What is a Camshaft and What Does it do?
Table of Contents
What is a Camshaft?
The camshaft, located in the cylinder head, is responsible for opening and closing the engine valves, allowing the intake and exhaust of the combustion cylinders. It does this by converting rotational movement into linear motion. The camshaft features lobes, to correlate with the combustion cylinders, and these sit in contact with followers. As the camshaft rotates, the followers match the displacement of the lobes and push down on the valve stem, allowing it to open. The valves are powered by springs, which allow them to return to their closed position.
The most Common Camshaft Configurations
Single Overhead Cam (SOHC)
A single overhead cam defines any engine that only features one camshaft per cylinder head. It is responsible for operating both the exhaust and inlet valves and can typically run 2-3 valves per cylinder.
Double Overhead Cam (DOHC)
DOHC defines any engine that features 2 camshafts per cylinder head, meaning that the inlet and exhaust valves each have a camshaft dedicated to them. With at least 4 valves per cylinder, this is a good way for manufacturers to increase the performance without adjusting displacement of the camshaft lobes.
As there are more valves in operation, it essentially doubles the airflow, increasing the power output while sacrificing fuel efficiency.
Camshaft Materials
Chilled-Cast
A chilled-cast camshaft is made from cast iron. A sand mould is used with pieces of metal, called chills, inserted into the cavities forming the shape of the camshaft. The chills have a higher thermal conductivity, so that when the molten metal is applied the areas in contact with the chills will cool faster and become harder.
This process is a lot easier to scale and therefore tends to be cheaper.
Steel Billet
Starting off with a blank cylinder of steel, everything, including the lobe seperation and journal, must be cut. It’s placed on a CNC machine and a computer controlled grind wheel will begin shaping it. Rough grinding creates the required shape and then it goes through a finishing to remove any imperfections.
The cam is finally put through a seperate hardening process to improve its wear resistance.
Steel billet tends to be tougher and requires a more technical manufacturing process which is why these are usually more expensive.
Differences in Tappets
The tappet, also known as a follower, is what converts the rotational motion of the cam and converts it into linear movement pushing down on the engine valves.
Flat Tappets
As the name suggests, flat tappets have more of a flat surface which sit on the cam lobe. Despite its appearance, and name, they are not completely flat and have a slight crown. The cam lobes are manufactured with a slight taper to enable the follower to spin as the lobe rotates over it. This creates a more uniform wear.
The flat tappet has less mass and weight, however it does require proper lubrication and a more extensive break-in process.
Roller Tappets
Rather than a solid piece of metal being contact with the lobes, roller tappets feature an additional part to roll against the cam. This reduces friction, freeing up more power that would otherwise be lost with flat tappets.
This also means the cam can have a more aggresive lobe profile without the followers digging in. These followers only require standard engine oil to lubricate.
Rocker Arms
In most engines, the camshaft sits directly above the valve train so the tappets are in contact with the valves. Sometimes, for the sake of a more compact design, the camshaft or valves are placed in a different location. When this happens rocker arms are used to redirect the movement.
Difference between a Camshaft and Crankshaft
The crankshaft is responsible for the pistons, located beneath the cylinder head. The camshaft and crankshaft are kept in sync, using VVTs and a crankshaft pulley, to ensure that the pistons and engine valves do not collide.
How can a Camshaft Fail?
On its own a camshaft shouldn’t really fail, unless there were some faults in the manufacturing process, however these are usually caught during QC. The main causes for a camshaft to fail are damage up-to and during installation, incorrect installation and insufficient maintenance.
Click here to read the 5 ways a camshaft can fail>
GT Automotive Camshafts
At GT Automotive, we stock a wide range of camshafts available for the most relevant applications. Before we expanded into the aftermarket space, we started off supplying OE camshafts globally to our elite customers. With over 2,000 part numbers over the last 40 years, our factory has become an established global OE manufacturer. Our in-house foundry and tight quality control makes us a competitive force within the market. Since 2015, we have been supplying this same level of OE quality for the aftermarket.
View our top Camshafts for September 24>
FAQ
What is a Camshaft?
The camshaft is a long rod, typically made of cast iron or steel, which features lobes responsible for opening and closing the engine valves. It works in sync with the crankshaft pulley, with the help of a timing chain or belt, to ensure the valves do not collide with the pistons.
How does a Camshaft Fail?
Overall, a lack of maintenance, improper fitting, or using a damaged camshaft can lead to failure. Additionally, pairing old lifters with a new cam or using the incorrect valve spring pressure can also cause camshaft failure.
What Happens when a Camshaft Fails?
If the camshaft begins to fail the engine will run sluggish and consume more fuel. The driver may experience engine backfiring or cylinder misfire. Ultimately, should the camshaft completely fail, the pistons and engine valves can collide causing massive damage.
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