Lap valves against valve seats to produce gastight fit.
What does a Valve Grinder do?
Laps valves against valve seats to produce gastight fit, using powered tools: Applies lapping compound to bearing surfaces of valve and seat. Inserts valve stem into valve guide and positions valve against seat. Engages holes or slot in top of valve with projections in powered rotary tool. Presses and rotates valve against seat, using powered tool. May test valve by connecting chamber to hydraulic or pneumatic pressure and observing leaks. May rotate valve against seat, using handtool.