7-19. AU crankcase. crankshaft and reciprocating parts are cleaned in accordance with the general instructions outlined in Section 3. When cleaning the crankshaft. clean the inside of all crankpin and main bearing journals and all oil passages with suitable brushes. after which flush thoroughly with clean solvent and compressed air.
INSPECTION
7-20. Inspect all crankcase, crankshaft and reciprocating parts in accordance with the general instructions contain-ed in Section 3. Specific instructions follow.
7-21. Bearings (Precision Type). AU precision type bearing inserts used for main crankshaft bearings and connecting rod bearings should be replaced with new bearing inserts at overhaul.
7-22, Crankcase (Visual Inspection). Check carefully for burrs, nicks and cracks around the bearing support webs. Check bearing bores and inspect tang slots for any roughness that might case improper seating of bearing inserts. Check all drilled holes.
7-23. Fretting on the contacting surfaces of the hearing saddle supports in the crankcase occurs on some engines. This condition is caused by slight motion between the con- tacting surfaces and results in erosion of the metal sur-face. The affected areas have tiny pit holes and a frosted appearance. as contrasted to adjacent shiny unaffected surfaces. See figure 7-4. This condition can be misleading because of its trivial appearance: nevertheless it can be the cause of severe engine damage.
7-24. Fretting, by inself in this area. does not appreciably damage the structure of the metal. but the metal removed by the fretting action does change the size of the bearing saddles sufficiently to cause loose thru-studs and under- size main bearing bares. If not detected during overhaul. excessively tight crankshaft bearing fits will result with eventual engine failure.
7-25. Crankcase (Dimensional Inspection). The following paragraphs on crankshaft and camshaft dimensions will also describe dimensional requirements of the crankcase.
7-26. Crankshaft (Visual Inspection). Carefully inspect all surfaces of the shaft for cracks. checking the baring sur-faces with particular care for scoring, galling, corrosion, pitting or other damage.
7-27. Crankshaft (Dimensional Inspection/. Place the crankshaft in Vee blocks supported at the locations called out in Table of Limits (reference 556) and using a surface plate and dial indicator measure the run-out at center main bearings. If this total indicator reading exceeds the dimensions given in reference 556 the shaft must not be reused. The crankshaft flange run-out may be checked at this time and if the total indicator reading exceeds the run-out given in Table of Limits (reference 607) the shaft must be rejected.
CAUTION
Any attempt to straighten a bent crankshaft will result in rupture of the nitrided surface of the bearing journals, a condition that will cause eventual failure of the crankshaft. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：莱康明发动机大修手册 OVERHAUL MANUAL LYCOMING 76 SERIES AIRCRAFT ENGINES(33)
