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3-17. Structural failures can be determined by several dif-ferent methods depending on the part involved. The following are a few of the methods employed: magnetic particle, dye penetrant, penetrant, x-ray and various elec-
tronic methods.
3-18. Dimensional inspections should be carried out in ac-cordance with the measurements and tolerances as called out in the Table of Limits (SSP2070).
3-19. It is recommended that an inspection and overhaul form, containing a list of all engine components, be utiliz-ed when disassembling an engine. This form should be prepared so that all inspection and overhaul procedures can be checked off and remarks noted. This will also assure that no part is inadvertently overlooked.
3-20. Bearing Surfaces. All bearing surfaces should be ex-amined for scoring, galling and wear. Considerable scrat-ching and light scoring of aluminum bearing surfaces in the engine will do no harm and should not be considered cause for rejection of the part, provided it falls within the clearances set forth in the Table of Limits. Even though the part may come within specified limits it should not be reassembled into the engine unless inspection shows it to be free of other serious defects. Ball bearings should be ex-amined visually and by feel for roughness, flat spots, flak-ing or pitting of races and for scoring on the outside of the races. All journal surfaces should be checked for galling, scores, misalignment and out-of-round condition. Shafts, pins etc. should be checked for straightness. This may be done in most cases by using vee blocks and a dial in-dicator.
3-21. Gears. All gears should be examined for evidence of pitting and excessive wear. These conditions are of par-ticular importance when they occur on the involute of the teeth; deep pit marks in this area are sufficient cause to re-ject the gear. Bearing surfaces of all gears should be free from deep scratches. However, minor abrasions may be dressed out with fine abrasive cloth.
3-22. Corrosion on Stressed Areas. Pitted surfaces in highly stressed areas resulting from corrosion can cause ultimate failure of the part. The followingareas should be carefully examined for evidence of such corrosion; interior surfaces of piston pins, the fillets at the edges of crankshaft main and crankpin journal surfaces, and thrust bearing races. If pitting exists on any of the sur-faces mentioned to the extent that it cannot be removed by polishing with crocus cloth or other mild abrasive, the part must be rejected.
3-23. Screwed Fittings. Screwed fittings (any parts such as threaded fastenings or plugs) should be inspected for condition of threads. Badly worn or mutilated threads must not be tolerated; the parts should be rejected. However, small defects such as slight nicks or burrs may be dressed out with a small file, fine abrasive cloth, or stone. If the part appears to be distorted, badly galled, or mutilated by over-tightening, or from the use of improper tools, it must be replaced with a new one.
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莱康明发动机大修手册 OVERHAUL MANUAL LYCOMING 76 SERIES AIRCRAFT ENGINES(8)
