If you have a modern bike, the chances are it has double overhead cams (DOHC) and four valves per cylinder. Though it’s the norm today, you may wonder where the technology originated. Maybe from the Grand Prix racing bikes of the 60s like the famously noisy Hondas?
If you’re interested in older bikes, you may even point to the Triumph-Ricardo of the 1920s, developed by Sir Harry Ricardo, but that still used pushrods. The four-valve Rudges of the 1930s used single OHC so they don’t qualify either. In fact, the first motorcycle with DOHC and four valves per cylinder was the Peugeot 500M introduced way back in 1913.
Imagine the impact that must have made on the early motorcycling world when most motorcycles still looked like they were derived from bicycles, typically with side-valve single-cylinder engines and many with pedals so the rider could assist the asthmatic motor up the steeper hills. It would have been like turning up to the Ace Café in the 1960s with one of today’s superbikes.
The 500M was an air-cooled 500cc parallel twin, inspired by the water-cooled four-cylinder car engines developed by Peugeot for racing. The motorcycle engine used a one-piece cast iron head and barrel with the cams being driven by gears running between the cylinders from the centre of the crankshaft. Though simple and without joints, the downside to this one-piece design meant even the simplest maintenance required a complete strip down.
Both the car and motorcycle engines were designed by a Swiss engineer, Ernst Henry, working out of a ‘skunk works’ within Peugeot’s Paris aero engine factory. No doubt the variety of aircraft industry suppliers in the immediate vicinity was a big help in getting the prototype engines together.
A 500M was timed at over 75mph in 1914 - a world record, but its competition lifespan was sadly cut short by the outbreak of WW1. After the war, the motorcycle passed through various evolutions, winning some races before Peugeot abandoned motorsport when the car and motorcycle brands separated in 1926.
So why didn’t the 500M set motorcycle engine design in a new direction? Basically, the alloy metals and lubrication that were available at the time were not advanced enough to make the engine reliable. In later evolutions the engine was simplified to just two valves per cylinder and with only a single OHC. It was no longer as advanced, or as powerful, but it was reliable.
Practicalities aside, the thinking behind the early Peugeot twin was brilliant, if too advanced for its day. The genius of Ernest Henry paved the way for race engines and technology to come, which makes this bike a sure contender for the title of a Milestone Motorcycle.
Do you agree? Let us know what you think in the comments below.