Iso­moto 125

Old Bike Australasia - - CONTENTS -

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?

RIGHT Wheels are in­ter­change­able; hubs stay in place when the wheels are re­moved. BE­LOW RIGHT Orig­i­nal muf­flers; very hard to come by. ABOVE Swing­ing arm rear sus­pen­sion with springs un­der the en­gine. RIGHT Rear frame sec­tion could ac­com­mo­date a pil­lion seat or a lug­gage rack. Bat­tery and tools re­side in cen­tral case. The split-sin­gle en­gine, with one pis­ton be­hind the other.

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