Description - Lycoming O-290 Operator's Manual

LYCOMING OPERATOR'S MANUAL
O-235 AND O-290 SERIES
The Lycoming O-235 series, O-290-D series and O-290-D2 series engines are four cylinder, direct drive,
horizontally opposed, wet sump, air-cooled models.
In referring to the location of the various engine components, the parts are described in their relationship
to the engine as installed in conventional airframes. Thus the power take-off end is considered the front and
the accessory drive section the rear. The sump section is considered the bottom and the opposite side of the
engine where the shroud tubes are located is the top. References to the left and right side of the engine are
made with the observer facing the rear of the engine. Thus the front cylinder on the left bank is number 2
and the rear cylinder is number 4. The front cylinder on the right bank is number 1 and the rear cylinder is
number 3. The direction of rotation for accessory drives is determined by the observer facing the drive pad.
The direction of rotation of the crankshaft, viewed from the accessory end of the engine is clockwise.
Cylinders – The cylinders are of conventional air-cooled construction with the 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 barrels, which are machined from chrome nickel molybdenum steel
forgings with deep integral cooling fins, are ground and honed to a specified finish.
The valve rocker shaft bearing supports and the rocker box housing are cast integrally with the head. The
valves are cooled by means of fins which completely surround the area of the exhaust valve and portions of
the intake valves. Valve guides and valve seats are shrunk into machined recesses in the head.
Valve Operating Mechanism – The valve operating mechanism is located on the topside. The camshaft is
located parallel to and above the crankshaft and operates in aluminum bearings. The camshaft in turn
actuates the valves by means of tappets. The valve rockers are supported on full floating steel shafts. The
valve springs bear against hardened steel seats.
Hydraulic tappets which automatically keep the valve clearance at zero are employed on the
O-290-D2 series engines while solid tappets are employed on the O-235 and O-290-D series.
Proper valve clearance on the latter models is maintained by means of an adjusting screw
located in the valve rocker.
Crankshaft – Made from a chrome nickel molybdenum steel forging. All bearing surfaces are nitride
hardened. The expansion plug in the crankshaft must be removed on those models employing a two position
hydro control or variable pitch propeller.
Crankcase – Crankcase assembly consists of two reinforced aluminum alloy castings divided at the center
line of the engine and fastened together by bolts and nuts. The mating surfaces of the crankcase are joined
without the use of a gasket, and main bearing bores are machined for use of precision type main bearing
inserts.
Oil Sump – Incorporates an oil suction screen, carburetor mounting pad, the intake riser and intake pipe
connections. The fuel-air mixture, as it passes through the riser, is vaporized by the heated oil that surrounds
the riser.
SECTION 1

DESCRIPTION

NOTE
SECTION 1
DESCRIPTION
1-1