Camshaft working pdf

Running along the shaft are lobes which are manufactured to sit at different angles. These lobes are positioned in such a way that — when the camshaft is rotated — they come into contact with rocker arms that then open the engine valves.

The valves themselves are spring-loaded, meaning that once the lobe has done its job of opening the valve, it naturally closes as the spring becomes uncompressed. The timing of the camshaft is all operated through the cambelt or timing belt which is synchronised with the movement of the crankshaft. While a SOHC system has a camshaft that completes both the intake and exhaust stroke valve movements, a DOHC system has two camshafts above each bank of cylinders — an intake camshaft and an exhaust camshaft.

The most extreme camshafts come in the shape of those featured on the Bugatti Veyron. It helps to protect the camshaft from breaking the engine block in case of engine failure.

Bearing shells keep the camshaft in a smooth rotation. During the rotation of the camshaft, the lobes work with the motion of the piston. The purpose of lobes is to open and close the valves for intake and exhaust gases. Its speed usually depends on the engine speed. When using a roller cam you will need to provide some means to support the cam at the rear of the engine. The thrust plate is attached between the cam and timing gear and mounted on the front cover for proper end play. A chain sprocket is attached to the camshaft end of the engine to retain the timing belt.

This sprocket is attached to a chain. These sprockets are capable of turning at the same speed even if they do not touch. The woodruff key is also the main part of the camshaft of the engine that is used to retain the cams at the right time.

The camshaft is operated by the crankshaft either by a pair of meshing gears timing gears or a pair of timing sprockets connected by chains. The camshaft gear or sprocket has as many teeth as the gear or sprocket on the crankshaft.

This gives a gear ratio. The camshaft rotates at half the speed of the crankshaft. Therefore every two revolutions of the crankshaft create one revolution of the camshaft and one opening and closing of each valve in the four-cylinder engine. The gear and sprocket maintain a definite time relationship between the camshaft and crankshaft to insure opening the valves exactly at the correct time in relation to piston position.

Timing marks on the gears and sprockets are used to set the shaft incorrect times with each other when the units are assembled. The figure shows that the smaller circle on the crankshaft timing gear must fall between the two smaller circles on the crankshaft timing gear to ensure correct valve timing.

The sprocket marks are in a straight line with the centers of both shafts to ensure correct valve timing. An engine camshaft is made of solid metal to achieve greater rigidity. Camshafts are usually made of cast iron as it gives more strength and is also used for mass production. Whether we're talking about axle ratios, compression, carburetor size, timing, or e. And perhaps nothing else is discussed as emotionally as camshafts.

Lift, duration, lobe center, overlap, and much more confer just how the camshaft will or will not alter an often theoretical engine's performance personality. In scientific terms, it's all about the area under the curve.

Just like that calculus class you wished you didn't have to take or avoided altogether , the camshaft in your engine is largely based on the same mathematical rules. To allow more airflow into your engine, a camshaft is designed with a profile or curve that provides a specific amount lift to the valve. So in this issue, we're going to do some heavy bench racing and delve into camshaft basics.

The better we understand how each of these terms affects an engine, the better armed we are to choose the best camshaft. So hang on, cam speak is coming up. One of the camshaft's most fundamental tasks is to transform its rotating motion into linear motion or lift. This is accomplished on a typical Chevy V-8 with 16 lobes an intake and an exhaust --all of them ground to an eccentric shape called a lobe to allow each lifter to raise and fall above a base circle.

Just how far mathematically each lobe raises the lifter is called the lobe lift. The lift that is typically referred to in a camshaft catalog is the valve, or gross lift, and is achieved by multiplying the lobe lift by the rocker arm ratio.

For most small-blocks, the standard rocker ratio is 1. By replacing the standard rocker arm ratios with a higher-ratio rocker arm, you can add valve lift and some duration. If we use the camshaft with the 0. Though these two gross lift examples are close to the upper end of a very high-performance small-block Chevy with a flat-tappet camshaft, the mathematical theory is the same for all engines.

Camshaft duration is the amount of crankshaft rotation that occurs as the cam lobe moves the lifter off of the base circle; it is measured in crankshaft degrees to make it easier to degree check the cam to make sure it is positioned properly in the engine.

Determining the specific point that the lobe begins to move, the lifter off of the base circle upwards can be difficult--so most camshaft companies use a standardized checking point to reference lift. Consequently, the camshaft industry has established a common duration checking point of 0. Generally, added duration is helpful in high-rpm engines, but not typically in low-rpm engines. This is because the added time that the valves are open in high-rpm engines allows the airflow additional time to enter or exit the cylinder.

But at lower rpms, the added duration opens the valves too long in relation to the piston's position in the cylinder, and the pumping pressure is lost. It's also important to discuss the opening and closing points of the valves. These points can be checked by degreeing the cam in the engine by degreeing or simply referencing from the information on the cam card supplied with each new camshaft. These values can therefore be verified when the cam is installed and degreed.

If you're not sure of the duration of your camshaft but have determined the intake and exhaust closing points, you discover the duration by adding the opening and closing point values to degrees. The profile on this cam keeps the intake valve open longer than the other cam profile. At low engine speeds, this rocker is not connected to any valves. At high engine speeds, a piston locks the extra rocker to the two rockers that control the two intake valves. Some cars use a device that can advance the valve timing.

This does not keep the valves open longer; instead, it opens them later and closes them later. This is done by rotating the camshaft ahead a few degrees. If the intake valves normally open at 10 degrees before top dead center TDC and close at degrees after TDC, the total duration is degrees. The opening and closing times can be shifted using a mechanism that rotates the cam ahead a little as it spins.

Closing the valve 20 degrees later is good, but it would be better to be able to increase the duration that the intake valve is open. Ferrari has a really neat way of doing this. The camshafts on some Ferrari engines are cut with a three-dimensional profile that varies along the length of the cam lobe. At one end of the cam lobe is the least aggressive cam profile, and at the other end is the most aggressive.

The shape of the cam smoothly blends these two profiles together. A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam. The shaft still spins just like a regular camshaft -- but by gradually sliding the camshaft laterally as the engine speed and load increase, the valve timing can be optimized. Several engine manufacturers are experimenting with systems that would allow infinite variability in valve timing.

For example, imagine that each valve had a solenoid on it that could open and close the valve using computer control rather than relying on a camshaft. With this type of system, you would get maximum engine performance at every RPM.

Something to look forward to in the future Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar.