From start to finish
The economic depression saw AJS in liquidation in 1931. The motorcycle component of the business was bought by the Collier Brothers, trading as Matchless Motor Cycles Limited. The AJS factory in Wolverhampton was closed and both brands were produced in the Plumstead Matchless factory in London. The company name changed to Associated Motor Cycles Limited (AMC) after the purchase of Sunbeam in 1937. AMC’s main production of motorcycles up to 1949 was based on single cylinder machines, but market acceptance of parallel twins forced AMC to follow suit.
Why so special?
Parallel twin engines have two pistons side by side. If they move vertically they are also called vertical twins. Compared to an equivalent sized single cylinder engine, the big thump power stroke is divided into two smaller thumps making power transfer more progressive, less aggressive and with less vibration. Dividing the compression stroke in half means easier kick starting and decompression mechanisms are eliminated. Parallel twins require smaller flywheels, saving weight and providing quicker, smoother acceleration. Compared to a V-twin engine, the configuration is more compact, usually lighter, allows a shorter wheelbase and locates more weight (ideally) nearer the front wheel. The exhausts are side by side exiting each side in equal lengths for ideal back pressure equalisation. The plumbing for the inlet is easy and one carburettor can be shared. The cylinders and the exhausts are directly in the air stream for more efficient and even cooling. The compromises are that parallel twins don’t produce as much torque as singles and are not as smooth running as V-twins.
Parallel twins go back to 1913 but only became common in 1937 when Edward Turner designed the Triumph ‘Speed Twin’. Turner’s design advantage was low cost. The Speed Twin’s success meant Triumph’s entire range of post-war motorcycles was parallel twins. BSA developed a parallel twin prewar but it didn’t make it to production until 1946. Ariel released their version in early 1948 with Norton and Royal Enfield following later that year.
The AJS/Matchless twin conception
Phil Walker conceived the AMC parallel twin. Originally the chief designer at AJS, he migrated across when the Collier Brothers took over. The resultant OHV engine had a bore of 66mm and stroke of 72.8mm (498cc). The engine consisted of an almost spherical, vertically split, polished alloy, dry sump crankcase. Within was a one-piece (Meehanite) crankshaft with roller bearings each end. Unique to AMC was an additional support between the conrods to prevent crankshaft flex. A two-piece shell bearing was fitted to a large circular aluminium plate and bolted around the centre journal of the crankshaft. This plate was recessed halfway into each crankcase half and bolted to studs on the drive-side half. The bearing shells had integral thrust washers on both sides which anchored the crankshaft axially, allowing the roller bearings to float laterally during expansion and contraction. Reports suggest this feature came from the previous Matchless Silver Hawk or the AJS Porcupine projects, but whether there was any significant benefit is contentious. Structurally it reduced crankshaft flex but some say it actually increased vibration at certain rpm. The definite advantage was that this allowed Phil to channel the main oil feed to the crankshaft centre where it then distributed equally to both ends. Their competitors had to feed oil from one end, risking oil starvation on the other and reducing engine life.
The conrods were similar-to the AJS Porcupine, highly polished and made from light weight Hiduminium RR56, the little end connecting directly to the gudgeon pin, with split ‘Vandervell’ shell type big end bearings. Studs for the clamping yoke were threaded into cylindrical steel bars press-fit in holes passing through the conrod for maximum strength. A cast iron cylinder barrel was designed to be used for both right and left side, protruding deep (2-1/2”) into the crankcase. Introduced by AMC in 1948, wire-wound aluminium pistons were included. 18swg high tensile steel wire was wound five times into machined grooves in the piston skirt just below the rings, then ground to an exact size. This reduced expansion of the alloy piston allowing tighter tolerances to the bore, smoother, quieter and more efficient running, while eliminating piston slap during cold start-ups. The barrels and separate cast aluminium heads were spaced apart to allow maximum air cooling. The head included angled cooling fins on top which directed air across and between the rocker boxes. Posts were castin either side of the valve to support the rocker assembly. An eccentric axle supported the forged steel rocker arm. It had a screwdriver slot on one end for valve lash adjustment, and a large flat head on the other end allowed clamping to the post with a small bolt. This feature came from the 350cc 7R single race engine. The camshafts ran high in the crankcase onto pivoting followers allowing short push rods made from light, high strength duralumin with hardened steel tips to be enclosed within the cylinder casting. The inlet and outlet camshaft was positioned at rear/front of the cylinders respectively.
