Many people have probably heard the abbreviation “cylinder head”. The abbreviation is simple: “cylinder head”. This complex and rather expensive unit is in every internal combustion engine. Moreover, the head is one of its main parts. To make it easier to understand what the cylinder head is, let’s remember the structure of the internal combustion engine. We explain as simply as possible, but with some important details.
Where is the cylinderhead
Let’s start with the simplest question about the MCC: what it is in the car and where it is located. The main (and most massive) part of the internal combustion engine is the cylinder block. In it, as you can understand from the name, there are cylinders in which the pistons move. From below, the block is covered by a tray, into which oil flows after lubrication of parts. The oil pump takes it from there to feed it back into the system.
The cylinder head is mounted on the cylinder block through a special gasket. It, in turn, is covered with a cap to prevent oil from splashing and dirt from getting inside the engine. The cylinder-head cover is the uppermost and most visible part of the engine. We see it when we open the hood, if there is no decorative plastic cover on it.
By the way, there can be not one, but several caps, as well as the cylinder-heads themselves. If the motor has a V-shaped or opposition design, each half of the cylinders will have its own head. And some large truck diesels were made with individual cylinder heads. And only the inline motor has only one.
What functions does the cylinder head perform
The next question is: why do you need a cylinder head at all? In fact, it has many complex functions.
With its lower part, located directly above the cylinders, the head forms part of the combustion chamber.
The cylinder head contains elements of the power and ignition systems – spark plugs or glow plugs (for diesels), as well as fuel injectors.
In the head there is a valve mechanism, thanks to which air or fuel-air mixture is supplied to the combustion chambers and exhaust gases are removed. For this purpose, the inlet and exhaust manifolds are docked to the cylinder head.
The cylinder-head is part of the cooling water jacket and lubrication system of the engine.
The construction and varieties of the cylinder-head assembly
What does the cylinder-head cylinder-head consists of? Its basis is a complex-shaped housing (it is also called a crankcase), cast from cast iron or aluminum alloy. Cast iron heads have high mechanical strength and heat resistance. They are not subject to deformation and warping when heated. But there is a disadvantage – heavy weight.
Aluminum heads are not only much lighter. This material has greater thermal conductivity, so it heats up less (or, more accurately, cools down more easily) and works better in high-compression motors. Most modern passenger car engines use aluminum cylinder heads.
But whether it is a cast iron or aluminum cylinder head, what does such a complex part consist of? Channels for coolant circulation, oil lines, notches for combustion chambers for each cylinder are necessarily made in the cylinder-head housing.
And most importantly, the modern cylinder head houses the valve train. For the plate of each valve in the head there is a seat, and for the rod – a sleeve. And just by the type of valve mechanism, cylinder heads are first of all differentiated. They can be:
- with one camshaft;
- with two camshafts;
- without a camshaft.
The SOHC (Single Over Head Cam) head has a single camshaft that drives both the intake and exhaust valves. The valves are opened either by the rocker arms or directly by the cams on the shaft. These heads usually have two or three valves per cylinder.
The DOHC (Double OverHead Cam) system involves two camshafts in the cylinder head. The first shaft controls the intake valves, which are mounted on one side, and the other shaft controls the exhaust valves on the opposite side of the head. Most modern cars have engines with a DOHC timing system, where there are four valves per cylinder. The DOHC design allows the intake valves to be at a greater angle relative to the exhaust valves, allowing for better filling of the cylinders with air or fuel-air mixture. But the DOHC design is the most complex. In addition to the two camshafts, the second shaft must be driven by a gear, belt or chain drive.
Head without camshaft refers to the system OHV (Over Head Valve), which literally means “valves in the head”. In this case, the design is such that the valves are driven via pushrods and rocker arms, and the camshaft is not installed in the cylinder head, but down inside the cylinder block. In the head with an OHV system, it is more difficult to install more than two valves per cylinder, and pushrods with rocker arms do not work well at high engine speeds. This design is considered cumbersome (although it greatly simplifies the timing drive, which is easily bypassed by a chain or belt) and is rarely used today.
Maintenance of the cylinderhead and signs of its malfunction
Although the structure of the cylinder-head unit is quite complex, the main maintenance is reduced to adjusting the clearances in the valve train, if they are not equipped with hydrocompensators. Such adjustment, depending on the design of the timing gear, is done in different ways – with the help of adjusting screws or by replacing (selecting) washers or tappets. The frequency of checking and, if necessary, adjusting the valves can be found in the instruction manual of the car. But sometimes it may be required ahead of time, if the engine is running, you hear a characteristic clattering noise from under the valve cover.
There are several symptoms that may indicate that something is wrong with the head:
- decreased engine power;
- complications with starting the engine, especially in winter;
- valve knocking;
- blue or whitish smoke from the exhaust pipe;
- emulsion in the engine crankcase and on the dipstick;
- oil stains in the expansion tank;
- loss of oil or coolant level.
Possible problems, their causes and solution
Let’s consider the most common problems and malfunctions of the cylinder head, as well as ways to solve them.
Gasket breakdown of the cylinder head. Simply put, its damage. It can be caused by overheating, but on cars “at the age” the gasket sometimes simply destroys due to aging or degradation of its material under the influence of oil, antifreeze and exhaust gases. As a result, compression drops, exhaust gases penetrate into antifreeze or antifreeze – into oil. There is only one way out – engine repair with gasket replacement.
Curvature of the butt plane of the aluminum cylinder-head. In this case, it is said that the head is “hanged”. Symptoms are the same as with a punctured head gasket. The most common cause of this problem is engine overheating. If the warp is not severe, it can be corrected by milling the mating plane in specialized workshops. In case of significant deformation, the head will have to be replaced with a new one.
Cracks in the cylinder head. Another consequence of engine overheating. An alternative option is improper tightening of its mounting bolts to the engine block. In rare cases, you can get rid of small cracks by welding. But usually requires replacement of the head housing.
Wear of valve bushings. The bushings can wear out when using low-quality oil or simply with high mileage. To solve the problem, they must be pressed out of the head housing and replaced with new ones.
Wear on the working surfaces of the valve plates and/or valve seats. This problem can usually be solved by lapping the valves to the seats so that they have the correct chamfers. But in the case of significant wear (e.g., cracking of the valve plate), which is manifested by unstable idling and a drop in engine power, you will have to replace the worn parts with new ones.
Knocking valves when the engine is running. In the mechanism without hydrocompensators it will be necessary to adjust the gap. In the mechanism with hydrocompensators – replacement of failed hydroporos of valves.
Leakage of the valve cover. It is necessary to replace the valve cover gasket that has lost its tightness over time or to renew the sealant if the cover is structurally installed without a gasket. In some motors, the plastic cover itself becomes deformed over time. In this case, a new one will be required.
Wear of the oil caps on the valve stems. One of the main causes of increased oil consumption and smoke from the exhaust pipe – grease flows down the rods into the intake manifold and from there enters the cylinders. If the corresponding symptoms appear, the caps are replaced with new ones. Usually this does not require disassembly of the cylinder head itself.
Totals
- The cylinder head, or cylinder head, is a part that covers the cylinder block and performs many functions in the engine.
- Based on the type of valve mechanism, cylinder heads come with one or two camshafts or without a camshaft.
- The cylinder head requires almost no specialized scheduled maintenance.
- The main faults of the cylinder head are gasket breakage, distortion of the cylinder head flats, cracks, wear of valve bushings, valve plate chamfers or valve seats, valve knocking, valve cover leaks and worn oil caps.