NMWR-9-2815-220 Overhaul Manual for M60 M88 Engine AVDS-1790-2CA, AVDS-1790-2DA, AVDS-1790-2DR Download
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NMWR 9-2815-220 CYLINDER ASSEMBLY OVERHAUL—Continued 0012 00 REPAIR – Continued (1) Seat dressing. A 45 degree angle stone must be used to grind the exhaust valve seat, and a 15 degree angle grinding stone must be used for the intake valve seats. Dress the seat on the insert with the stone using a valve seat grinding machine. After dressing the seat of the insert, inspect valve contact as described in Inspection paragraph 4 (b) of this work package. (2) Seat width. When 360 degree contact is obtained, narrow the seat on the insert to the width specified in Figure 11 by grinding the inner wall and exposed face of the insert to the angles specified. Keep valve seat area as near as possible to the center of the valve face. Valves should never seat at the top or bottom of the valve face area. (c) Valves. Discard valves that have warped, cracked, pitted, or burned faces. Also discard valves having badly pitted, scored, or scratched stems or locking grooves. Reface slightly pitted or burned valves that do not have 360 degrees of contact to limits specified in Figure 11. Discard valves that cannot be refaced to these limits. Check valve length from seat contact to tip of stem after grinding, as shown in Figure 11. Discard valve if length is not within the limits specified. (d) Cylinder bore. Cylinder bores should be reground to the next oversize according to oversize standards listed in Table 12 when bore dimensions are not within limits. After the cylinder bore has been reground oversize, the cylinder assembly identification number (Figure 2) should be changed in accordance with the part numbers listed in Table 1 to reflect the reground bore size. The cylinder assembly should also be reground oversize when the cylinder bore is found to have excessive scratches, scoring, ring ridge, or when the bore is glazed or smooth. All cylinder bores must be honed after grinding and/or before new piston rings are installed. Cylinder bore honing specifications and recommended procedures are outlined below. (1) Cylinder bore honing specifications: a Cross hatch angle to be 35 degrees off the horizontal. b Cross hatch to be cut uniformly in both directions. c Cross hatch to be clean-cut, but not sharp, and free from torn or folded metal. d The micro-finish roughness should average between 35 and 45 micro-inches, rms (root- mean-square deviation from the mean), as measured on a profilometer. e The plateau area should be 1/2 to 2/3 of the surface area. f The plateau should be free from burnished or glazed surfaces. g The surface must be free of embedded particles. 0012 00-13 Change 1