Yanmar 3YM20, Руководство по обслуживанию

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5. Inspection and servicing of basic engine parts
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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 straight-edge and combustion
surface with a feeler gauge.
(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:
mm
Standard Wear limit
Cylinder head
distortion
0.05 or less 0.15
Seat angle
Intake 120°
Exhaust 90°
Seat width Standard Limit
Intake 1.07-1.24 1.74
Exhaust 1.24-1.45 1.94
(Distortion at combustion surface)
Straight-edge
Thickness gage