The engine of your car is its most vital component and includes hundreds of parts, all working together to make it move as efficiently and as comfortably as possible. Among them, a camshaft stands apart as a quite simple part, yet it’s a very important piece of every internal combustion engine.
In this article, we’re going to explain what is a camshaft, what it does, why it’s important and what happens when it goes bad. Obviously, we’ll also give you some pointers on how to quickly figure out what the problem is depending on the situation and what you can do to fix it.
What is a camshaft?
A camshaft is a lobed shaft that runs the length of your car’s engine head. Its main purpose is to open and close the intake and exhaust valves in sync with the position of the pistons.
At first glance, a camshaft looks like a cylindrical rod with lobes strategically placed throughout it. These lobes are called cams and they are located over each valve in the head. The lobes are constructed to force the valves to open by pressing them as the camshaft rotates.
Of course, the camshaft has gone through various refinements over more than a century of automotive mass production. However, unlike other moving parts of the engine, the camshaft is still a simple part with the same basic working principle as in the early days of automobiles.
The reason for that is because primitive camshafts were there long before cars. Similar systems have been in use since as early as the 13th century. As such, they’ve been a staple of modern mechanics and their use is not limited to the automotive industry.
In cars, the rule of thumb is that the number of camshafts correlates with the configuration of the cylinders. An inline engine has one cylinder head, hence one or two camshafts, whereas V engines have two cylinder heads, hence two or four camshafts. Boxer engines from classic VWs and modern Porsches and Subarus also have two or four camshafts. A bit later, we’ll proceed to explain why some engines have one camshaft per cylinder head, and why others have two.
How do camshafts work?
In short, a camshaft rotates in sync with the crankshaft, to open and close the valves at exactly the right moment during the combustion cycle. The drive ratio is always 1:2. The cam turns at half the speed of the crank. This is because the crankshaft in a four-stroke engine makes two complete revolutions for every power cycle (intake stroke, compression stroke, power stroke, and exhaust stroke). To achieve perfect timing, the crankshaft and camshaft are connected via a timing belt or a timing chain.
As previously said, the lobes of the camshaft are placed to control the valve’s opening, either for letting fresh air in or letting the exhaust gasses out. The lobes press the valve tappets, opening and closing them in predefined intervals.
Whereas older engines had one camshaft operating both the intake and the exhaust valves, most modern engines have two overhead camshafts instead. The dual overhead camshaft (DOHC) construction proved to be more complex, yet more efficient both in terms of power and fuel consumption. It enabled the engine to have one camshaft for intake valves and the other for exhaust valves.
This setup increased the engine’s revving capabilities. It also enabled more valves per cylinder and better placement for spark plugs and other engine’s head components. That’s why dual overhead cam configurations quickly became the industry standard when it comes to achieving high performance.
Speaking of performance, the main parameters resulting in performance increase are valve opening duration and valve lift. The opening duration is the number of degrees of rotation during which the valves are active. The lift determines the movement of the valves. More lift increases the vertical movement of the valve, significantly increasing airflow in the combustion chambers.
How are camshafts made?
Depending on the age and type of your car, camshafts come in different materials and follow different manufacturing processes.
However, the most common materials camshafts are made of are iron and steel.
Iron camshafts are made from castings to make the camshaft hard and durable, while the chilling process grants its resistance to wear. Cast iron ones are also cheap and simple to produce. As such, this production method is used for most mass-produced vehicles.
Steel camshafts are commonly used in luxury and high-performance cars. Naturally, these camshafts are of higher quality, but they’re also harder and more expensive to produce. Steel models are made by forging or CNC machining.
While camshafts look similar to each other in basic design, there are some variations. Most cars use solid camshafts, while some manufacturers opt for a hollow cylinder to reduce weight and increase the overall performance of the engine.
