Bryson Jones Per. 6-7 Auto Final Paper The four-stroke cycle is a common way for an engine to go through the four steps of the combustion prosses that powers the crankshaft. The cycle will start with the intake stroke when the intake valve opens and the piston moves from TDC (Top Dead Center, where the piston is at its highest point) to BDC (Bottom Dead Center, where the piston is at its lowest point), By doing this the cylinder is filled with the air/fuel mixture (air/fuel mixture is about 14.7 parts air to 1-part fuel it’s like this because of atmospheres common pressure at sea level is 14.7 pounds). When it reaches close to BDC the intake valve closes sealing the combustion chamber. The reason that this process works is that the volume of the cylinder will increase making a low pressure, similar to pulling on a nerfs gun plunger, with this low pressure the high pressure will rush to the low pressure thus filling the cylinder with the air-fuel mix. Near BDC is where the compression Stroke will begin with both valves sealed and the cylinder filled with the air/fuel mix the piston will begin to travel to TDC while doing this the volume in the combustion chamber will decrease thus compressing the air/fuel mixture (this is where compression ratio will come into play, compression ratio is the volume of the combustion chamber at BDC over volume at TDC 8:1 is a normal gas car compression ratio this means the volume at BDC is about 8 times bigger than the volume at TDC). This will raise the temperature of the mix and will make ignition more efficient. The piston will be approaching TDC when the air/fuel mixture will be ignited, the ignition will cause the fuel gasses to expand and begin the power stroke while the gasses expand the cause high pressure in the combustion chamber and the top of the piston shoving it from TDC to BDC this is where this energy that powers the crank comes from. As the piston is about at BDC the exhaust valve will open. Once again, the piston will move from BDC to TDC and will push all the burnt gasses out of the cylinder through the exhaust valve which was opened at the end of the power stroke. Once the piston reaches TDC the exhaust valve will close and the intake valve will open and begin the cycle all over again. During this process, the crankshaft will have completed two complete rotations. The cylinder head has many important components it is also where all the engines power comes from. The cylinder head holds many sealing parts, for example, it holds the intake and the exhaust valves these two components are vital for the engine for the engine to work they will seal the combustion chamber where compression is formed, and the gasses push off of to push down on the piston. The actuation of the valves is done by the rocker arms which when pushed down will press down on the valve spring and valve stem which will push down and unseal the valve, when this happens it allows the passage of gas in or out of the cylinder. The camshaft will do the job of pushing down on the rocker arms in an OHC (overhead cam) assembly or pushing up on the valve lifter in an OHV (overhead valve) assembly which will, in turn, push up on the bottom of the rocker arm opening the valve. The combustion chamber is also formed in the head and the top of the combustion chamber is where the valves are located. The size of the combustion chamber is determined by how deep the head designers decide to make it, it can also be determined by the head gasket the size of the gasket can also contribute to combustion chamber size. The cylinder head also holds passages for intake of the mix of air/fuel to the cylinder. The engine block is the largest part of the engine and holds together the whole engine assembly. The engine block holds many key parts of the engine including the cylinder wall the cylinder wall is where the piston will be held and, where the piston will go to TDC and BDC to pull, compress, and push out gasses. The piston assembly is also held in the engine block the piston assembly is made up of the piston which is then attached to the connection rob by a wrist pin which will also allow for back and forth movement of the piston in the chamber then the connection rod will attach around the crankshaft with connection rod bearing that allow the crankshaft to spin inside of the connection rod and connection rod end cap there is also rings on the piston that allows for the piston to seal to the side of the cylinder. The crankshaft turns the up and down movement of the pistons and translates that to the rotational movement that powers not only the drive train but also the cam through the timing-belt. The whole assembly is held together by the main bearing end cap that holds the crank to the bottom of the block. The lubrication system takes the job of moving oil around the entire engine, the reason this is important is that oil serves many applications including lubricating, cushioning, cleaning, cooling, and sealing. Lubricating oil come in three varieties conventional meaning it comes from crude oil and not man-made, synthetic its man made this type of oil is more expensive but it does work better, and a synthetic blend that is a mix of the two. All oil has additives that will allow it to work better, additives are what make crude oil into lubricating oil. The crude oil in the lubricating oil is not what wears out over time rather the additive will slowly be burned or used up and once this happens the oil will have to be replaced. If the lubricating system did not do its job it risks the engine seizing or over-heating, the job of the lubricating system is to move the lubricating oil around the engine, it can do this in two basic ways, one way is splash lubrication when the engine relays on moving parts in the engine to splash the oil around the engine, the other way it can move the oil is in a closed system that uses a mechanical pump to pull the oil from the sump and transfer it around the engine through multiple galleries around the head and block. Oil will also help cool the engine, it can do this by running the hot oil through a radiation like a device that the oil will conduct its heat on to. If the oil does not cool its life will be cut short because the additives will burn off faster. Engine oil has a specified life cycle depending on your car but you should check the oil every two gas ups. The engines cooling system is a vital part of performance and efficiency of engines. Because the engine is using heat energy to power itself it is vital that we cool the engine properly, improper engine cooling can result in poor performance or in worst case scenario severe engine damage. The cooling system is usually liquid cooled, meaning the heat of the engine is conducted into a liquid and then that liquid is cooled by a radiator that uses the car’s movement to push air over its’ fins and conduct the heat from the liquid into the air. Older engines would air cool the engine but it was ineffective and would overheat, often. The cooling system is often an overlooked part of engine repair but it could be the reason for critical engine faults. One, for example, it the air intakes filter could be clogged and this could cause no air to be going into the intake and not allow the car to start. Many technicians may overlook the cooling system and throw money the engine to make it work this issue may only be a few dollars to fix. The cooling system in a liquid cooled engine consists of many parts it has soft tubes that move the coolant from the radiator to the engine it is moved to these areas by a water pump, it then moves around the engine in galleries and back out through the same type of tube to the radiator, if the coolant is not cooled properly it may overheat and boil and this is where the bypass comes into play by removing some of the gas it will reduce the pressure and will cool the coolant and prevent it from boiling.