What not to touch during engine maintenance: Valve Adjustments All diesel engines require periodic valve adjustments. Mack Boring teaches boaters how to do this if they want, but it’s a very technical ...

Yanmar is a manufacturer of high-speed commercial marine diesel engines, and the 12AYM-WGT is its largest, ... deeper combustion chambers and reshaped 4–valve-per-cylinder heads.

And, man, this engine likes to rev. From 2,500 rpm to 6,000 rpm, the power ramps up on a 45-degree angle, crossing the 400-horsepower mark by 4,300 rpm and 500 horsepower by 5,100 rpm.

We spoke with Erik Christensen from Mercury Racing, who told us that the cylinder heads use a valvetrain that's similar to their 9.0L Quad Cam Four Valve (QC4V) stern drive marine engines, which ...