Lapping of valves

The valves are lapped on the removed cylinder head. To remove the valves from the guide bushings of the cylinder head, it is necessary to remove the valve springs by compressing them with a special tool and removing crackers from the spring plates (see «Replacement of valve stem seals»). For lapping valves, it is most convenient to use a special mechanical device (reversible drill).



In addition, ready-made manual valve holders are available for sale.



In the absence of ready-made fixtures, you can use a fixture made according to the drawing (pic. 5.11).

Instead of a rubber hose and clamps, a tip can be welded to the fixture stem, in the side wall of which a through threaded hole is made, into which a bolt is screwed to fix the valve stem.


In addition, you will need: lapping paste, kerosene, a weak spring, passing through the valve seat hole along the outer diameter.

1. Clean the valve from carbon deposits.



2. Apply a thin, continuous layer of lapping paste to the valve face.

3. Place a pre-selected spring on the valve stem and insert the valve into the guide sleeve from the combustion chamber side, lubricating the valve stem with a layer of graphite grease.

Note. Graphite grease keeps the guide bushing free of lapping paste abrasive and facilitates valve rotation during lapping.

4. Place a valve lapping tool on the valve stem (or with some tightness a rubber tube to connect the valve to a reversible drill).

5. Turning on the drill at the minimum speed (in reverse mode) or rotating fixture (in case of manual lapping) alternately in both directions for half a turn, lap the valve, periodically pressing it to the seat, then loosening the pressing force.

Note. In the absence of any device, you can grind the valve with an eraser, pressing and turning the valve with it. Loosen the pressure of the valve by pressing on the end of its rod with the other hand.

6. Grind the valve until a matte-gray continuous monochromatic band at least 1.5 mm wide appears on its facet, while a matte band at least 1.5 mm wide should also appear on the valve seat after grinding.



7. After lapping, thoroughly wipe the valve and seat with a clean cloth and rinse to remove any remaining lapping paste. Check the tightness of the valve, for which install it in the head with springs and crackers. Then put the head on its side and pour kerosene into the channel that is closed by the valve. If kerosene does not seep into the combustion chamber within 3 minutes, the valve is tight.