Straight cut gears ran off the crankshaft, rotating the camshafts, magneto, dynamo and oil pumps. This was AMC’s first engine with shell bearings where oil pressure is critical, so gear drive oil pumps were used. Driven by rectangular spigots nested into end slots of each camshaft, the front feed pump had narrower gears (less capacity) while the rear pump returned the oil back to the oil tank. A bleed line from the feed pump ensured the return pump was always primed. A felt oil filter was incorporated in the crankcase alongside the exhaust camshaft. Apart from the oil lines to the oil tank, lubrication was channelled within the engine making it oil tight. The large cast aluminium timing chest cover differed for each marque. The Matchless unit ballooned in one smooth curve with a small flat area at the crankshaft position displaying a recessed ‘Flying M’ painted red. The AJS version was a closer fitting shape. Two bulges cleared the protruding oil pumps and between them was recessed ‘AJS’ lettering painted black. A beautiful small circular chrome badge was staked to the crankcase drive side. The Matchless badge displayed the ‘Flying M’ surrounded by red vitreous enamel while the ‘AJS’ letters surround was blue.
The twin twins are born
Displayed at Earl’s Court in October 1948, it was 1949 before AMC released its parallel twins. The twin twins were christened the ‘AJS Model 20 Springtwin’ and its sibling the ‘Matchless G9 Super Clubman’. They were rated 29bhp with the Model 20/G9 birth weights 394/400lb respectively.
The twins dressed differently with the AJS’s including touches of blue and gold while the Matchless used red and silver. The frame and tinware were generally inherited from their single cylinder family. The inner chain case, oil tank, exhausts and the fuel tanks looked similar with a few slight differences. The inner chain case dynamo hole was removed, the fuel tank underside changed to clear the rocker covers, the AJS silencers were left and right handed.
Unique parts included brackets to brace the heads to the frame, Matchless (only) megaphone silencers and ‘Dunlopillo’ dual seat, and AJS (only) 4-gallon fuel tank. The AJS tank included a unique screw-on ‘U’ shaped deflector in the rear cutaway (where the seat front fits neatly) which directed overflowing fuel away from the rider’s tender regions. The AMC twins were only available with a swing arm rear (along with Royal Enfield) while other manufacturers continued with their (less sophisticated) plunger or sprung hub frames. The AMC patented “Candle Stick” rear dampers worked extremely well and the machines were highly acclaimed for their handling. Too many evolutionary changes were made to list in one article. Many of the frame and tinware changes were shared with the single cylinder models which sold side by side. The twins evolution (and singles for that matter) was driven by the US market which loved British motorcycles but demanded larger capacity more powerful engines. AMC performance models were regularly introduced in the US a couple of years before the home market and in some cases were actually modified locally. Australia was a beneficiary of the US push falling under the ‘Export Only’ banner.
