.
• The rear chain guard had extended side valances down to the fork arm.
• Attachment of the lower end of the sub-frame had been strengthened by lengthening the lugs and employing a second upper bolt fixing, in addition to the long bolt running through the bridge member which carried the rear fork pivot.
• The cradle tube extensions. which formerly supported the silencers and carried the pillion footrests were replaced by shapely box section brackets which were welded to the rear sub-frame tubes. The brackets embodied a threaded boss for the attachment of the lower rear connection of a sidecar chassis.
• There was a modified attachment of the tail of the rear mudguard and only one bolt was employed at the top of the guard instead of two. Of spigot type, the washer engaged in a keyhole slot in the tongue on the tail.
• On the lighting side, sounder earthling of the battery positive lead was provided, the cable being taken to a small ear in the angle between the top and seat tubes of the frame.
• The Jampots were also modified in that the bottom spring abutment was no longer screwed to the slider. The abutment became a shell moulding located in position by a circlip. An internal change to the damper assembly eliminated cavitation of the damper fluid, which had sometimes occurred previously.
• Oil supply to the heads was effected by a brass jet, thus obviating the distributor bush's former role.
• With the modified lubrication to the pushrod ends (mentioned earlier) the hole formerly drilled in the rocker pillar for this purpose became redundant.
• Engine numbers after 26762 are fitted with the original oil distributor bush but the hole is enlarged to 1/16" (previously 3/64") to increase the oil supply to the rockers.
• A larger diameter shaft was used for the intermediate pinion and this incorporates a larger diameter bush.
• The oil pressure relief valve spring was held captive on the valve body to stop it springing off on removal and getting lost and not being replaced on reassembly.
• The new full width hub required a new method of rear chain adjustment, in the form of two screws with locknuts incorporated in the rear fork ends, for movement of the wheel.

1956

• The first departure from the original sized motor was made for the 1956 season, when the AMC marque followed all the other manufacturers and expanded the capacity to 600cc. The G9B/20B 550cc models were discontinued. This extra size was obtained by an increase in the bore size of the barrel. However, it was not just overboring the 500 barrels; it was a completely new unit. The 500cc barrels had six fins and the 600cc barrels seven, so identification of the barrels is easy.
• Wider scraper rings were used in the engines .
• The 500cc engine had the compression ratio raised from 7.0 to 7.8 to l by changing the combustion chamber shape. The 600 ratio was 7.5 to 1.
• The oil tank fabric filter was replaced by a magnetic drain plug incorporated in the sump.
• A ring of internal ventilation holes were provided near the outlet of each of the Matchless type silencers to overcome the tendency to corrode.
• A complete new frame configuration was introduced, the seat member, instead of running diagonally from under the seat to the engine and gearbox plates, lay vertically behind the gearbox. Lateral rigidity was improved in comparison with earlier rear sprung frames, by housing the rear fork pivot in a sturdy malleable iron lug, which was clamped between the cradle tubes and brazed to the lower end of the seat tube. (Previously the pivot spindle was carried in a light alloy casting, linking the seat tube with the rear of the cradle). The line of the rear sub-frame carried on the horizontal line of the fuel tank base through to the rear top mounting of the suspension unit. The fabricated sidecar attachment brackets on the rear sub-frame were strengthened by the use of a one piece pressing wrapped around, the tube and welded to it.

