Updated at: 17-07-2022 - By: Lucas

During valve lapping, the intake and exhaust valves are seated perfectly on their seats in the engine cylinders. Lapping is usually done after an engine overhaul or when new valves are installed.

As a result, the combustion chamber is kept as clean as possible and the engine’s performance is maintained to the highest possible standards.

When valves are not lapped, some of the kinetic energy of the combusted gases is wasted, resulting in underperformance of the engine.

The form of the valves in certain modern autos is controlled by an automatic control system. It does not require any manual lapping because it simply grinds the valve.

Valve lapping can be done at home, but it does involve some mechanic abilities, and if you are not that person, you should seek the help of a mechanic.

Tools like lapping paste, a tool for removing the valves, and others will be discussed in this post as we progress through the process.

What tools are required for valve lapping?

lapped valves (2)

In order to complete this technique, you’ll need to remove the cylinder head first, thus you’ll need a cylinder head removal tool. Using a conventional screwdriver or padlock keys will work, but a torque wrench is required in order to properly replace the cylinder head. This is because the cylinder head bolts must be tightened, and only a torque wrench can accomplish this.

You’ll need the following items for valve lapping:

Electric screwdriver or a drill. Both an electric drill and an electric screwdriver are suitable for lapping since they can rotate in both directions.

  • A paste for grinding valves. You can buy this ready-made paste from automotive shops. If you have some skills, you can make this composition on your own.
  • Manual valve holder. You can find this tool when buying the special paste for valve grinding, they often will be sold together or you can buy them separately
  • A hose and a spring. The spring must have a low rigidity, its diameter is 2 or 3 millimeters larger than the diameter of the valve stem. So is the hose, so it can be put on the rod. You can also use a small clip to secure it. You also need a short metal rod with a diameter similar to the piston rod so that it fits in the rubber hose.
  • Kerosene. Needed for checking the lapping and cleaning.
  • A dry cloth. To wipe the treated surfaces.
  • Solvent. To clean the work surfaces

How valve lapping is done?

Two methods are available for valve lapping. Manual lapping and automated lapping are two methods that can be done with the help of a drill or an electric screwdriver, which we’ll cover in more detail later.

Remove the cylinder head and then the valves from the cylinder head, no matter what method you use to remove the valves. After that, you must remove any carbon deposits from the valves.

Abrasive surfaces and particular cleaning solutions should be used in order to get rid of grease and filth.

Lap valves using a drill

The quickest and most efficient method of lapping valves is to use a drill.

  • Take a prepared metal rod and put a rubber hose with the same diameter on it. To fix it better, you can use a clamp.
  • Attach to a metal rod in the chuck of the drill or electric screwdriver.
  • Put a spring on the valve’s stem and install it in its seat
  • Pull the valve out of the cylinder head and apply lapping paste around the perimeter of its plate.
  • Insert the valve stem into the rubber hose, and, if necessary, use a clamp of the same diameter for better fastening.
  • Use the drill at low speed and start grinding the valve in its seat by moving the drill back and forth, the installed spring will help here. After that, reverse the movement of the drill in the opposite direction until a matte band appears on the valve body.
  • After lapping, wipe the valve from paste residues, preferably with a solvent. It is necessary to remove the paste not only from the valve’s plate but also from its seat. Don’t swap the valves, because lapping is performed for each valve individually.

Valve lapping is no longer necessary in most current engines because they are constructed of aluminum, and the risk of valve replacement is much greater if an engine part is damaged.

How to check valve lapping?

You can tell if your valves have been properly lapped by checking the flow of gases through them when they are under stress. Because the valve holes are on top and the collector well holes are side-by-side, the cylinder head must be positioned upside down.

After that, fill the valve outlet cavity with a little amount of fuel. Adding a little air to the intake and exhaust manifolds with a compressor is a good idea. No air bubbles should form around the valves if they have been effectively lapped. This is true even if the compressed air pressure is applied to the valves.

A lack of tightness or improper lapping is indicated by the presence of air bubbles coming out from under the valves.

These steps are simple to follow and may be applied to any engine.


It’s possible to do valve lapping on your own, but only if you have the requisite expertise and tools. You should avoid doing something if you have any doubts about it and believe it is wrong.