What Is an Engine Valve?- Definition, Working, and Types

The heart of any vehicle engine lies in its internal combustion process, and at the core of this are the valves.

Often overlooked but essential to engine performance, valves play a crucial role in controlling the flow of air and fuel into the combustion chambers and expelling exhaust gasses.

If you want to learn about these simple, yet important components, make sure to join us in this article and we will go over everything you need to know!

What is an Engine valve?

Engine valves are mechanically opened and closed, to admit air or expel exhaust gasses, into the engine cylinder(s); the valves are located in the head casting of the engine. The area where the valve seals against the head is called the valve seat.

Most medium-sized internal combustion engines have either intake ports and exhaust valves, or both intake and exhaust valves. Smaller two stroke petrol/gasoline engines use intake and exhaust ports i.e. no valves.

Engine valves are common to many types of combustion engines, whether they run off a fuel such as gasoline, diesel, kerosene, natural gas (LNG), or propane (LP). Engine types vary by the number of cylinders which are the combustion chambers that generate power from the ignition of fuel.

They also vary by the type of operation (2-cycle or 4-cycle), and by the design placement of the valves within the engine [overhead valve (OHV), overhead cam (OHC), or valve in block (VIB).

The function of engine valve

Engine valves aren’t just fancy metal parts. They’re multitaskers that:

• Regulate the intake of air and fuel
• Expel exhaust gases
• Maintain pressure in the combustion chamber
• Help cool the engine
• Reduce noise
• Prevent backflow of gases

In short, they’re the bouncers of your engine, controlling what goes in and out.

Intake and Exhaust Valves

There are two main types of valves – the intake and the exhaust.

Intake valves are responsible for allowing the mixture of air and fuel to enter the engine’s combustion chambers. When the engine’s piston moves down on its intake stroke, a vacuum is created within the cylinder.

The intake valve opens at precisely the right time, allowing the air-fuel mixture to be drawn in from the intake manifold. The timing and duration of the valve opening are meticulously controlled by the engine’s camshaft.

Exhaust valves, on the other hand, facilitate the expulsion of burnt gasses from the combustion chambers after the power stroke. As the piston moves up on its exhaust stroke, it pushes the exhaust gasses out of the cylinder and into the exhaust manifold.

The exhaust valve opens at the appropriate moment to release the gasses into the exhaust system. Like the intake valves, the exhaust valves’ timing and duration are precisely synchronized with the engine’s camshaft.

Valve Timing and Lift

The timing and lift of the valves are crucial to optimize engine performance. The camshaft, driven by the engine’s crankshaft, is equipped with lobes that push against the valves’ valve stems, causing them to open and close.

The camshaft’s design determines the precise timing of valve opening and closing, which influences the engine’s power, torque, and efficiency.

Valve Train Components

The valve train consists of several components that work together to ensure proper valve operation. These components include valve springs, lifters (tappets), pushrods (in pushrod engines), and rocker arms or cam followers (in overhead cam engines).

The valve springs ensure that the valves remain closed when not actuated by the camshaft lobes. The lifters transmit the camshaft’s movement to the pushrods or rocker’s arms, which then open and close the valves.

OHC (Overhead Cam) engines feature the camshaft positioned above the cylinder head, allowing direct actuation of the valves. In contrast, pushrod engines have the camshaft located within the engine block, relying on pushrods and rocker arms to actuate the valves.

OHC engines are typically more compact and offer better valvetrain efficiency, while pushrod engines are simpler and often used in V-configured engines.

How does car engine valves work?

As mentioned above, valves in the car engine are responsible for controlling the flow of air-fuel mixture into the cylinder and letting the remaining gasses out of the combustion chamber. Below is more of a detailed explanation of how car valves work.

The engine valve’s mechanism is achieved through the camshaft, which is itself driven by a crankshaft. When the camshaft rotates, the lobes control the opening and closing of the valves according to the engine’s timing.

When the piston moves downward, the intake valves open up and create a vacuum in the cylinder. This particular action lets the air-fuel mixture into the combustion chamber from the intake manifold.

Once the intake valves are closed after the intake stroke, the piston moves upward, leading to the compression stroke. This stroke compresses the air-fuel mixture in the cylinder, and then the spark plug ignites the compression mixture to initiate the power stroke.

After the power stroke, the piston moves upward again, and the exhaust valves open. This allows the remaining burnt gasses to vent out of the cylinder and pass into the exhaust manifold.

Types of Engine Valves

There are 3 different types of engine valves as follows:

• Poppet valve
• Sleeve valve
• Rotary valve
• Reed Valve.

#1. Poppet Valve.

It is also known as a mushroom valve because of its shape. It is used to control the timing and quantity of gas flow into an engine. This is the most widely used valve in an automobile engine. The poppet valve is given the name because of its motion of popping up and down.

It consists of a head and a stem. The valve face usually with an angle of 30° to 45° is ground perfectly, since it has to match with the valve seat for perfect sealing.

The stem has a spring retainer lock groove and its end is in contact with the cam for up & down movements of a valve. In exhaust, a pressure differential helps to seal the valve. In intake valves, the pressure differential helps open them.

