1924 Model 5 vs. 1925 Model 6 Longstroke Sports

[Mar 24, 2008]

Sunbeam motorcycles were built by John Marston Ltd. starting in 1912 in Wolverhampton, England, as an outgrowth of Marston’s highly successful Sunbeam bicycle business.  Marston began his career in 1851, manufacturing ‘japanware’; glossy enameled home accessories and furniture with a luxurious black or red finish and gold leaf accents, modeled after traditional Japanese lacquer ware.  Japanware was all the rage in the late 1800s, and in 1887 Marston took the advice of his wife Helen and expanded his business into the booming bicycle trade.  With over 30 years of experience in top quality paint and gold leaf, Marston’s Sunbeam bicycles were renowned for the superb black and gold finish, and for the patented pressed-metal ‘Little Oil Bath’ chaincase that kept the rider’s trousers clean.  Sunbeam bicycles were expensive, but designed to last a lifetime, and many a centegenarian+ Sunbeam bicycle still retains its original finish in perfect condition.

A Sunbeam gentleman’s bicycle of 1915. [Wikipedia]
Marston began building Sunbeam cars in 1902, which were also high-quality vehicles, and expensive, with a beautiful finish.  The car division was separated in 1905 as the Sunbeam Motor Car Company, manufactured in Blakenhall, a suburb of Wolverhampton.  The car division was successful, but a business slump spurred Marston to expand into the booming motorcycle business.  The first Sunbeam motorcycle appeared in 1912, when Marston was 76 years old: it featured a 350cc sidevalve engine (from AJS), and a 3-speed gearbox with all-chain drive and fully enclosed chaincases.  It was, as one would expect, a superb machine and worthy inheritor to the Sunbeam bicycle’s reputation, and Marston dubbed it a ‘gentleman’s motor bicycle’.

George Dance in 1919 at the Kop Hillclimb, on his hand-made OHV conversion, using a 1913 350cc crankcase and aircraft OHV cylinder and head. The chassis of this racer is basically standard, although he would evolve his sprinters into extremely light and very fast tools. Note the utter lack of safety equipment, barring goggles. [The Vintagent Archive]
It was natural that Sunbeams were raced, and from the very first they performed extremely well in the important road trials of the era. By 1914 their development engineer John Greenwood had tuned a trio of Sunbeams for the factory’s first Isle of Man TT, where they took the Team Prize.  George Dance joined the factory as their star rider, and after WW1 he would cement the factory’s name in racing history, as he was virtually unbeatable on his specially-tuned racing Sprint specials.  During the war, Dance had been an aircraft mechanic, and built his first sprint racer in 1919 using an OHV cylinder head and barrel from an aircraft atop a Sunbeam crankcase, with an extremely light chassis, for an all-up weight of under 200lbs.  Dance was a gifted rider and fearless racer, and the only contemporary sprint racer of similar success and skill was George Brough…who wisely raced in events where Dance was unlikely to appear, and kept his own perfect race record, winning 53 events.

Alec Bennett in 1921 aboard his factory racing Sunbeam sidevalver: note the ‘dummy rim’ brakes, which are useless in wet weather. [Keig Collection]
John Marston died in 1918, and Sunbeam was sold to Nobel Industries (later ICI), who according to rumor merely wanted to acquire Sunbeam’s exquisite paint technology, but they retained ownership of Sunbeam until 1937, when the brand was sold to Associated Motor Cycles (AMC).   In the mid-1920s, John Greenwood employed engine research specialist Harry Weslake to improve the performance of their motorcycles, resulting in the new OHV Models 8 (350cc) 9 (500cc) roadsters, and corresponding Models 80 and 90 racers, plus a special Sprint racing model that took advantage of George Dance’s press, all appearing in the Sunbeam catalog in 1924.  When the OHV models appeared, Sunbeams won seemingly every important race and trial in the UK and Europe from 1924-30.  Sunbeam raced the last sidevalve machine to win the Isle of Man TT (1922 – Alec Bennett), and second-to-last pushrod OHV machine to win the Senior TT (1929 – Charlie Dodson).  The writing was on the wall for pushrod OHV racers by 1926, when Velocette cleaned up at the Junior TT with their new K-series 350cc OHC racers, and Norton’s new CS1 OHC took the Senior TT under Stanley Woods.  Sunbeam responded with a few experimental OHC racers of their own – read our Road Test of the 1925 ‘Crocodile’ here.

