Lycoming O-320 76 Series Operator's Manual page 11

LYCOMING SERIES OPERATOR'S MANUAL SECTION 1
O-320 DESCRIPTION
SECTION 1
DESCRIPTION
General – The Lycoming O-320 aircraft engine is a four cylinder direct drive, horizontally opposed, wet
sump, carbureted, air cooled engine.
In referring to the location of the various engine components, the parts are described in their relationship
to the engine as installed in the airframe. Thus, the power take-off end is considered the front and accessory
drive end the rear. The sump section is considered the bottom and the opposite side of the engine where the
shroud tubes are located the top. References to the left and right side is made with the observer facing the
rear of the engine. The cylinders are numbered from the front to the rear, the 1 and 3 cylinders are on the
right side, 2 and 4 cylinders are on the left. The direction of rotation of the crankshaft is clockwise, viewed
from the rear of the engine. The direction of rotation for the accessory drives is determined with the
observer facing the drive pad.
Cylinders – The cylinders are of conventional air cooled construction with two major parts, head and barrel,
screwed and shrunk together. The heads are made from an aluminum alloy casting with a fully machined
combustion chamber. The rocker box is cast as an integral part of the cylinder head which forms the housing
for both intake and exhaust valve rockers. The cylinder barrels, which are machined from chrome nickel
molybdenum steel forgings, have deep integral cooling fins and the inside of the barrels are ground and
honed to a specified finish.
Valve Operating Mechanism – A conventional type camshaft is located above and parallel to the crankshaft.
The camshaft actuates the hydraulic tappets which operate the valves through push rods and valve rockers.
Valve rockers are held in place by the use of a rocker arm fulcrum. The valve springs bear against hardened
steel seats and are retained on the valve stems by means of split keys.
Crankcase – The crankcase assembly consists of two reinforced aluminum alloy castings with the accessory
housing as an integral part, fastened together by means of studs, bolts and nuts. The mating surfaces of the
two castings are joined without the use of gaskets and the main bearing bores are machined for the use of
precision type main bearing inserts.
Crankshaft – The crankshaft is made from a chrome nickel molybdenum steel forging. All bearing journal
surfaces are nitride hardened.
Connecting Rods – The connecting rods are made in the form of "H" sections from alloy steel forgings.
They have replaceable bearing inserts in the crankshaft ends and bronze bushings in the piston ends. The
bearing caps on the crankshaft ends are retained by two bolts and nuts through each cap.
Pistons – The pistons are machined from an aluminum alloy. The piston pin is of the floating type with a
plug located at each end of the pin. The pistons employ half wedge rings. Consult the latest revision of
Service Instruction No. 1037 for proper piston and ring combinations.
Oil Sump – The sump incorporates an oil drain plug, oil suction screen, mounting pad for the carburetor, the
intake riser and the intake pipe connections.
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