• A sleeker aspect was obtained by the integration of the tool box and the oil tank, which has its capacity increased from four to five and a half pints, was of the pannier type and fitted neatly into the sub-frame loop. To balance it, the tool box and battery holder were combined into a tool box of similar shape on the left side. The two were bridged at the front by a detachable cover. A shield was mounted on the outside of the oil tank with a 1/4" gap to dissipate heat. The tool box had a lid, hinged at its lower edge and housed the battery in the forward end, secured by a quick-release rubber strap and separated from the tool compartment by a bulkhead.
• The voltage control unit was housed at the upper rear corner of the tool box and surrounded by sponge rubber as had been used on the Works I.S.D.T. bikes.
• The horn was concealed under the twinseat.
• The twin seat itself was increased in length by two and a half inches.
• A combined horn button and dip switch was introduced by Lucas and the cables of the wiring harness were plastic covered.
• The primary chain adjuster was moved to a position between the gearbox plates, concealed by a snap-on cover.
• The front stand/lower mudguard attachment was replaced by a simple tubular stay.
• The front brake plate was rotated through 180 degrees so that the cam lever lay above the wheel spindle and behind the fork leg.
• The rear brake-plate was covered by a chrome-plated plate.
• The rear brake adjuster was transferred to the forward end of the operating rod. The modified rear brake pedal had a straight shank and the shorter arm was inclined at approximately the same angle as the rear sub-frame. The adjustable stop was clamped between the pedal-spindle and the frame.
• The design of the wheel spindle retaining caps on the front forks was simplified by being cast-in one with the slider and milled off later.
• At the top of the legs, the deeply domed push-in caps were replaced by shallower domes incorporating socket hexagons. Rubber bungs filled the socket holes.
• Short plastic sleeves held together air and front brake cables on one side and ignition and clutch cables on the other. Moreover, on each side of the malleable iron fork top yoke was an "ear" with a hole, through which those cables passed.
• Cable casings were plastic covered and lubrication nipples were fitted to clutch and throttle casings.
• To distinguish between the 500cc and 600cc twins the petrol tanks of the larger models had chromium plated side panels.
• On the AJS model the three dimensional tank motif was 1/4" larger in diameter than before.
• Motor modifications included discarding the oil pressure relief valve, restricting the oil hole in the distributor bush to 1/32" and introducing two metering jets into the oil channel machined between the crankcases to balance the oil feed to the cam tunnels and rocker gear. The oil feed to the rocker gear was diverted to the top front crankcase bolt, the sealing of which was ensured by the use of a steel washer with a rubber insert.

1957

The alteration of greatest note for the 1957 season was the adoption of the AMC type gear box, which had been completed and tested during 1956. Liberal use of synthetic rubber 'O' rings and a special mainshaft oil seal behind the final drive sprocket, were adopted to ensure oil tightness of the new box.

