Hall Scott started building aviation engines in 1911. But the first project, owing to Elbert J. Hall and Bert C. Scott from the Hall-Scott Motor Car Co in Berkeley and San Francisco, began in 1910. It was the A-1 that gave 32-40 hp at 1,500 rpm. It had 4 in-line cylinders and was water cooled.

-The A-2 from 1911 gave 60 hp at 1,400 rpm and had 8 cylinders in V that were water cooled.  It had a displacement of 402 cu. in.

“A-2, 60 HP”

-The A-3 from 1912 gave 80 hp at 1,400 rpm, with 8 cylinders in V and was water cooled as well.

“Hall-Scott A-3, 80 HP”

-The A-3 was similar to the A-2, increasing the piston stroke to obtain additional power.

-The A-4 from 1912 is known as a V-8, giving 100 hp at 1,200 rpm and 120 hp at 1,500 rpm.

-The A-5 had two versions, the one that gave 125 hp with a displacement of 824 cu. in., and the A-5a that gave 165 hp with a displacement of 909 cu. in. They had 6 in-line cylinders and were water cooled.

“Hall-Scott A-5a”

-The A-7, of 1916, gave from 90 to 100 hp with 4 cylinders in line. It displaced 550 cu. in. There also was the A-7a version giving 110 hp with a displacement of 606 cu. in.

“Hall-Scott A-7a”

-Parts of the V-8 and the A-5 served as inspiration for the design of the "Liberty".

-The A-5 flew in the Boeing 1 from 1916 and the A-7a in the Boeing 2, 3 and 4, in addition to the Aeromarine 39A.

-The A-8 was a V-12, with the cylinder lines at 60°. It was designed in 1917, and gave an output power of 450-500 hp with a displacement of 1,650 cu. in. and was water cooled.

“Hall-Scott A-8”

-As from 1920 the L-4 and L-6 came out. The first one we see in an illustration at a museum. They were Liberty engines, made under license.

“L-4”

-The L-4 gave 130 hp at 1,675 rpm with a displacement of 549 cu. in. (like the A-7) and it had the same four upright in-line cylinders, and was water cooled as well.

-The cylinders and valve train were Liberty.

-Another new illustration for the L-4, viewed from the exhaust side.

“Hall Scott, L-4”

“L-4 rear and front views”

-By 1920, the L-6 engines were from 212 to 250 hp for the Special. It had 6 in-line cylinders and gave 224 hp at 1,700 rpm and 244 to 1,830 rpm.

-The "Post Office Dept." made an important order for these engines in 1922. They were also seen on the Dayton-Wrights.

-It was an important engine, the L6. It was a major 6-cylinder version of the L4.

“Hall-Scott Liberty L-6, viewed from both sides”

-The L-6a had a similar appearance as the A-6, as well as in dimensions.

-It had six upright in-line cylinders and was water cooled. It gave 200 hp at 1,700 rpm without gear.

“Hall-Scott L-6a”

From Appendix 6: Despite what is mentioned on the notice placed in front of the Hall-Scott L-4 engine and the mounting of this engine on a model-C Boeing, it is quite clear that the cylinders and upper half block are from a Hall-Scott-made Liberty L-4.

-What confuses, is the lower crankcase by its shape, which is subject to further investigation.

-Possibly it is a marine installation of this concrete engine.

“L-4 at the museum in Vancouver, Canada”

-We recovered the illustration of the 60 hp Hall-Scott engine with only one valve per cylinder and different strokes. (A-2).

“V8 single-valve engine, the A-2”

“Single-valve details”

-From the Hall-Scott Motors factory in San Francisco, the 8V engine of the year 1915 is the first one that we show.

-The A-4 model is considered 100 hp. It's starter handle has a surprisingly long radius.

“Hall-Scott 8-cylinder V engine”

-And the A5 (the one mentioned in the main text is the A5a), had 6 cylinders in line and gave 125 hp.

“Hall-Scott A5”

From Appendix 10: The engine department began to work in 1910, with the first engine, the A-1 that had four water-cooled cylinders in line, leaving the factory in 1911. It gave 40 hp.

“A-1 with propeller”

"Hall-Scott engine assembly hall"

-In the photo of the factory's assembly hall in 1911 we see clearly an A-1 fitted with a propeller, and ready for running tests. The rest are A-2 engines.

“Illustration of an A-2 from 1911”

"Rear view of another A-2"