Sunday, June 08, 2008
The 'humble' side-valve single was officially rendered obsolete in 1922, when Sunbeam won the last TT with this type of engine. Not.
Although the flathead single never again won the TT, dogged tuners continued to cultivate speed through the 1930's and beyond.
Everyone knows, or should know, that Norton singles were considered the ne plus ultra of racing singles in the Pioneer and early Vintage era, thanks mainly to the exploits and tuning skills of Don O'Donovan (top photo), who worked for Norton until the mid-1920's, tuning their BS (Brooklands Special - an example of which he is astride) and BRS (Brooklands Road Special) 500cc models. Each machine was timed at the eponymous track and guaranteed to have reached 75mph. On June 14, 1915, this photo was snapped after taking the flying-start kilometer record at 82.85mph. This is a single-speed, direct belt drive machine, with no clutch and almost no suspension - quite a feat. After he was married and had a child, D.R. O'Donovan gave up racing, and took up tuning Nortons for others, including Rex Judd, Albert Denly, and Chris Staniland, all of whom took important speed records on the machines he tuned.
This charming photo from July 9, 1921, shows O'Donovan in the saddle, with his protege Rex Judd in the lightweight sidecar. The racing team is standing under a Japonism-era paper parasol (a rare hot day in Byfleet), with Judd resting on his elbow, looking 3 decades out of place among the Edwardian gents, with his black turtleneck and casual air. Judd would have lain prone in the chair during the race, as passengers were essentially ballast at Brooklands, unlike the 'monkey' antics of sidecar road racing. Very few of these 'chairs' survive in original condition, as they were built solely with light weight in mind, and the wood or canvas or paper cladding didn't last long. I had an aluminum chair of this general layout, which weighed less than 100lbs - one with a canvas skin might only be 65lbs total. And yes, the sidecars were pretty wobbly when that pared down - only the TT Hughes (with 6 chassis fixing points and a full cage of tubing around the passenger) handled well over Brookland's bumps.
After O'Donovans retreat into development, Judd became Norton's works tester. Interestingly, only the engines on the BS and BRS models were tested, not the whole motorcycle. The engines were placed serially in O'Donovans belt-drive 'hack', nicknamed 'Old Miracle'; something like 25 engines per month were so tested.
Here is Judd on the new 16H model, distinguished by a 3 speed Sturmey-Archer gearbox and clutch.
The date is March 29, 1921, and he has just won 35 Guineas for having covered the flying kilo at 92.44 mph.
[I'm still looking for a photo of A.L. Loweth's 1930's 16H, with which he recorded an all-time sv lap record at Brooklands in 1934. Anyone have one?]
We're skipping ahead in time now to the mid-30's, where legendary tuner Laurence Hartley has turned his attention to a 1926 Model A Ariel. Hartley was famous for tuning up sv and ohv Ariels to go indecently fast, and his machines were winning races and astonishing riders of 'superior' machines into the 1950's (a gentleman named Ferbrache especially loved to goad the 'ton-up boys' at the Ace Cafe with his ancient and filthy Hartley Ariel, winning many bets on point-to-point races).
The machine in these two photos was property of Jock West, later well known for racing works Nortons and coming second at the '39 TT on a supercharged BMW, behind George Meier.
This Ariel Model A lapped Brooklands at over 80mph, and was timed over the flying kilo at 95.54mph. Reputedly Jock took this machine to 97.7mph in 1957, which was the highest speed ever attained by a sidevalve single at that date. It's set up for the street in these pics, with an Enfield 8" front brake and full mudguards. Hartley's machines always seemed the opposite of, say, the immaculate all-nickel bikes of Bill Lacey - in photos they're gloriously scruffy. Note the sheet behind the bike in the second photo; as mentioned in an earlier post, sheets were often waggled behind a motorcycle in a photograph, in order to ease the re-toucher's job, for publishing the bike on a white background in a magazine.
Last photos are from an article in Classic Bike (November 2001), and show a 500cc BSA M20 which has been radically tuned by owner Bill Gough of Australia. Gough, in typical Aussie fashion, built amazing hotrods from humble origins, and decided to break 100mph on a flathead. Compression was limited to 6:1 by the combustion chamber shape, the flywheels were homemade but the rod and piston were standard, the crank was balanced at 66%, and the 2.5" inlet valve was fed by two 1 1/8" Amal TT carbs (!) for maximum breathing potential, helping it to rev to 9000 rpm in the low gears. In February 1960, the bike was timed at 104.6mph on the beach.
He made additional tuning efforts using a 1935 BSA M20, which had a better combustion chamber shape (enabling 8.5:1 compression), and he estimated a top speed in the 120mph range on a harder surface than sand, although I don't know if he was successful.