ARIEL SQUARE FOUR - RED HUNTER
The Ariel Square Four was the brainchild of Edward Turner, perhaps the most
commercially successful designer the motorycling world has known (he gave us
the Triumph Speed Twin, its descendants, the Cub, the Tina and the Tigress
Scooters).
The square layout was conceived to make a four fit a conventional frame. The prototype 500, way back in 1928, was so compact that even with a unit gearbox it slotted into the current 250 Ariel frame. Beefed up and separated from the gearbox, the first production 500 (1931, overhead camshaft) fitted the frame employed for the big-single range. It was enlarged to 600 cc the next year but retained a tendency to overheat. For 1937 it was redesigned with pushrod valve operation and enlarged to 1000 cc, a 600 cc version being added later.
For 1950 the switch to light-alloy for the cylinder block and head saved weight but brought problems with head holding-down studs. A further redesign of the head to produce the 4-port Mark 2 version was undertaken before production ended with the concentration on the Leader twostroke design. The early ohc engines had overhung cranks with the crankshafts coupled by centrally-mounted spur gears. The pushrod engines had full crankshafts and coupling gears on the drive side. Noise from the coupling gears was always a problem and fibre rings were rivetted to the gears to damp the sound. Though capable of approaching 100 mph in 1000 cc form it was not an engine amenable to tuning. It is shown here in its alloy 2-port form for the 1950 season, complete with coil-ignition distributor and concave pistons to suit the Pool petrol of 4. the day.
The square layout was conceived to make a four fit a conventional frame. The prototype 500, way back in 1928, was so compact that even with a unit gearbox it slotted into the current 250 Ariel frame. Beefed up and separated from the gearbox, the first production 500 (1931, overhead camshaft) fitted the frame employed for the big-single range. It was enlarged to 600 cc the next year but retained a tendency to overheat. For 1937 it was redesigned with pushrod valve operation and enlarged to 1000 cc, a 600 cc version being added later.
For 1950 the switch to light-alloy for the cylinder block and head saved weight but brought problems with head holding-down studs. A further redesign of the head to produce the 4-port Mark 2 version was undertaken before production ended with the concentration on the Leader twostroke design. The early ohc engines had overhung cranks with the crankshafts coupled by centrally-mounted spur gears. The pushrod engines had full crankshafts and coupling gears on the drive side. Noise from the coupling gears was always a problem and fibre rings were rivetted to the gears to damp the sound. Though capable of approaching 100 mph in 1000 cc form it was not an engine amenable to tuning. It is shown here in its alloy 2-port form for the 1950 season, complete with coil-ignition distributor and concave pistons to suit the Pool petrol of 4. the day.
The 1936 Ariel 500 cc Red Hunter
Why Ariel chose a horse as a motif in the Thirties is a mystery,
unless it was intended to suggest horsepower. But it led to the name Red Hunter
for their first out-and-out sports model in 1933, a name that came to be well
respected amongst riders of fast machines though the firm never ventured into
the racing field. The first Red Hunter was a four-valve 500 which could top the
90 mark but this was soon shelved in favour of two valvers.
By 1936 the design
was becoming tried and trusted with a longstroke 81 x 95 mm configuration and a
choice of single or twin exhaust ports. In deference to the then current fad
for enclosure of the valve gear, Ariel hurriedly arranged little cannisters to
enclose the springs and clip-on covers for the rockers. This gave them time to
go back to the drawing board and design a new cylinder head to take a
cast-alloy rockerbox for 1937. That provided true enclosure and lubrication
which was to serve them well right up to the Fifties.
As an example of clean-cut
no-nonsense design, typical of the best-selling bikes of the post-vintage era,
the Selly Oak Red Hunter is outstanding. It was robust, durable, reliable and
oiltight. It gave good performance whithout harsh manners and returned a
creditable fuel consumption. The Ariel marque is part of the Norton Villiers
Triumph empire today — C.E.Allen.
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