WHEELPRODUCES WHEEL
GRINDINGSTEP
HERE
SEAT
VALVEGUIDE
UIDE
Figure 5-11. Rejection of Valve Seat
5-49. On intake valve seats, use a 15 grinding wheel
to grind the top surfaces of the valve seat to produce
uce the outer face diameter (dimension "A"). Bring the face of the intake valve seats to the specified width (dimensi"C"
on"C") by narrowing the throat with a 75 wheel.
5-50. On exhaust valve seats, use a 15 grinding wheel
to grind the top surface of the valve seats to produce
uce the outer face diameter (dimension "B"). The width of the ex-haust valve seats should now conform to dimension"D"
on "D".
5-51. If seat wear has progressed to the extent that the en-tire face of the 150narrowing wheel must be brought into contact with the seat in order to achieve the specified diameter, the seat must be replaced. (See figure 5-11.)
5-52. Valve Seat Removal and Replacement. Valve seats that are loose, damaged or worn to the extent that they cannort be reground to the dimensions shown in figure 5-10 must be replaced.
NOTE
When it is necessary to replace intake or exhaust valve seats, the recess in the cylinder head must be cut .010,.020 or .030 oversize and the corresponding oversize seat in-stalled.
5-53. Valve Seats. "Allison" type seat employed on all cur-rect subject engines.
5-54. Place the applicable valve seat replacement fixture on a suitable surface and fasten securely. Fabricate a removal tool in accordance with the material and dimen-sions shown in figure 5-12.
5-55. Heat cylinder to a temperature of 600°F. and secure to fixture. Soak the sponge of the removal tool in cold water. Insert the tool down through the valve seat, the seat will shrink and cling to the sponge. Withdraw the tool being careful not to cock the seat. This entire pro-cedure should be performed as swiftly as possible after removing the cylinder from the heat.
5-56. Measure the ID of the valve seat recess in the cylinder head. Compare the measurement with the original manufactured diameter of the recess (seeTable of Limits) and determine which oversize seat is to be install-ed.
5-57. Refer to Table 5-1 and select the proper cutter and pilot. Install the pilot in the cutter, tighten and install cut-ter in special drive. Install on drill press and proceed to cut the recess in the cylinder head to proper size. Note that the pilot engages the ID of the valve guide hole in the cylinder head. Remove no more metal from the bottom of the recess than is necessary to clean up the major diameter.
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(23)