• The seat lug was redesigned to provide a more robust sidecar seat-stay fixing point. The locating eye was of 5/8" diameter, instead of 1/2". This involved the reshaping of the rear frame loop and resulted in a modified fixing point for the fuel tank and seat. This point was moved forward slightly and the lug was formed integrally with the rear tank support lug. (Previously two separate lugs were used).
• AMC also adopted Girling shock absorbers for the rear suspension but as a contravention to the norm the lower attachment yoke was a cast light-alloy split ear (probably a sentimental link with the old jampot). The upper attachment was a single eye and this necessitated the fitting of box section units to the rear sub-frame. Polished light alloy split collets were used to retain the upper spring cover. The new units were not interchangeable with the old.
• Considerable alterations had been made to the five pin drive of the quick-detachable rear wheel. Pins which were formerly solid were replaced by hollow, larger diameter pins, rubber sleeved externally. The radius at which the pins were disposed from the hub had been doubled. In the brake drum casting, the holes in which the pins engage took the form of tubular bosses about 7/8" long connected by an annular rib.
• The toolbox lid was no longer hinged at the bottom. Instead, two ears were formed at the lower edge of the lid and engaged with slots in the box. The lid could be completely detached from the box. A black moulded rubber strap replaced the endless red rubber band which formerly held the battery in place. The lower end of the strap carried a transverse steel peg which hooked into slots in the battery platform. The battery box cover and oil tank cover had three horizontal ribs embossed on them and this necessitated the deletion of the long transfer introduced in 1956 and the adoption of the smaller, rounded type transfer.
• The rear half of the primary chaincase had some changes designed to prevent oil leaks. The edge of the hole through which the engine shaft protrudes was turned outward and a composite cork washer was interposed between crankcase and chaincase at that point. A sliding oil thrower, consisting of two dished plates riveted together, one on each side of the slotted hole in the case, located on the gear-box mainshaft and moved with the gear-box / primary chain adjustment.
• The new clutch contained wedge-shaped rubber blocks, which served as a transmission shock absorber.
• The new method of clutch operation employed a ball and roller to work a suitably profiled flowing cam lever.
• The face-cam spring type engine shock absorber was no longer used and the drive side crankshaft was shortened. The outer chaincase cover had a much shallower dome at its forward end, though the clutch adjustment cover was retained.
• The inlet and exhaust camshafts were modified to give an increased power output. The valve timing periods of 24 degrees, 65 degrees, 63 degrees, 25 degrees provide increased horsepower but retained the docility and quiet running.
• The end cap of the oil filter tunnel was made in one piece with the non-return ball-valve entombed inside the unit. It was no longer possible to interchange the springs with the by-pass ball valve or reverse the ball and spring on reassembly, as had happened before with disastrous results.
• The hole in the oil distributor was increased to 3/64 inch.
• The new petrol tank embellishment consisted of separate chrome-plated side panels fixed to the tank by the two screws which retained the plastic motif and by two more screws, which held the knee grip plates in position. Plastic beading round the edge of the panel sealed the gap between it and the tank sides. Colours of beading and tank enamel were blended so that the AJS had a royal blue tank and light blue beading and the G11 had a dark red tank with black beading. On the 500cc twins, which were enamelled black, the AJS beading was light blue and the Matchless was red.
• A mid-season alteration to front fork damping was continued for 1957. On shock and recoil movements the hydraulic check was more progressive in action, with the result that front end pitching was said to be eliminated.
• Shielding of the rear chain was increased by extending the chain guard further downward behind the rear wheel sprocket and fixing a curved guard to the back of the primary chaincase to cover the rear chain where it ran onto the gearbox sprocket.
• The adoption of Neoprene push-on oil pipes dispensed with the need for threaded unions.
• At the return-delivery point in the oil tank, two additional holes were provided to relieve oil pressure and give multi-outlet dispersal.
• A more streamlined form was given to the yoke at the rear end of the brake rod.
• The depth of the rear mudguard valance was increased slightly at the rear end.
• Plastic handlebar grips were standardised.
• There was a restyled end cover for the Lucas dynamo and the shell was polished instead of rough machining as previously.
• The oil breather intake was shrouded within the tank, to minimise escape of oil by frothing and the pipe was located externally.
• Clutch sprocket and plates in the new clutch contained loose friction inserts.
• A larger diameter inlet valve head was introduced. The inlet port for the 600cc models was enlarged to 1,1/16".
• The Tufnol diaphragm for the crankcase pressure relief valve was discarded and replaced with a steel component.
• A larger carburettor was fitted to the 600cc.

1958

• The most visual change for 1958 was the adoption of the aluminium alloy primary chaincases. The marque finally followed the trend of most other manufacturers in this regard.
• Sports twin models of both AJS and Matchless were marketed. The advent of these new models resulted from a modification which was made to the frame of the single cylinder scrambles machine. It was redesigned around the crankcase fixing points and the opportunity taken to modify it so that it accommodated either a single or twin cylinder unit. The twin engine used was the 592cc "near square" (72 x 72.8mm) motor, designated the AJS model 30CS and Matchless G11 CS. Special features which distinguished them from the roadster models were Siamesed exhaust pipes and a 2 gallon petrol tank. Unseen was the compression ratio at 8.5 to 1: As an option the machines could be ordered with the standard 3 3/4 gallon tank, twin-pipe exhaust system and Western style high-wide-and-handsome handlebars. The sports twin dual seat was redesigned and covered in Vynide "pigskin" material. The wheels were shod with either 3.50 x 19 or 3.00 x 2l front tyres with 4.00 x l9 rear covers. Quickly detachable lighting was offered and polished light alloy mudguards were fitted.
• A soft, low rate coil spring was fitted to all the foot change mechanisms to smooth the gear selection.
• The riding position of the touring models was lowered by half an inch, brought about by internal changes in the rear suspension unit.
• A new bridge mounting beneath the seat housed the horn.
• A new Lucas magneto end cover was employed for the sports twin.
• The 3/64" hole in the oil distributor bush was deleted and instead the bush had a flat, machined on its outside diameter.
• CS models were fitted with bonded insert type clutches.
• The twin side lamps on the headlight, used for many years, were deleted
• A new translucent type of battery introduced.

