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Measuring piston pin bore diameter
Using calipers or a cylinder gauge, measure the pis-
ton pin bore diameter. If the service limit is exceeded
replace the piston.
Piston pin bore diameter, mm [in.]
Normal value ............. Ø70 [Ø2.76]
Assembly standard ... 70.002–70.015 [2.75598–2.75649]
Service limit .............. 70.040 [2.75747]
Measuring piston protrusion
Measure the protrusion (height from cylinder head to
piston head) of each piston at top dead center. If it is
not within standards for piston protrusion measure-
ment, inspect the clearance of the parts.
1. Set the dial gauge to zero (0) on top of the crank-
case and measure the protrusion at four places
on top of the piston head. Average the four mea-
surements to determine the protrusion.
2. Subtract the piston protrusion from the thickness
of the cylinder head gasket (as installed) to deter-
mine the clearance between the piston top and
cylinder head.
Piston protrusion, mm [in]
Assembly standard ... 0.06 60 0.065 [0.0024 to 0.0256]
Cylinder head gasket thickness, mm [in]
Assembly standard ... 1.77 to 1.83 [0.0697 to 0.0720]
Piston top and cylinder head clearance, mm [in]
Assembly standard ... 1.22 to 1.95 [0.0480 to 0.0768]
IMPORTANT! Keep the piston protrusion within
assembly standard range to prevent the valves
from stamping on the piston and to maintain
high engine performance.
Inspecting piston ring grooves
Check the piston ring grooves for wear and damage,
replace the piston if necessary. Pay special attention
to the Ni-resist insert in the top groove (A) for cracks.
Group 21 Engine Body
99
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