Ariel KH 500 Fieldmaster




Make Model

Ariel KH 500 Fieldmaster


1948 - 57


Four stroke, stroke, twin


498 cc / 30.4 cu in
Bore x Stroke 56 x 86 mm
Cooling System Air cooled
Compression Ratio 7.5:1
Lubrication Dry sump
Exhaust 2-into-2, Chrome


Starting Kick

Max Power

20.9 kW / 28 hp @ 6500 rpm
Clutch Dry clutch


Bruman 4-speed
Final Drive Chain
Frame Duplex loop

Front Suspension

Telescopic forks

Rear Suspension

Rigid, spring loaded saddle (as from 1957: swinging arm)
Wheels Steel, laced wire spokes
Front Rim 3.00 x 20
Rear Rim 3.50 x 19
Wheelbase 1422 mm / 56 in

Dry Weight

177 kg / 390 lbs

Fuel Capacity 

17 L / 4.5 US gal
Top Speed 145 km/h / 90 mph
Colours Chrome and scarlet enamel
Source Bonhams

Designed by Val Page, Arielís KH 500cc twin was produced between 1948 and 1957; starting out as the Red Hunter, becoming the Huntmaster and then the Fieldmaster (surely a name more appropriate for a tractor?), these revisions reflecting its change in role from sportster to tourer. At the time of its launch Arielís new twin seemed to have a bright future. With a top speed of around 90mph, the KH was as fast as a BSA A7 or Triumph Speed Twin, and a real eye-catcher with its red-and-chrome petrol tank. Judged solely on its looks, the Ariel should have been a winner. However, with no competition pedigree and an image that swiftly became one of stolid rustic dependability, itís no wonder the relatively expensive Ariel was never a top seller.

Although Pageís design was similar in layout to that of Edward Turnerís Triumph Speed Twin, using the same 63x80mm bore/stroke dimensions, it differed greatly in detail, particularly at the bottom-end where Page opted for a one-piece forging with bolt-on central flywheel rather than a built-up crankshaft. Like Triumph, the Ariel employed separate camshafts but with the pushrods at the four corners of the barrel, enabling cooling air to flow unobstructed between the cylinders. The transmission featured Arielís familiar dry clutch and Burman gearbox. A rigid frame was standard, with Arielís Anstey-designed rear suspension an option, while the design of the tele-forks was shared with parent company, BSA. In 1954 the KH came in for substantial revision, adopting the alloy cylinder head of the short-lived KHA model and a duplex-loop swinging-arm frame. Two years later the single-sided hubs were superseded by Arielís handsome full-width alloy ones and the KH continued in this form until the end of 1957 when the model was dropped. Its demise marked the end of the line for the true Ariel twin, although the BSA-clone Huntmaster continued until 1959.