Early life in America
Frank Cooper (Cooper Motors) was a keen California motorcycle desert racer and became a west coast AMC distributor. Indian dealers serviced the rest of the USA due to a deal with J. Brockhouse and Company, a UK concern which loaned The Indian Company a substantial amount in 1949. The conditions were that John Brockhouse (the founder’s son) be appointed to the Board. Indian manufacturing continued independently but Brockhouse’s new Indian Sales Corporation would control the distribution of all Indian motorcycle production along with AMC and other British brands. The twins were pretty much exclusively ‘Export Only’ for 1949 and 1950. Most went to the USA but some were sent to Australia and New Zealand. The
Shepparton Advertiser reported that Gribben’s Motorcycles had a new Matchless twin on display on 22nd October 1949. The Daily Mercury (Mackay, Qld) advertised Matchless twins for sale on the 3rd November 1949. Harry Louis, editor of Classic Bike is said to be one of a few who secured a Matchless twin in the UK. It was 1951 before the home market got a limited allocation of twins. The significant change was the famous ‘Jampot’ large capacity rear dampers replacing the ‘Candle Sticks’. AMC’s race department also put together a competition version of the twin engine in the 7R frame. This would become the Matchless G45 and its history documented in OBA 57. Cooper continued promoting AMC through racing. A January 1952 report described his Matchless G9 preparation for Bud Ekins to tackle the famous Big Bear Run.
USA growth spurt
In 1953 an optional racing kit was offered globally following recent success at the Manx Grand Prix. It included higher lift camshafts, twin carburettors, high compression pistons, rear sets, megaphone silencers and optional rev counter. This upgrade was not enough and Frank Cooper needed a larger capacity motorcycle to match his competitors. Reports say Cooper built a prototype boring the cylinders to suit 750 V-twin (2.745”/ 69.7mm diameter) Harley Davidson pistons to produce 555cc. He chamfered the holes in the centre web bearings to improve lubrication, took it to AMC in the UK and pleaded for them to make the upgrade. He didn’t succeed and reportedly Frank
had Dick Brown uncrate new G9s and modified the engines locally. These became known as ‘Cooper Twins’. These early cylinders had external grooves (just below the base flange) allowing oil passage to the top end. When Cooper bored these cylinders, very thin walls resulted at the grooves. The Indian Motorcycle Manufacturing Company closed in 1953. Brockhouse quickly organised Indian replacements by painting Royal Enfields red, rebadging them and continued business while controversially selling AMC machines in the same showrooms. In 1954 AMC introduced a 69.0mm bore, 544.4cc model. A report stated a former AMC employee Brian Slark (a now Missouri dealer) pressured AMC for an upgrade. This report didn’t mention Cooper, but it may have been both that finally got AMC to act. The weight remained the same but power increased to 32bhp. ‘Export Only’ and created hastily, AMC shipped these machines with an extra (loose) parts list and christened them Matchless G9B and AJS Model 20B. AMC removed the grooves from the base of their cylinders and instead cut a pocket into the left hand crankcase. The result removed the thin areas of the Cooper twins and made them easy to tell apart. A 1960 AMC Service Bulletin listed 247/165 Matchless G9B and 204/136 AJS Model 20Bs were exported in 1954/1955 respectively. In 1955 the race kit for the G9 now included the rev counter, racing magneto and racing sprocket assembly with a large capacity oil tank offered as an option. Frank Cooper advertised two variants of the 550cc twins. Standard was the ‘Super Clubman Vertical Twin’. The other a ‘Sport Twin’ (both AJS and Matchless) included alloy fenders, high handlebars, Dunlop Universal Trials tyres and a 21” front wheel which was a twin version of AMC’s competition single. Was this another AMC ‘Export Only’ or did Cooper raid the singles parts bin and modify them locally given that AMC didn’t release a competition twin globally until 1958?
