For a couple of decades before and after the war, if you really wanted to go fast then you needed an overhead cam. Paul Miles rides two black-and-gold beauties back to back, and dares to suggest which one is the better…
For a couple of decades before and after the war, if you really wanted to go fast then you needed an overhead cam. Paul Miles rides two black-andgold beauties back to back, and dares to suggest which one is the better…
Many long summers ago, as a novice rider, I sat listening to the greybeards discussing the riding sensation of a ‘cammy’ Norton. At the time it seemed odd to single out a Norton. After all, aren’t all four-strokes equipped with camshafts? Older (much) and wiser (…erm) I now understand they were referring to a particular type of Norton single, the ohc International.
Why overhead cam? To win races, cammy engines rev higher and faster, meaning more power. They also cost far more to produce, especially back in the days of skilled labour working on simple machinery. This exotic and expensive design effectively precluded the sale of ohc machines to the general public, the limited production almost entirely being reserved for the racing fraternity. Other manufacturers also produced ohc racing singles to devastating effect, notably Velocette in the 350cc class. Where there’s a wallet there’s a way, however, and a small number of machines from each marque tricked onto the market and into the hands of the well-heeled enthusiast.
I was recently fortunate enough to have fine examples of both Velocette and Norton’s bevel-driven loveliness in my shed with the opportunity to compare them – too delicious a prospect to resist. Although different in capacity (one a 350, the other a 500) and year (with the Velocette being the last model produced before the war and the Norton the first after hostilities had ended), they both exemplify the ‘handbuilt for sporting enthusiasts’ axiom.
‘Win on Sunday, sell on Monday’, the saying goes. Nobody clung to it more than Velocette and their racing machines were very successful, the 350 cammy single being an especially potent weapon. For road use, though, the factory would rather your valves
were operated by pushrods. Rumour had it that Veloce Ltd lost money on every new ohc bike produced for retail.
Designed by Percy Goodman in 1924, the K (Kamshaft) models were powerful and reliable racers, with the over-the-counter KTT crowding the grids at racetracks around the world. TT winners in 1926, 28 and 29, their prowess was easy to spot. By 1936, the Mk2 version, including an all-alloy engine with enclosed valves, was offered for sale. Available in two forms, the KSS (super sports) had larger wheels and skinnier mudguards than the otherwise very similar KTS (touring sports).
The KTS you see on these pages emerged from the factory in 1939 and the four-speed, 25bhp, 265lb machine rests on 19” wheels protected by heavily valanced mudguards. The differences between the two models effectively ended there. This example has only had three owners in its near 80-year life and has never been fully restored. Wearing its age astonishingly well, it looks every inch the quintessential pre-war British aristocrat. Quality exudes from every casting, the lines of the tinware and overall fit and finish. High end 1930s machines benefit from the decades of skilled craftsmanship coupled with emerging new technologies and a mentality where price is secondary to product – something we see the almost total inversion of in the post-war era. It was described to me as a ‘gentlemen’s express’ and is, perhaps, the two-wheeled equivalent of a Bentley.
Starting a Velocette is often fraught with drama and I feared the worst, but, provided the instructions were followed to the letter, the narrow-crankcase cammy fired up first kick virtually every time, settling quickly into a rock-steady idle. The almost-too-quiet engine rustling its camshaft, offset by the gentle chuff from the fishtail, the KTS seemed too, well, nice, to be considered a roadgoing racer.
The four-speed, positive-stop gearbox, another Velocette first, proved beyond criticism, as was the faultless clutch. The troublesome nature of post-war Velo clutches reflects, perhaps, the company’s changing attitudes towards profit, rather than innate poor design.
The KTS’s performance was bright, with power building steadily and the engine feeling unflustered. Gear ratios were well spaced allowing it to quickly reach its natural cruising speed of… 55mph. The handling and brakes were as good as almost anything I’ve ridden from the era and complemented the performance perfectly.
Utterly delightful to ride, gently chuffing around the Dorset lanes, feeling unbreakable and relaxing to ride, it was hard to believe this sophisticated single, albeit one of relatively modest capacity, could in the right hands be a potent racing weapon, capable of being hurled around the TT course. And yet, the robustness Velocette had engineered into their ohc machines meant precisely that, with the cammy engine reliably delivering whatever performance it had all day long. To finish first, one must first finish and all that.
I have little doubt the KTS would have steadily motored me to John O’Groats without complaint or special preparation, it was that good. But it would prefer to do so at 50mph, with the 80mph top speed being reserved for special occasions only.
NORTON MODEL 30
Norton’s ohc engine, like the Velocette, also originated in the roaring Twenties with the CS1, although the exposed hairspring valve International model first appeared in 1931. Technically available as a roadgoing machine, the Inter was really the preserve of racers, both factory sponsored and privateers, with riders like Stanley Woods and Jimmie Guthrie becoming household names in the era. Factory racing specification didn’t really filter into the road machines as so few were actually purchased as pure roadgoing motorcycles, but by 1938 the racer could specify plunger rear suspension, the new Roadholder telescopic forks and an all alloy engine – providing he knew the right people to ask.
So fast and rugged was the Inter that Model 30s were issued to the military police, under the control of Sir Malcolm Campbell, for fast protection of the Royal family should they need urgent evacuation in the event of a German invasion.
WW2 ended production of course and it wasn’t until 1947, the model year of this machine, that ohc production finally resumed. Available in two capacities, 350cc (M40) and 500cc (M30) Norton had finally begun to standardise specifications. All machines now came equipped with the ‘garden gate’ plunger frame and long Roadholder forks. The engine was only available in iron head and barrel form, and a close ratio gearbox was supplied as standard.
The Model 30 500cc machine on these pages is an older restoration. Like most other Inters it has some racing history, and was entered for the 1947 IoM TT. Restored to road specifications around 30 years ago it is fairly representative of an ex-factory road machine, although some of the controls are pattern. The 29.5bhp Norton
Above: Velocette’s camshaft single, seen here in road-going KTS form, apparently the TS stands for Touring Sports. Seems fair Left: Veloce certainly understood who rode their motorcycles!
Velo’s 1939 brochure reveals that the engine could be supplied either a with a compression ratio of 7.5:1, making it suitable for ‘ethyl spirit’, or 8.4:1, suitable for a 50% petrol / benzol mixture. Times change
And here’s how that engine works. It all looks simple to 21st century eyes, but making these relatively complex machines work reliably in the 1930s was not easy at all
The engine, most definitely the major selling point of ohc machines in those distant days
Velo’s ohc singles used essentially the same transmission arrangements as the ohv machines. The primary chain runs inboard of the clutch, and the front chaincase extension contains a belt drive to a Miller dynamo, which in turn has its voltage control...
No shot of a Velo single – any Velo single! – is complete without the fishtail
View from Velo heaven, reveals the sportingly bare handlebar layout, and the top links of the girder forks