#2. Sleeve Valve.

The sleeve valve as the name implies, that it is a tube or sleeve that fits between the piston and the cylinder wall in the cylinder of an internal combustion engine, where it rotates/slides.

Ports on the side of the sleeves come into alignment with the cylinder’s inlet and exhaust ports at the appropriate stages in the engine’s cycle.

The inner surface of the sleeve forms the inner cylinder barrel in which the piston slides. The sleeve is in continuous motion allows and drives out the gases by virtue of the periodic coincidence of port cut in the sleeve with ports formed through the main cylinder casting.

Advantages: These valves are simple in construction and are silent in operation. There is noise because there are no noise-making parts like valve cams, rocker arm, tappets valves, etc., Sleeve valve has less tendency of detonation. Cooling is very effective as the valve is in contact with water jackets.

#3. Rotary Valve.

There are many types of rotary valves. The figure shows the disc-type rotary valve. It consists of a rotating disc that has a port. While rotating, it communicates alternately with the inlet and exhaust manifolds.

Advantages: Rotary valves are simple in construction and are manufactured at cheaper costs. They are suitable for high-speed engines. These valves have fewer stresses and vibrations. Rotary calves perform smooth, uniform, and noise-free operations.

#4. Reed Valve.

Reed valves are made of flexible strips of metal that perform the function of check valves. These strips when pushed to move by the incoming air-fuel mixture first allow it to enter the engine needs and at the same time prevent the exhaust gases from escaping.

Reed valves are typically found in two-stroke engines and are preferred due to their ability to regulate the air-fuel ratio.

Bad Engine Valve Symptoms

Issues with intake valves can lead to poor combustion, compromising the proper operation of the vehicle over time and reducing its performance. The indicators of valve issues include noise (ticking), loss of power, any ignition difficulties, high fuel consumption, and excessive smoke from the exhaust.

Removing and replacing the engine valves is not a task for anyone. The main check is for valve seal integrity, without which clean combustion cannot occur. Initially, valve wear leads to high oil consumption, worsening motorcycle performance, and over time, heat in the combustion chamber can damage other engine parts.

Symptoms of damaged valves are not always easy to recognize, as the damage can vary depending on the cause and the defect that shows up. Key elements to watch for are a loss of power or any unusual noises from the engine, particularly metallic ticking.

The symptoms of bad valves include:

#1. Cold Engine.

A cold engine test will give you a good idea if your valve seal is faulty.

Here’s how to check:

After your car has been left outdoors overnight, and on checking the top of the cylinder’s head inside the valve cover, you notice that there is residual oil on it, then it is a sign that you have a worn valve stem seal.

Similarly, when the engine is on, the residual oil is sucked down through the bad seal into the combustion area – As a result, a blueish smoke emerges from the tailpipe.

These bad valve symptoms show that your valve needs replacement to ensure it does not lead to other problems.

#2. Off-Throttle Braking.

Engine braking involves employing different means to slow down your car asides from the external braking.

In throttle braking, for instance, you can ascertain if the valve is faulty, especially while descending from a steep downgrade where the accelerator pedal remains static.

If a high intake manifold vacuum has already been created and there is a downward slant of the engine, it will cause the oil to accumulate at the front of the valve cover over the head. What’s more, burned oil will tend to exit the tailpipe in large amounts when the accelerator is pushed after a long coast.

#3. Rough Idling.

Bad valve seals typically appear when the car is idling at stop lights. The cause of this symptom is that prolonged idling of the vehicles causes significant levels of vacuum to build up at the intake manifold.

This causes oil to be drawn into the heads and collected at the valve stems. When there is a poor valve seal, the oil will be drawn to the valve guide and pass through the rapidly disintegrating seal when accelerating.

Checking your valve seals is necessary if you have rough idling and blue smoke.

#4. Excessive Oil Consumption.

One of the bad valve symptoms is Excessive Oil Consumption. Oil consumption will be extremely high due to faulty valve seals. Bad seals will result in an oil loss which you can witness on the oil dipstick.

A noticeable oil reduction caused by the oil being burned alongside the fuel can be found by accurately recording the oil level on the dipstick.

A typical engine holds about 4 litres of engine oil, and if you continue to drive your car while the valve seals are leaking, you can see the oil level dropping. If there are no visible engine oil leaks to account for the loss, faulty valve seals are the reason.

#5. Excessive Smoke.

The high presence of exhaust smoke, especially one that is blue-white and lasts longer after starting the car or accelerating is something of concern.

However, the smoke may disappear after a while, which could be misleading that all is well.

Nonetheless, bad valves may signal themselves in the issue of excessive oil burning while faulty piston rings and valve guides will cause excessive production of smoke.

#6. Loss of Engine Power.

Lack of acceleration power, when you engage the gas pedal, is also a result of faulty piston rings and valve seals.

Here, a compression test will help you to ascertain if the problem is due to the valve seal or the piston ring. You need to remove the EFI fuse and crank the engine, and then use the compression gauge to check the result.

FAQs.