1948 Ariel Sq. 4 Mk 1

With Ian Falloon

Though a four-cylinder motorbike is regular right now, it wasn’t all the time so. Earlier than World Battle II inline fours, with the engine lengthwise, had been thought-about unwieldy, and across-the-frame fours too large.

Then someday in late 1928 a London motorbike seller named Edward Turner sketched the thought of two parallel twins two by two on the again of a cigarette packet.

Turner made a visit to the Midlands attempting to promote the thought, and whereas BSA practically purchased it, it was Ariel that offered Turner a small drawing workplace and the assets to see his thought to fruition.

Turner went on to grow to be arguably probably the most influential individual within the British motorbike trade, and his square-four, or Squariel, grew to become a legend in its lifetime.

The primary manufacturing square-four appeared in 1931 and was a cast-iron 500 with a chain-driven single overhead camshaft. The fundamental structure of cylinders on the corners of a sq. with two 180 diploma crankshafts geared collectively and contra-rotating would set the sample for the longer term.

To make the engine extra appropriate for sidecar use a 600 cc model was added in 1932, however there have been many issues with the preliminary design.

Early square-fours didn’t take to tuning, and though Ben Bickell managed to lap Brooklands at over 175 km/h his supercharged 500 saved blowing cylinder head gaskets and he by no means completed a race.

Comparable issues befell Somerville Sykes within the 1931 Senior TT. His blown 500 cc square-four produced 40 horsepower however he retired with a blown cylinder head gasket.

To beat these issues the square-four engine was utterly up to date for 1936. Though the brand new engine retained the two-by-two cylinder format, in most different respects it was completely revised.

As a substitute of the sooner overhead camshaft the valves had been now pushrod-operated. The crankshafts had been coupled by outboard gears on the left aspect and the big-end bearings modified from curler to white steel in light-alloy connecting rods.

The capability was elevated to 1000 cc, and the burden decreased. Aside for a sprung hub that grew to become an choice in 1939, the square-four continued till the outbreak of struggle largely unchanged.

Resurrected after World Battle II, the square-four initially retained the cast-iron 65 x 75 mm 997 cc engine of the pre-war Squariel. However the addition of telescopic entrance forks and the compensated-link plunger rear springing noticed the primary post-war fashions now weighing over 225 kg.

Ariel figured it was time to shed some weight and for the 1949 Mk 1 the previous cast-iron cylinder block and head had been scrapped and substituted with alloy castings. The claimed weight saving was an optimistic “half a hundredweight” (25 kg), however the true weight saving was 15 kg.

The redesigned alloy cylinder head now included 20 fixing factors as an alternative of 12 and integrated the rocker packing containers and inlet and exhaust manifolds. The alloy castings additionally improved cooling and with 6:1 compression ratio, to deal with the 72-octane “pool” petrol, and an automotive model bi-starter Solex carburettor, the ability was 34.5 horsepower at 5400 rpm.

Coil ignition, with a car-type distributor, and a big 70-Watt separate dynamo changed the Lucas Magdyno. As on the pre-war examples lubrication was dry sump and the gearbox a four-speed Burman.

The brand new engine additionally improved the Squariel’s legendary attribute; its acceleration. The rotary twist grip offered unusually delicate throttle management, this mixed with comparatively low flywheel weight and 4 cylinders giving prompt response. The lighter engine additionally contributed to marginally improved dealing with and liveliness however the engine was all the time an excessive amount of for the body.

The Mk 1 body was half cradle, and with an oil-damped telescopic entrance fork, and with the choice of an undamped plunger hyperlink sprung hub the burden was 197 kg.

Inflexible body variations weighed 187 kg. Rolling on a 1422 mm wheelbase the Mk 1 Squariel was a surprisingly compact machine for its capability.

The tyres had been additionally fairly massive for the day at 3.25 x 19in entrance and 4.00 x 18in rear. The four-pipe Mark II Sq.-4 appeared in 1954, lasting till 1958.

All later Sq. Fours had plunger rear springing, though two prototype pivoted-fork fashions had been constructed however not put into manufacturing.

With manufacturing spanning 27 years Ariel’s square-four was by no means a mainstream motorbike. Revered for its smoothness, consolation and acceleration, the Squariel was all the time costly and appealed as a standing image slightly than common transportation.

After manufacturing had formally ended George and Tim Healey began making their very own spares and in 1973 launched the Healey square-four with an Egli-designed body.

Solely 20 Healeys had been manufactured, the final in 1977. Ariel Sq.-4 engines had been additionally produced beneath licence in Canada and utilized in pairs to energy helicopters. Finally an absence of improvement resulted in square-four’s demise however now it’s acknowledged as one among Britain’s best basic bikes.