1959

• The 1959 programme certainly started off with a fanfare of trumpets for the expansion of the range of models, extended from three to eight. Once again (as in 1956) the capacity is upped, this time from 592cc to 646cc. This was achieved by the use of a longer stroke crankshaft and in fact, the only marked external difference is that the barrels are longer and have an extra fin. With the existing cylinder centres the limit on bore had, at 72mm, been reached on the 600cc models, so the stroke was lengthened from 72.8mm to 79.3mm, enabling common connecting rods and pistons to be used. However the conrods and big end caps were chamfered for clearance. The pushrods were lengthened by ½ inch which is not recorded in the parts list.
• The Monobloc carburettor was increased to 1.1/8" from the l.1/16" which had been used on the 600cc model.
• There were four AJS and Matchless twins in each capacity class. The specifications of corresponding 500cc and 650cc models differed only in respect of the power unit and gear ratios. The four models comprised standard and de luxe roadster, scrambler and sports twin (in effect a road equipped scrambler). For the 498cc machines the familiar G9 (Matchless) and model 20 (AJS) designations were retained with the suffixes "del, CS and CSR" for the de luxe, scrambler and sports twin variations. G12 and model 31 denote the corresponding 650cc models with the same suffixes.
• On the standard and de luxe 650cc models the compression ratio was 7.5 to l, whereas the two sporting versions of each make had 8.5 to 1 pistons. Power output was further increased on .the CS and CSR models by a modification to the shape of the inlet tract. Development engineer Jack Williams was responsible for this change, the benefit of which was proved by Vic Willoughby's 102.9 miles in the hour at M.I.R.A. in April 1958 on a 592cc sports twin Matchless. Another feature of these machines was the Siamesed exhaust system in place of the separate pipes and silencers of the other twins.
• A Lucas RM1l5 alternator was fitted to the 1959 standard twins but separate magneto and dynamo continued on the remaining twins. Lighting equipment was an optional extra on the scramblers. The outer half of the alloy primary chaincase enveloped the alternator. The rotor keyed to the drive side mainshaft required a shaft extension compared to the generator models. The "standard" models were fitted with coil ignition instead of a magneto. Incidentally, wire wound pistons were still used.
• All twins had a single down tube frame with the sporting twins using a heavier gauge for the front down tube. The rear loops were also shorter on this model and resulted in greater inclination of the suspension units. The scrambler twins had a 2 gallon petrol tank as standard but on the remaining twins a new 4.1/4 gallon tank replaced the former 3.3/4 gallon units. The new tank differed in construction from the old, in that the welded seam was on the centre line of the machine and not along the bottom edge. On the scramblers the sports tyres were 3.00 x 21 (front) and 4.00 x 19 (rear). A black tank was standard on the standard twins and chrome panels were used on the de luxe models. There were two alternative optional extra colour schemes. On the Matchless models mudguards, oil tank and tool box could be arctic white (instead of black) with the choice of an arctic white tank with chrome panels or a two-colour white-over-red tank. Blue formed the alternative AJS colour with light grey for the lower portion of the two-tone tank. A chrome plated strip separated the two tank colours in each instance. The road equipped sports twins normally had the appropriate red or blue tank with chrome plated side panels. The colour was repeated on the oil tank and tool box. The alternative finishes were available on these models also. Black was specified for the tanks of the scrambler twins with the options of red or blue.
• New camshafts were introduced, giving a varied contour to previous configuration. These were stamped SS in 1959 only and are suitable for all models. The four metering plugs in the cylinder heads were discarded.

