Great Bikes?

No 1. The MGC, France, 1935

MGC N3BR. 1932. 250cc

We take aluminium very much for granted these days and cast aluminum components of a motorbike chassis are nothing unusual; any number of bikes have them. But it was not always so.

Aluminium was widely adopted in industry – particularly by motor and motorcycle manufacturers - after WW1 for its light weight, good heat conductivity and shine. However, it lacks, especially in cast form, steel’s ability to resist vibration fatigue. It would take years of foundry progress before cast aluminium could be widely used in motorbike chassis and an equally long time before engine refinement reduced vibration to an acceptable level to make use of the material a viable proposition.

The principal casting comprising the tank, top frame member and headstock.

Marcel Guiguet was a French motorcycle dealer who became obsessed with the idea of casting as a single piece many of the previously separate structural and functional frame components of a motorcycle. His idea was to enclose the engine between an upper member comprising the tank, headstock and chassis beam and lower member which comprised the oil tank and the lower frame structure extending back to the rear wheel, the two joined by vertical aluminium struts.

Showing the various pieces of the puzzle. As well as
 the main tank structure, all other components were
also cast from aluminium. 

The early castings were porous and prone to cracking from shrinkage – no-one had attempted large hollow, thin-walled castings before. His material of choice was a high silicone alloy called Alpax, and he eventually cured the porosity with heat treatment and drying oils. The parts were still prone to cracking in use, however and, even when current, the survival rate of machines was low; the skill to weld aluminium successfully without distorting the structure simply did not exist in the workshops of the day.

Production began in 1929, the machine called the MGC – Marcel Guiguet & Co.

Proprietary and familiar engines - mainly the British JAP 500c single – were used so at the 1928 Paris Salon all eyes were on the revolutionary chassis.  

Nothing like it had been seen before and it generated great interest but the bike was a financial flop – it was simply too expensive to produce and only around 200 were made and that was the end of MGC.

Exceptionally narrow frontal aspect

He had started something, though. But the world had to wait more than 50 years for the MGC frame concept to become viable through increased knowledge and techniques with aluminium and it was the 1985 Suzuki GSX R 750 that heralded the true dawn of the age of extruded and cast aluminium beam-framed bikes. 




























This article first appeared in www.iauto.co.za