Your car idles at about 750-900 revolutions per minute, rpm, this requires the valves to open and close 750-900 times a minute. Without the camshaft you wouldn’t have a working engine. It is what allows air into, and exhaust out of, the engine via the intake and exhaust valves.
What is a camshaft?
What a question! A camshaft is usually constructed out of metal and has a range of lobes set at different angles. It has a timing gear at one end, this is what connects to the timing belt or chain. As the camshaft rotates the lobes press down on the valves which opens them.
How does a camshaft work?
On the intake stroke, the camshaft will open the intake valve, via the rocker arm, as the piston travels down. This sucks air and fuel in through the cylinder head, into the combustion chamber. The camshaft lobe then keeps rotating, the valve closes thanks to the valve spring and the piston travels back up to compress the mixture. The spark plug ignites the mixture and the piston travels down, transferring that energy through the connecting rod to the crankshaft.
Now the camshaft comes back into play, the air and fuel has been ignited and used, the exhaust gasses need to exit stage right. The exhaust lobe on the camshaft rotates around and pushes the exhaust valve open. The gases are forced out via the piston coming back up again.
Now the piston needs to go back down, intake valve opens and we start all over again.
What different kinds of camshaft are there?
As many as engineers can imagine, they can be a weird bunch.
The most common ones are SOHC, DOHC and in some V engines ‘Overhead Valves”.
SOHC stands for “Single Over Head Camshaft”. This means there is one camshaft, controlling intake and exhaust movements, and it’s based on the top of the cylinder head. Therefore it’s a single overhead camshaft.
DOHC stands for “Dual Over Head Cam”. You guessed it, there’s 2 of them now. One operates the intake valves, the other controls the exhaust valves. These are more high performance due to better timing, duration and amount that they can open the valves.
In V engines, you can camshafts in ‘the valley’ or on top of the cylinder heads. If they’re in the valley, they use pushrods to push the rocker arms and open the valves. If they sit over the top of the cylinder head of each ‘bank’ then you can pretend to know some jargon and call them a “quaddie” or “Quad cam engine”.
What’s valves got to do, got to do with it,
Little Tina Turner reference for you there.
Your camshaft opens and closes valves to allow air/fuel in and exhaust out. It can do that more efficiently with more valves per cylinder.
If you have 4 valves per cylinder then there’s 2 intake and 2 exhaust valves. 5 usually means 3 intake, 2 exhaust.
What do variable valve timing and variable valve lift mean?
Well variable valve timing, VVT, means that there is a hydraulic system in the camshaft to control when the valve opens. Making the car more efficient and produce less emissions.
Variable valve lift, VVL, means that the valve lift is variable. It can increase lift to allow more air in and exhaust out when the rev’s get higher. This is mainly used for performance to allow the engine to ‘breathe better’ throughout the rev range.
There’s something wrong with my engine
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