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What is a Cylinder Head?

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  • Written By: Jeremy Laukkonen
  • Edited By: Michelle Arevalo
  • Last Modified Date: 29 November 2016
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Internal combustion engines typically include a cylinder block, which houses the pistons and the cylinders through which they move, and a cylinder head to cap off the block. Certain engine configurations have multiple cylinder heads, each of which sits upon its own bank of cylinders. In some engines, such as the flathead type, the cylinder head can be very simple and designed solely to provide a sealed, removable top-end for the head. Other engines have either part of valve train, or both the valve train and the camp shaft, within the head. In either case, the cylinder head is generally mounted to the block with a graphite or metal head gasket, effectively turning the cylinders into sealed combustion chambers.

Simple engines, such as those used in lawnmowers and inline engines — like L4 and L6 units, have a single cylinder head to seal up all of the combustion chambers. Other common engines, such as the V6 and V8, contain two parallel banks of cylinders. This requires two cylinder heads, mounted in such a way to form the appearance of a V, in order to seal the cylinder block. Another type of engine that uses two cylinder heads is the flat, or boxer, engine. This configuration is similar to the V-formation in that both banks of cylinders are driven off a single crankshaft, though, in the case of the flat engine, the banks are aligned on the same horizontal plane.

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The complexity of a cylinder head depends largely on the type of engine it is used in. Many older automobiles utilized what is known as a flathead engine. As the name implies, these engines used a head that was a simple, flat panel, mounted via the head gasket, to a cylinder block that itself contained the entire valve train. Cylinder heads in these applications still performed the vital function of sealing the combustion chambers, though they lacked much of the functionality found in more modern units.

Modern cylinder heads are typically used in overhead valve (OHV) or overhead cam (OHC) configurations. A cylinder head in an OHV engine generally contains valve train components, such as pushrods, poppet valves and other components that are operated by a camshaft located in the cylinder block. By contrast, OHC engines have the camshaft itself in the head, making for an even more complex unit. These types of cylinder heads usually contain the entire valve train.

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istria
Post 8

@highlighter- I have not heard of any aftermarket cylinder head kits for a 5.4L mustang, only custom worked heads, but I do know of a kit for a 4.6L ford block.

Summit racing makes a kit for the 4.6L 3v engine that adds serious power to your engine. The kit will set you back, and it is a more advanced install than most can handle. Expect to spend at least $3,200 just for the kit, and who knows how much on the install. I do not know if you need a new ECM for this kit.

I am not sure if this helps, but it is the only kit I know of. You may be able to get an upgraded cylinder head gasket set for the 5.4L, and I have heard of people dropping a 2v on the 5.4L to get some serious gains.

highlighter
Post 7

Does anyone know where I can find performance cylinder heads for a 2006 F-150? I have been looking and I can't find any anywhere. I just want to know if they exist, who manufactures them, and about how much they cost. I can find an actual retailer myself. Thanks wiseGEEK.

Amphibious54
Post 6

@GiraffeEars- The most common reason for a cylinder head exchange is a neglected water pump leak or other coolant leak. The coolant coursing through your engine protects your cylinder heads, block and gasket. The coolant keeps the engine at a normal operating temperature, allowing for the proper thermal expansion of your head gasket.

Part of the reason that your car should stay within a certain operating temperature range is to protect your head and the gasket, highlighting the importance of your car's cooling system. The metal pieces in a motor are still bound by the rules of physics, and too much heat will make them expand and cause moving parts to seize. Honestly, you are actually lucky you did not

seize the motor and only had to repair the top-end.

Other symptoms that are a good indicator of a head gasket problem are things like oil that looks like a milkshake, the smell of exhaust in your coolant, or high temperatures. As soon as you notice any of these cars, get your vehicle to a mechanic as soon as possible. Sometimes it may be as simple as fixing a broken thermostat, but left unchecked can result in a possible total loss of the vehicle.

cougars
Post 5

@Framemaker- You should be careful with that last bit of advice because it can easily be misleading. All cars eject water vapor and a number of oxides from their tail pipes because these are the natural products of the combustion of gasoline. A clean combusting hydrocarbon produces carbon dioxide and water as its products. Gasoline is a hydrocarbon (with other things added of course).

You may have noticed that the bigger a motor, the more exhaust you see out of its tailpipe on a cool day. This is because the engine consumes more gasoline, meaning it will produce more water vapor per unit of time. It would be perfectly normal to expect a wet spot from an engine with a

high displacement.

I would say that if one noticed more water vapor than normal, then a liquid has been introduced to the combustion cycle, and you have a head gasket leak. It would be easier to use your cardboard test on a smaller displacement motor. Additionally, you would also need to know approximately how much water vapor the vehicle was emitting before to know if what you have is more than normal. These are just my thoughts.

FrameMaker
Post 4

@Aplenty- An engine cylinder head needs to be taken to a machine shop and pressure tested to know for sure if it is cracked. This should be done before you repair your head gasket so that you are not wasting your money.

There is no definitive way to know if there is actually a blown seal on your head gasket, but there are a few tricks and things to look for that might point you in that direction. Sweet smelling exhaust is a symptom that you have head gasket problems. This indicates that coolant is leaking into the cylinder and coming out with the combustion gases. Bubbles and light grey smoke coming out of your coolant tank when the cap

is off and the motor is running is another sign.

One easy trick you may be able to perform is to hold a piece of cardboard an inch or two away from the exhaust. If you see a wet spot form, or see water dripping out of the exhaust, you may have a cylinder head or head gasket leak.

GiraffeEars
Post 3

@aplenty- I would like to know a little more about these problems too because I just forked over $2500 for a cylinder head replacement. I brought my car in because it seemed like it was running hot. When I brought my car in, my local mechanic told me that there was a crack in the cylinder head and I needed a new water pump.

How would a slight overheating cause this to happen? I do not know how long the car was overheating, but I brought it in within two weeks of noticing the problem. This experience was a huge expense, and I would love to know what I missed to make a car with 65,000 miles do this. I was without a car for a week, and the bill was outrageous.

laukkonen
Post 2

There are a few ways to tell if you've got a blown head gasket or cracked head, but most of them require special tools. If there is engine oil in your antifreeze (or coolant in your engine oil) that's the only thing you can really see with your bare eyes. Those things don't always happen though.

One of the main ways to tell is by testing for combustion gasses in the radiator. That's usually done with a special device that sits on radiator fill tube. The device has fluid in it that changes color in the presence of combustion gasses, which is a sure sign of a blown head gasket or cracked head.

It is also sometimes possible to pressure

test the cooling system, which can force coolant into one or more cylinders if there is a blown head gasket or cracked head. Sometimes a leakdown test is also used, and if the problem has been going on for a very long time then it's sometimes possible to tell by examining the spark plugs.

It's usually impossible to tell whether it's a head gasket problem or a cracked head until the head is off. At that point the gasket can be physically examined, and it becomes possible to test the head before reassembly.

aplenty
Post 1

I have a few questions. How do I tell if I have a blown cylinder head gasket? How can I tell if I have a cracked cylinder head?

My car is having some serious issues, and my friend says it sounds like a problem with the head or the gasket. I want to know how to tell if I might have a problem with the cylinder head so I know what my mechanic is talking about. I do not know much about cars so I only need to know about stuff I can diagnose with my basic senses.

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