Bump starting

Bump starting, also known as push starting or pop starting, is the process of starting an internal combustion engine - typically in a motor vehicle - without the use of the starter motor. This can be useful when the starting battery is dead or the starter motor is broken.

The process is as follows. The vehicle transmission is placed in either first or second gear, and the clutch is depressed. The key must be in the run position. The car is then rolled forward either by gravity when on a hill or by additional persons or vehicles pushing. Once the car is moving 3-5mph the clutch is engaged abruptly. This causes the movement of the vehicle to drive the engine back through the transmission. This will turn the engine over in much the same way as the starting motor would. Once the engine has started, the clutch can be quickly disengaged to avoid stalling the car, but this is not always necessary.

Bump starting a car is typically only possible in manual transmission vehicles, as automatic transmissions often rely on hydraulic transfer of power from the engine to the gearbox for their operation.

Urban legend

There is an urban legend about a stranded motorist who attempts to push start his car by having another car push his up to the speed required. It dates to the 1950's. [http://www.snopes.com/autos//techno/pushcar.asp]