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1933 The Mighty Atom; Gibbons, J.S.; 1933; CMM224

1933 The Mighty Atom; Gibbons, J.S.; 1933; CMM224
Name/Title
1933 The Mighty Atom
About this object
The diminutive and unique ‘Mighty Atom’ was hand built by a Mr J.S. Gibbons of Onehunga, Auckland, New Zealand, around 1933. He hand crafted many of the components, including the frame and stamped his name in the brass fuel tank cap. Much of the information mentioned here was printed in the 1st August, 1933 edition of NZ Motor Cycle magazine, as quoted in New Zealand’s Motorcycle Heritage, Book 2: 1932-1962 by M.A. Bull.

The frame and front fork are fabricated from 1/6-inch sheet steel pressed to channel section with solid lugs and welded corner pieces. A single, central spring is employed on the front fork using the Webb principle. The 8-inch wheels are fitted with aeroplane section tyres and the rear wheel is equipped with an external contracting brake that is entirely home-made. Its wheelbase is only 31 inches (788mm) and the saddle height is only 18 inches (457mm).

The overhead-valve, two-port engine has been built using a mixture of parts. The crankcase is an A.K.D. (Abingdon King Dick of Birmingham) item with an external flywheel and a previous owner, Charlie Emmerton of Ellerslie, Auckland, was of the opinion that it was out of a Rex Acme motorcycle. Rex Acme used an A.K.D. overhead-valve, 173cc engine in a 1926 model. The cylinder is of unknown origin but it is fitted with a liner and an alloy piston. With bore and stroke both of two inches, its swept volume is 103cc and the compression ration is estimated at around 7:1.

The two-speed gear cluster has been fitted within a Douglas gearbox shell with the gears cut to accommodate a cork clutch within the narrow width of the frame. It features all-chain drive and the carburettor is an Amac unit. Mr Gibbons said that he used the Mighty Atom daily and had already ridden it about 600miles (965km) when interviewed by NZ Motor Cycle magazine, suggesting that he had completed it not long beforehand. He claimed that is had repeatedly matched the speed of a car doing 38mph (61kph) and that it was capable of 50mph (80kph).

It was acquired for the NZ Classic Motorcycles collection at auction in Auckland, NZ, in March, 2009. It was acquired by Transport World for their Classic Motorcycle Mecca collection in May 2016.

Maker Role
Manufacturer
Date Made
1933
Object number
CMM224

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