Yanmar 4LHA-HTP Operation Manual page 335

Chapter 2 Basic Engine
4. Cylinder Head
4-1 Inspecting the cylinder head
The cylineder head is subjected to severe operating conditions
with repeated high pressure, high temperature and cooling.
Thoroughly remove all the carbon and dirt-after disassembly
and carefully inspect all parts.
4-1.1 Distortion of the combustion surface
Carefully check for cylinder head distortion as this leads to
gasket damage and compression leaks.
(1) Clean the cylinder head surface
(2) Place a straight-edge along each of the four sides and di-
agonal. Measure the clearance between the straight-edge
and combustion surface with a feeler gauge.
Measurement procedure
Straight-edge
Feeler gauge
StandardWear
0.05 or less
Cylinder head
(0.002)
distortion
4-1.2 Checking for cracks in the combustion surface
Remove the fuel injection nozzle, intake and exhaust valve
and clean the combustion surface. Check for discoloration or
distortion and conduct a color check test to check for any
cracks.
Valve seat Valve seat
Valve Valve
Length of Length of
valve valve
4-1.3 Checking the intake and exhaust valve seats
Check the surface and width of the valve seats.
If they are too wide, or if the surfaces are rough, correct to the
following standards:
mm(in.)
limit
0.2(0.0079)
Seat angle
Seat width
Intake
Exhaust Exhaust
2-15
Standard dimension
Exhaust valve seat
Intake valve seat
5]
0» -
c
IS ~
< i = d H >
^ - 1 2 0 °
4LHA-HTE/HTP
Intake Di 42.5(1.67)
Exhaust D2 37.0 (1.46)
Intake di 43.5 (1.71)
Exhaust d2 37.5(1.48)
Intake Lt 121.0(4.76)
Exhaust L2 121.0(4.76)
Intake
Exhaust
Standard
All 1.38-1.62
2.015-2.227
STE/DTE/STP/DTP
HTE/HTP
.4LHA Ser
1
mm(in.
4LHA-DTE/DTF
4LHA-STE/STP
45.5(1.79)
39.0 (1.54)
46.0 (2.56)
39.5 (1.56)
121.5(4.78)
122.0 (4.80)
120*
90*
mm
Wear limit
2.12
2.73
1.24 1.80