If you go back a couple of decades, almost every jumping jack on the jobsite was powered by a 2-stroke engine. They were loud, they belched blue smoke into the trenches, and if the "greenhorn" on the crew forgot to mix the oil into the gasoline perfectly, the engine would seize and die before lunch. Today, the industry has almost universally transitioned to premium 4-stroke overhead cam (OHC) gasoline engines, and from my perspective as a veteran operator, it is one of the best upgrades the industry has ever seen.
The modern 4-stroke engine on a high-operating efficiency impact rammer brings a level of reliability that is mandatory when you are racing a concrete schedule. First and foremost, you run straight, unleaded gasoline. There is no mixing, which eliminates the number one cause of operator-induced engine failure. Secondly, 4-stroke engines offer significantly better low-end torque. When a machine is lifting itself off the ground 600 times a minute, it needs torque to maintain that rhythm when the soil gets sticky and tries to suction the shoe to the ground.
Furthermore, these engines have been specially modified by the manufacturers to survive an environment that would destroy a standard lawnmower engine in a day. The carburetors are heavily shielded from vibration, the fuel lines are reinforced against harmonic fatigue, and the oil lubrication systems are designed to function even when the machine is tilted at aggressive angles in a steep ditch. They run cleaner, which is a massive safety benefit when you are working down in a hole where exhaust fumes tend to pool. The 4-stroke revolution made the dirt crew's life easier, cleaner, and vastly more productive.