Common camshaft issues
Like virtually every other part of the engine, the camshaft is prone to wear and various connected issues. Generally speaking, a failure could be the result of extended use and normal wear, but also improper installation and break-in. It’s important to point out that cam problems are not that frequent. If you stay on top of your car’s maintenance schedule, change your engine oil regularly and use the right oil grade, it’s unlikely that you’ll ever have to have your camshaft replaced.
However, if your engine overheats or runs dry because of an oil leak, the cam might suffer excessive wear and lead to important problems. If it’s your case, here are the most common causes of camshaft failure to help you identify what might be the problem with your vehicle.
Lack of lubrication
Proper lubrication is the most important way to preserve your car’s camshaft. Lubrication prevents premature wear by reducing friction and overheating. Camshafts don’t use journal bearings like crankshaft do. If the oil supply stops for any reason, the cam will sit and rub directly onto the engine head. When it happens, the cam will start grinding the engine head. At first, you might see oil beginning to leak around the end seals. If the engine keeps on running, the cam might become loose and may cause timing problems.
Increased friction will also gradually wear the cams down, disabling the camshaft from completely pushing the valves down. Consequently, this can lead to decreased power, reduced fuel-efficiency as well as all sorts of complications such as cylinder leaks and an incorrect air-fuel ratio.
Improper lubrication can be caused by many faulty components. A malfunctioning oil pump or clogged oil passages can easily bring the oil pressure down and damage the cam. Using the wrong oil grade will also make it harder for the fuel pump to buildup enough pressure to support and lubricate the camshaft.
Excessive end play of the camshaft
On flat-tappet cam systems, the camshaft is prone to excessive end play. Flat tappet systems force the camshaft into its natural position. End play is a bigger issue than with roller camshafts which allow the cam to move and shift depending on temperature gain.
When end play becomes excessive, it pushes the cam further into the engine block. This increases friction between tappets, causing the camshaft to wear even faster. With increased wear, it can no longer move the valves as efficiently as before. Excessive end play also causes issues of the distributor gear, leading to timing problems which decrease performance and fuel economy.
When a new camshaft is installed, it’s important to properly lubricate it and to follow the break-in process. An improper mounting and tightening procedure as well as omitting to follow the manufacturer’s recommendation regarding the pre-lubrication of the cam can lead to significant problems quite quickly.
Each engine has a specific procedure to ensure the cam is installed correctly and lasts as long as possible. When in doubt, get your hands on your car’s repair manual for more info on the specific procedure for your engine.
Old lifters paired with a new cam
Specific lifters are mated to specific lobes and that’s why it’s important not to improvise when installing new camshafts. It’s also why it’s essential to mark lifters when removing them for any other reason. Lifters should always be re-installed in the same position as they were before.
When installing a new cam, using the same old, slightly worn lifters will often reduce the lifespan of both components. If you plan on installing a new cam or even when replacing it with a used one, you should think about replacing the lifters too.
On the other hand, the reverse is not true. You can very well install new lifters and pair them with a good used cam.
A camshaft can break due to various reasons. Improper installation and cracks or fractures in the cam during the shipping process may happen. A loose connecting rod or another rotating part is the main cause of camshaft fracture. We wish it never happens to you.
Signs of a faulty camshaft
The most common signs of a faulty cam are timing problems and misfires. If, for one reason or another the timing of the camshaft changes, the valves won’t open at the right time and may cause multiple misfires.
However, physical damage is the only clear sign of your car having issues. You simply can’t know if the problem comes from the cam or not until you visually inspect it. Pitting of the lobes is a normal wear process. However, if ignored for long, it can cause failure and damage to other vital components of the engine.
Pitting of the lobes can also be caused by dirt and debris. It’s important to make sure that the camshaft is installed in a clean environment and that your engine oil is replaced on time.
To sum it up
Even though it looks simple and easy to manufacture, a camshaft is an important part of your car’s engine. Because of that, it needs to be maintained to prevent issues and to keep your motor in good health. Whether your engine has one, two or four cams, proper maintenance, and good lubrication are the keys to your engine achieving its full capacity.