Valve adjustment on a Cummins engine in a Freightliner

The first valve adjustment should be done at around 60,000 miles, then every 200,000 miles. This truck has over 500,000 miles, and it looks like the valves have never been adjusted.

Why does it matter? Valve clearances change over time. Incorrect clearance can affect engine performance, power, fuel economy, and increase wear in the valvetrain. Valve adjustment is an important part of Cummins diesel engine maintenance.