A burnt valve refers to an engine valve that is damaged by burning on the area where the seat seals the opening in the cylinder head. When combustion gases escape between the valve and the valve seat, not sealed properly, the hot combustion gases forced past the valve begin to burn the valve’s edge. This gets worse, the longer it stays without being rectified. This type of failure affects the exhaust valves but can also damage the intake valves.
The cylinder’s head valves are crucial components of the engine that undergo massive stresses while opening and closing up to 2500 times each minute while under normal working conditions. When the valves are damaged, the results can be poor fuel consumption, reduced power, or even the engine’s complete failure.
How does it Work?
The external combustion engine mainly uses two different types of valves differentiated as the intake and the exhaust valve. The intake valves let the fuel and air mixture get into the cylinder while the exhaust valve lets them evacuate the cylinder. It is a continuous process that takes place in order for the engine to run. They are made of hardened metal that must withstand the extreme process and condition of the combustion chamber.
They have a slim stem leading to a flat face. The intake valve is usually larger than the exhaust valve. The modern engines have two intake and two exhaust valves in each cylinder. The more the air runs in and out of the engine, the more efficient and powerful the engine will be.
In the internal combustion engine, four events must take place to ensure a smooth and successful operation. These events are called strokes. Different tasks are performed in different strokes;
- Intake Stroke
This is the first stroke. During the intake stroke, the fuel and air mixture is drawn into the combustion chamber through the intake valve’s opening. In the direct injection engines, the fuel is injected after the air has been let in.
2. Compression Stroke
This is the second stroke. Both the intake and the exhaust valves close containing the fuel and air mixture in the combustion chamber. The piston is then forced upward, compressing the fuel and air mixture, making it to be highly compatible.
3. Power Stroke
This is the third stroke. A spark plug ignites the compressed fuel and air mixture while the exhaust and intake valve remains closed. The ignited mixture quickly expands, forcing it back downwards in the cylinder. This consequently spins the crankshaft, which in return eventually turns the wheels of the vehicle through the power train.
4. Exhaust Stroke
This is the fourth stroke. During this stroke, the piston begins to head upwards again while pushing the expanded mixture through the open valve. The exhaust valve then closes after the exhaust gases have escaped the cylinder and the intake stroke occurs again.
This whole cycle occurs about 1250 times per minute if you are driving at freeway speed.
Valves can fail due to a number of reasons but the most common being burnt valves. When a damaged or burnt valve is suspected, the first step of diagnosis is a leak down a step. What happens during this step?
- The engine, with the intake and exhaust valve closed, is rotated until the cylinder’s top clear center is achieved.
- Through the spark plug hole, the compressed air is injected into the cylinder.
- The ability of the cylinder to hold pressure is measured using a leak down gauge.
If the leakage is discovered coming from either the exhaust or the car’s throttle body, then the valves are damaged. The valves can also be inspected by inserting a borescope into the cylinder. You may be required to remove the valve cover.
What Are the Possible Causes of the Burnt Valve?
Burnt valves usually occur when the valve can no longer seal correctly due to extreme temperatures damaging the valve’s material. It is important to note that some causes can produce burnt valves on their own, while for others, it is a combination of several causes that eventually results in a burnt valve.
- The concentration of combustion gases escaping past the valve at one point.
- Incorrect valve clearance can endanger the valve sealing and cause it to burn.
- Excessive localized heat.
- Weak valve springs.
- Incorrectly set tappets. This can be confirmed before the strip down. Hydraulic tappet depression should be checked too.
- Incorrectly cut seat. The position of a seat contact of a valve should be around 1 to 1.5 mm away from the valve margin.
- You have incorrectly faced valves. You can check the face finish to ensure it is okay, and without any chatter or flats. Check out for the correct face angle and valve run out.
An irregular valve sealing with the cylinder head valve seat
- Carbon residues generated by poor mixture (irregular combustion) appears at the seat region and put the sealing between the valve and its seat at risk.
- Running a dry fuel like L.P.G causes inadequate lubrication of the valve seat resulting in the valve seat failing to and consequently the valves.
- Another factor is deficient refrigeration due to partial obstruction of the cylinder head cooling. This results in the valve cooling inadequately.
Exhaust valves are more prone to burning as they run hotter than the intake valves, between 1,200- and 1,350-degrees Fahrenheit. Most of the time, when they burn, they cause a loss in compression.
The burnt valve is a common car tribulation experienced by car owners. However, you can save the exhaust valve from burning if you discover the symptoms before it is destroyed completely. Experts suggest getting familiar with burnt valve symptoms to ensure that you detect them before the problem becomes bigger.
You Treat Your Car Badly
Most vehicle owners understand that a vehicle must be inspected and serviced from time to time, as referred to as routine maintenance. For those who don’t, the likelihood of problems that cause a burnt valve is extremely high. If the vehicle is not inspected routinely, small problems can escalate to major problems that are much more expensive to fix. This is also true for vehicles that sit for long periods of time.
