The oil cooler doors are adjusted in a manner similar to that  used to adjust the cowl flaps. In some cases, the procedure  is reversed in so far as the door is first adjusted to retract to  a specified point, and the limit switch on the motor is set to  cut out at this point. Then, the jackscrew is adjusted to permit  the door to open only a specified distance, and the open limit  switch is set to stop the motor when this point is reached. After the engine has been completely installed and connected,  install the propeller on the aircraft. Before doing so, the thrust  bearing retaining nut should be checked for correct torque. If  required, the propeller shaft must be coated with light engine  oil before the propeller is installed; the propeller governor and  anti-icing system must be connected according to applicable  manufacturer’s instructions. Before the new engine is flight tested, it must undergo a  thorough ground check. Before this ground check can be  made, several operations are usually performed on the engine. To prevent failure of the engine bearings during the initial  start, the engine should be pre-oiled. When an engine  has been idle for an extended period of time, its internal  bearing surfaces are likely to become dry at points where  the corrosion-preventive mixture has dried out or drained  away from the bearings. Hence, it is necessary to force oil  throughout the entire engine oil system. If the bearings are dry  when the engine is started, the friction at high rpm destroys  the bearings before lubricating oil from the engine-driven oil  pump can reach them. There are several methods of pre-oiling an engine. The  method selected should provide an expeditious and adequate  pre-oiling service. Before using any pre-oiling method,  remove one spark plug from each cylinder to allow the engine  to be turned over more easily with the starter. Also, connect  an external source of electrical power (auxiliary power unit)  to the aircraft electrical system to prevent an excessive drain  on the aircraft battery.  In using some types of pre-oilers, such as that shown in  Figure 8-12,  the oil line from the inlet side of the engine- driven oil pump must be disconnected to permit the pre-oiler  tank to be connected at this point. Then, a line must be  disconnected, or an opening made in the oil system at the  nose of the engine, to allow oil to flow out of the engine.  Oil flowing out of the engine indicates the completion of the  pre-oiling operation, since the oil has now passed through  the entire system. In order to force oil from the pre-oiler tank through the  engine, apply air pressure to the oil in the tank while the  engine is being turned through with the starter. When this  action has forced oil through the disconnection at the nose  of the engine, stop cranking the engine and disconnect the  pre-oiler tank. A motor-driven oil pump can also be used to  pump oil through the engine during the pre-oiling operation. When no external means of pre-oiling an engine are available,  the engine oil pump may be used. Fill the engine oil tank,  or crankcase, to the proper level. Then, with the mixture  in the idle cutoff position (reciprocating engine), the fuel  shutoff valve and ignition switches in the off position, and  the throttles fully open, crank the engine with the starter  until the oil pressure gauge mounted on the instrument panel  indicates oil pressure. After the engine has been pre-oiled, replace the spark plugs  and connect the oil system. Generally, the engine should be  operated within 4 hours of being pre-oiled; otherwise, the  pre-oiling procedure normally must be repeated. To purge the fuel system of air locks, and to aid in flushing  any traces of preservative oil from a pressure carburetor,  fuel injector unit, or fuel control (turbine), remove the drain  plug in the fuel unit chamber that is farthest from the fuel  inlet to the fuel unit. In its place, screw a threaded fitting to  a length of hose leading to a suitable container. Then, set  the fuel control unit to flow fuel so that fuel is permitted to  flow through the system. After ensuring the fuel shutoff and  main fuel tank valves are open, turn on the fuel boost pump  until there are no traces of preservative oil in the fuel being  pumped through the system. The passage of air is indicated  Fuel System Bleeding Preparation of Engine for Ground and  Flight Testing Pre-Oiling Figure 8-12. Pre-oiler tank.  8-13