Yanmar 4LHA-HTP Operation Manual page 337

Chapter 2 Basic Engine
4. Cylinder Head
4-3.2 Inspection of valve seat wear and contact surface
Inspect for valve seat scratches and excessive wear.
Check to make sure the contact surface is normal. The
seat angle must be checked and adjusted if the valve seat
contact surface is smaller than the width of the valve seat.
Note: Bear in mind that the intake and exhaust valves
have different diameters.
4-3.3 Valve sinking
Over long periods of use and repeated lappings, combus-
tion efficiency may drop. Measure the sinking distance
and replace the valve and valve seat if the valve sink ex-
ceeds the tolerance.
Sink
Cylinder head
Depth gauge
Standard
Valve sink
.4LHA-HTE/HTP
(Intake/Exhaust)
0.2 - 0.4
• 4LHA-STE/STP
DTE/DTP
(Exhaust)
Valve protrusion
4LHA-STE/STP
0.6 - 0.8
(Protrusion)
DTE/DTP
(Intake)
4-3.4 Valve guide
(1) Measuring inner diameter of the valve guide.
Measure the inner diameter of the valve guide and
replace it if it exceeds the wear limit.
TT
7
mm
Wear limit
.
1.8
0.6 (sink)
2-17
Intake
(0.3543 - 0.3549)
Valve guide Valve guide
inside dia. inside dia.
Exhaust
(0.3543 - 0.3549)
NOTE: The inner diameter standard dimensions assume a
pressure fit.
(2) Replacing the valve guide
Use the insertion tool and tap in the guide with a
mallet.
The intake valve guide and exhaust valve guide are of
different shapes/dimensions. The one with a groove
around it is the exhaust valve guide and the one
without is the intake valve guide.
(3) Valve guide projection
The valve guide should protrusion 11.5 mm from the top of
the cylinder head .
7777
,4LHA Serie.
mm (in.)
Standard Wear limit
9 . 0 0 - 9 . 0 1 5 9.1
(0.3583)
9 . 0 0 - 9 . 0 1 5 9.1
(0.3583)
T
77