Operating instructions

5-3
torn, install the next larger oversize stud. If the old
stud was of the maximum oversize, of if the thread is
damaged, the hole may be tapped and a helical coil
insert installed for a standard-size stud. Coat the new
stud's coarse thread with Alcoa thread lube if the hole
is blind or with National Oil Seal compound if the
hole goes through to a cavity subject to oil spray. It is
advisable to drive the new stud with a tee handle stud
driver. Turn it in slowly, and compare the estimated
torque values listed in the Table of Limits. Drive the
stud in until it projects a distance equal to the
appropriate "Setting Height" listed in Table X.
5-19. HELICAL COIL INSERT INSTALLATION.
Bronze helical coil inserts are installed at the factory
in four tapped holes of each crankcase bottom flange,
in three holes in the left crankcase parting flange and
two in the right crankcase parting flange and in four
bolt holes at each cylinder head intake port flange.
Stainless steel helical coil inserts of special design are
installed in all spark plug holes. Any of these inserts
may be replaced, if damaged, with the aid of tools
which are available through Authorized Distributors
of the Heli-Coil Corp., Danbury, Connecticut 06810.
The manufacturer's Bulletin No. 650-R lists both
manual and power-driven installing tools, tang break-
off tools, special taps and plug gauges. A tap drill
bulletin is also available from the manufacturer.
Helical coil inserts are available in both National
Coarse and National Fine series in lengths equal to 1,
1-1/2 and 2 times nominal diameter and in pipe thread
sizes. They are made of either carbon steel, phospher
bronze or stainless steel, as specified by part number.
They are supplied with or without a notch above the
driving tang. The notch is provided to facilitate
breaking off the tang in open holes.
5-20. Helical coil inserts are helical coils of wire with
a diamond-shaped cross section forming both a male
and a female thread. The diameter of the insert, when
compressed into a special tapped hole at the widest
part of the wire (between male and female threads), is
equal to the nominal screw size. The special finishing
taps size the casting hole so that the pitch diameter of
the female thread of the installed insert conforms to
class 3 fit with standard bolt threads or class 4 (tight)
fit with standard-size studs. The difference in fit is
due to a difference in pitch diameters of bolts and
studs, so that only one set of helical coil special taps is
required for installation of these inserts in both bolt
holes and stud holes. Tap drilling depths and tapping
depth for helical coil inserts to be installed in blind
holes should conform to the recommendations relative
to inserts of length equal to 2 times nominal diameter,
as tabulated in the manufacturer's Bulletin No. 650-R.
Helical coil tap drills and special taps must be run in
perpendicular to the machined surface of the casting.
Drilling should be done in a drill press after the
casting is firmly supported and clamped and
alignment checked. The tap will tend to follow the
drilled hole. For drilling and tapping aluminum alloy
castings use a lubricant made by mixing one part lard
TABLE VII. STANDARD AND OVERSIZE STUD IDENTIFICATION