A Cub has only about a 6 to 1 or 7 to 1 compression ratio whereas a diesel engine requires a minimum of 14 to 1 compression ratio to get the air hot enough so nthat when the fuel is sprayed into the engin it will ignite. The early IH diesels, WD-40, Farmall MD, WD-6 WD-9 etc used about 14 to 1 compression ratio with the third valve and extra cylinderhead chamber reducing it to 6 to 1 compression ratio for gasoline starting (and also to enable the operator to crank the engine over). The 1950s, 1960s, German IH diesels use a 19 to 1 compression ratio. With the high compression raios used in diesel engies it is almost impossible to hand crank the engine and on a WD-40 cranking by hand was the only way of starting. A lot of small diesels (marine etc) have a means of holding the exhaust valves partially open, i.e. decompressed, until the person cranking the engine has is up to a sufficient speed that the flywheel has enough inertia to carry it through the full compression to start. The British Marshall diesel tractors used a burning wick in the cylinder head for starting with the engine being turned while decompressed. Later a cartridge, like a rifle cartridge without the bullet, was fired into the cylinder to provide the energy to turn the engine over for starting. The Lanz Bulldog semi-diesel engine used a 4.5 to 1 compression ratio but it was the hot-bulb in the cylinder head that started the combustion of the diesel fuel when it was sprayed into the cylinder. The early Allis Chalmers KO crawler tractors and the 1940s Case tractors burning diesel fuel used a spark plug to start the burning process and were, therefore, not diesel engines.
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Today's Featured Article - Talk of the Town: Repairin a Gas Tank - by Staff. This interesting discussion is from the Tool Talk Discussion Forum. Remember that safety is your first priority - make sure you know what you are doing before attempting a potentially dangerous activity!
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