What is a Cylinder Head?
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes at the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket.
A cylinder head is usually located on the top of the engine block. It serves as housing for components such as the intake and exhaust valves, springs and lifters, and the combustion chamber.
The passages in the cylinder head allow air and fuel to flow inside the cylinder while permitting the exhaust gases to flow out of it. The passages are otherwise called ports or tracts.
The cylinder head also channels the coolant into the engine block, thereby cooling down the engine components. The cylinder head uses a gasket that aids in preventing water or oil from leaking into the combustion chambers.
Most original equipment manufacturers made cylinder heads from cast iron. A cylinder head made of cast iron is more durable and less expensive. However, cast iron is heavy and provides a lesser efficiency in dissipating heat.
For this reason, some manufacturers prefer using cylinder heads made of aluminum. These cylinder heads are much lighter than cast iron cylinder heads. Performance cars and race cars commonly have aluminum cylinder heads.
Cars with inline (straight) engines have one cylinder head and automobiles with V engines have two cylinder heads, one for each cylinder bank. In some vehicles, where cylinder banks are very close to the V engine, one cylinder is all that is needed.
Large industrial vehicles may have one head per cylinder. This makes replacing a cylinder head much more affordable.
Types of Cylinder Heads
- Flathead Cylinder Heads: These were the first type of cylinder heads. Flathead cylinder heads simply protect the cylinder block and have no moving parts. These cylinder heads do not allow for an efficient air flow, and thereby provide a poor engine performance.
- Overhead Valve Cylinder Heads: These cylinders heads are superior to flathead cylinder heads. Overhead valve cylinder heads have the camshafts above them. These heads have their pushrods and valves connected to provide a smooth airflow.
- Overhead Camshaft Cylinder Heads: These are the most advanced designs of cylinder heads. Overhead camshaft cylinder heads have the camshafts inside the cylinder head, eliminating the need of pushrods. This provides a better airflow, and in turn, increases the efficiency of the engine.
How Does a Cylinder Head Work?
The cylinder head allows the engine to perform at maximum capacity by connecting to the intake and exhaust manifolds to allow the quick burn of fuel and air that moves the engine’s pistons.
The intake manifold feeds air into the head, where it is combusted with fuel to produce exhaust gases, which are expelled through the exhaust manifold.
It’s important that the intake and exhaust valves, which allow the entry and exit of relevant gases, open and close at the correct times to keep the engine running smoothly.
Why Do Cylinder Heads Fail?
The most common reason for cylinder head failure is overheating caused by, for example, coolant loss, head gasket failure, or restricted flow of coolant.
In extreme cases, a cracked or damaged cylinder head can result in terminal damage to the entire engine! You must deal with any problems as soon as possible to try and prevent this from happening.
Cylinder heads can also warp because of the tremendous pressure placed on them by extreme temperature changes.
This means that it is no longer providing a flat surface to hold the head gasket in the right position, which can lead to expensive problems later on in the form of major repairs or total engine replacement being required.
Warping is a particular problem for cylinder heads made of aluminum. Different engines have different levels of tolerance for cylinder head warping – some can withstand a high amount of warping while still working effectively.
If your cylinder head does warp, you may be able to take it to a mechanic who specializes in realigning them – if not, you will probably need a replacement.
5 Symptoms of bad Cylinder Head
#1. Overheating.
One of the most common symptoms of an issue with a diesel engine cylinder head is overheating.
As the cylinder is put under pressure by the heat, it causes the components inside the internal combustion engine to overheat, as they can’t pass coolant through and, therefore, they distort in shape.
To avoid damage to the cylinder head, make sure your radiator is full and in good condition to prevent overheating from happening.
#2. Poor Engine Performance.
A very clear indicator of a cylinder head problem is when there is poor engine performance. This issue can be due to the diesel engine cylinder head breaking or cracking, which can result in the engine not being able to burn fuel efficiently.
This poor performance will be instantly noticeable as the engine won’t be running the same, and you’ll find you may have to restart the car more frequently.
#3. Oil Leaks.
If you find you have oil leaking from the vehicle, this may be a result of a cracked cylinder head.
Even if you can’t see a leak yourself and the oil light appears on the dashboard, check the engine to see if there’s any evidence of oil around the cylinder head.
As a diesel engine cylinder head contains oil, if it’s cracked, it may cause the oil to leak out.
#4. Drop-In Coolant Level.
A drop in the level of engine coolant may cause a leak, which can be easily identified and be seen on the cylinder head.
A leak could be caused due to a crack in the diesel engine cylinder head, and this could cause more long-term issues as the engine starts to heat up from the lack of coolant.
#5. Smoke.
Smoke coming from the exhaust is the clearest indicator that you could have a cracked cylinder head. The crack and damage are most likely to be a lot more severe in this instance.
If this has occurred, you should try and get this problem fixed as soon as possible by a professional, to ensure no further damage is caused to the engine.
#6. Engine Misfires.
Within an engine’s cylinders, air and gas form a pressurized mixture which explodes upon ignition, creating power.
A cracked cylinder head may be unable to create the required atmosphere for proper combustion within those cylinders, leading to failures to combust, or engine misfires. The engine may die repeatedly during use, or fail to start at all.
This is a more severe sign and usually is indicative of serious damage. It’s always better to take a cylinder head in for repairs or replacement if it starts to show signs of wear, to avoid even higher repair bills when the cylinder head’s failure leads to damages elsewhere in the vehicle.
How Much Does a Cylinder Head Replacement Cost?
The cost of replacing a cylinder head will depend on the make and model of your vehicle and the cost of parts and labor. You can expect the average cost to be $3,000 or more if you have the job done at an auto shop.
If you are adept at fixing cars, you may save yourself some money by doing the job yourself.
The procedure for replacement of a cylinder head differs depending on the placement of the camshaft in the engine. In general, a technician will remove any components that are in the way of the cylinder head (i.e. the throttle body, steering pump mounting bracket, air cleaner system, etc.).
The spark plugs are pulled and the intake and exhaust manifolds are detached. The valve covers are removed and the entire valve train (valves, springs, guides, lifters, etc.) is disassembled.
An overhead cam engine will have one or two camshafts in the cylinder head and require that the timing belt or chain be removed to free up the camshaft. The cylinder head bolts are taken out and the head is carefully removed from the vehicle.
Once the old gasket material is cleaned from the mating surface on the engine block, a new gasket is used and the new cylinder head is set in place. The head bolts are torqued and the rest of the components are reassembled to manufacturer’s specifications.