1960

• The major change in 1960 was the introduction of a full cradle frame. A single 1 1/2" diameter 12 gauge top tube and a vertical seat tube linked up with dual front down tubes which continued under engine and gearbox. The front fork trail was increased. The new frame required a three point petrol tank mounting, two posts at the front and a bracket at the rear.
• The gearbox internal ratios were altered to give more even spacing by reducing the gap between third and top. Bottom was a little higher at 2.56 to 1 (formerly 2.67), second remained unchanged at 1.77 and third was raised to 1.22 (formerly 1.33) with top, as always, direct drive of l to 1. The previous ratios were still available to special order.

• The cylinder heads were completely redesigned. The combustion chamber shape was hemispherical and this enabled flat top pistons with small recesses for the valves to be used, instead of the former high-domed type. Pistons were no longer wire wound but compression ratios remain unchanged in the new configuration. The redesigned inlet tract described an arc between the carburettor and the inlet valve to promote swirl to the incoming charge. A further effect was that the valve stem and protruding portion of the guide were at one side of the tract where they offer less restriction to the gas flow.
• Two noticeable external differences on the heads were thicker lugs at the front for attachment to the head steady and an additional horizontal fin. Cast into the underside of the additional fin were three short fins, disposed diagonally to the direction of air flow. These were designed to improve cooling in the region of the exhaust port. (maybe Suzuki copied it and called it Ram-Air). In conjunction with the new shape of the combustion chamber and inlet port, the valve included angle had been reduced to 40 degrees. The bolt-on induction manifold was also modified to suit the redesigned ports. Two-rate valve springs were introduced in place of the former single-rate types.
• In the motor, the former spring loaded felt oil-filter was superseded by one employing wire gauzes of two different mesh sizes.
• A spring-loaded pressure release valve was fitted, located inside the front of the timing chest (the bottom of the filter tunnel timing side). Oil released from it flowed into the timing chest, thence to drain into the crankcase.
• The cylinder head stud spacer bobbins were discontinued.
• Cylinder top spigot diameter was increased from 76mm to 78mm on the 650 engine. The pushrod length was increased.
• Increased oiling to the drive side crankcase by a 3/16 inch hole in the inlet camshaft tunnel and drive side cylinder spigot. This proved to be unsatisfactory due to over oiling, dealers were then instructed to fit the drilled barrel only to the timing side of the engine.
• A new Lucas 12-amp-hour battery of compact design was used and a more compact headlamp was fitted. It still housed the speedometer.
• The rear brake warning lights were finally adopted as standard after being an optional extra since 1953.
• Another innovation for the roadster models was a two-level dual seat designed to provide extra comfort for the pillion rider without raising the riding position too high.
• A 3/32" hole was drilled in the cylinder spigot aperture (drive side only). The intention was to increase the oil supply to the drive side cylinder and piston.
• The bonded type clutches became standard-fit for all models.

1961

• 1961 saw quite a few detail modifications to the engine section of the models. Withdrawal of the 646cc scramblers from the range reduced the numbers from ten to eight for the coming season.
• The lubrication system was modified again. Previously oil from the rocker gear drained into the camshaft tunnels and thence, by way of the timing chest into the crankcase. The new arrangement permitted oil from the exhaust camshaft tunnel to drain directly into the left side of the crankcase ensuring a more even distribution. Oil returning from the inlet camshaft provided adequate lubrication for the timing gear.
• On the sports twin models the Siamesed exhaust pipe was realigned so that it ran below, instead of inside, the right footrest hanger. The new shape gave the drive side exhaust pipe a "squarish" configuration rather than the previously more rounded type. A modified footrest assembly dictated the run of the exhaust pipe below it. Formerly, the footrest brackets clamped directly to the frame tubes but there was no allowance for any height adjustment. Placed transversely at the-rear of the engine there was now a square rod to which the rests were secured. On the touring models the deeply valanced front and rear mudguards were shortened. Tyre clearance at the leading edge of the front mudguard was increased.
• Common to all models were the redesigned transfers and an increased size of the three dimensional tank badges. The latter also had an alteration in the actual nature of the motif. Revised and extended colour schemes were also available for the new season. In the AJS range a shade of birch grey replaced blue as the predominant colour in two-tone finishes.

