Desaxe

A desaxe engine, in engineering (usually automotive, but also steam engines), means one in which each cylinder is not positioned with its exact center (the bore axis) directly above the centerline of the crankshaft; instead, the cylinder is offset slightly. "Désaxé", in French, means "unbalanced"; it is not (despite remarks to the contrary) the name of the inventor of French origin.

If the offset is in the direction of rotation, it has the effect of increasing the leverage applied to the crankshaft during the "power" stroke, and reducing thrust wasted against the cylinder wall.

It also distorts the duration of the four strokes, or cycles of combustion. In a conventional engine, each of the strokes (intake, compression, power, exhaust) is nominally 180°, totaling 720° for the complete 4-stroke combustion cycle. A desaxe engine adds to the duration of the two downward strokes (intake and power), and subtracts the same amount from the two upward strokes (compression and exhaust), with the total remaining 720°. A typical desaxe engine will have events timed 185° - 175° - 185° - 175°, etc., with the differential roughly (but not directly) proportionate to the percentage of offset distance to stroke length.

The relative proportion of offset distance vs. stroke length ranges from very small to almost 20%; viz. an engine with an 80mm stroke may have a cylinder offset of 20mm.

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