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 TM 55-1905-223-24-3
(o) Be sure that the valve face has the correct contact against the valve seat.
(p) Put marks on the valve face as shown in Figure 4-11. Use a liquid metal marker.
(q) Install the valve in the valve guide.
(r) Hold the valve against the valve seat and rotate the valve at least 10 degrees. The correct contact against
the set will cause the marks on the valve face to be broken.
(s) If the marks are not broken, check the adjustment of the facing machine and the condition of the grinding
wheel.
(t)
Valves and valve seats that are correctly machined do not require the use of lapping compound to make an
airtight seal. If the Valve Seating Test shows leakage, you can use a small amount of lapping compound on
the valve and seat to make an airtight seal.
(u) The correct conditions of the valve and valve seats are:
1
No marks or scratches on the valve face or valve seat.
2
No marks or scratches in the valve guide.
3
The angle of the valve face must be exactly 30 degrees.
4
Valve guide to valve stem clearance must be a minimum of 0.0022 inch (0.056 mm).
(3) Replace any valves which have any cracks or damage or which do not have a rim thickness of at least 0.124 inch
(3.15 mm).
g.
Valve Springs. Inspection and replacement.
NOTE
Weak valve springs can cause wear and damage to the valve and valve seat. Weak springs can also
change the valve timing and cause the valve to hit the top of the piston.
(1) Use the valve spring tester to test the valve spring. Compress the spring to the "working length" given in Table 4-
1.
(2) Use spacers under the valve spring when the valve and valve seat have had a total of 0.030 inch (0.76 mm)
material removed. Do not use more than two spacers under a valve spring.
4-39
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