Inspecting The Cylinder Head - Yanmar 3YM30 Service Manual

5.2.1 Inspecting the cylinder head

The cylinder head is subjected to very 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.
(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 each diagonal. Measure the clearance
between the
surface with a feeler gauge.
Cylinder head
distortion
(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.
(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:
Intake
Seat angle
Exhaust
Seat width
Intake
Exhaust
straight-edge and
Standard Wear limit
0.05 or less 0.15
120°
Standard Limit
1.07-1.24 1.74
1.24-1.45 1.94
5. Inspection and servicing of basic engine parts
Straight-edge
combustion
mm
Thickness gage
(Distortion at combustion surface)
90°
108