Not the first piston engine with valves, it might be the first with a camshaft driven by gears.
Power is provided by 6 Juno’s per cylinder. With fuel cheat enabled it will run for 4.5 hours or more, at 50% throttle. Current engine speed limit: 7.5 rad/s. At 100% throttle it will overheat the valves.
This engine use the magical properties of sphere colliders (RCS balls), making most older bearing types obsolete. They’re also great for gears, liners, followers etc. The crankshaft & camshaft are built out of LY-10’s, the cams are radial RCS tanks. Piston rods are small radial decouplers. The pistons are small xenon tanks. The FPS is pretty good because I tried to avoid mesh colliders.
I could try and tune this engine for many hours or just start over from scratch with different specs.
Built in the SPH in KSP version 1.3.0.