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Two-stroke engines which use crankcase compression do not require a crankcase ventilation system, since all of the gases within the crankcase are then fed into the combustion chamber. Many small four-stroke engines such as lawn mower engines and electricity generators simply use a draught tube connected to the intake system.
An overhead valve engine, abbreviated (OHV) and sometimes called a pushrod engine, is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with flathead (or "sidevalve") engines , where the valves were located below the combustion chamber in the engine block .
In an OHV engine the camshaft located within the engine block below the cylinder bank(s) pushes the pushrod upwards. The top of the pushrod presses upwards on one side of the rocker arm located at the top of the cylinder head, which causes the rocker arm to pivot downward on the top of the valve, opening it.
A crossflow head gives better performance than a Reverse-flow cylinder head (though not as good as a uniflow), but the popular explanation put forward for this — that the gases do not have to change direction and hence are moved into and out of the cylinder more efficiently — is a simplification since there is no continuous flow because of valve opening and closing.
In two-stroke gasoline engines the crankcase is part of the air–fuel path and due to the continuous flow of it, two-stroke engines do not need a separate crankcase ventilation system. Valve train above a diesel engine cylinder head. This engine uses rocker arms but no pushrods.
An early documentation of the design occurred sometime between 1174 and 1206 AD in the Artuqid State (modern Turkey), when inventor Al-Jazari described a machine which incorporated the connecting rod with a crankshaft to pump water as part of a water-raising machine, [8] [9] though the device was more complex than typical crank and connecting ...
The most common kind of small engine compression release uses a camshaft mounted mechanical lever that pushes the exhaust valve tappet slightly, venting engine compression through the exhaust valve. Once the engine spins to starting speed, centrifugal force causes the lever to move out of the way, and the exhaust valve is allowed to seat fully.
Gardner 0 stationary engine (a plate acts as a safety shield but the crankshaft is not fully enclosed). Early engines were of the "open-crank" style, that is, there was no enclosed crankcase. The crankshaft and associated parts were open to the environment. That made for a messy environment, because oil spray from the moving parts was not ...