TM 5-3810-289-34
replacement limits shown in table 2-2, mark for
replacement.
(d) Inspect the sharp edge of tapered valve
guides for chips, cracks, burs; if damaged, mark for
replacement.
(3) Valve springs. Weak valve springs may
cause valve flutter which results in excessive wear on
both valve and seat. Valve flutter interferes with valve
timing and may cause valve to strike the piston head.
Valve warping, cracking and breaking are the results
of weak valve springs.
(a) Test valve spring on spring tester that is
capable of very accurate measurements of spring
lengths by means of standards as listed in table 2-2 and
dial indicator gage, figure 3-153.
(b) One spacer may be used under valve
spring when insert and valve have been refaced to make
Figure 3-148. Checking push tube ball end with radius
valve check within load limit.
gage.
Figure 3-150. Minimum valve head rim thickness.
Figure 3-149. Checking push rod socket end with
adjusting screw.
rim thickness (A, fig. 3-150); it should be a minimum of
1/16 inch.
(b) Stems, figure 3-151, are scored or worn
beyond wear limits shown in table 2-2.
(c) Collet recesses are worn so new collets
will not fit securely in recesses.
(2) Valve guides.
(a) A plug gage is not satisfactory to gage
worn holes. It will not detect an out-of-round hole.
Instead use a small bore gage.
(b) To use a small bore gage, set it with
Figure 3-151. Valve stem measurement.
accurate micrometers at 0.0002 inch larger than worn
replacement limit shown in table 2-2. Then use bore
gage as a UNo-Go" gage, figure 3-152. Gage the hole at
several points crosswise and endwise of head.
(c) If old valve guides are worn beyond wear
3-54
