How to Lap Valves

Would you like to learn how to lap valves? Then this article is going to be the solution for you. We are going to teach you everything about the valve lapping process.

What Is Valve Lapping?

Through this process, you will have a precise fit when it comes to the intake and exhaust valves that are part of the engine cylinders. Generally, this task is done after performing an engine overhaul, or when current valves need to be changed. 

By performing a valve lapping, the combustion chamber is going to be safer thanks to an improved chamber. Also, the engine will work efficiently and every single component inside it, it’s going to improve when it comes to productivity. 

Keep in mind that if you don’t perform a valve lapping to your valves, the energy won’t be enough, and the engine won’t have the firepower to start. There are modern vehicles that come with an automated system that can control the shape of the valves.

There won’t be a need to do manual procedures, and this is one of the main benefits of owning a modern car. Besides, this process can be done without having to visit a professional.

Nonetheless. it requires the use of specific tools. So if you don’t know how to do it, then you are going to need assistance. 

Tools Required For Valve Lapping

Before getting started, you will need certain tools. Pay close attention to the list:

  • A special paste. You can get this tool at specific shops. If you know something about grinding valves, then you can do it by yourself. 
  • Valve holder (Manual). Just like the paste, you can buy this tool at a special shop. 
  • A spring and a hose. Make sure the spring doesn’t present too much rigidity. It can only be 3 millimeters larger than the valve steam. Next, you can put the hose on the rod. Try to find a small metal rod for it to fit down the rubber hose perfectly. 
  • Kerosene. Check the lapping and clean it. 
  • Clothes. This is going to help you clean all the surfaces.
  • Solvent to clean. Combine it with a dry cloth to clean the surfaces a lot better. 

How to lap valves: The procedure 

1. Remove the valves 

Start by removing every valve from the head. While at it, take the opportunity to remove the dirt adhered with a small brush. Depending on the condition of the valves, new ones must be installed and then lapped to have the right seal. 

2. Put the valves in place 

Ensure both the valve and the seat and clean them the best way you can before applying the grinding paste. Now, insert the valve into the correct port and press hard enough for the head to fix. 

3. Search for changes 

Rotate the lapper and rub it between your hands. There is going to be a sound, and it will go from a grinding sound to a smooth sound. After listening to the tone, lift the valve and apply the paste all over the face of the valves. 

4. Pinpoint the port that has lapped 

Don’t stop the procedure until the valve and the seat are bright enough. Try to identify which valve is lapped to a certain port, and clean every remaining valve and head. 

Install the valve assembles correctly. 

Ways To Check Valve Lapping

Once you finish valve lapping, the best way to find out if you did everything right, is by checking the gas passage through the valves under load. Place the cylinder head upside down for the valve holes to be on top. 

Add fuel into the valve cavity. An air compressor will be needed to add air in the opening of the exhaust and intake manifold. If everything was done correctly, the air formation bubbles should not be present under the valves. 

On the other hand, if you notice air bubbles under the valves, it will mean that the lapping was not successful, and you are going to have to do it from the start. 


Is lapping valves necessary?

Lapping is effective; however, it is time-consuming and probably unnecessary if the valves are not already leaking. If the valves are leaking, it is usually because the guides have become misaligned as a result of wear.

Can you lap valves too much?

It is not necessary or good to over-lap the valves, but it is unlikely but possible, to remove too much. If you are unable to achieve a consistent grey ring, the seats are probably worn out and will require cutting. Do not attempt to remove more than three times of lapping.

How much does a valve job usually cost?

As a result, a complete valve replacement can cost more than $1,000. Know how much you should expect to spend to repair your car. In the United States, the average cost of a valve adjustment ranges from $246 to $336. Labor costs range from $220 to $278, while component prices range from $26 to $58.

How do I know if my valves are seating?

Using a new valve – or one that you are sure is in excellent working order – install it in the guide, press the valve hard against the seat, and watch to see if it bounces back into the seat. A poor seat tends to dampen the action, making the valve feel as if it is stuck in the seat.

Can I do a valve job myself?

Valve installation is a simple process. You can purchase a valve seat grinder and perform these tasks yourself, as well as replace the seals.

What is lapping tool?

Lapping is a soft material that is loaded with an abrasive and used to cut harder materials. A lapping machine uses a piece of lead loaded as a lap to cut a piece of hardened steel. It is also used for precision surface finishing, often in conjunction with loose abrasive compounds.

Final Thoughts – Valve Lapping

The process of sanding the surfaces of valves and their heads where they come in contact with an internal combustion engine is known as valve lapping. If there is a malfunction or damage to the valves or valve seats, this procedure should be performed to ensure proper operation.

If the valves and accompanying seats are broken or defective during the compression stroke of the engine, air and fuel can leak out of the engine.

Liam Dare

As CEO of, my passion for the automotive world motivates me to build online businesses that provide information and entertainment to users. I am proud to contribute in a positive way to the automotive community.