Nelson Bros. 'Jumbo Line' High Speed Engines

With the introduction of its line of air-cooled singles Nelson Bros. moved in a new direction.


| June/July 2003



1 HP HS series engine

The 1 HP HS series engines were equipped with a finned flywheel and sheet metal air shroud.

L-head Engines

The L-head engines were built in 1-1/2 HP to 3 HP ratings with operating speeds of 1,800 to 2,600 rpm. They shared a common bore and stroke of 2-3/4-inch by 3-1/4-inch. They had an appearance similar to some Briggs & Stratton engines of their era.

The VC and VD model engines looked identical, with a stamped sheet steel air shroud enclosing the finned cast iron flywheel. The carburetor throat diameter and different compression ratio heads appear to be the only difference in these engines. The heads were deeply finned cast iron on the VC and aluminum on the VD and VG engines. The cylinder jug was a separate iron casting bolted to the crankcase.

The 3 HP VF was a bit different. It was built similarly to the VC and VD, but had a different, more contemporary appearance thanks to a cast aluminum flywheel shroud and companion cast aluminum shroud that completely encased the cylinder and head. This shroud was slotted at the rear to vent cooling air only at the rear. I would guess this design was intended to improve the cooling of the higher horsepower engine. The 3 HP VF was the only model offered with a spark retard lever on the magneto to facilitate safer hand cranking.

Later 3/4 HP HB series engines were equipped with a finned flywheel and sheet metal air shroud instead of the standard open flywheel.

The 2 HP L-head VD series looked similar to contemporary Briggs & Stratton engines. Cylinder heads on the 2 HP engines were cast aluminum.

The cast air shroud on the 3 HP VFG completely encased the cylinder and head. This was the only model equipped with a spark retard lever.