I will think about that. It depends on the rigour and competence of the shop. Every machinist has an opinion and I try to avoid folklore experts. Often they don't keep quality records, nobody audits them and are hardly accountable for errors. And of course I find pleasure in this.
First I need to check the flatness, I only need to remove scratches. I don't even know if they are cosmetic or risks. There are movies on youtube which describe the process but details are missing, people often us rough grit and for this specific engine there is a high risk to damage the head. Target flatness is assumed lower than 0.01mm, Target roughness 0.2-0.4 microns [metric]. Step 1 cleaning: P1000. Step 2 finishing P1500-P2000. MLS are coated.
