Simanaitis Says

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YESTERDAY, LAURENCE POMEROY’S book The Grand Prix Car and William Court’s piece in Classic Cars in Profile, Volume 4 offered introduction to the racing Peugeots of 1912–1913. Here in Part 2, we see how au courant these French cars of more than a century ago are today.

Desaxé Designs. Pomeroy notes that the Peugeot cylinder block was “mounted markedly desaxé in relation to the crankshaft with a view to reducing thrust losses in the pistons, these being of steel, weighing 32 ounces…” The French word desaxé means “off-center,” implying an offset of the cylinder bore with respect to the crankshaft centerline.

This practice originated with heavy steel pistons of the era. Lighter ones of aluminum first appeared in World War I aero engines. Plenty of engines today display desaxé layouts, including those of the Toyota Prius as well as Honda and Kawasaki motorcycles. The 1930s’ Ford Flathead V-8 was another.

Art of the 3-liter Peugeot. One of the many fine plates illustrated by L.C. Crestwell for Pomeroy’s The Grand Prix Car. Crestwell’s art has previously appeared here at SimanaitisSays.

Inclined Valves. Inclination of the four valves, two for intake, two for exhaust, gave a hemispherical combustion chamber with room for a centrally mounted spark plug. Both of these features promoted good breathing and optimal combustion.

Pomeroy estimated that the 7.6-liter Peugeot produced perhaps 130 hp at 2200 rpm; the 3.0-liter engine, perhaps 90 hp at 2900 rpm. By comparison, earlier Grand Prix engines of larger displacements were decidedly lower-revving: Pomeroy cited the 1908 Italia 12.0-liter engine producing its 100 hp at 1600 rpm; the 1911 Fiat 10.0-liter, 120 hp at 1650 rpm.

Details of the 1912 Peugeot’s twin-camshaft drive. Illustration by L.C. Crestwell in The Grand Prix Car.

“Stirrup” Tappets. The Peugeots’ dual overhead camshafts actuated the valves through D-shaped “stirrup” tappets.

A Peugeot “stirrup” tappet, with its clearance adjustment and return spring. Illustration by L.C. Crestwell in The Grand Prix Car.

The cam rotating within the inner surface of the D produced both a downward motion opening the valve as well as an upward motion. The latter gave it something of a valve-closing desmodromic action, aided by a tappet return spring.

In reviewing racing Peugeots of the era, William Court noted in his Profile article, “… between 1912 and 1919, they won fifteen out of nineteen major races for Grand Prix pattern cars. It is a record not lightly to be gainsaid or trifled with.”

Laurence Pomeroy concluded his analyses with, “In addition to their performance, these car were astonishingly reliable and they set a trend in design which lasted for many years.” ds

© Dennis Simanaitis,, 2019

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