G.5Part. N. 8000 B0148 (02-2008)
ENGINE OVERHAULING
Valve guides
Carry out a careful visual check of the valve guides.
The valve guides should be checked for wear by measuring the clearance be-
tween the valve stem and valve guide; use a dial gauge and measure the clear-
ances on the “x” and “y” axes.
Inlet valve (250-450-510): nominal clearance 0.000315÷0.00138 in.
Wear limit: 0.002 in.
Exhaust valve (250-450-510): nominal clearance: 0.0007÷0.00177 in.
Wear limit: 0.003 in.
Replacement of valve guides
Use a suitable drift and drive out the guide from the cylinder head.
Make sure that the cylinder head isn’t damaged.
Heat the cylinder in an oven to 170°C (338°F).
Use a suitable drift and install a new valve guide from the top of the
cylinder head. Put some oil on the guide before mounting. Mount new seal rings.
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