5-72. APU CYLINDER HEAD - Continued
b. Cleaning and Inspection/Repair.
Death or serious injury could occur if compressed air is directed
against the skin. Do not use compressed air for cleaning or
drying unless the pressure is/has been reduced to 30 psi (2.11
kg/cm2) or less. When working with compressed air always use
chip guards, eye protection, and other personal protective
Discard and replace all seals and O-rings.
(1) Thoroughly clean with dry cleaning solvent (Item 3, Appendix E) and air dry all components of the
cylinder head assembly. Remove all the carbon deposits from the intake and exhaust ports and clean
all gasket surfaces.
(2) Remove all carbon and check each valve for burning, pitting or warped stem. Refinish valves that are
slightly pitted or burned on an accurate valve grinder. Refinish intake valves to a 420 angle and
exhaust valves to a 450 angle. If they are badly pitted or have a thin edge when refacing, replace them.
(3) Check refinished valves for a tight seal to the valve seat with an air-pressure-type testing tool, or by
applying marking compound (Item 56, Appendix E) to the valve face and rotating it against the seat.
(4) Check valve guide to valve clearance, .001 5"-.0030 (.0381-.0762 mm) intake, and .0030"-
.0050"(.0762-.127 mm). If the proper clearances cannot be obtained by replacing the valves, replace
the valve guides. Drive the old valve guides into the valve chambers and lift them out. Drive new
guides in until they protrude 1 1/32 in. (8.73 mm) from the rocker box side of the head. Ream the new
exhaust valve guide to .3445"-.3455" (8.750-8.776 mm) and the intake valve guide to .3425"-.3435"
(8.699-8.725 mm) to obtain the proper clearance.
(5) If the valve seats are pitted, refinish them. Using conventional seat grinding equipment, reface each
seat to a 450 angle and a seat width of 3/64 in. to 1/1 6 in. (1.1 9 to 1.59 mm). You should be able to
reface each seat several times before it becomes necessary to replace it. If, however, the valve seats
are loose or cannot be refaced, replace them.
(6) Install in a drill press to remove each valve seat. Adjust the tool Hem to cut 1/64 in. (.397 mm) from the
edge of the seat. Oil (Item 1 0, Appendix E) the pilot to prevent it from seizing in the valve guide. Cu
each seat down to a narrow rind on edges and bottom and break Ht out with a sharp tool. Be careful not
to cut into the counterbore bottom.