Growing even bigger
In 1956 AMC introduced a 72mm bore, 593cc upgrade. Christened the AJS Model 30/Matchless G11, these burly twins were introduced globally and replaced the ‘Export Only’ 550cc models. The new barrels were taller including an extra cooling fin (now 7) making them easy to recognise. New pistons, bigger valves and redesigned combustion chamber resulted in a compression ratio of 7.5:1 (Model 30/G11) while the Model 20/G9 went from 7.0 to 7.8:1. The listed weight remained the same while power was now 33bhp. This year saw Cooper Motors become the exclusive AMC distributor for the whole of the USA, severing links with the Indian Sales Corporation. Cooper named the 593cc AJS and Matchless standard twin as the ‘600 Super Clubman’ and the ‘600 Sport Twin’ for his competition version. Marlon Brando was reported to have purchased a 600cc Matchless twin which was custom-built for him. In 1957 power figures disappeared from publication. Cooper’s 1958 models were renamed the ‘Hurricane Super Clubman’ and the ‘Hurricane Scrambles Twin’. The ‘Hurricane’ engine was an upgrade, exclusive to Cooper and fitted to all four of his models. His advertisement listed them as including “racing cams, new head design, high velocity porting, 1/8” larger inlet valve, 8.5:1 compression, crossed over and tucked in exhaust and a big carburettor.” The AJS was listed with a 3.00”x 21” front tyre while the Matchless had a 3.5”x 19” item.
Developing finesse and a competitive nature
In 1958 AMC listed four variants of the 498cc and 593cc twins globally. The standard models now had a coil/alternator electrical system. The De Luxe models retained the magneto/dynamo and included the quick detachable rear wheel and flashy chrome panels on the fuel tank. Finally, AMC followed Cooper, offered ‘Competition Scrambler’ (CS) and ‘Competition Sports Roadster’ (CSR) versions. Engines for CS and CSR models had high compression pistons, lightweight Siamese (two into one) exhaust with a single silencer (mimicking Cooper’s Hurricane engine). The CS models used a modified (one piece, fully welded) single cylinder scrambler frame, high bars, wider section knobby tyres, light alloy competition mudguards, 2-gallon competition fuel tank, lightweight competition dual seat, a quick detachable headlight and a headstock mounted speedo. The CSR model varied by retaining standard, handle bars, fuel tank and road tyres. Interestingly the Siamese exhaust (introduced to save weight) produced an extra 2.5bhp and a nice wide power curve.
Significantly, AMC waivered their policy (not to supply the media motorcycles) by offering a Matchless G11CS twin to The Motor Cycle magazine for an attempt at covering 100 miles in one hour at a UK high speed track. Vic Willoughby covered 102.9 miles in the hour comfortably, achieving a 103.9mph maximum. Alan Baker (magazine technical manager) then witnessed the engine teardown commenting favourably on the lack of oil leaks and reporting no appreciable wear apart from a minute amount of pick-up on the offside piston. The new, polished, cast aluminium chain case finally cured the leaks from the earlier pressed metal unit. Unfortunately, AMC removed the adjacent gorgeous crankcase badge at the same time. The USA received another exclusive upgrade to 646cc, christened the Model 31/G12. The crankcase cylinder spacing prevented a bore increase so AMC increased the stroke to 79.3mm using the current G11 (7 fin) cylinder and fitted new shorter pistons to suit. Cooper’s headline read “It’s the greatest 40-incher” (40 cubic inches in US lingo), and called them “Super Hurricane Twins”. His CS version interestingly carried the older kidney shaped
toolbox and open battery carrier. No AMC records exist and it was reported that AMC’s competition shop supplied them.
Growing pains and a divorce
In 1959 AMC introduced the 646cc twin models globally. It included a taller 8 cooling fin cylinder, 1/2” longer pushrods, while retaining the 593cc pistons. This was different to the engine supplied to the USA in 1958 and it replaced the 593cc Model 30/G11. The 1958 variants were available but only the standard version of 498cc models remained by year’s end. Increased vibrations from the stroked 646cc engine was reported to cause fuel tank cracks so a new 4-1/4 gallon, two half/vertically split, fully welded and rubber buffer mounted fuel tank was introduced. Crankshaft breakages and an abnormal incidence of blown light bulbs also occurred prompting quick AMC reaction to protect their stellar reputation. In 1959 AMC decided to buy The Indian Sales Corporation from Brockhouse. This allowed AMC to control distribution of their product directly through the extensive Indian showrooms. October advertisements reported the merger of the two companies and a huge new facility housing Indian and Matchless spares, servicing and showrooms being built in West Massachusetts. The company was named ‘Matchless Indian’. Rebadged Royal Enfield models understandably were deleted except for the 700cc Indian Chief and other sourced motorcycles that AMC couldn’t substitute. Frank Cooper lost the AMC distributorship but advertisements as early as November 1959 had Frank now distributing the Royal Enfield range.
