Isomoto 125
Split Personality
If you’ve never heard of an Isomoto motorcycle, you’re not alone. When I spied this funny little bike with its tiny wheels in Classic Style Australia in Melbourne, I initially thought it was a home-made special. Then owner Jon Munn explained to me it was no such thing; it was in fact a pedigree Italian marque, and not only that, it was bloody fast. So I did some homework...
Renzo Rivolta was born in Desio, north of Milan in 1908, into a family of respected industrialists whose main business was milled wood products. In 1939 Renzo bought Isothermos, a small company producing refrigerators and heaters, and he moved the business to his family property – which included a magnificent villa on a large estate – in Bresso, near Milan, in 1942. The beautiful mansion still exists as Villa Rivolta.
The post-war boom in scooters did not escape Renzo’s attention, but rather than start from scratch he decided in 1948 to purchase the manufacturing rights to the Furetto, a 65cc two-stroke that used pressed steel bodywork over a tubular steel frame, with 12 inch wheels. In 1950, Iso introduced their own engine, a split-single two-stoke displacing 123cc. Four years later came a 236cc version, with forced lubrication and shaft drive. Iso became Iso Autoveicoli S.p.A in 1953 to more closely associate the company with motorised transport production.
The 236cc twin-piston engine and four-speed gearbox was used to power the Iso Isetta (Isetta being Italian diminutive for ‘Little Iso’), a ‘bubble car’ with a hinged front door and seating for two people. The Isetta (in 125cc form called the Isocarro) at first used two front wheels and a single rear, but the Isetta was prone to tipping over, so twin rear wheels spaced 48mm apart were soon added in the interests of stability. Around 20,000 of these little cars were made by Iso, but Rivolta’s stroke of genius was to licence the concept to several manufacturers in Britain, South America and Spain, but most notably to BMW, who used it to power their own Isetta, building around 130,000 from 1954 to 1962.
Iso continued with scooters and small motorcycles powered by an ever-expanding range of engines, from the 49cc two-stroke that was a clip-on fitment for bicycles, to a twin-cylinder horizontally-opposed 400cc four-stroke. The 400 was stretched to 500cc in 1961 but this model never went into production. By this stage Rivolta was easing out of two wheelers and into the luxury end of the car market, although some of the Iso models continued to be built in Spain under licence. The first car was the famous IsoRivolta GT, combining a fine-handling Italian chassis with muscle from a Chevrolet 5.5 litre V8. Initially, the cars were all powered by Chevrolet V8s with GM automatic transmission, but Ford engines were used from 1971.
When Renzo died in 1966 his son Piero took over the management of the company and relocated to a modern factory in nearby Varedo, but sold out to an American investor, Ivo Pera in 1973. The company was renamed Iso Motors and continued to produce fast road cars like the revered Grifo as well as contesting international Sports Car racing, and even Formula One when Piero Rivolta joined forces with a young English car dealer named Frank Williams, with sponsorship from Marlboro. When Piero sold the company, Williams continued with the cars and the team eventually became the Williams F1 outfit.
So what have we here?
The Isomoto was, as noted, a quick little jigger, with rapid acceleration, thanks to a fully fuelled weight of only 103kg, and a top speed of just less than 80 km/h. The engine is a 125cc split single, with one piston behind the other running on a common crank pin, with two bores in the cylinder barrel and a common combustion chamber. The second piston helps to fill the combustion chamber of the first, and expel gases through a second exhaust port, achieving very efficient fuel burning. Each bore was 38mm with stroke of 55mm. Carburation is by a Dell’Orto MA18BS, and ignition from a FILSO flywheel magneto. Power was quoted as 6.7hp at 5,200 rpm, with a three-speed foot-change gearbox. The split single, although popularised by Puch, originated with the Italian Garelli, first seen as far back as 1912.
The Isomoto 125, known as the Tourist, had a reasonably long production run, from 1951 to 1962. The basic model is characterised by the use of 12 inch wheels with 3.00 x 12 tyres, however a Sport model appeared midway through the production life of the model, with 4-speed gearbox in new crankcases, 19 inch wheels, lighter mudguards, longer travel front forks, conventional swinging arm rear suspension and
an expansion chamber exhaust system. The Tourist changed very little except for the adoption of the conventional rear suspension and an optional dual seat. Later a 150cc version also appeared.
The motorcycle featured here was imported by Classic Style Australia in Melbourne from the USA and is a 1952 model, as verified by the very official looking plate attached to the headlight bracket. The 12 inch wheels are interchangeable front and rear, with tiny spool hubs and 125mm brake drums, which remain in place when the wheels are removed. Front suspension is telescopic fork, with swinging arm rear suspension controlled by two springs located horizontally under the engine. A big selling feature was the Isomoto’s frugal appetite for petrol, returning 2.2 litres per 100km. With a tank capacity of 9.5 litres, you could do a lot of riding between top ups. This olive grey Iso found a new home shortly after the photos were taken, but Classic Style owner Jon Munn was so impressed with the little machines, and especially its performance, that he found another in the USA and brought it in with one of his regular shipments. So now there are two Iso 125s in Australia, or perhaps, more?