莱康明发动机大修手册 OVERHAUL MANUAL LYCOMING 76 SERIES AIRCRAFT ENGINES(36)

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7-33. If it is necessary to make a standard shaft journal
surface more than 0.003 inch undersize or a renitrided
0.003
inch undersize more than 0.006 inch undersize, the crankshaft must be ground to undersize and renitrided. Standard shafts may be ground to 0.006 inch or 0.010 inch undersize, renitrided 0.003 inch undersize shafts must be ground to 0.010 inch undersize. Shafts must be fitted with the corresponding undersize bearing inserts. Grinding the crankshaft is a delicate operation requiring adequate grin- ding facilities and a great deal of skill. A properly dressed wheel (Carborundum (GA54-J5-V1O or equivalent) must be used with generous amounts of coolant. The wheel must be fed to the journal or pin very slowly and the final ground finish maintained during the complete operation. This procedure must he followed to eliminate possibility of grinding cracks. After grinding, the crankshaft must be carefully inspected by the magnetic particle method. If any cracks or checks are found. the shaft must be re- jected.

1.
Parallel Blocks 2. Check Points

Figure 7-6. Checking Squareness of
Connecting Rods

NOTE

If one crankpin bearing surface is ground undersize all crankpin bearing surfaces must be ground to same under size. If one main bearing surface is ground undersize all
76 SERIES AIRCRAFT ENGINES
main bearing surfaces must be ground to some undersize. Main bearing surfaces ma be ground without affecting A crankpin surfaces and similarly crankpin bearing surfaces
._may be ground without affecting the main bearing SUP-faces. After any grinding operation the crankshaft must

be renitrided It is recommended that the shaft be return- ed to Lycoming for renitriding.
7-39. Crankshaft -Straightening Flange. Maximum per-missible flange run-out is 0.018 inch TIR. If the flange
run-out exceeds 0.016 inch the crankshaft must be re- jected. If the flange run-out is less than 0.016 inch the flange may be straightened as described in the following paragraphs.
straightening operations, the
removed. When the surface

been reduced as much as possible, the front face of the flange must be trued up by grinding. However. if the minimum width of the flange after grinding (Dimension “A”. figure 7-7 is less than the dimensions as called out in Table ‘7-1, the shaft must be re- jected.
TABLE 7-l

ENGINE MODEL MIN. WIDTH OF FLANGE
0-320-H .260 inch
0-360-E .370 inch
CAUTION

Extreme care must be exercised during an straightening
operation to avoid damage to the nitride surfaces of the
crankshaft. The nitrided surfaces extend from the front
face of t h e slinger to the crankshaft gear mounting sur-
face. These nitrided surfaces are glass hard and will crack
if shaft is bent, dropped or handedl carelessly.
Section 3.
PILOT DIAMETER
(MUST RUN TRUE WITH FRONT
ANDREAR MAIN BEARINGS
　
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