Indian blood brothers
In 1960 AMC introduced a nodular iron (aka Noddy) crankshaft for the 646cc twin. Stamped with the
letter “N” for identification, breakage issues were cured. New light weight alloy heads with bigger ports, reduced 40 degree included angle valves and dual rated valve springs were introduced. New modern flat top pistons included a high performance outer perimeter ‘squish’ area which also reduced tendency for detonation with low grade fuels. The new Matchless Indian headquarters were opened in 1960 and the US range became blood brothers, christened with new ‘Indian-type’ nicknames but retaining their Matchless and AJS badges. The Model 20/G9 became the ‘Tomahawk’, the Model 31/G12 the ‘Trailblazer’ and the Model 31CS/G12CS and Model 31CSR/G12CSR the ‘Apache’. In 1961 the Model 31CS/G12CS was dropped from the local market. Motor Cycle magazine tested a Matchless G12CSR in 1961 reporting a top speed of 108mph. AMC’s investment and attempt at US motorcycle distribution wasn’t working and in 1961 announced that it had lost £350,000.
1962 saw additional cost-cutting and the original Model 20/G9 was sadly discontinued, leaving only the 646cc standard and CSR models. Names were introduced for the home market. The Model 31 became the ‘Swift’, the Model 31CSR the ‘Hurricane’, the G12 the ‘Majestic’ and the G12CSR the ‘Monarch’.
In April a CSR speed kit option was offered lifting compression to 10.25:1, adding hotter cams and twin carburettors. CSRs were also offered an optional fibreglass bikini fairing in blue (AJS) or red (Matchless). A replica of AMC’s racing cowl, it included a small plastic screen, speedometer, amp gauge and light switch with a headlight suspended in place of the race number pad. A tachometer was optional. A March advertisement announced a (US only) 750cc model, christened the Matchless G15/45. The ‘45’ being cubic inches is hardly an Indian name but could inappropriately be linked to the ‘Colt 45’, “the gun that won the west”. Reports state the barrels still had eight cooling fins, the bore was increased to 77mm, compression ratio 7.3:1 and capacity was 738cc. 72mm bore was previously quoted a maximum. Reports quoted that this engine had very thin (less than 498cc) head studs which may explain how the bore increase was achieved. Only available as a standard road model, it had battery/coil ignition, a single Amal 389 carb, 19” front and 18” rear wheel like the current CSR models.
At 430lbs reports stated the ‘45’ was no faster than the 646cc but cheaper than the G12CSR. In November 1962 AMC announced that all Indian Motorcycle rights were sold to Joseph Berliner, already a huge distributor of imported motorcycles including AMC’s other marque, Norton. The new company became J.B. Matchless Corporation. Interestingly Berliner never used the Indian brand name. In 1963 AMC introduced a new full length silencer producing better low down and mid-range punch when coupled with the optional CSR speed kit. 18” wheels were fitted to the standard model while the Hurricane/Monarch (Model 31CSR/ G12CSR) retained the 19” items. Berliner removed the feathers and war-paint nicknames listing Matchless (only) as G12CS, G12CSR and the G15/45.
