Measure the diameter of the valve stem with a micro-
Since the stem wears unevenly, take measure-
ments at four places up and down the stem, keeping
the micrometer at right angles to the stem.
Replace the valve if the stem is worn to less than
the service limit.
A. Valve Stem
Valve Stem Diameter
the valve, and measure the inside diameter
of the valve guide using a small bore gauge and micro-
meter. Since the guide wears unevenly, measure the
diameter at four places up and down the guide.
any measurement exceeds the service limit,
Valve Guide Inside Diameter
A. Small Bore Gauge
If a small bore gauge is not available, inspect the
valve guide wear by measuring the valve to valve guide
clearance with the wobble method, as indicated below.
Insert a new valve into the guide and set a
against the stem perpendicular to it as close as
to the cylinder head mating surface. Move the stem
back and forth to measure valve/valve guide clearance.
the measurement in a direction at a right angle
to the fi rst.
If the reading exceeds the service limit, replace the
NOTE: The reading is not actual valve/valve guide clear-
ance because the measuring point is above the guide.
Move the valve.
ValvelValve Guide Clearance
seat inspection and repair
The valve must seat
the valve seat evenly around
the circumference over the specified area. If the seating
area is too wide, the seating pressure per unit of area is
reduced, which may result in compression leakage and
carbon accumulation on the seating surface.
seating area is too
heat transfer from the valve