>Anybody mention the Tucker automobile engine, a helicopter engine
>conversion but boxer none the less.
>
>Stan

Was that a boxer? Must/ve been a Lycoming or Continental?

>Do any horizontal engines count here or do the cylinders have to be on
>opposite sides of the crank?
>   In the 50's John Deere tractors had two large horizontal cylinders
side by side with the top of both pistons facing forward.  To start them
you hand cranked an exposed flywheel on the side of the tractor.

That would be a flat parallel twin, but not a boxer. The crank would
have been behind the cylinders, not between them. Similar layout to
most motorcycle twins. Toyota's rear-drive/4WD Estima/Previa/Tarago
had a flat-four, but it was a normal I4 laid flat on its right side.

A boxer MUST have a central crankshaft with paired cylinders, one of
each pair on each side of the crank ie 180 degrees apart. Think of a
boxer as a 180-degree V-engine (V-twin, V4, V6 etc), rather than a 60
or 90-degree, ie with the two banks of cylinders pushed down flat.