How to Lap in Valves

How to Lap in ValvesThe valves’ job is to open to let fuel mixture in and exhaust gas out – but also to seal perfectly when closed so everything’s kept firmly inside the combustion chamber. The sealing surfaces can become worn, pitted, damaged and contaminated over time, which has a highly detrimental effect on the engine’s performance. Place the valves in a drill and use abrasive paper to remove deposits from both sides of valve head. Be careful not to touch the working surface of the stem or the sealing surface of the head. Start with P60; finishing off with P800. Clean the ports and combustion champers with thinners and a scouring pad.

Place each valve in its respective port with a little oil on the stem and a smear of coarse valve grinding paste around the sealing surface. Use a valve grinding tool to rotate the valve back and forth, then lift it, turn slightly, drop it down and repeat. Do this until the sealing surfaces of both valve and seat are a uniform, dull grey. Switch to fine paste to finish off. Clean thoroughly before reassembly.

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