Connecting Rods - Lycoming O-290 Operator's Manual

SECTION 1 LYCOMING OPERATOR'S MANUAL
DESCRIPTION O-235 AND O-290 SERIES
Connecting Rods – Made in the form of "H" sections from alloy steel forgings. They have replaceable
bearing inserts in the crankshaft ends and split type bronze bushings in the piston ends. The bearing caps on
the crankshaft ends are retained by means of two bolts and nuts through each cap.
Pistons – Machined from an aluminum alloy. Two compression rings and an oil regulating ring are
employed on all pistons. In addition, the O-235 series employs an oil scraper ring below the piston pin. The
piston pin is of the full floating type with a plug located at each end to prevent the pin from touching the
cylinder wall.
Accessory Housing – Made from an aluminum casting and is fastened to the rear of the crankcase and the
top rear of the oil sump. It forms a housing for the oil pump and the various accessory drives.
Gears – Are of the conventional type and precision machined, hardened to insure long life and satisfactory
operating qualities.
Cooling System – These engines are designed to be cooled by air pressure actuated by the forward speed of
the aircraft. Close fitting baffles build up a pressure and force the air through the cylinder fins. The air is
then exhausted through gills or augmentor tubes usually located at the rear of the cowling.
Lubrication System – The full pressure wet sump lubrication system is actuated by an impeller type oil
pump contained within the accessory housing.
Induction System – These engines are equipped with either of two Marvel-Schebler carburetors, MA-3A or
MA-3SPA. See Table 1 for model application. Both carburetors are of the single barrel float type and are
equipped with manual mixture control and "idle cut-off". Particularly good distribution of the fuel-air
mixture to each cylinder is obtained from the center zone induction system, which is integral with the sump
and is submerged in oil, insuring a more uniform vaporization of 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.
Ignition System – Dual ignition is furnished by two magnetos. Consult Table 1 for proper model application.
Depending on installation, the ignition wiring is so arranged as shown in either Figure 5-1, 5-2 or 5-3.
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