The Continental O-170 engine is the collective military designation for a family of small aircraft engines, known under the company designation of A50, A65, A75 and A80. The line was designed and built by Continental Motors commencing in the 1940s. It was employed as the powerplant for civil and military light aircraft.
The horizontally opposed, four-cylinder engines in this family are all identical in appearance, bore, stroke, dry weight and piston displacement. All feature a bottom-mounted updraft carburetor fuel delivery system. The higher power variants differ only in compression ratio and maximum allowable rpm, plus minor modifications. The lower power versions are fully convertible to the higher rated versions.
In all models of this family of engines the cylinder heads are of aluminum alloy, screwed and shrunk onto steel barrels. Spark plug inserts and intake valve seats are made from aluminum-bronze alloy, while the exhaust valve seats are steel. The engines all employ hydraulic tappets which operate in aluminum guides that are machined into the crankcase. The tappets are built from four parts, a cam follower body, cup, cylinder and piston and operate with clearances of 0.03 in (1 mm) to 0.11 in (3 mm). The pushrods are steel and feature pressed-in ball ends.
Lubricating oil is delivered under pressure from the 4 US qt (4 L) oil sump to the drive bearings and the crankpins though the crankshaft. The cylinder walls and pistons are spray lubricated. Normal operating oil pressure is 35 psi, with minimum idle oil pressure 10 psi.
50 hp (37 kW), Compression ratio 5.4:1, max rpm 1,900, fuel consumption at cruise 3.8 US gph
65 hp (48 kW), Compression ratio 6.3:1, max rpm 2,300, fuel consumption at cruise 4.4 US gph. The exhaust valves have stellite faces. The pistons have three rings, although some early production A65s had four piston rings.
75 hp (56 kW), Compression ratio 6.3:1, max rpm 2,600, fuel consumption at cruise 4.8 US gph. The exhaust valves have stellite faces and the connecting rods have a 0.125 in (3 mm) hole drilled in the rod cap to improve lubrication. The pistons have three rings and smaller piston pins.
80 hp (60 kW), Compression ratio 7.55:1, max rpm 2,700, fuel consumption at cruise 5.2 US gph. The connecting rods have a 0.125 in (3 mm) hole drilled in the rod cap to improve lubrication. The pistons have five rings and smaller piston pins.
Military designation for the A55, A65, A75, A80 family of engines.