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| Can someone explain how cams work in simple terms please https://ausmini.com/forums/viewtopic.php?f=2&t=15694 |
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| Author: | Baracade [ Tue Jan 31, 2006 8:10 am ] |
| Post subject: | Can someone explain how cams work in simple terms please |
Can someone explain how cams work in simple terms please |
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| Author: | simon k [ Tue Jan 31, 2006 8:44 am ] |
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how simple...? a cam (same for single, twin, quad whatever) is driven by the engine crank shaft via a chain or belt, it pushes valves open in sequence with the current stroke of the motor, for each cylinder's set of valves - the cam will open the inlet valve on intake stroke, keep both valves closed on the compression and power strokes, and open the exhaust valve on the exhaust stroke, over and over 1000's of times a minute. The profile of the cam lobes can be altered to give different characteristics - leaving the valves open longer, making them open further, giving a little overlap between when the exhaust valve closes and the inlet valve opens... simple enough? |
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| Author: | Simple [ Tue Jan 31, 2006 8:46 am ] |
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http://auto.howstuffworks.com/camshaft.htm |
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| Author: | Mike_Byron [ Tue Jan 31, 2006 8:47 am ] |
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Okay I'll try In the early days of motoring the inlet valve was opened by the cam on the downward induction stroke of the piston and the resultant vacuum sucked in the fuel /air mixture. The piston started to rise and the inlet valve closed allowing compression of the mixture until the piston was at the top of the stroke and then the spark plug fired and the resultant expansion of the fired mixture forced the piston down. As it rose again, the exhaust valve opened and the rising piston forced out the burnt gaseous mixture. Now that was a simple motor with early fairly volatile fuels. As the fuels improved the octane ratings rose and this had the effect of actually slowing down the speed of the combustion but aslo giving a more thorough burn of the fuel air mixture. This meant that the valve opening sequences needed to be changed to cope with the slower burning fuels and the result was that the ignition of the fuel mixture is actually happening while the piston is still sucking the mixture in through the open inlet valve. Power is made by getting the maximum amount of mixture into a cylinder as quickly as possible, getting the maximum bang from the burning and getting the exhaust gases out as quickly as possible. Camshafts control the timing of opening and closing of the valves and with modern engines reaching higher revolutions, some degree of overlap (that is; both the inlet and exhaust valves may be partially open while the bang is happening) needs to happen. Efficient inlet systems (twin carbies or bigger carbies) and an exhaust system that actually creates a vacuum to extract the burnt gases out of the engine mean that the timing of the valve openings can be manipulated to give more power at certain points in the rev range. Basically that is in simple terms how a cam works. Beyond that is starts to get complex quickly |
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| Author: | Baracade [ Tue Jan 31, 2006 9:40 am ] |
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Well that info has been perfect... I understand enough... & currently dont want to go into any more depth... Thanks for the help everyone |
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