If you want to avoid burnt valve problems or other issues and save $100s of dollars that you’ll spend at the auto repair shop, you’ll need to service your vehicle often – you can use our mechanic-rated Auto Maintenance and Repair Manual to do this. It’s basically what mechanics use to go through your vehicle to check if there are any problems that need fixing. As soon as they notice the most minor problem, they’ll ask you to fork out some money even though it’s a problem you can fix yourself in minutes – the manual will teach you how to maintain your vehicle every few thousand miles and it’ll teach you how to fix minor problems that mechanics will ask you to pay for; saving you money in the long run.
A lot of our readers have the Auto Maintenance and Repair Manual printed on their garage wall and 92% of them haven’t visited the auto repair shop in the last year because they know what to do to avoid problems. All it takes is giving your vehicle a little attention every few thousand miles and you’ll never spend money at the workshop again.
What Are the Symptoms of a Burnt Valve?
Poor Engine Performance
A burnt valve causes reduced performance of the engine. They often have huge holes leaking out all the gases, eventually reducing compression resulting in the engine’s poor performance. Chances of burning the valves if other compression problems are not fixed are very high.
Misfiring
Misfiring is a term used when the cylinder in the engine does not discharge the required amount of fire. Good compression, the right spark at the right time, and a proper mixture of air and fuel re essential for the cylinder to work properly. Typical signs of misfires include steering vibration, the engine shaking while idle, or if the engine experiences difficulties to start or stalls when starting. Misfiring could also mean losing compression if it occurs when the cylinder loses a large part of fuel and air mixture before ignition. If not for a blown head gasket or misfires due to loss of compression, then there is a burnt valve.
Complexity in Starting the Car
A car cannot start as it should if the valve is burnt. A burnt valve does not let the car to gas up the way it should. The car may eventually start, but this is still an indication that you should check your valves.
Power Loss
Loss of power is an indication of a burnt exhaust valve. It is linked to ignition misfires since a misfiring cylinder causes up to 25 percent of power loss problems.
Puffing or Puttering Sound
A burnt exhaust valve often makes puffing or puttering sounds. Some people refer to it as a chuff- chuff sound. The sound usually goes off every time the cylinder tries to fire. There is a trick that car owners can hold a dollar bill and let it flap over the exhaust pipe. If it is sucked in, it most likely means that the exhaust valve is burnt.
Failed Emission Test
The engine will blow hydrocarbons out of the tailpipe if the exhaust valve is burnt. This is a major cause for many vehicles to fail emission tests. If your car fails this test, then it is time to check your exhaust valve.
Having exhaust valves that are functioning properly is important for automobile maintenance as exhaust valves that function poorly lead to poor oil consumption, compression leaks, valve train noise, and complete valve failure. Here are ways to help you prevent a burnt valve.
- Use good quality fuel to help prevent carbon build-up on the valve seats.
- Have your mechanic check to make sure that the valve clearances are within specification.
- If your vehicle uses the L.P.G fuel system, make sure the engine is L.P.G compatible since most of them are not. Valve failure is inevitable if the engine is running L.P.G but isn’t L.P.G compatible. It is generally less costly to remove the cylinder head and modify it for L.P.G before the valves begin to burn than to wait until the damage is done. Once completed, it will be safe to use the modified L.P.G without fear of damaging the engine.
- Maintain a clean and efficient cooling system so that your engine doesn’t run too hot.
Considering that exhaust valves are more susceptible to burning, how can you cool down the exhaust valve?
- Provide a suitable number of jets on the channel through which cold water direct from the radiator is pumped. The water flowing from these jets or nozzles comes in contact with the areas adjacent to the exhaust port and the exhaust valve, which are then cooled.
- Improved cooling can also be achieved if cooling jackets are provided elaborately near the exhaust port and exhaust valve.
- You can also achieve better cooling by filling part of the exhaust valve stem with sodium. The sodium melts at a high temperature of about 150 degrees centigrade. The motion of the exhaust valve throws it up and down. The heat from the hot regions is then conveyed to the comparatively colder regions. Sodium has a high boiling point and is a very good conductor of heat.
If there is a failure in one or more valve seals, the stems need to be replaced. Valve replacement is a very big job requiring an engine tear down. The repairs can take up to 35 hours to complete after diagnosis. Value repairs cost can surpass $5,000 for just labor. Usually, many gaskets can be replaced, and many other parts can be removed since the engine is broken down during the repairing process. You may consider taking advantage of this time by having other needed repairs done as you may get discounts for overlapping labor.
It is very unusual to burn an intake valve. Unlike the intake valve, which has the cool intake charge flowing over its head, the exhaust valves burn because they have hot exhaust gases flowing over their head. A burnt valve reduces the general performance of the vehicle and poor fuel consumption. Continual driving with a burnt valve causes a lot more damage to the engine and will cost more to repair in the long run.