how to lap valves

Clean the valves and seats like you’re prepping an operating theatre—no carbon, no grit, no shortcuts.

Apply a thin ring of lapping compound to the seat, drop the valve in, stick a suction-cup tool (or fuel hose on the stem), and rotate back and forth—lift, rotate, reseat, repeat.

You’re chasing a uniform, dull-grey contact ring all the way around; patchy means keep going, but don’t overdo it or you’ll widen the seat and ruin sealing.

When the ring looks even, wash every last grain of compound out with solvent, then refit with fresh stem seals, set clearances, and torque like you actually read the manual.

Finish with a leak-down or kerosene test for peace of mind—finding a leaker after assembly is how engines turn into expensive ornaments.