10-5
Too much clearance in the intake guide admits air
and oil into the combustion chamber, affecting car-
buretion, increasing oil consumption, and making
heavy carbon deposits. Clean metal is a good heat
conductor but carbon insulates and retains the
heat. This increases combustion chamber temper-
ature which causes warping and burning.
Unburned carbon residue gums valve stems and
causes them to stick in the guide. Deposits of hard
carbon can form sharp points that become hot and
cause pre-ignition and pinging.
Stems and Guides:
Always check the stems and
guides for wear as shown in Figure 10-8. Use a mi-
crometer to measure the valve stem diameter in at
least three locations. Use a hole gauge to measure
the valve guide at several depths. When clearance
with stem exceeds original clearance by 0.002
inch(0.05 mm), replace the valve or cylinder head,
which includes the valve guide, or both.
Springs:
Check the valve springs for cracks, worn
ends, and distortion. If the spring ends are worn,
check valve retainer for wear. Check for spring dis-
tortion by placing the spring on a flat surface next to
a square. Measure the height of spring (A) and ro-
tate it against a square to measure distortion (B),
see Figure 10-9. Replace any valve spring that is
weak, cracked, worn, or distorted.
VT-1012-1s
VALVE FACE
VALVE STEM
VALVE GUIDE
FIGURE 10-8. VALVE FACE, STEM, AND GUIDE
FIGURE 10-9. VALVE SPRING CHECKS
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