Operating instructions

5-4
oil with two parts kerosene to prevent over heating of
the metal and tearing of the thread.
5-21. To remove a damaged helical coil insert use the
proper size of extracting tool for the nominal thread
size. Tap it into the insert so that the sharp edges get a
good "bite"; then turn the tool to the left, and back out
the helical coil until it is free. To install a new insert
in a properly tapped hole (after blowing out all liquid
and chips), slide it over the slotted end of the driving
mandrel of the proper size of installing tool and
engage the driving tang (bent end) of the helical coil
in the mandrel slot; then wind the insert slowly into
the tapped hole (See Figure 5-2). The outer end of the
insert should lie just within the first full thread of the
hole. Break off the driving tang of a notched helical
coil by bending back and forth across the hole with
long-nose pliers or with a special tang break-off tool.
5-22. CYLINDERS.
5-23. FIN REPAIRS. Straighten slightly-bent barrel
fins with long-nose pliers. File to smooth the edges of
broken head fins. If it becomes necessary to cut out a
vee notch to stop a head fin crack, a slotted drill
bushing to fit over the fin and a 3/16 inch twist drill
may be used to cut the notch. Its apex must be
rounded and the edges should also be rounded. If
such repairs and previous breakage have removed as
much as 10% of the total head fin area the cylinder
assembly has reached the limit of such repair.
5-24. SPARK PLUG HOLE HELICAL COIL
INSERTS. Before attempting to back out a damaged
insert, use a sharp pointed tool to pry the teeth at outer
end away from the cylinder head metal. Tap a helical
coil extracting tool into the insert until it has a good
bite (See Figure 5-3). Place a new helical coil in the
cut -out side of the installing tool sleeve with its
driving tang toward the threaded end. Engage the tang
with the slotted end of the driving mandrel and wind
the insert into the sleeve thread, thus compressing it.
Hold the sleeve so that the helical coil can be seen
through the slot in the threaded end, and turn the
mandrel crank until the insert starts into the cylinder
head hole. If the sleeve is then not in contact with the
head surface, grip sleeve and mandrel and turn until
the sleeve touches lightly (See Figure 5-4). Wind the
helical coil into the cylinder head until its toothed end
lies just within the first full thread. The teeth should
be in position to enter the depressions made by the
original insert. If driven too far, the insert will emerge
in the combustion chamber and will have to be wound
on through. When the helical coil is in correct
position, use long-nose pliers to bend the driving tang
back and forth across the hole until it breaks off at the
notch. Coat a Heli-Coil Corporation No. 520-2
expanding tool threaded end with Alcoa thread lube or
a mixture of white lead and oil, and screw it into the
new insert until its final thread forces the teeth firmly
into the cylinder head metal (See Figure 5-5).
5-25. VALVE GUIDES. If the valve guides are to
be replaced, the new guides must be installed so that
the valve stem hole is accurately square and aligned
with the valve seat. When pressing or driving out a
worn guide, the cylinder assembly should be firmly
supported in the inverted position with space below to
allow the guide to drop out. The driving tool should
pilot inside the guide and drive on its inner end. All
carbon must be removed from the guide's inner end.
If the cylinder head hole is not scored or enlarged, a
standard size guide may be installed as a replacement.
If the head hole is rough it must be broached or
reamed to a diameter smaller than the next larger
oversize guide by the amount of interference ("T")
specified in the Table of Limits. Valve guides are
supplied in oversizes of 0.005, 0.015 and 0.020 inch.
The cylinder assembly must be supported firmly while
the new guide is driven or pressed into place with a
driver which fits over its end and bears on the filleted
flange. Driving on the guide end will spread it.
Before installing a new guide, dip the end to be
inserted in engine lubricating oil. The flat side of the
guide flange must go against the cylinder head.
Watch for peeling of bronze and correct misalignment
which causes it. It is not necessary to freeze the new
guide before installing it. Valve guide broaches may
be purchased from the Borrough's Tool and
Equipment Company, Kalamazoo, Michigan. Sizes for
intake and exhaust valve guides are slightly different.
These tools are very expensive and may be broken
during the operation if not perfectly aligned with the
hole. They are intended for use in a broaching
machine not normally available in overhaul shops.
Valve stem holes may be reamed if solid spiral
reamers of correct diameters and with 0.431 inch
diameter pilots are available. (Refer to the Table of
Limits for stem hole finished sizes.)
NOTE
Due to the choke specified for the cylinder
barrel bore, a cam-controlled grinder is
required to regrind worn barrels to the
allowable 0.015 inch oversize dimension.