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.


vintagent said...

Although I have no intention of racing my Ariel VB (55 engine, rest of the bike is older) I am toying with the idea of setting it up for the new E85 alcohol fuel. I think Hartley etc often used alcohol fuel, and alcohol needs a raised compression ratio. Raising the comp ratio on a VB would appear to mean replacing the cylinder head – and I happen to have a large block of aluminum and a milling machine……..
Do you have any info on what kind of comp ratio would be needed for alcohol fuel, and what combustion chamber shapes work best?

Anonymous said...

Laurence Hartley ran a motorcycle shop (Carter and Hartley) in
Plumstead, South East London. He tuned bikes with much success,
particularly Ariels, usually Red Hunters, and concentrating on the use
of alcohol based fuels.

As I was told it, the fast 1926 sidevalve Ariel was the result of
Hartley saying he could get a sidevalve engine as fast as an OHV one
given equal compression ratios. He was challenged to prove it. He
bought an old sidecar outfit from a local tradesman, sold the sidecar
and tuned up the bike. As far as I know it was always run on alcohol
fuel, even on the road.

It legendarily earned Jock West a good few bob from lads who didn't
recognise him or the bike. The bike's scruffiness and "old" appearance
played a part in this.

My dad was a friend of Laurie and was offered the bike at the start of
WW2 but sadly he said there were other priorities at the time!

Pat Jeal

Andy Brown said...

In the late 1960s after Carter had left for Australia, Laurence Hartley was running down the business, but opened the shop a couple of days a week, and was very happy to talk of his views and experiences in engine tuning and bike preparation. I was lucky enough to spend several afternoons talking with him, and obtained some special flywheels from him for a Matchless OHV V-twin. He talked of his SV Aerial, and some of the experiments carried out with it. One was to find the effects of polishing the flywheels, conrod and timing gear, the result being a 1mph increase only on a Brooklands lap. He also maintained that the best shape for an exhaust valve was absolutely flat within the combustion chamber to give minimum area to hot gasses, and that any engine whatever the compression ratio would always perform better on alcohol fuel than on petrol. He was meticulous about eliminating friction and vibration as they waste power and also insisted on necessity for good crankcase breathing to eliminate pumping lossaes. Talking of breathers, he told the story of one failed Brooklands record attempt, when he appeared to run short of fuel on the final stage, and found that the culprit had been a bee that had been attracted by the smell of alcohol and had crept up his fuel tank breather pipe and blocked it, causing a vacuum in the tank as the fuel was used up! Subsequently he put little gauze baskets at the end of all breather pipes.I am fairly sure he said that his original intention with the SV Aerial was a lap of Brooklands of 90 MPH, which he certainly did.