Where chrome plated fuel tank panels are fitted the tank was grey with blue panel beading. The Matchless models with a two-tone finish had the colour dominance reversed, so that cardinal red took preference over Arctic white. Those machines fitted with chromium plated tank panels had an overall finish of red.

• The 3/32" hole in the crankcase spigot was transferred to the end of the inlet camshaft tunnel. This augmented the oil supply to the nearside cylinder.
• The four head metering plugs, which were discarded in 1959, were reintroduced.

1962

• A pruning of models once again took place for the 1962 programme. The forerunners of all the AMC twins the G9 and Model 20, were dropped along with the deluxe versions of the 650s. The four models catalogued were the Matchless Majestic (G I2) and the AJS Swift (31 ) as the standard 646cc twins, while the high performance models were the Matchless Monarch (G12CSR) and the AJS Hurricane (31CSR) both hitherto known as the sports twins.
• The most noticeable feature was the new petrol tank motif. This was a large zinc alloy pressure die casting which was chromium plated and fixed with two screws. Less apparent were the new soft rubber tank mountings. At the rear, the tank rested on a sponge rubber pad taped to the frame top tube and held down by a rubber band passing under the tube and hooked over ears on the tank. At the front, two tubes were let into the tank bottom. Into these tubes fitted long rubber sleeves, expanded by self-locking nuts and bolts passing through lugs on the frame.
• The oil tank was modified on standard models. A breather tower was formed at the top to prevent oil loss at sustained high speeds. (Already standard on the sports twins).
• A stronger kick starter spring was introduced to prevent flapping on severe bumps. An extension on the centre stand gave it a roll-on action, considerably reducing the muscular effort required.
• On the electrical side the translucent case type of battery was discarded and the larger, more conventional, type reverted to. The enclosure box was slightly enlarged to suit the larger unit.
• There was also a new pattern Lucas horn, smaller, lighter and louder.
• Ignition was controlled by a detachable key in the light switch, instead of by a separate non-detachable switch.
• The dynamo had finally been made redundant with the adoption of the alternator for the CSR twins and so the era of the dynamo - CVC · DC generation system faded into the mists of the past.
• The standard twins could be specified with magneto ignition and a quickly detachable rear wheel, to virtually make them a deluxe version.
• Poundage of the front fork springs on the standard twins was increased to bring it in line with the CSR models.
• On the CSR models the pillion footrests were carried on brackets extending rearward from the sub-frame (as on the standard twins), instead of being brazed direct to the sub-frame. The mountings were stronger and better placed.
• Duaflex rings were incorporated for the pistons
• There was a new type felt-on-gauze filter for the crankcase.
• Stellite was introduced for the pads on the cam followers.
• A heavy duty five plate clutch was introduced for the CSR models. The new type steel plates were dimpled.
• The famous nodular iron crankshaft was introduced.

