How This 10.3-Liter, One-Cylinder Tractor ‘Runs’ at Zero RPM


Since it has no valves, the Lanz Bulldog’s engine can run both clockwise and counter-clockwise. There’s even a gauge to show you which direction it’s turning and, in some cases, that’s the only gauge—period. Rumor has it that many Bulldog tractors didn’t even have a reverse gear, so operators would simply reverse the engine by lowering the revs and kicking it the other way. It’s all pretty wacky, and you can see that as well as the unusual starting process in the clip above.

At the 20-second mark, the operator cranks the engine counter-clockwise, “bouncing” the piston off the compression phase and causing it to run the other way. Since the hot-bulb unit is capable of running so slowly, it can allow fuel in and combust it without completing a full rotation. Thus, it goes back and forth, “running” at zero rpm. 

For reference, the Bulldog featured in this video has a 10.3-liter engine making roughly 45 horsepower.

Hot-bulb engines can be cantankerous as the bulb itself needs to be kept warm enough for combustion. Under load with the throttle applied, this isn’t a problem as the constant combustion maintains the necessary temperature, which varies depending on the fuel you’re using. Many hot-bulb-powered tractors had auxiliary heaters that would keep everything at operating temps, and total-loss lubrication was the norm, though later Lanz tractors utilized a scavenge pump that drew excess oil from the crankcase and returned it to a separate reservoir.

We’ve long since engineered our way past this horizontal-moving oddity of a power plant, but it’s nevertheless cool to look back on. There might not be one on every corner in the States like there once was in Europe, but you could probably get your hands on one if you tried hard enough.

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