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These blow-by gases, if not ventilated, inevitably condense and combine with the oil vapor present in the crankcase, forming oil sludge. Excessive crankcase pressure can furthermore lead to engine oil leaks past the crankshaft seals and other engine seals and gaskets. Therefore, it becomes imperative that a crankcase ventilation system be used.
Crankcase dilution occurs when the fuel oil from the engine gets into the lube oil of the engine. This can be caused by the walls being wetted due to the fuel condensing in the cylinder. If the engine is cold, or there is an excess amount of cooling around the cylinder, [ 1 ] the fuel oil will condense and have a higher chance to end up in the ...
Manifold vacuum, or engine vacuum in a petrol engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere. Manifold vacuum is an effect of a piston's movement on the induction stroke and the airflow through a throttle in the intervening carburetor or throttle body leading to the intake manifold. It is a ...
Engine oil is recirculated around a four-stroke engine (rather than burning it as happens in a two-stroke engine) and much of this occurs within the crankcase. Oil is stored either at the bottom of the crankcase (in a wet sump engine) or in a separate reservoir (in a dry sump system). [3]
[1] [2] An equilibrium pressure will be reached when the rate of gases entering the crankcase (blow-by gases past the piston rings, but also air leaks and oil vapor) equals the rate of gas removal from the scavenge pump capacity beyond what's required to remove just the oil. Alternatively, the crankcase may be kept near atmospheric pressure by ...
An oil catch can is fitted in line of the crank case breather system. It is placed in between the breather outlet and the intake system. As the crank vapors pass through the catch can the oil droplets, un-burnt fuel, and water vapor condense and settle in the tank. This stops them from reaching the intake and causing the issues mentioned above.
A wet sump design can be problematic in a racing car, as the large g force pulled by drivers going around corners causes the oil in the pan to slosh, gravitating away from the oil pick-up, briefly starving the system of oil and damaging the engine. However, on a motorcycle this difficulty does not arise, as a bike leans into corners and the oil ...
Day cycle engines are crankcase scavenged and port timed. The crankcase and the part of the cylinder below the exhaust port is used as a pump. The operation of the Day cycle engine begins when the crankshaft is turned so that the piston moves from BDC upward (toward the head) creating a vacuum in the crankcase/cylinder area.