TM-9-2815-200-35 Maintenance Manual for AVDS-1790-2M AVDS-1790-2A and AVDS-1790-2AM Engines Download
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measurement (90 degrees) to first measurement. Average the two measurements. (b) Take two measurements of diameter bore at bottom of ring travel. Measure diameter of bore approximately parallel to line of valves, and then take cross measurement (90 degrees) to first measurement. Average the two measurements. (c) Head-end average must not exceed flange-end average. (d) Compare the measurements taken 90 degrees apart. Each two measurements (top or bottom) must be within 0.003 inches of each other. If the difference exceed 0.003 inches, the cylinder is out-of-round and must be marked for repair. (4) Camshaft bearing surface. Inspect cam shaft bearing surface for pitting, galling, burs, and nicks. Check bearing diameter, with rocker arm cover installed, against limits specified in overhaul standards (table 6-15). (5) Cylinder exterior. Inspect cylinder head and barrel cooling fins for possible repair (para 6-33 f). d. Valve Rocker Arm Covers and Associated Parts. (Refer to fig. B-4) (1) Valve rocker arm cover. Inspect valve rocker arm cover (39) for cracks. Inspect cam shaft bearing surface in cover for galling, pitting, burs, and nicks. Check cover against limits specified in overhaul standards (table 6- 15). Check valve adjusting cover plate (29) for cracks and for warpage. Replace cylinder assembly when cover is unserviceable. (2) Valve rocker arms. Inspect valve rocker arms (33 and 34) for cracks, using a magnifying glass and a strong light. Inspect the bushing-type bearings in the rocker arms for scoring and secure fit. Check bearings against limits specified in overhaul standards (table 6-15). Inspect valve rocker arm rollers for scuff or score marks and for looseness on hub. Rotate roller and check clearance between roller and hub by mounting rocker arm securely in a soft-jawed vise. Set a dial indicator against contact surface of roller and move roller through the extremes of its travel. Check reading on the dial indicator. Limits should be 0.006L in. maximum. Mark worn or damaged rollers and hubs for repair. Inspect adjusting screws (36) for stripped or dam aged threads. Check screw by turing screw in and out of rocker arms. Screw must turn freely. Check swivel pad on adjusting screw for free rotation, Mark damaged parts for replacement. (3) Valve rocker arm shafts. Check valve rocker arm shafts (22 and 35) for cracks, nicks, scoring, or plugged oil passages. Check shafts against limits specified in overhaul standards (table 6-15). Replace unserviceable shafts. (4) Valves. (a) Valve head. Check intake and exhaust valve (11 and 12) for evidence of pitting, im- perfect seating, or warping on valve head. Heavy discoloration, burning, erosion, or a heavy carbon deposit on valve face indicates a warped valve. A light frosted appearance or minor discoloration on valve face does not indicate a warped or unserviceable valve. (b) Value stem. Inspect the valve stems and the locking groove in the stems for pitting, scoring cracks, or damaged tips. Checks valves against limits specified in overhaul standards (table 6-15). Replace valves that are warped, cracked, or unserviceable. (5) Valve springs. Inspect inner spring (18), intermediate spring (17), and outer spring (16) for wear, cracks, set, or other evidence of failure. Check all springs against limits specified in the overhaul standards (table 6-15). (6) Valve spring retainers, valve rotors, and locks. Inspect valve spring retainers (19 and 38) and intake valve spring seat (15) for wear and cracks. Check exhaust valve rotor (40) by rotating inner section. Inner section must rotate freely. Inspect rotor for wear or cracks. Inspect spring retainer locks for wear or cracks. Worn locks will have ridges on top face. Replace any unserviceable parts. 6-56