Engine Valves: What They Are and How to Free a Stuck Valve
If you have a stuck engine valve, your vehicle won’t run as it should. An engine valve, or exhaust valve, is also known as a butterfly valve. It is used to allow or restrict the flow of fluid or gas that moves while your engine operates.
When it is working properly, the engine runs more quietly at low RPM and starts quickly and smoothly. The heat from the exhaust manifold warms the fuel-air mixture for a cleaner start.
Although a stuck valve may sound like a minor issue, this tiny valve can cause numerous problems — even engine failure. The most common causes of valves sticking are heavily leaded fuels and resin deposits.
You may also have superheated exhaust gases trapped in the exhaust manifold. This can affect the car's performance because the trapped gases will not allow enough fuel to enter the engine to allow it to start effectively. The hot gases can cause warping or cracking of the exhaust manifold and may warp the valve itself.
The valves are found in your vehicle's cylinder head. Instead of paying a mechanic to fix your car's stuck valve for you, follow these steps to rectify the problem.
Step 1 - Inspect
At about 50,000 miles, the exhaust valve may develop problems with sticking closed. While the engine is cold, inspect the exhaust valve to see why it might be sticking. You should check your engine regularly for any signs of wear, like a stuck valve, to keep your car working at its best.
If you don’t know what your valves should look like, check your manual for reference. If you find a buildup of debris, move on to Step 2. If your valve is defective rather than dirty, skip to Step 3 to repair it.
Step 2 - Clean
If the fuel that’s been used in the engine has caused a carbon deposit build-up around the valve, it can get stuck. Try using a small brush to apply a solution of alcohol mixed with powdered graphite to serve as a lubricant for the valve shaft.
If this does not loosen the shaft, spray it with a spray solvent that removes rust. The spray can penetrate where the liquid graphite solution will not reach. This removes built-up particles and allows the valve to rotate properly again around the shaft with just the vacuum pressure provided by the engine.
Step 3 - Repair and Replace
If any of the components that are used to fix the engine valve in place have come loose or broken off, you must repair these. Find replacement parts at your local auto parts store or online.
The issue can often be fixed during an oil change by rotating the counterweight that controls the motion of the valve. If the valve shaft is jammed so that the exhaust valve will not rotate, tap the ends of the shaft with a hammer to free them.
If this process is not effective, replace the entire valve. In a 6-cylinder engine, you will need to remove the exhaust manifold to get at the exhaust valve to remove it.
For more severe valve problems, like extra corrosion or broken pieces, you will likely need to remove the head the valves are attached to. You can do so by first removing the fasteners and then lifting them out of place. To ensure you purchase the correct replacement parts, bring the broken parts into the store to have an employee help you match them.
Step 4 - Prevent Stuck Valves
If the valve is stuck open, your engine will not get a warm start because the exhaust will be channeled straight out the tailpipes, instead of around the base of the carburetor to warm up the engine. You will find your engine is slow to start and will not stay warm.
The gas-air mixture will be too rich because the automatic choke will not activate at the proper time to allow in air for a balanced fuel mixture. Unburned gasoline will slosh around the inside of the cylinders, causing your spark plugs to foul. Lubricant will also be washed off the engine parts, causing increased friction and poor performance.
To prevent the valves from sticking in the future, use quality fuel and occasionally add a good gas treatment at fuel fill up.
Step 5 - Deal with Loose Springs
The chattering sound you hear when the engine is first starting may be due to a loose or broken butterfly valve spring. Remove the spring with a screwdriver and replace it.
If the valve spring breaks in an 8-cylinder engine, you will need to replace the entire exhaust heat thermostat containing the butterfly valve. The valve is usually welded to the thermostat shaft after it is assembled.
Mistakes to Avoid
Do not lubricate the exhaust valve with any kind of oil. Even the thinnest oil will make the valve seize and seal it tighter than before in either the open or closed position.
By following these steps, you will be able to fix a stuck engine valve and ensure your car runs smoothly.
If you have a small engine, you may be wondering if the above applies to you. The answer is yes. The process for dealing with a stuck engine valve will be very similar. You will first need to inspect the valve and then clean it. You will also have to replace any damaged pieces and should take care to prevent future issues.
The main difference is size. It can be harder to see what is going on in a small engine, so be careful what you are doing. Some of the replacement pieces may also be harder to find. Someone at an auto repair shop should be able to help you, though, even if it takes a little bit longer as they may need to order replacement parts rather than have them already available.
Motorcycles also have exhaust valves which allow things to enter the combustion chamber and have gasses exit. Dealing with a stuck one is a similar process as in a small engine or a regular engine, but if you aren't familiar with the process you may want to get professional help to repair yours.