Engine Overview

1.1 General Description

The Continental O-200-A is a four-cylinder, horizontally opposed, air-cooled, direct-drive engine rated at 100 horsepower.

Horizontally opposed means the cylinders are arranged in two banks facing each other on either side of a central crankshaft, rather than in a line or a V. This layout keeps the engine narrow and low-profile, which improves forward visibility in single-engine aircraft.

Direct-drive means the propeller is mounted directly to the crankshaft, with no reduction gearbox between them. The propeller therefore turns at the same speed as the crankshaft.

Air-cooled means the engine relies on airflow over finned cylinders — rather than a liquid coolant circuit — to manage operating temperature. Cooling airflow is directed by the baffling and cowling system described in Section 2D.

1.2 Major Components

Source: D971-13, Section 11, paragraphs 11-7 and 11-27.

The engine is built around a split crankcase carrying the crankshaft and camshaft, with four individual cylinders bolted to it — two on each side.

• Crankcase — The structural core. It houses the main bearings that carry the crankshaft, the camshaft bearings, and the drilled oil galleries that feed them. The rear crankcase cover cavity contains the accessory drive gears.
• Crankshaft — Converts the reciprocating motion of the pistons into rotation, and drives the propeller directly. The cylinders are staggered along its length so that each connecting rod has its own throw. Drilled passages inside the crankshaft carry oil from the main bearings out to the connecting rod bearings.
• Cylinders (4) — Each carries cooling fins on its outer surface and a head containing the intake and exhaust valves and two spark plug holes, which are fitted with heli-coil thread inserts.
• Pistons and connecting rods — The pistons are driven downward by combustion; the connecting rods transmit that force to the crankshaft. Cylinder walls, piston pins and connecting rod bushings are lubricated by oil spray thrown off the main and rod bearings.
• Camshaft and valve train — The camshaft operates hydraulic tappets, which act through hollow push-rods on the rocker arms to open the valves. Oil reaches the valve mechanism through those hollow push-rods.
• Accessory section — At the rear of the engine. It drives the magnetos and the starter, and the engine carries a vacuum pump adapter pad on its front lower side.

Detailed dimensions, clearances and wear limits for these parts are engine overhaul data. D971-13 paragraph 11-7 refers internal repair and overhaul to the publication issued by the engine manufacturer, so those values are not reproduced here.

1.3 Operating Principles

Source: FAA-H-8083-32 (four-stroke cycle); D971-13, Section 11, paragraphs 11-7 and 11-8 (compression ratio, firing order, cylinder numbering, timing).

The O-200-A is a four-stroke engine: each cylinder completes four strokes — two crankshaft revolutions — to produce one power impulse.

• 1. Intake — The piston travels down with the intake valve open, drawing in the fuel-air mixture metered by the carburetor.
• 2. Compression — Both valves close and the piston travels up, compressing the mixture. The O-200-A compresses it to a ratio of 7.00:1, which is why it is described as a low-compression engine.
• 3. Power — The spark plugs fire and the burning mixture drives the piston down. This is the only stroke that produces power; the other three are carried by crankshaft momentum and by the other cylinders.
• 4. Exhaust — The exhaust valve opens and the rising piston pushes the burnt gases out into the exhaust system.

Firing order and cylinder numbering

Cylinders are numbered from rear to front. The right rear cylinder is No. 1, and the right-hand side carries the odd numbers 1 and 3. The left rear cylinder is No. 2, and the left-hand side carries 2 and 4.

• Firing order — 1 – 3 – 2 – 4. The power impulses are spread across the engine rather than running down one side and back along the other, which keeps it running smoothly.
• Ignition timing — Both magnetos fire at 24° (+1° / -0°) before top centre. The spark is delivered slightly before the piston reaches the top, so that peak combustion pressure arrives just after it starts back down.
• Dual ignition — Each cylinder has two spark plugs fed by separate magnetos. This gives redundancy if one magneto fails, and burns the charge more completely by igniting it from two points at once.

1.4 Engine Identification

Source: D971-13, Section 11, paragraph 11-8; Continental Publication M-0, Table 6-1 (serial-number breakpoint).

Reading the model designation O-200-A:

• O — Opposed cylinder arrangement.
• 200 — Approximate displacement in cubic inches. The actual figure is 200.91 cu in.
• A — The variant within the O-200 series. The O-200-A is the version installed in the Cessna 150J, K, L and M.

Full engine data — bore, stroke, displacement, weight, pressures and torques — is collected on the Specifications page.