be removed by rubbing with steel wool, the pitting is too  deep for safety. Always wipe the mounting pad, flange, and coupling clean  before mounting the accessory, and install the proper gasket  between the mounting pad and the accessory mounting  flange. Lubricate the accessory drive shaft if so indicated in  the manufacturer’s instructions. On older aircraft, check the pulleys in the control system  for freedom of movement. It is easy to spot a pulley that is  not turning freely, for both it and the cable are worn from  the cable sliding over the pulley instead of rolling free. The  bearings of a pulley may be checked by inspecting the pulley  for excessive play or wobble with the tension removed from  the cable. The cable must also be inspected for corrosion  and broken strands. Locate any broken strands by wiping  the cable with a cloth. The engine nacelle must be cleaned thoroughly before it is  inspected. The design of an engine nacelle varies with different  aircraft. Basically, it is a framework covered with removable  cowling, in which the engine is mounted. This assembly is  attached to the aircraft and incorporates an insulating firewall  between the engine and the airframe. The interconnecting  wiring, tubing, and linkages between the engine and its various  systems and controls pass through the firewall. Check bonding for fraying, loose attachment, and cleanness  of terminal ends. The electrical resistance of the complete  bond must not exceed the resistance values specified in the  applicable manufacturer’s instructions. Inspect the exhaust stacks, collector ring, and tailpipe assembly  for security, cracks, or excessive corrosion. Depending on the  installation, these units, or parts of them, may be mounted on  the engine before it is installed in the aircraft. Inspect the complete engine nacelle for condition of the  framework and the sheet-metal cowling and riveted plates  that cover the nacelle. The engine mounting frame assembly  should be checked for any distortion of the steel tubing, such  as bends, dents, flat spots, corrosion, or cracks. Use the dye  penetrant inspection method to reveal a crack, porous area,  or other defects. The engine mounting bolts are usually checked for condition  by magnetic particle inspection or other approved process.  While the bolts are removed, the bolt holes should be checked  for elongation caused by the movement of an improperly  tightened bolt. Check all air ducts for dents and for the condition of the  fabric or rubber anti-chafing strips at the points where  sections of duct are joined. The dents may be pounded out;  the anti-chafing strips should be replaced if they are pulled  loose from the duct or are worn to the point at which they  no longer form a tight seal at the joint. Thoroughly inspect the engine oil system and perform any  required special maintenance upon it before installing a  replacement engine. If an engine is being changed at the end  of its normal time in service, it is usually necessary only to  flush the oil system; however, if an engine has been removed  for internal failure, usually some units of the oil system must  be replaced and others thoroughly cleaned and inspected. Check the outer surface of all exposed electrical wiring for  breaks, chafing, or other damage. Also, check the security  of crimped or soldered cable ends. In addition, carefully  inspect connector plugs for overall condition. Any item that  is damaged must be repaired or replaced, depending on the  extent of the damage. If the engine has been removed because of internal failure,  the oil tank is generally removed to permit thorough  cleaning. Also, the oil cooler and temperature regulator  must be removed and sent to a repair facility for overhaul.  The vacuum pump pressure line and the oil separator in  the vacuum system must also be removed, cleaned, and  inspected. Internal failure also requires that the propeller  governor and feathering pump mechanism be replaced if  these units are operated by engine oil pressure. Always replace a control rod if it is nicked or corroded  deeply enough to affect its strength. If the corrosion cannot  Before starting to work on the aircraft or reciprocating engine,  always be sure that the magneto switch is in the off position.  Aircraft engines can be started accidentally by turning the  propeller if the magneto switch is on. Before installing an engine, inspect all tubing in the nacelle  for dents, nicks, scratches, chafing, or corrosion. Check all  tubing carefully for indications of fatigue or excessive flatness  caused by improper or accidental bending. Thoroughly  inspect all hoses used in various engine systems. Weather  checking (a cracking of the outside covering of the hose)  sometimes penetrates to the hose reinforcement. Replace any  length of hose that shows indications of the cover peeling or  flaking or has exposed fabric reinforcement. Replace a hose  that shows indications of excessive cold flow. Cold flow is  a term used to describe the deep and permanent impressions  or cracks caused by hose clamp pressure. Preparing the Engine for Removal 8-6 Inspection and Replacement of Powerplant  External Units and Systems