Kicked out by their step brother
Norton production moved in 1964 to Plumstead and serious ‘Nortonization’ of AJS/Matchless models began. Norton Roadholder forks replaced the AMC Teledraulic units and all models now had 18” Norton wheels. The standard and CSR, 646cc models continued with their head studs increased to 3/8” diameter. The (US only) 738cc AMC twin was replaced (apparently only two batches of 100 were ever made) by the 748cc Norton Atlas engine with a relatively low 7.6:1 compression ratio, twin carburettors and sports camshafts. Claimed power was 49bhp @6500rpm. This reborn Model33/G15 was released in October. Berliner who had distributed Nortons since 1958, became a Norton fan and apparently instigated the engine change. By 1965 the model line-up was a jumbled collection of AJS, Matchless and Norton engines in AMC, Jubilee and Featherbed frames and the model names were dropped. The 646cc models were joined by the 748cc Norton powered twins in standard and CSR form. The 748cc G15CSR design philosophy was revised to follow café racer trends with lower handlebars, rear set pegs, shortened alloy mudguards, front fork gaiters, exposed spring rear shocks and swept back twin exhausts. The AJS Model 33CSR was introduced a little later. The end for AMC came in 1966 when it sadly slipped into receivership. In September, Manganese Bronze Holdings took over, renaming the company Norton Matchless Ltd. This later became a part of Norton Villiers who a few years later would also take over the ailing BSA empire, including Triumph, renaming itself Norton-Villiers-Triumph (NVT). The 646cc models were dropped mid-1966, laying the AMC parallel twins to rest and leaving their Norton step brothers to continue but it wasn’t long before they too faded into non-existence.
My 1955 AJS Model 20
In 1981, I received an assortment of parts as a house warming present for a gratis job I did on a friend’s motorcycle. From then on I began sourcing parts to suit the 1955 twin engine. Every Saturday with pay in hand I’d head to various motorcycle stores and purchase what I could. I bought a bitsa to speed things up. Luckily I found the unique 1955 spring frame which I swapped a duplex frame for from the late Stan Wilmot. Stan also supplied the fuel tank which he said was an optional long range item. It had the correct underside for the twin engine and a screw-on deflector (exclusive to early AJS twins) but with correct screw locations for the 1955 plastic badge. The unique 1955 through bolt fixed oil tank and battery carrier came eventually. I did the mechanics, polishing, panel beating and painting while out-sourcing the plating and specialist machining. Perhaps the most difficult part was the rubber air cleaner manifold. It is a weird shape so I had to carefully profile some plasticine from which I made an aluminium mandrel which I had wrapped with rubber to make the sleeve. The bike took shape in the lounge room until completion in 2003. I then got my motorcycle license. Insurance was interesting. I rang Shannons who were contemplating motorcycle cover and I was to ring a guy (‘Chook’) in the NSW office for details. I sent some photos, we agreed a value and I believe my AJS was one of the first bikes they ever insured. It has been a faithful companion and we have covered many miles and one crash together. While it is a little heavy for an old guy it is comfortable and the twin exhausts have a wonderful bark at full song and burble on the down shift. Its most famous moment was winning ‘Bike of the Show’ at the Laverda Concours in 2012.
ABOVE The original AJS twin with the “Candle Stick” rear units. BOTTOM LEFT A page from the 1953 catalogue showing the Model 20, now with “Jampot” rear shocks.
LEFT Crankshaft assembly with centreweb plate fitted. RIGHT Sectioned drawing of the AMC Parallel twin engine.
ABOVE February 1955 Cooper Motors advert featuring Matchless 550 twin.
ABOVE The Matchless/Indian marriage of 1960. RIGHT Matchless G9 Super Clubman and Matchless G11 from the 1956 catalogue.
Cast frame lug and triangular plate head brace introduced 1953. Oil tank filter and filter cap. AJS crankcase badge is a bit of jewellery. Unique through stud casting with Vokes air cleaner and rubber manifold. Headlight dashboard with bullet park lights and domed covers over the stanchion nuts.
ABOVE The unique ‘spool’ shaped 1954 full width alloy front hub.
ABOVE Infamous pressed metal chaincase with removable clutch cover for 1955.