Check to see that all fuel selectors or solenoid-operated fuel  shutoff valves are closed. The fuel selector valves are either  manually or solenoid operated. If solenoid-operated fuel  shutoff valves are installed, it may be necessary to turn the  battery switch on before the valves can be closed, since the  solenoid depends on electricity for operation. These valves  close the fuel line at the firewall between the engine and the  aircraft. After ensuring that all fuel to the engine is shut off,  disconnect the battery to eliminate the possibility of a hot  wire starting a fire. If it is anticipated that the aircraft will  be out of service for more than 6 days, the battery is usually  removed and taken to the battery shop and placed on charge. Also, a few other preparations should be made before starting  to work on the engine removal. First, make sure that there are  enough fire extinguishers near at hand to meet any possible  emergency. Check the seals on these extinguishers to be sure  the extinguishers have not been discharged. Then, check the  wheel chocks. If these are not in place, the aircraft can, and  probably will, inch forward or back during some crucial  operation. Also, if the aircraft has a tricycle landing gear, be  sure that the tail is supported so that the aircraft cannot tip back  when the weight of the engine is removed from the forward  end. It is not necessary to support the tail on some multiengine  aircraft if only one engine is to be removed. In addition, the  landing gear shock struts can be deflated to prevent them from  extending as the engine weight is removed from the aircraft. After taking these necessary precautions, begin removing the  cowling from around the engine. As it is removed, clean it  and check for cracks so that the necessary repairs can be made  while the engine change is in progress. Place all cowling that  does not need repair on a rack where it can be readily found  when the time comes to reinstall it on the new engine. After  removing the cowling, the propeller should be removed for  inspection or repair. Place a large metal pan (drip pan) on the floor under the  engine to catch any spilled mixture or oil. Next, secure a clean  container in which to drain the oil or corrosion-preventive  mixture. Place the container beneath the engine, open the  drain valve, and allow the oil to drain.  Figure 8-4  shows the  points at which a typical aircraft engine oil system is drained.  Other points at which the oil system is drained can typically  include the oil cooler, oil return line, and engine sumps.  All valves, drains, and lines must remain open until the oil  system has been completely drained. After draining the oil,  reinstall all drain plugs and close all drain valves. Then, wipe  all excess oil from around the drain points. Electrical disconnections are usually made at the engine  firewall. When the basic engine is being removed, the  electrical leads to such accessories as the starter and  generators are disconnected at the units themselves. When  disconnecting electrical leads, it is a good safety habit to  disconnect the magnetos first and immediately ground them  at some point on the engine or the assembly being removed.  Most firewall disconnections of electrical conduit and cable  are simplified by use of (Army/Navy) AN or (Military  Standard) MS connectors. Each connector consists of two  parts: a plug assembly and a receptacle assembly. To prevent  accidental disconnection during airplane operation, the outlet  is threaded to permit a knurled sleeve nut to be screwed to  the outlet and then fastened with safety wire, if necessary. A typical plug fitting assembly is shown in  Figure 8-5.  It  also shows a typical junction box assembly, which is used as  a disconnect on some aircraft engine installations. After the  safety wire is broken, remove all of it from the sleeve nuts that  hold the conduit to the junction boxes, as well as from the nuts  Drains Figure 8-5.  Electrical connections. Figure 8-4. Oil system drain points. Draining the Engine Electrical Disconnects 8-7