Can you spot the mistake?

Did this mechanic just ruin the cylinder head with a wire wheel?! 🤬⚙️ When an engine burns oil, thick carbon sludge bakes onto the combustion chamber and valves. To restore lost horsepower, the entire cylinder head must be cleaned and rebuilt! In this video, a mechanic uses a spinning wire brush on a drill to aggressively blast the black carbon out of the chamber! This is highly controversial because wire wheels can easily scratch soft aluminum engine blocks! Next, they coat the brand-new replacement valves in a dark, gritty grinding paste. Using an old-school suction cup tool, they rapidly spin and tap the valve against the engine to custom-grind a perfect, airtight seal!