By David Beare
It is unlikely that Louis Delagarde, the designer of Panhard’s flat-twin engine, could have foreseen the scale of competition successes his diminutive power-unit would achieve when he began work at his drawing-board during the dark days of World War II.
Delagarde’s brief from Jean Panhard was to create a small-capacity, simple, lightweight engine to power and equally simple, lightweight economy car which could eventually be sold to French motorists come peacetime- whenever that might be. At the time an invincible Nazi Germany was offering the world a one thousand-year Reich so the signs were not at all promising. Delagarde was a life-long motorcyclist and recognized the inherent advantages of horizontally-opposed pistons (balance) and air-cooling (simplicity) – much as had Ferdinand Porsche with the KdF-wagen, aka the Volkswagen Beetle, in 1934.
Additional wartime problems to be solved when drawing up Panhard’s new engine included scarce and poor-quality materials such as gaskets, white-metal for bearings, spring-steel wire for valve springs and lubricating oil. Delagarde had to design his way round these limitations and in so doing came up with a unique series of solutions. “Run” crankshaft bearings were a common occurrence so his solutions were roller-bearing rod big-ends with ball-bearing mains, the unbreakable heart of Panhard’s engine. The rod roller bearings were a new design which incorporated small inverter rollers between load-bearing rollers, so everything turned in the same direction, allowing sustained high revs- something future race car builders would much appreciate. Other advantages were low friction losses and oil quality not being so critical with roller and ball bearings, though manufacturing costs were unfortunately much higher than with conventional bottom-ends, as would be replacement crank & rods assemblies when they eventually wore out.
Head-gasket failure- again very common- was eliminated by the simple expedient of using cylinders without detachable heads. The absence of mating surfaces for gaskets meant large valves in hemispherical combustion-chambers could also be used, maximizing gas flow. Unreliable valve-gear had long given engine designers headaches (one reason Panhard had used Knight sleeve-valves since 1910), with breakages of helical-wound coil valve-springs or valves being commonly responsible for many a wrecked engine. Delagarde bypassed most of these problems in a unique way, by using unstressed slim torsion-bar valve return springs. The weight of the valve-spring itself did not move up and down with the valve, reducing inertia loadings and valve-float at high revs. The torsion-bars were linked at their free ends, thus increasing closure pressure on the shut valve when the other opened.