Lycoming O-320 76 Series Operator's Manual page 12

SECTION 1 LYCOMING SERIES OPERATOR'S MANUAL
DESCRIPTION O-320
Cooling System – The engine is designed to be air cooled by air pressure. Baffles are provided to build up a
pressure and direct the air through the cylinder fins. The air is then exhausted to the atmosphere through the
rear of the lower cowling.
Induction System – The engine is equipped with a Marvel-Schebler single barrel, float type carburetor,
equipped with a manual mixture control and idle cut-off. Distribution of the fuel-air mixture is obtained
through the center zone induction system, which is integral with the oil sump and is submerged in oil,
insuring a more uniform vaporization of the fuel and aiding in cooling the oil in the sump. From the riser the
fuel-air mixture is distributed to each cylinder by individual intake pipes.
Lubrication System – The lubrication system is of the pressure wet sump type. The oil pump located on the
exterior of the crankcase accessory section, 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 section to
the oil pressure screen 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 connection in the oil pressure screen housing from which
point a drilled passage conducts the oil to the oil pressure relief valve, located at the bottom of the accessory
section.
The pressure relief valve regulates the engine oil pressure by allowing the excessive oil to return to the
sump, while the balance of the pressure oil is fed to the main oil gallery. The oil is distributed by means of a
separate drilled passage to the main bearings of the crankshaft. Angular holes are drilled through the main
bearing to the connecting rod journals. Oil from the main oil gallery also flows to the camshaft and valve
gear passages and is then conducted through branch passages to the hydraulic tappets and camshaft bearing.
Oil enters the tappets through indexing holes and travels out through the hollow push rod tubes to the valve
mechanism, lubricating the valve rocker and valve stems. Residual oil from the bearings, accessory drives
and rocker boxes is returned by gravity to the sump where after passing through a screen it is again
circulated through the engine. Pressure build up within the crankcase is held to a minimum by means of a
breather located on the top rear of the crankcase.
Priming System – Provision for a primer system is provided on all engines employing a carburetor.
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