A little more research on the Baker company and their gasoline engines reveals more information, although much of it seems conflicting.
They manufactured horizontal engines at 3 hp (4" bore), 5 hp (5" bore), 8 hp (6" bore), 11 hp (7" bore), and 15 hp (8" bore), all horizontals.
I think the designation for horizontal engines began with "H", and the Type was "HJ" on the nameplate.
The designation "J" appears to refer to "Jump-Spark" ignition.
The designation "V" is vertical engine, and these included the ball hopper type, and the vase-shaped engines.
Baker does not seem to make it very clear why they made two varieties of vertical engines, at least it is not clear to me.
The typical vertical vase-shaped hopper small pump jack engine you see so many of were 1 1/4 horsepower, and were referred to as the "Little Monitor Pumping Engine".
This engine had a single flywheel, with a headless design, and valve cage cast into the cylinder.
The vase-shaped hopper engines I think had a model number such as "VJ", and apparently came in 1 1/4 hp (3.5" bore), 2 hp (4" bore), 4 hp (5" bore), and 7 hp (6" bore).
The Baker company seemed to be very consistent with their piston sizes, and it appears the piston size and maybe to some extent the stroke, drove the horsepower rating.
The ball hopper engines apparently also came in 2, 4, and 7 horsepower, and I am not sure if they used the same piston and piston size as the vase-shaped vertical engines.
I have seen references to a 1 hp and 6 hp ball hopper monitor, so I don't know if that was just a variance in stamping the nameplate rating for a particular application, or what.
Comparing the bore sizes between the horizontal and vertical engines, the horizontal engines produced more horsepower for the same piston diameter, for some reason.
One photo of a Monitor nameplate shows an "RV" designation, but I am not sure which engine that nameplate goes with; listed as 1 5/8 horsepower.
The nameplates on the vase-shaped vertical Monitor clearly says "Type VJ".
I can't find a photo of a ball hopper monitor nameplate, but it would appear that they were elipsoidal in shape, located on the side of the cylinder opposite the valve cage.
One nameplate photo shows a rectangular nameplate, but I am not sure which engine this goes with.
I am assuming that the ball hopper monitor nameplate did not have a "Type", but just a horsepower, rpm, and maybe a serial number (not positive about this).
There is a lot of information available for the Little Monitor vase-shaped hopper, and many photos.
Apparently everyone and their brother and cousin had a Little Monitor pump jack engine.
Ball Hopper Monitor information seems to be rare, sort of like finding snow in hell, and very few ball hopper engine photos or videos.
Finding photos of a disassembled ball hopper monitor are exceedingly rare.
The spark plug appears to be on the front of the valve cage on the 2hp, and on the left side of the valve cage on the 4hp (check me on that).
For the larger vertical engines, where both valves are on the bottom, the spark plug appears to be on the top of the valve cage.
The larger engines have both valves actuated to give 10% better fuel economy.
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