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I am new to understand engines. One thing that got me confused is the location of the camshaft. At first I seen it go above the valve so I thought it sat in the cylinder head. Now as I'm watching videos and reading more, it states that the camshaft go inside the cylinder block and use rocker arms etc to move the valves. Which one is it? Is it based on the engine type, v-line, inline etc?

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There are a number of different engine designs and these govern not only the location, but also the number of camshafts within an engine. Some terms you will encounter include

OHV which means Over Head Valve (the cam is usually in the block, below the valves and acts upon the valves with pushrods and rocker arms) An example of this being the Austin Morris A-series engine as found in the original Mini.

OHC which means Over Head Cam (the camshaft is typically located within the cylinder head and is higher than the valves. It usually acts upon the valves via cam buckets, also known as tappets). An example of this being the Volkswagen EG / DX 8v engines as used in the original Golf GTI.

DOHC which is Double Overhead Cam (there are two camshafts, typically one cam runs the inlet valve set and one the exhaust set. Some DOHC engines have multiple inlet and multiple exhaust valves for each cylinder). Two examples of this which are slightly different being the original Lampredi Fiat / Lancia Twin Cam (8v) engine which ran twin cams but only single inlet and exhaust valves per cylinder and the other being the Mk2/Mk3 Golf GTI 16v engine, a DOHC design which featured two inlet and two exhaust valves per cylinder.

You'll also encounter designs where the engine runs multiple banks of cylinders such as V or boxer engines. When these engines run an OHC design, the typically have a camshaft per bank of cylinders. This is the type if engine where you may encounter a "Quad-Cam" design. Essentially the engine has four camshafts, i.e. two per bank in a doubled up DOHC setup. Good examples to look at include the Alfa Romeo Boxer engine series and the Subaru Impreza series of engines. Both of these are boxer engines (could also arguably be described as a 180 degree V).

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    the difference between boxer and 180° V: a boxer has one crank pin per cylinder, so opposing cylinders are 180° out of phase: they both move toward the crankshaft at the same time. A 180° V engine has one crank pin per two cylinders, so the two opposing cylinders always move in the same direction. – Hobbes Jul 5 '16 at 9:42

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