4.6.1 Cylinder head
The cylinder head is the body, which contains the camshafts, valves, intake and exhaust ports, as well as coolant channels that are associated with the cylinder block jacket and oil channels of the lubrication system. There are different layouts of the camshafts in the cylinder head. So, if one says: "Engine with an overhead camshaft", they mean that the camshaft is located in the cylinder head. They are often designated as OHC (Overhead Camshaft) or SOHC (Single Overhead Camshaft). That is, one camshaft is installed inside the cylinder head. In case if two camshafts are installed in the cylinder head - intake and exhaust (opening the intake and exhaust valves, respectively), then this layout is called DOHC (Double Overhead Camshaft). Various schemes of the valve mechanism drive are shown in Figure 4.24.
Figure 4.24 Various ways of valve gear actuation.
It is also worth mentioning, to put it mildly, an outdated design with a lower position of camshaft and valves in the cylinder head. This layout of valve train placement has not lost its relevance for certain car models with "registration" in the United States. It was called OHV (Overhead Valve).
Recesses that form combustion chambers are made in the head above the cylinders*, as shown in Figure 4.25. In addition, valve seats are located in the cylinder head. The seats are installed (we talked about them when we examined the valve mechanism), and the inlet and outlet channels are cast in these valve seats. Holes for screwing in spark plugs are located in the cylinder head.
Figure 4.25 Cylinder head.
* In a diesel engine, the combustion chamber is located in the piston top and the cylinder head surface is flat.
Cylinder head of most engines is cast from an aluminum alloy. It has a high thermal conductivity, as a result of which the temperature of the working mixture in the engine cylinders at the end of the compression strokes decreases. Therefore, it seems possible to increase the compression ratio of the engine without the appearance of detonation combustion of fuel when the engine is running.
Cylinder head is attached to the block by the means of nuts on studs or bolts. A sealing gasket is installed between the cylinder block and the cylinder head. This gasket eliminates the passage of gases from the cylinders and the flow of coolant from the cooling jacket of the cylinder block at the junction of the head and the block.
Good to know
Every time after removing the cylinder head, it is necessary to clean and rinse the contact surfaces on the block and the head. It is also necessary to always replace the cylinder head gasket after removing the cylinder head, because there are special crushable metal rings for better sealing of the cylinders on the gasket. And these rings, unfortunately, are disposable.
The intake and exhaust manifolds are attached to the cylinder head. We will discuss these manifolds below in the "Intake and Exhaust System" chapter. Various additional equipment, which is necessary for the proper functioning of all ICE systems, can also be attached to the block head, which does not make sense to mention yet.