911 SC valve adjustment,do it every 15,000km

The air-cooled flat six needs its valve clearances checked regularly. The SC spec is 0.10mm intake and 0.10mm exhaust, measured warm. Loose valves are noisy but survive. Tight valves are quiet but burn. I've seen SC engines with burnt exhaust valves because the owner thought the quiet engine meant everything was fine. Adjustment takes about 90 minutes once you know the procedure. The critical tool is a proper feeler gauge set and a 13mm thin-wall socket for the adjusting nut.