In this tutorial, Frank Burguera of California Motorcycles explains how to perform valve lapping. Lapping should be performed when replacing valves, valve seats, valve guides, or any other type of cylinder head repair.
To achieve a uniform finish and perfect seating of the valve in its seat, we must proceed step by step using specific techniques and tools.
In this video, we'll show you the valve grinding process. The valve type and diameter are irrelevant; the important thing is the uniformity of the gray color when blending the angle of the valve and the cylinder head seat with the emery paste. Achieving a perfect fit guarantees the tightness of the combustion chamber's unit volume (mixture), thus achieving a higher compression ratio without pressure losses.
Not only do we need to maintain the full compression ratio, but we also need to have the maximum amount of thermal conductivity between the valve and its seat. Why? Well, we need to remove the maximum amount of heat from the chamber, and that's through the seat, where it's transferred to the internal cooling system of the cylinder head and, of course, with each exhaust gas flow.
Perfect seating provides a higher airflow rate (cfm) as it will prevent carbon buildup from sticking to the seat, which could cause poor valve sealing, and poor seating. This can only be achieved with perfect valve grinding. If the paste is not monitored and runs down the valve guide, we will create axial and radial lines that will increase the valve's radial clearance, promoting carbon buildup on the seat, creating more height and poor sealing, losing compression, and promoting valve self-ignition. The valve will not make maximum contact with its seat and will not vent its temperature, potentially creating hot spots, resulting in self-ignition and engine destruction.
When performing the process, we must remember to mark the number of each valve and its seat with White-out or chalk on the base of the valve. This is because each valve, when individually ground, will adapt to its small imperfections. It is very important not to mix them up. The number of passes is almost as important as the height of the passes when regrounding a cylinder head and leaving all the valves at the same height. This is because the wear and tear on the valves will determine the finish and perfection. A good average would be 10-15 passes per valve.
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