Ever since I did an article last year about the Ten Craziest Old Engines over on Hooniverse, this particular one has stuck in my head. It’s called the “Commer Knocker”. It’s a three-cylinder, two-stroke, six piston, horizontally opposed, direct-injected, high-revolution diesel engine. Yeah, I know.
It’s a bloody hard one to understand, in a way, but it utilizes opposed pistons, whose movement also causes the valves to open and close. Kind of. The pistons are horizontally opposed, but connected to a common crankshaft by way of rocker arms, in much the same way that the valvetrain is connected to the camshaft on a conventional pushrod engine. Kind of.
It’s one of those moments of engineering that make you sit back and think, “And you did this… why?” After all, there were boxer and flat-four or flat-six engines in production at the time; since the motivation was to try and create an engine that would be nice and flat to accommodate the new “cab-forward” (or what we North Americans would call “cabover” or “COE”) trucks they were developing, one wonders why it wasn’t possible to develop a boxer diesel.
You know, besides the horrible experiences that Subaru has had with theirs in the last few years.
Sounds pretty cool though: