10.9
Section 10
Inspection and Reconditioning
10
Valve Seat Inserts
Hardened steel alloy intake and exhaust valve seat
inserts are press-fi ed into the cylinder head. The
inserts are not replaceable but can be reconditioned if
not too badly pi ed or distorted. If cracked or badly
warped, the cylinder head should be replaced.
Recondition the valve seat inserts following the
instructions provided with the valve seat cu er
being used. A typical cu er is shown in Figure 10-10.
Cu ing the proper valve face angle, as specifi ed in the
Valve Specifi cation table and the proper valve seat
angle (89.5°-90°) will achieve the desired 0° (1° full
cut) interference angle where the maximum pressure
occurs on the outside diameters of the valve face and
seat.
Figure 10-11. Valve Stem Seals.
Always use new seals when the valves are removed
from the cylinder head. The seals should also be
replaced if deteriorated or damaged in any way.
Never reuse old seals.
Pistons and Rings
Inspection
Scuffi ng and scoring of pistons and cylinder walls
occurs when internal engine temperatures approach
the welding point of the piston. Temperatures high
enough to do this are created by friction, which is
usually a ributed to improper lubrication and/or
overheating of the engine.
Normally, very li le wear takes place in the piston
boss-piston pin area. If the original piston and
connecting rod can be reused a er new rings are
installed, the original pin can also be reused but new
piston pin retainers are required. The piston pin is
included as part of the piston assembly – if the pin
boss in the piston or the pin are worn or damaged, a
new piston assembly is required.
Ring failure is usually indicated by excessive oil
consumption and blue exhaust smoke. When rings
fail, oil is allowed to enter the combustion chamber
where it is burned along with the fuel. High oil
consumption can also occur when the piston ring
end gap is incorrect because the ring cannot properly
conform to the cylinder wall under this condition. Oil
control is also lost when ring gaps are not staggered
during installation.
When cylinder temperatures get too high, lacquer and
varnish collect on pistons causing rings to stick, which
results in rapid wear. A worn ring usually takes on a
shiny or bright appearance.
Valve Seat Cutter
Pilot
Figure 10-10. Typical Valve Seat Cutter.
Lapping Valves
Reground or new valves must be lapped in, to provide
fi t. Use a hand valve grinder with suction cup for
fi nal lapping. Lightly coat valve face with fi ne grade
of grinding compound, then rotate valve on seat with
grinder. Continue grinding until smooth surface is
obtained on seat and on valve face. Thoroughly clean
cylinder head in soap and hot water to remove all
traces of grinding compound. A er drying cylinder
head, apply a light coating of SAE 10 oil to prevent
rusting.
Valve Stem Seals
These engines use valve stem seals on the intake and
exhaust valves. See Figure 10-11.
Valve Stem
Seals
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