Valves should only be lapped with fine-grained lapping paste. For lapping, a rubber suction cup is used, which is fixed on the valve plate. To prevent grooving of the lapping surfaces during lapping, regularly lift the valve from the seat and rotate the valve in both directions.
Attention: After lapping, carefully remove the remnants of lapping paste.
The quality of grinding is checked by the contact patch using Prussian blue, white lead or fuel. To do this, insert the valve and pour fuel into the combustion chamber. Fuel must not seep through the valve guide. Otherwise, repeat the lapping process.