This is a story about the iconic Sunbeam Longstroke.
In 1920, as the dust of the war settled, the Isle of Man TT was back in full throttle. Sunbeam sent their team ready for action with specially tailored leathers to reduce wind resistance, and their fabled 500cc machines. The combination was a success, with Tommy de la Hay winning the Senior at an average race speed of 51.79 mph, and George Dance setting a new lap record before breaking at inlet valve at Creg-ny-Baa and having to wait for a new one to be dropped to him to enable him to continue.
The 3½ hp Sunbeams had proven their worth at the most important and respected circuits in the world… and it was about to get even better. In 1921 Sunbeam introduced a new weapon – the “Longstroke”. An update on the existing 85mm x 88mm powerplant, it now had a 77mm x 105mm ratio which provided a fast and thrilling 492cc engine. The 1921 French Grand Prix proved a successful testing ground for the Longstroke as Alec Bennett won the race in style.
Alec Bennett astride a Sunbeam at the 1921 IOM TT
The legend that is the Longstroke was born, and would be the flagship model of the fleet. It was the quickest side-valve out there, and quickly earned the well-deserved title – the Speedman’s Machine. The motto stuck and the name was used to promote the first production model in the 1922 Sunbeam catalogue – the 3½ HP TT Sporting Model. This was very much an over-the-counter racing machine based on the GP bikes – no kickstart, slimline mudguards and dropped handlebars; and this proved an enticing proposition for young dare-devils eager to follow in the footsteps of their racing heroes.
A 1923 TT Longstroke
The Longstroke TT was stamped into the 1922 Sunbeam brochure beside the current 3½ models (Standard, Semi-Sporting and Sporting Solo TT). The reputation of the machine was boosted that year when Alec Bennett took a Longstroke to the TT, and won in style (this was in fact the last side-valve to win a TT race).
The addition of the sensational new bike to the Sunbeam range was music to the ears of nascent boy-racers who were desperate to follow in the footsteps of their TT heroes. Anyone who was able to stump up the cash now had the opportunity to purchase their very own racer for the road – all well timed, as the amateur TT series, the Manx Grand Prix arrived on the scene. The first of the races was won by Les Randles on a factory-standard Longstroke at 52.77mph.
An extract from the 1922 Sunbeam brochure
The Longstroke was a brute of a side-valve, however the conquests on the race scene were short-lived as the wave of over-head valve machines soon flooded the tracks. 1923 was a calamitous year at the TT, with broken engines and mediocre results. The curtains had officially closed on side-valve Sunbeams at the TT, and the factory set to work on honing their over-head valve bikes.
In 1924 the Sunbeam line-up was revised with each machine allocated a model denotation. There were a total of three 500cc side-valves on offer with individual characteristics. The long-standing 3½hp that had been around since 1915 was appointed the Model 3, the Longstroke became the Model 6, and new to the squad was a short-stroke version of the Model 6 – the Model 5 “Light Solo”.
The civilian side-valves were soon under assault by their over-head valve counterparts, however the appetite was still there – the side-valves were reliable, economical and simple to work on… plus there was no fear of a broken valve head dropping into the cylinder head!
In 1925 the side-valves were fitted with drum brakes, if pretty small ones. It is often said that this style of machine – simple, skeletal, and fast – was the high point of the motor-bicycle.
A 1925 Sunbeam Longstroke Sport
In 1927, there was a shift in the side-valve camp. The 3½ (Model 3) hp that had braced Sunbeam since 1916 was discontinued, leaving behind the M5 Shortstroke and M6 Longstroke. The frames and cycle parts of all Sunbeam models were beefed up as a result of failures on the rutted tracks of the TT. The days of the slimline Sunbeams were numbered, as frames became heavier to account for the more powerful engines. Sunbeam had stuck with the lightweight motorcycle for as long as they could, and even in 1925 were berated for using thin-section tyres on their more sporting mounts, despite the reported better handling! The iconic and classic transverse coffee-pot silencer had also disappeared, replaced instead with pipes arching around the engine to a silencer. Still, the simple and superb flat tank, housed in a split frame was still in play, and would be for another couple of years…
A 1928 Sunbeam Model 6
In November 1928, Sunbeam introduced the saddle tank in a single-tube diamond frame using the engine as a stressed member. At the time, this was a popular transition as the flat-tank motorcycles of the 20’s were seen to be outdated, while the sleek and slender saddle tanks were very much in vogue. The side valves were now hidden and protected by a pair of aluminium bolt-on covers – a shame as the pulsating action of the valves is strangely hypnotic!
In June 1930 a new 492cc side-valve machine was introduced, christened “The Lion” in recognition of the Imperial Chemical Industries (ICI) ownership of John Marston Ltd – the lion being the ICI symbol. It was basically the Longstroke in disguise. In 1931 the Lion could be ordered in a chrome-plated petrol tank with black and gold panels, a feature that lasted for just for the one year.
The Lion was fitted with a four-speed gearbox, a pushrod clutch and interchangeable wheels, and the Druid girder forks had been replaced with Webb centre-spring forks. In 1932 a 599cc version of the Lion was added as the Model 7A and the 500 was named the Model 6A Lion.
A 1934 Sunbeam Lion side-car outfit. Credit: H&H Classics.
The Lion remained in play for the life of the company and the subsequent AMC take-over in late 1937, when production was transferred to the Matchless factory in Plumstead, London. There was enough stock of parts and work-in-progress to ensure that the Marston design of Longstroke continued to be assembled in Plumstead for the 1938 and 1939 seasons, the only difference being the return of the light alloy cylinder head for 1938. The AMC bikes even retained the Lion name. In 1940 the 600cc Lion (the C30) was still listed in the final ‘Sunbeam’ leaflet, alongside the new high-camshaft B-series machines. As demand from the army for the Matchless G3 ramped up, production of Sunbeams were discontinued, and John Marston Ltd’s iconic Longstroke ceased along with the others…
The Longstroke, some would argue, is the epitome of Sunbeam and represents the firms quest for high quality and reliable craftmanship, and fast, thrilling machines… and we couldn’t agree more. As above, if you get the chance to ride one, it is well worth it for a taste of simple, involved, and exciting vintage motorcycling.
an article by The Girder Club
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