Nelson Bros. 'Jumbo Line' High Speed Engines

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

3/4 HP HB series engine

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

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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.

The L-head engines were available with rope starting or a hand-crank. Judging by surviving engines, the hand-crank engines were more popular. The crank handles look great displayed on these little engines, but don't let their size fool you. Despite what I had always heard about a hand-crank's tendency to kick back, I had to learn for myself - don't spin the crank handle if you don't want it to kick back on you. The rope pulley, if you can find one, is a much safer way to start the L-head engines.

On the drive end, L-head engines where furnished with either a 2-inch by 3-inch flatbelt pulley, a 4-inch by 3-inch flatbelt pulley, or a 4-inch double groove 'B' section V-belt pulley.

Fuel System

Jumbo Line air-cooled engines were available with either one of two different fuel systems; a gravity-style fuel tank and float carburetor or a base fuel tank with a fuel pump and overflow carburetor. With 'no float valve carburetor to leak,' Nelson Bros, advertised the overflow fuel system as safer than competitive gravity systems. It was, no doubt, safer only because Nelson offered it and Briggs & Stratton didn't.

The overflow fuel system had the fuel tank cast integral with the engine base and oil sump, with a plunger-style pump situated in the crankcase. The fuel pumps were quite simple, with one internal and one external ball check valve. To keep fuel from getting into the oil, the fuel pump piston had a relief cut into it to collect fuel leaking past the piston, routing it to a drain hole in the pump barrel and back to the tank. The fuel was pumped to a cast iron Nelson overflow carburetor. An overflow line drained excess fuel back to the tank. Various carburetor throat diameters are found on this style, depending on horsepower rating. Interestingly, by 1938 it appears Nelson had dropped the 'safer' overflow fuel system from their line.

The gravity fuel system had a sheet metal fuel tank and commonly used a Nelson two-piece cast iron float carburetor. The float was a free-floating hollow brass sphere operating a small poppet valve. A Tillotston float carburetor is common on L-head engines. I have not seen Tillotston carburetors on any OHV models, but they are shown in available literature.


Internally, the OHV and L-head engines were quite similar in design and appearance. The connecting rod dips into an oil trough (which is itself kept full by a plunger-style oil pump) and splash lubricates the engine. The OHV engine oil pumps have a small copper oil line from the oil pump barrel to the sheet metal oil trough. If not fitted properly, these oil supply tubes can work loose, causing engine seizure. Oil pumps fitted to the L-head engine are a two-piece casting with internal flow -they are more substantial and look more dependable.


The Wico F series magneto appears to have been the only magneto used on Nelson air-cooled engines. Most F series magnetos had two coils, but some FGS magnetos were shipped with only one coil. The single coil magnetos look odd because they have laminations to take two coils. The spark plug was a standard 18-mm thread, and Nelson manuals noted they were 'interchangeable with those used on 1929, 1930 or 1931 Chevrolet cars.'

Contract Engines

Nelson Bros, air-cooled engine models were privately labeled and sold by many different companies, with Montgomery Ward's Sattley brand the most commonly found of the privately labeled engines. Nelson also made some engines for Montgomery Ward that were not made under the Nelson Bros. name. An excerpt from an original 1935 Nelson Bros, service department letter to a local dealer attests to this, reading, 'This particular engine was made by us for the Montgomery Ward people, using their patterns, jigs and tools.'

Stover also sold the Nelson OHV VB engines, which they marketed as the Stover 501. A Nelson-made 501 is pictured in the Stover section of C.H. Wendel's American Gas-oline Engines Since 1872. The Stover 501 had a relatively crude sheet metal flywheel air shroud instead of the more common cast shroud. Nelson Bros, engines were also sold by Fairbanks-Morse, who offered the 3/4 HP VB engines on their home water pump systems as seen in the 1937 Fairbanks-Morse general line dealer catalog. Nelson Bros, also built their own line of water pumps, AC and DC generator sets, table saws and concrete mixers, all powered by their air-cooled Jumbo Line engines.

Paint colors seem to be hunter green for earlier engines and machinery gray for later models. Many of the engines were painted other colors by Nelson customers. I have found original OHV engines painted bright red, and Sattley-labeled OHV horizontal engines were brown and L-head engines were gray.

The serial number on these engines is found on an engine identification tag and is also stamped on a machined flat on the crankcase. Many engine castings will have the parent model designation preceding the casting number. I have not run across any serial number information on the number of engines made.

I have not met many collectors specifically interested in these engines, although any Nelson Bros, air-cooled OHV engines for sale at engine shows rarely sit around long, as they are one of the more unusual air-cooled engines available to today's collectors. The horizontal engines are more unique, and generally seem to be more attractive to collectors than the vertical models. The VA engine is my favorite, however. It is small and easy to handle, which appeals to me more and more as the summers go by.

A GEM article on Nelson Bros, in the January 1993 issue might also be of interest. I always like to know more, so if anyone has any additional information, literature or corrections to my information, I would certainly like to hear from them.

Contact engine enthusiast Jeff Conner at: 8269 Dunham Road, Baldwinsville, NY 13027, or e-mail at: