SECTION 1 LYCOMING OPERATOR’S MANUAL
DESCRIPTION IO-320 SERIES
Pistons – The pistons are machined from an aluminum alloy. The piston pin is of a full floating type with a
plug located in each end of the pin. Depending on the cylinder assembly, pistons may employ either half
wedge or full wedge rings. Consult the latest revision of Service Instruction No. 1037 for proper piston and
ring combinations.
Accessory Housing – The accessory housing is made from an aluminum casting and is fastened to the rear of
the crankcase and the top rear of the sump. It forms a housing for the oil pump and the various accessory
drives.
Oil Sump (Except AIO Series) – The sump incorporates an oil drain plug, oil suction screen, mounting pad
for fuel injector, the intake riser and intake pipe connections.
Crankcase Covers (AIO Series) – Crankcase covers are employed on the top and bottom of the engine.
These covers incorporate oil suction screens and oil scavenge line connections. The top cover incorporates a
connection for a breather line and the lower cover a connection for an oil suction line.
Cooling System – These engines are designed to be cooled by air pressure. Baffles are provided to build up a
pressure and force the air through the cylinder fins. The air is then exhausted to the atmosphere through gills
or augmenter tubes usually located at the rear of the cowling.
Induction System – Lycoming IO-320 series engines are equipped with a Bendix type RSA fuel injector.
The fuel injection system schedules fuel flow in proportion to air flow and fuel vaporization takes place at
the intake ports.
A brief description of the fuel injector follows:
The Bendix RSA type fuel injection system is based on the principle of measuring airflow and using the
airflow signal in a stem type regulator to convert the air force into a fuel force. This fuel force (fuel pressure
differential) when applied across the fuel metering section (jetting system) makes fuel flow proportional to
airflow. A manual mixture control and idle-cut-off are provided.
Lubrication System – The lubrication system is of the pressure wet sump type. The main bearings,
connecting rod bearings, camshaft bearings, valve tappets, push rods and crankshaft idler gears are
lubricated by means of oil collectors and spray. The oil pump, which is located in the accessory housing,
draws oil through a drilled passage leading from the oil suction screen located in the sump. The oil from the
pump then enters a drilled passage in the accessory housing, where a flexible line leads the oil to the
external oil cooler. In the event that cold oil or an obstruction should restrict the flow of oil to the cooler, an
oil cooler bypass valve is provided. Pressure oil from the cooler returns to a second threaded connection on
the accessory housing from which point a drilled passage conducts the oil to the oil pressure screen, which
is contained in a cast chamber located on the accessory housing below the tachometer drive.
The oil pressure screen is provided to filter from the oil any solid particles that may have passed through
the suction screen in the sump. After being filtered in the pressure screen chamber, the oil is fed through a
drilled passage to the oil relief valve, located in the upper right side of the crankcase in front of the
accessory housing.
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