International Harvester Company Cub Lo-Boy C-60 Service Manual page 22

cylinder head bolts to the specified foot-
pounds torque and in the sequence recom-
mended. Valve clearances are also affected
in this manner. Thus any abnormal wear,
warpage or distortion affecting a valve
guide will destroy its function as an ac-
curate bearing to maintain the valve head
concentric with its seat, and will prevent
leak-proof seating.
Warpage, burning and pitting of valves is
mainly directed against the exhaust valveswhich
are exposed to the high temperature
flow of exhaust gases. Such defects are
generally caused by valves failing to seat
tightly and evenly, permitting exhaust blow-
by. This, in turn, can generally be traced
to hard particles of carbon being present
on the slopes of the valve seats. It may,
however, be due to weak springs, insuf-
ficient valve clearance, or warpage and
misalignment of the valve stem or guide.
Oil and air sucked past worn intake valve
stems and guides into the combustion
chamber, cause excessive oil consumption,
form excessive carbon, and dilute fuel.
Warpage, chiefly occurs on the valve stem
due to its exposure to heat. Out-of-round
wear occurs when the seat has been pounded
by a valve head which is not in line with its
stem or g1lide.
Mis~nment is a result of wear, warpage,
and distortion. Wear, when accentuated by
insufficient lubrication, will eventually
create sloppy clearances with resultant
misalignment.
Examine the engine for signs which may
indicate the reason for the need of valve
reconditioning. Dry and rusted valve
springs are an indication that the oil pas-
sages to the valve levers may be blocked,
causing wear on the valves and guides, and
resulting in inlproper valve action. A de-
fective gasket under the valve cover will
permit the entrance of dirt which will
cause undue wear on the valve stems and
guides and damage to the valve springs.
Warpage
of the valves, and in known ex-treme
instances, that of the crankcase, can
result from the engine overheating due to ablocked,
dirty or insufficiently filled cool-
ing system.
Valves
Most frequ~ntly, however, warpage of avalve
stem or a guide is due to uneven tem-peratures
being applied along its length.
The lower part of the guide and stem is
near the combustion heat, and the upper
portions are closer to cylinder head waterpassages.
Valve materials are carefully
chosen to withstand such varying tempera-
tures. However, an engine that is allowed
to operate continually in an overheated con-
dition is definitely open to valve stem and
guide distortion and warpage. Distortion
can also be caused by failure to tighten
1. Remove all carbon from the valvehead
and stem. Valve stems should be
lightly polished with an extremely fine
abrasive cloth sufficiently to remove the
carbon deposits only. Because of the
nature of the valve deposits, solvent clean-
ing ordinarily will not remove all the de-
posits from the valves. Wire brushes will
do this job satisfactorily, but only brass
wire brushes should be used since steel
brushes may scratch the surface. Such
scratches are likely to cause localized
stresses in an operating valve and may
eventually result in fatigue fractures of
the valve. For similar reasons the use of
coarse emery paper should be avoided.
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