IO-390-D Series Engine Maintenance Manual
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Introduction
March 2020
Page xxi
IO-390-D Series Engine Maintenance Manual
INTRODUCTION
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 1 and 2 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 have an optional propeller governor installed on the
rear of the engine. Whereas, on the IO-390-D1B6 and -D3B6 engine models, 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.
Figure 1
IO-390-D1A6, -D3A6 Engine
Figure 2
IO-390-D1B6, -D3B6 Engine
Engine Model Nomenclature
The table below identifies the basic nomenclature of the IO-390 engine models. Hyphenated
numbers and letters in the suffix (D1A6, D3A6, D1B6, or D3B6) of the engine model number are
configuration designations associated with the core engine.
Model Number
Meaning
I
Fuel Injected
O
Horizontally Opposed
390
Displacement in cubic inches
Engine Serial Number
Every engine sent from the factory is identified by
a unique serial number. The engine serial number
is identified on the engine data plate (Figure 3).
Do not remove the engine data plate.
If an engine data plate is ever lost or damaged,
refer to the latest revision of Service Instruction
No. SI-1304 for engine data plate replacement
information.
Figure 3
Engine Data Plate