Your scribe Paul d’Orléans in 1999 with a 1923 ex-factory Sunbeam Isle of Man TT racer, one of the factory team machines, still in its original paint. “I gave it a good thrashing on the rural roads in East Sussex, and found its speed terrific, but its brakes dismal, which led to some dramatic moments. Still, a superb motorcycle.” Note the straight-through exhaust pipe, racing handlebars, and André friction dampers on the Druid racing forks. [Paul d’Orléans archive]
But, the bulk of Sunbeam’s racing and road trial successes had been made on their reliable and surprisingly fast sidevalve models, which were the gold standard internationally for a proper Grand Prix racing machine, until their overhead valve models began dominating races everywhere. Road tests of the era report their superb smoothness, quality of manufacture, and surprising speed, and Vintage era Sunbeams are highly coveted today for all these reasons.

What are they like to ride?

Since my 1925 Sunbeam Model 6 Longstroke arrived two weeks ago (March 2008), I’ve been curious to compare its character to that of James Johnson’s 1924 Model 5 touring model. They’re both sidevalvers from the mid-20’s, with very similar running gear and mechanical configurations, from the same esteemed manufacturer; how different could they be?

My 1925 Sunbeam Model 6 Longstroke Sports on the left, James Johnson’s 1923 Model 5 Touring on the right. [Paul d’Orléans]
1925 Model 6 Longstroke Sports

The Longstroke was developed from Alec Bennett’s 1922 TT-winning (at 58.31mph) machine, and was initially known as the ‘Model 6’. The ‘Longstroke’ name was added for 1925, to what would have been the ‘Sports’ model in that year, but was called the ‘TT Replica’ in 1923. How quickly things changed in those critical years between 1923-25, where the Longstroke dropped in esteem from TT Replica to a ‘Sports’ model in just 2 years. That’s because Sunbeam added a new overhead-valve engine to its line in 1924, the Model 9 (and its variants), which sounded the death knell to the sidevalve as a racing machine.

Long, low, and lean: the drive side of the 1925 Model 6 Longstroke Sports, showing Sunbeam’s fully enclosed primary drive, which covers the cork-lined clutch, which is very effective. [Paul d’Orléans]
Surprisingly, even with the real advantages of the OHV engine, racers continued to develop the sidevalve for racing at events other than the Isle of Man TT; Brooklands, European races, trials, hillclimbs, etc. In fact, although Bennett’s win in ’22 was the last for a sidevalver at the Island, they continued to be successful for many years in private hands. Take for example A.L. Loweth’s record of 94mph on a Norton 16H at Brooklands, in 1934! Supposedly ten years after the model had become obsolete for speed work. Food for thought. I admit my own bias in thinking sidevalve machines couldn’t be sporting, and would never satisfy a speed merchant such as myself. Gradually, while investigating Sunbeam and Norton racing history, I came to respect the humble flathead.  And of course, in the United States, Class C rules meant the flathead carried on racing through the 1960s, with its ultimate variant, the 750cc Harley-Davidson KRTT, recording 150mph at Daytona in 1968!

The 1925 Sunbeam Model 6 Longstroke Sports. [Paul d’Orléans]
1924 Model 5 Touring

James purchased his ’24 Model 5 from British Only Austria about two years ago, and has spent considerable time in his workshop, making the 84-year old Sunbeam perfectly reliable. Now he feels confident in its mechanical soundness, and several long rides (including one 800 miler!) have borne out his conviction that his Sunbeam can be ridden as the maker intended.

A proper motorcycle: the 1923 Sunbeam Model 6 Touring, with deeper mudguards, an upright riding position, and footboards. [Paul d’Orléans]
The biggest jobs he’s had to tackle were rewinding the magneto and replacing a broken steering stem; otherwise it’s been a matter of getting all the details functioning smoothly (cables lubed and adjusted, clutch working properly, brakes working, etc), which is really what ‘sorting it out’ means. It takes time to do those hundred small jobs in your off-work hours. That his bike runs so well is a testament to James’ persistence.

1923 Sunbeam Model 5 Touring, with period accessory wicker basket. [Paul d’Orléans]
By comparison, the Longstroke has just started down the road to ‘sorted’. Noted in a previous blog are my efforts to replace hoses and taps, get the clutch and carb working normally, and make footrests. The bike’s oiling is very curious for a total-loss setup, as there is no breather on the crankcase, but there IS an oil drain from the crankcase back to the oil pump – a semi-recirculating loop. The excess oil seems to be burned off, as the bike smokes a bit, even though the oil pump feed is turned well down.