1963

• 1963 is known as 'the year of the interim wheels' as the twins came in for an extensive face lift. A slimmer front hub housed a wider 7" brake with 1.1/8" linings in place of the 7" x 7/8" anchor used formerly and henceforth reserved solely for the CSR versions of the 650cc twins, (G12CSR and 31 CSR).
• The introduction of 18" diameter wheels lowered the riding position but still used tyres with the same section as before.
• The steering head was sloped back one degree more to restore the standard fork trail.
• The new full width hubs had tapered sides and the number of circumferential ribs was reduced from seven to five. The new cast aluminium shoe plate was internally ribbed.
• Whilst reducing mudguard radius to suit the smaller wheels the factory changed the blade section from C-section to D-section and incorporated a rib along the middle.
• The bolted-on rear sub frame was shortened and rigidity was increased. As a result the suspension struts slope forward and streamlined the rear end look.
• There were minor alterations to the pivoted fork. For the brazed-on wheel spindle lugs steel plates were used instead of malleable iron castings. Two small cross tubes were let into the left side fork arm to accept fixing bolts for a fully enclosed rear chaincase. The new chaincase was of conventional design, comprising upper and lower steel pressings. The front end of the case was overlapped by a pressed sprocket cover so that no part of the chain was exposed.
• The stronger rear fork also had new spring unit anchorages. The clevis lower end of the latter were replaced (finally) by the conventional Girling mounting. Thus the last link with the old Jampot trademark was finally vanquished.
• Mounted inside the new sub frame was a retailored pannier-type oil tank and matching toolbox-cum-battery box. The new oil tank had an in-built froth-tower, following previous design.
• The dual seat width was narrowed at the rear and the depth reduced at the front. In conjunction with the new wheel size, this alteration dropped the seat height by 1.1/2".
• The reshaped fuel tank used the same mounting system as before but the knee position was scalloped with stuck-on knee pads. The capacity remained 4.1/4 gall. The filler cap was moved to the centre line of the tank and main and reserve fuel supplied were controlled by a single two-level tap instead of twin taps.
• A baffle type silencer of circular cross section had been developed, It reduced noise output and slightly increased power output.
• The main engine modification was the adoption of the double capacity oil pump, with corresponding increased width of timing cover. The pump featured double pumping volumes on both delivery and return sides by means of doubling the width of the pump gears. However the gauze mesh filter which was used for a short time was deleted and there was a return to the earlier felt filter.
• In summary the models G12 and 31 featured the lowered riding position, slimmer tanks and more powerful brakes, with the 18" wheels. The CSR models retained most of the previous year's specification though they featured the new fuel tank and silencer. One interesting item, which could be specified as an extra, was a glass fibre headlamp cowl embodying an instrument facia and carrying a small perspex screen. It was available for the sports models, coloured blue or red to match the petrol tank. It was similar to the front number plate of the 7R and G50 models. In the facia were a speedo, rev-counter, ammeter and light switch. The Lucas pre-focus light unit had the car type beam. Adjustment was achieved by employing a double rim and three spring loaded screws. Also available for the 650 CSRs were high compression pistons, (giving a ratio of 10.25 to 1), road-race type camshafts and twin carburettors and fittings.
• Shown at Earls Court for the l963 season was a model especially assembled for the American market and for export only. Basically it used similar engine components to the CSR models apart from larger pistons, special crankcases and modified heads allied with bigger cylinders.
• Not mentioned previously, but of great importance, was the fact that the "interim" wheels (18" size) used journal type wheel bearings with no adjustment required, to replace the taper roller type. Taper roller bearings were still used on the CSR models.
• Cam followers were still stellite padded but are now forged to overcome problems which the butt-welded version caused, when it snapped.

1964

• Norton models were evident at Plumstead and standardisation was in vogue. The roadsters were given Roadholder forks and hubs with frame modifications to suit. Sidecar forks were available and both types were spaced to take 4" tyres. The CSR had 18" wheels, rounded oil tank and toolbox and altered frame as the 1963 standard models. Mudguards were chrome plated.
• Electrics changed to 12V with twin points on the standard models, but the CSRs retaining the magneto.
• 3/8" cylinder head studs were introduced with changes to the crankcases, barrels, heads and gaskets.
• The oil pressure relief valve was moved to the pump carrying plate. The 1952-1959 felt type oil filter was used with matching end cap.

1965

New diamond shaped tank badges appeared whilst finish was basically unchanged. A small number of standard 650s and CSRs were built but in the middle of 1966 the 650s were axed bringing an end to the AMC twins.