Griffon vs Merlin rotation.

[Tom Griffith]

Originally Posted by Smilin_Ed

The Allison engines in the P-38 Lightning were identical but were installed facing different directions to get the props to rotate in opposite directions. This was simpler than building the engines differently by using different valve camshafts and simplified the supply problem. Does anyone know if the Merlins and Griffons were capable of being installed "backwards"?

The above is a very OLD post, so maybe someone has clarified it, but Allisons (and, as far as I know, no OTHER aircraft engiine) could be installed "backwards" to effect a prop rotation direction that was opposite the standard rotation direction.

Allisons were built with left and right-rotating crankshaft versions. They could fairly be changed-over to the OTHER direction by replacing a few bits and bobs.

(All references to direction of rotation are as viewed from behind the engine)

Note...the Allisons with right-handed (Clock-Wise or "CW") props had crankshafts that were left-handed (Counter-Clock-Wise or "CCW" or Anti-Clock-Wise in the UK "ACW"), and the prop reduction gear assembly gave a prop that turned opposite in direction from the engine's crankshaft. The ones with left-handed/CW props, the reverse was true.

That said, ALLLLLL Merlins had left-handed crankshafts, and a prop reduction gear assembly similar to that of the Allison - two gears in the assy, so the prop turned to the RIGHT. The Merlins with left-handed props had a THREE gear assembly and therefore, their props turned to the LEFT. This setup was seen on the Merlin-powered P/F-82 Twin Mustangs and the Hornet/Sea Hornets. There were several Marks of Merlins where an engine with a right-handed prop had a "mirror-image mate" - with a different Mark.

Isn't this a LOT of fun!