conditioning, or run-in, may result in unsatisfactory engine  operation with high oil consumption. A process called bearing  burnishing creates a highly polished surface on new bearings  and bushings installed during overhaul. The burnishing is  usually accomplished during the first periods of the engine  run-in at comparatively slow engine speeds. The failure of any part during engine testing or run-in  requires that the engine be returned, repaired, and completely  retested. After an engine has successfully completed test  requirements, it is then specially treated to prevent corrosion,  if it is shipped or stored before being installed in an aircraft.  During the final run-in period during testing, the engines  are operated on the proper grade of fuel prescribed for the  particular kind of engine. The oil system is serviced with a  mixture of corrosion-preventive compound and engine oil.  The temperature of this mixture is maintained at 105 °C to  121 °C. Near the end of final run-in, corrosion-preventive  mixture (CPM) is used as the engine lubricant. The engine  induction passages and combustion chambers are also  treated with CPM by an aspiration method. CPM is drawn  or breathed into the engine. The test cell requires an area to mount and hold the engine for  testing. The cell needs to have the controls, instruments, and  any special equipment to evaluate the total performance of the  engine. A test club should be used for testing instead of a flight  propeller.  [Figure 10-34]  A test club provides more cooling  air flow and the correct amount of load. The operational tests  and test procedures vary with individual engines, but the basic  requirements are generally closely related.  The test cell control room contains the controls used to  operate the engine and the instruments used to measure  various temperatures and pressures, fuel flow, and other  factors. These devices are necessary in providing an accurate  check and an evaluation of the operating engine. The control  room is separate from, but adjacent to, the space (test cell)  that houses the engine being tested. The safe, economical, and  reliable testing of modern aircraft engines depends largely  upon the use of instruments. In engine run-in procedures, the  same basic engine instruments are used as when the engine  is installed in the aircraft, plus some additional connections  to these instruments, and some indicating and measuring  devices that cannot be practically installed in the aircraft.  Instruments used in the testing procedures are inspected  and calibrated periodically, as are instruments installed in  the aircraft; thus, accurate information concerning engine  operation is ensured. Engine instruments can operate using different methods,  some mechanically, some electrically, and some by sensing  the direct pressure of air or liquid. Some of the basic  instruments are: Instrument markings, ranges of operation, minimum and  maximum limits, and the interpretation of these markings  are general to all the instruments. Generally, the instrument  marking system consists of three colors: red, yellow, and  green. A red line, or mark, indicates a point beyond which  a dangerous operating condition exists. A red arc indicates  a dangerous operating range due generally to an engine  propeller vibration range. This arc can be passed through,  but the engine cannot be operated in this area. Of the two,  the red mark is used more commonly and is located radially  on the cover glass or dial face. The yellow arc covers a given  range of operation and is an indication of caution. Generally,  the yellow arc is located on the outer circumference of the  instrument cover glass or dial face. The green arc shows  a normal and safe range of operation. When the markings  appear on the cover glass, a white line is used as an index  mark, often called a slippage mark. The white radial mark  indicates any movement between the cover glass and the  case, a condition that would cause mislocation of the other  range and limit markings. Figure 10-34.  Test club.  1.  Carburetor air temperature gauge 2.  Fuel pressure gauge 3.  Fuel flowmeter 4.  Manifold pressure gauge 5.  Oil temperature gauge 6.  Oil pressure gauge 7. Tachometer 8.  Exhaust gas temperature gauge 9.  Cylinder head temperature gauge 10. Torquemeter Test Cell Requirements Engine Instruments 10-21