Classic bikes: A different twin… – Motorcycle news, reviews & riding…

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Classic bikes: A different twin.

Although the AJS twins lacked the chutzpah of the other British twins of the day, we reckon they were decent bikes.

When it comes to post-war British four-stroke twins Triumph, BSA and Norton tend to grab the limelight. But there is worthy opposition from other British manufacturers, in particular the AJS/Matchless AMC Twins. The AMC twins have a reputation as solid and stodgy performers but that doesn’t do them justice.

Unlike the more fancied British triumvirate the AMC twins were less highly strung and provided their owners years of reliable, if unexciting, riding. These were motorcycles that would last over 110,000km before a major overhaul, a rare feature for 1950s motorcycles.

All British manufacturers were obliged to follow the parallel-twin example of Triumph’s Speed Twin but AMC decided to do it differently. Its designer Phil Walker created an engine with separate alloy cylinder heads on individual iron barrels. To provide more support for the 360-degree crank a centre plain bearing supplemented the outer caged rollers.

Walker’s idea was to minimize crank flex and vibration but it wasn’t totally successful; the AMC twin soon earned a reputation for severe vibration at higher rpm. But if you were used to British singles and parallel twins, vibration was just par for the course.

As with the Triumph twin the valves were operated by two gear-driven camshafts and pushrods. Carburetion and electrics were standard for the time, the former by Amal and the latter coping with Lucas’ (known to many as ‘The Prince of Darkness’) best dynamo and magneto. The four-speed gearbox was separate and the primary drive chain enclosed in AMC’s distinctive ‘tin-pressing’ arrangement.

Well nigh unsealable, this contained 250ml of oil to ensure smooth running of the engine shock absorber.

One of the AMC twins’ most annoying features was that copious amounts of lubricant would emerge if the crankcase breather-valve failed. Also the clutch would slip if the primary case was over-filled. Fortunately this was a rare occurrence because the chaincase leaked – an AMC twin always left a telltale signature oil stain wherever it was parked.

AMC also departed from tradition by eschewing the popular plunger rear end and incorporating twin shock absorbers and a swingarm. With most of the chassis parts shared with the 500cc AMC “heavyweight” singles, the handling was pretty good. Even the distinctive “Jampot” shock absorbers worked well enough, as the 500 was quite light at around 179kg.

The brakes were also from the single but for 1954, as pictured, the front brake was full width.

The AMC twin appeared in 1948 with 500cc capacity, and was offered as an AJS Model 20 or nearly identical Matchless G9. Originally for export only to the US, the 66 x 72.8mm engine produced enough power to propel the Model 20 to nearly 150km/h.

While the AMC twins were overshadowed by the more glamorous twins from Triumph, BSA and Norton, AMC owners learned to appreciate their machines’ superior build-quality and handling. In nearly every respect the AMC twins embody a near-perfect combination of the attributes sought by many classic bike enthusiasts.

Many thanks to Allen and Loraine Smith of the Australian Motorcycle Museum, Haigslea, Queensland for the use of the AJS Model 20 pictured.

Five Matchless things about AMC Twins

AJS was founded in Wolverhampton before the First World War by Albert John Stevens and his brothers. It was named after Albert because he was the only brother with three initials.

In 1931 Matchless acquired AJS motorcycles. It became AMC (Associated Motorcycles Ltd.) in 1938.

Although most AMC twins were produced as AJS and nearly identical Matchless, the racing 500 twin was only available as the G45 Matchless.

The 500cc Model 20 AJS and G9 Matchless were made until 1961. A 600 Model 30/G11 appeared in 1956 and a 650 Model 31/G12 in 1959. Production of all twins ended in 1966.

AMC acquired Norton in 1953, and by 1963 all motorcycle production was at Plumstead in London. The company finally went into receivership during 1966, and became Norton Villiers. From 1967 only Matchless survived as the G15 with a Norton engine.


The AJS and Matchless Owners Club is one of the largest and best organised in the classic world. They also provide a full spare parts service

An interesting appraisal as to why AMC twins are unappreciated can be found here .

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To comment on this article click here Published. Friday, 15 October 2010

AJS Model 30 650
AJS Model 30 650
AJS Model 30 650

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