MODULE 1

• Reliable ways to identify parts worn beyond limits is to:

  -          disassemble the engine

  -          thorough inspection
• Engine manufacturers - provide overhaul instructions with general instructions and specific tolerances to determine airworthiness of each part
• The basic steps of the overhaul process:

  1.       Receiving inspection

  2.       Disassembly

  3.       Cleaning

  4.       Visual inspection

  5.       Structural inspection

  6.       Dimensional inspection

  7.       Repair and replacement

  8.       Reassembly

  9.       Installation

  10.   Engine testing and run-in

  11.   Preservation and storage
• Receiving Inspection - determine the general condition of the engine when it is received, provide an inventory of the engine and all its accessories and associated parts
• Repair Station - should maintain a complete record of all repair operations and inspections performed on each engine or component overhauled
• Airworthiness Directives – issued by the FAA pertaining to aircraft and engines whenever it appears that certain changes should be made to correct discrepancies or to improve the reliability of the unit
• Disassembly – a process where a typical aircraft engine follows a sequence specified in the overhaul manual
• Inspection Record - should show the dimensions of each part measured and all fits and clearances
• Cleaning – necessary before disassembling and assembling the engine parts
• two types of cleaning are required when an engine is overhauled:

  1.       degreasing

  2.       decarbonizing
• Two of the principal methods for removing the residual lubricating oil and loose sludge arc

  -          washing in a petroleum solvent

  -          employment of a vapor degreaser
• Vapor Degreaser - consists of an enclosed booth in which a degreasing solution such as trichloroethylene is heated until it vaporizes
• Decarbonizing – next method after the degreasing process has been completed
• The most common methods of decarbonizing are:

  -          stripping

  -          grit blasting

  -          vapor blasting
• Stripping – a process is used to remove paint and various resinous varnishes which have formed in the engine during its operation
• Soft Grit Blasting - offers one of the most satisfactory processes and used for the removal or hard carbon from the insides of cylinders and the tops of pistons
• Sandblasting – is not employed in the cleaning of engine parts except the valve heads and will erode the metal
• Vapor blasting - is employed for special cleaning jobs and accomplished by means of specially designed equipment and materials
• Materials that should not be used for cleaning parts or removing hard carbon:

  -          wire wheels

  -          steel scrapers

  -          putty knives

  -          abrasives
• Visual Inspection - is accomplished by direct examination and with the use of a magnifying glass
• Visual inspection - will usually reveal cracks, corrosion, nicks, scratches, galling, scoring and other disturbances of the metal surfaces
• Structural Inspection - determine the structural integrity of each part
• Engine parts are structurally inspected by some or all of the following methods:

  1.       Magnetic particle testing

  2.       Liquid penetrant inspection

  3.       Eddy-current inspection

  4.       Ultrasonic inspection

  5.       Radiography
• Magnetic particle testing - is a nondestructive method for locating surface and subsurface discontinuities (cracks or defect) in ferromagnetic materials such as steel
• Flux Leakage - occurs where the lines of flux leave the surface or the material. resulting in a concentration of magnetic strength at the discontinuity
• Liquid Penetrant Inspection - commonly used include crankcase halves. accessory cases. oil sumps, and cylinder heads
• Ultrasonic Inspection - utilizes high-frequency sound waves to reveal flaws in metal parts
• Ultrasonic inspection - can be accomplished satisfactorily by a well-trained and experienced TECHNICIAN
• X-ray Inspection - is particularly effective in detecting discontinuities inside castings, forgings and welds
• Radiographic Inspection – other term for X-ray Inspection
• Eddy-current inspection - is also effective in discovering defects inside metal parts
• Eddy-Current Tester - applies high-frequency electromagnetic waves to the metal and these waves generate eddy currents inside the metal
• If the metal is uniform in its structure, the eddy currents will flow in a UNIFORM PATTERN and this will be shown by the indicator
• Eddy-Current Inspection - is not routinely used for engine overhaul.
• Eddy-Current Tester - can be of great value to a technician who is experienced and knows what type of rests can be made effectively
• Special Service Bulletins – a bulletin issued by engine manufacturers that require alterations or parts replacements designed to improve the performance and reliability of the engine
• Dimensional Inspection - requires the use of precision measuring instruments such as micrometer calipers, telescoping gauges, and dial indicators
• Dimensional inspection - \is employed to determine the degree of wear for parts of the engine where moving surfaces are in contact with other surfaces
• Manufacturers have designated several parts as recommended or mandatory replacement items at overhaul regardless of their condition. Manufacturer generally agree that these parts should be replaced at overhaul:

  •  Pistons
  •  Piston pins
  •  Piston rings
  •  Main and rod bearings
  • All bushings Connecting-rod bolts and nuts
  • Exhaust valves
• Repair and Replacement - a process where unrepairable parts and components should have been discarded, repairable parts labeled and parts requiring no further action organized for reassembly on a parts rack. The discrepancy list and labels on repairable parts will serve as a guide for work to be done.