The engine room of the Model 6 Longstroke Sports.  Note the ‘square’ ML magneto, later Amal carburetor, double-champer Pilgrim oil pump, and finned ‘fir cone’ valve cover. Also note the upper cylinder casting has straight fins; otherwise the engines are nearly identical. [Paul d’Orléans]
I haven’t found its top speed yet, but I would estimate in the high 70mph range. That’s going some for a bike which has very little braking power.  The front drum is essentially useless (both ‘Beams can be pushed forward with the inverted lever fully squeezed), and the back brake is merely OK. James has relined his brakes, and suggests the rear brake should lock the wheel. Suspension movement from the Druid forks is minimal, and the springing is very stiff. But, for all that, it’s a cracker! As it weighs only about 240lbs, it accelerates smartly, with strong engine pulses. The engine definitely has a long stroke at 105.5mm(x77mm), but it revs fairly freely, and thrives on higher rpm than might seem likely – it has plonk at low rpm, but there is a power surge at around 3500 rpm at which the engine smooths out, and she really starts to fly. The Longstroke engine feels slightly skittish and revvy, and surprisingly high strung for a 20’s bike.

The Sunbeam Model 5 has an indent curve on the upper cylinder casting, and a restrictor on the carburetor intake. Also, a single-chamber Enots oil pump, ‘square’ ML magneto, and priming tap atop the cylinder, for pouring neat gasoline into the combustion chamber for very cold starts. [Paul d’Orléans]
The handling is very stable at speed, although when stationary, the whole bike seems very wobbly. In first gear, the front end seems to ‘fall into’ corners, but as speed increases (I’ve seen around 60mph so far), cornering feels intuitive and takes less effort. The handlebars are brazed in place and very low, with no adjustment possible, and you must lean over the bike to reach the ‘bars. Clearly, you mold yourself to this motorcycle, not the other way around.

The Model 6 Longstroke has a conventional chainguard… [Paul d’Orléans]
The Model 5 has a completely different character; it’s a true gentleman’s machine, with a comfortable riding position and mellow traits. With footboards and high, pulled-back handlebars, you are seated in the classic British ‘L’ riding position. Where the gear selector on the Longstroke is stiff, the Model 5 shifts softly and easily (especially as the clutch releases fully). The power band is consistent and gradual, building speed with less drama than the Longstroke, yet never feeling sluggish, just mannerly. The engine is almost ‘square’ at 85x88mm, but the heavy flywheels keep it from feeling like a short-stroke. One might think it retrograde to add 20mm to the stroke for a racing machine, but as they won the TT with this new long-stroke engine, they knew what they were doing.

…unlike the Model 5, which has Sunbeam’s ‘little oil bath’ fully enclosed rear chain – they used this on their bicycles too. Also, this machine has footboards. [Paul d’Orléans]
The handling on the ’24 feels consistently smooth, with no change in feel from low to high speed; I wonder if the riding position has something to do with this? On the Lonstroke, my weight – which is only 50lbs less than the motorcycle – is much further forward, shifting the bike’s center of gravity towards the front wheel. The Druid forks have softer springs, for a more comfortable ride. The engines have a slightly different head/barrel casting (seen in the photos), and I of the would surmise that the Longstroke manages a higher compression ratio (6:1?) than the Model 5 (5:1?). Carb size is the same on both, with a choke of 1″. The earlier machine came fully equipped with acetylene lights front and rear (which work!), and a ‘little oil bath’ rear chaincase, a fully valanced front mudguard, a wider rear mudguard, and a luggage rack. James’ bike is probably 20lbs heavier than mine, but I’m probably 10lbs heavier than James, so the weight difference is a wash.

James Johnson with his 1923 Sunbeam Model 5 Touring. [Paul d’Orléans]
In the end, both Sunbeams have tremendous charm, and are full of the appeal for which Sunbeams are famous, as quality products that led the world in sporting events in the 1920s.  They both function amazingly well as motorcycle today,

Our Road Test bikes, plus my 1928 Sunbeam TT90, a revolutionary upgrade with a super-sports OHV engine. [Paul d’Orléans]
At the end of our test ride (or ‘shootout’ in moto-press speak), I rolled out my 1928 TT90 Sunbeam for James to try, for a REAL contrast. The 3 years between my Longstroke and the ’90’ are a lightyear in performance- with the later bike feeling, as James noted, ‘planted’ and stable, with about twice the power of the earlier bike, and a four-speed gearbox to boot. ‘We are probably the only people in North America to ride three Vintage Sunbeams in a day’, said James, and he’s probably right.


Paul d’Orléans is the founder of TheVintagent.com. He is an author, photographer, filmmaker, museum curator, event organizer, and public speaker. Check out his Author Page, Instagram, and Facebook.


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