McCulloch Aircraft Engines
by Kimble D. McCutcheon
Published 21 Dec 2014; Revised 2 Feb 2022

Introduction

By the time he was 24, Robert Paxton McCulloch had inherited a fortune, won two national outboard hydroplane racing championships, obtained an engineering degree from Stanford, married Barbara Ann Briggs, (daughter of Stephen Forster Briggs, of Briggs and Stratton Motors), and formed McCulloch Engineering Company, which manufactured racing engines and superchargers. He sold the company to Borg Warner in 1943, and about six months later, formed McCulloch Aviation to manufacture target drone engines. The first ones were Model O-15-3s, designed by Righter Manufacturing Company and built under contract for the U.S. Government.

Target Drone Engines

Bob McCulloch moved his company from Milwaukee, Wisconsin to Los Angeles, California in 1946 and changed its name to McCulloch Motors Corporation. By this time, McCulloch had designed its own engines, all of which were air-cooled, rotary-valve, gasoline-fueled two-strokes.

The 4-cylinder Model 4300C (O-90-1) had a 3.000" bore, 3.125" stroke, displaced 88.36 in³, produced 65 hp at 4,100 rpm, weighed 78 lb, and was built from 1945 until 1952.

The 4-cylinder Model 4318 (O-100-1) had a 3.1875" bore, 3.125" stroke, displaced 99.75 in³, produced from 72 hp to 84 hp (depending on model) at 4,100 rpm, weighed 77 lb, and was built from 1950 until 1988; variants were used for several manned gyrocopters.

The 6-cylinder Model 6318 (O-150-2) had a 3.1875" bore, 3.125" stroke, displaced 149.62 in³, produced from 110 hp at 4,100 rpm, weighed 114 lb, and was built from 1955 until 1972. A turbocharged variant, the TC6150 (-150-4, -4A) produced 120 hp at 4,100 rpm and weighed 142 lb.

In 1949, McCulloch introduced a product that would make it a household word, the light weight chain saw. In 1953, McCulloch introduced a new line of automotive superchargers that were sold by the Paxton Automotive Division.

McCulloch Model 4318 (Courtesy of Tim Wheat)	McCulloch Model 4318 (Courtesy of Tim Wheat)	McCulloch Model TC6150 (Courtesy of Paul Woodford)	McCulloch Model TC6150 (Courtesy of Daniel Berek)