Information on cylinder head contact surface - AH01.30-P-1000-05A
WARNING: This page does not describe the selected car, but rather 203 other vehicles, including the 2020 Mercedes-Benz SLC300, 2020 Mercedes-Benz SL550, 2020 Mercedes-Benz SL450, 2020 Mercedes-Benz S65 AMG, and 2020 Mercedes-Benz GLA250. However, it is still accessible from the selected car via links, so may be relevant.
ENGINE 112/951/976, 113
The cylinder head contact surface should only be machined if there is mechanical damage.
It should not be machined (by face grinding) if the contact surface of the cylinder head is uneven (warped) in the longitudinal and transverse directions.
When the cylinder head is mounted again, surface warping will be evened out when the cylinder head bolts are tightened.
Stock removal from the cylinder head and cylinder crankcase of an engine should total no more than 0.3 mm.
If the cylinder head contact surface is machined, the valve seats must be reset.