Push start
Push starting, also known as bump starting, clutch starting or crash starting is a method of starting a motor vehicle with an internal combustion engine by engaging the manual transmission whilst the vehicle is in motion.[1] The technique is most commonly employed when other starting methods (automobile self starter, kick start, jump start etc.) are unavailable.[2]
The most common way to push start a vehicle is to put the manual transmission in second gear typically, switching the ignition to on/run, depressing the clutch, and pushing the vehicle until it is at a speed of 5 to 10 mph (8 to 16 km/h) or more, then quickly releasing the clutch to suddenly make the engine rotate and fire, and hopefully keep it running by quickly depressing the clutch so it does not stall. This can be done by one person pushing a lightweight automobile, pulling or being pushed by another vehicle or even rolling down a hill.
Types
Push starting is most successful when the automobile is using a gasoline (or petrol) engine, uses a carburetor, and uses a capacitor discharge ignition (CDI) or an inductive discharge ignition system. Automobiles with other types of engine, ignition, and fuel delivery configurations may work, but may be more difficult to start. Some engines must have a battery providing some electricity since fuel injection systems must have power to operate.
Automatic or manual gearbox
A vehicle equipped with an automatic transmission (inluding semi automatic) is very difficult if not impossible to push start since selection of transmission gears is only possible when the internals of such a gearbox are rotating. Neutral or Park will be selected gear regardless which position the gear selector displays. To be able to change gears within an automatic gearbox, the engine (and not the drive wheels) must be rotating the torque converter to a sufficient speed to enable gear change. A manual gearbox it best suited to push start a vehicle since any gear can be selected even when completely stationary.
Gasoline or diesel engines
A diesel engine uses heat and high compression (compression ratios commonly 22:1 versus 9:1 for gasoline) to ignite the fuel. When normally starting a modern diesel engine, it typically uses glowplugs to preheat the cylinder(s). If a battery is completely discharged then it may not provide the necessary electrical power to 'glow' the glowplugs. Manually push starting a vehicle with a diesel engine may be almost impossible. Rolling down a long hill or being pushed or pulled may work.
A gasoline engine uses a more volatile fuel irrevelent of type or ethanol blend so it is easier to ignite and uses spark plugs to do so. A gasoline engined vehicle is much easier to push start manually unless it uses a fuel injection system.
Fuel delivery systems
Fuel injection is most common for modern gasoline and diesel engines. Fuel injection needs electrical power to open and close the fuel injectors. If a battery is of a sufficiently discharged state that it cannot provide the power to turn an automobile self starter then it may also not be possible to activate the injectors. The most common method to start such a vehicle engine is to jump start it.
A fuel pump is used for fuel injection. It can be mechanically driven or is electrically driven. If electrical then the same probelm may arise which the battery cannot turn the pump because it is heavily discharged. A carburettor only needs suction from the internal combustion engine to work best when push starting. Once the engine is running, a fuel pump (mechanical or electrical) will continue to supply fuel to the carburettor.
Ignition systems
A modern gasoline engine contains an electronic ignition system which precisely times the electrical pulse to the spark plug. The advantage of such a device is that it can deliver a full power electrical pulse to the spark plugs even when the alternator is turning very slowly (as in push starting a motor). The out-dated method of a mechanically timed ignition system is that is cannot deliver a full electrical pulse at very low engine revolutions per minute (RPM). This may affect the ease of push starting an engine to life.
Manual gear best selection
When releasing the clutch there is posssibility that the moving vehicle may all of a sudden jolt to a stop or the drive wheels may lockup momentarily. This happens due to the ratio (drive wheel rotation versus stopped engine inertia) being too high. On a wet or muddy road this may result in loss of control. To cease this phenonmenon, select a higher gear (3rd, 4th etc). If a person is pushing an automobile and the vehicle suddenly stops, personal injury may result.
Conversely, if a too high of a gear has been selected then the internal combustion engine may not rotate fast enough, thus, not provide enough compression. Gas pressure may escape down past the piston rings or (in 4-stroke engines) the poppet valves may not seal firmly.
Causes of a flat battery
The most common problem of not being able to start a motor is due to leaving the headlights on which can completely discharge a lead acid battery overnight. If maintenance of a lead acid battery has been disregarded then it is possible that the lead plates are lacking in fluid and thus cannot provide enough power to crank an engine.
History
In the early 20th Century, many motorcycles could only be push started; the 1908 Scott was distinguished by introducing a kick starter feature.[3] Excelsior Motor Company's Welbike, intended to be carried by paratroopers in World War II, was designed to be started only by push starting.[3]
Push starts in motor racing
Motorcycle road races required push starts by the riders. This involved all riders starting from normal positions on the starting grid, with stopped engines. This practice was banned in the mid to late-1980s.
References
- ^ [1] Driving Tips - Workshops
- ^ [2] AskMen.com - Push-start car
- ^ a b Walker, Mick (2006), Motorcycle: Evolution, Design, Passion, JHU Press, p. 32, 45, ISBN 0-8018-8530-2