System Description; Cylinders - Lycoming IO-390-D Series Installation And Operation Manual

IO-390-D Series Engine Installation and Operation Manual

SYSTEM DESCRIPTION

The Lycoming IO-390-D series engines are direct-drive four-cylinder, horizontally opposed, fuel-
injected, air-cooled engines. Each engine has tuned induction and a down exhaust.
There are different IO-390-D engine models. Figures 1A and 1B show the IO-390-D engine models.
The main difference between the engine models has to do with the location of the propeller
governor. The IO-390-D1A6 and -D3A6 models (Figure 1A) have an optional propeller governor
installed on the rear of the engine. Whereas, on the IO-390-D1B6 and -D3B6 engine models (Figure
1B), the propeller governor is installed on the front of the crankcase.
There are different propeller flange bushing configurations for these engine models. Refer to the
latest revision of Service Instruction No. SI-1098 for the configuration for your engine model.
NOTICE: Refer to Appendix B for engine performance data.
Figure 1B
Figure 1A
IO-390-D1B6, -D3B6 Engine
IO-390-D1A6, -D3A6 Engine

Cylinders

There are four cylinders on this engine. Each
cylinder (Figure 2) contains a cylinder head,
barrel, piston, angled intake and exhaust valve
guides and valve seats, rocker shafts, rocker
covers, and fins.
Fuel and air enter the cylinder through the
cylinder head for mixing and combustion within
the cylinder.
The engine has intercylinder cooling baffles.
Figure 2
Engine Cylinder
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March 2020 Page 1