4. Bore Crankcases
NOTE: Boring cylinder spigot holes in cases to accommodate big
bore cylinders will machine a notch on center case bolt. This bolt
must be replaced with a special stud which is installed into the
top crankcase bolt hole in the cam side case half.
Perform following procedure to bore crankcases:
A. In 1986-1990, four speed cases, the center crankcase bolt
must be replaced by S&S
®
stud 31-2046. In 1991 and
later, 5 speed cases, the center crankcase bolt must be
replaced by S&S stud 31-2047. The stud will be installed
in the threaded hole in the camside crankcase half that
the stock center crankcase bolt normally screws into.
1. Before final installation of stud, screw stud into
hole to make sure installed height is correct.
See
Picture 2.
Stud should extend 2.570"- 2.630" from
crankcase to top of stud for 1986-1990 crankcases,
and 2.270"- 2.330" from crankcase to top of stud
for 1991 and later crankcases. If driveside case is
set in place, stud should extend far enough that
there is full thread engagement with 12 point nut
31-5024 when washer is in place.
See Picture 3.
2
. If stud can not be screwed in far enough to obtain
specified stud height, hole must be drilled and
tapped deeper. It is recommended that this drilling
operation be done on a milling machine or drill
p
ress to avoid destroying existing threads.
3. If stud can be installed to correct height, clean stud
and threaded hole with lacquer thinner and install
s
tud to correct height using red Loctite
®
o
r other
permanent thread locking compound.
B
. Clean cases thoroughly and assemble using all case
bolts. Tighten all case bolts as in final assembly.
C. Place masking tape over both ends of camshaft and
mainshaft bearings to keep chips out.
D. Bolt boring plate to bench or stand leaving squared end
of plate protrude over edge approximately 7".
E. Using 4
3
⁄8 -16 thread nuts, bolt cases to plate using all
four studs. Boring spacer, Part 53-0007, is used to
space cases using stock Harley-Davidson
®
Sportster
®
models studs. If Sportster
®
model studs have been
replaced with late, male style big twin studs, use both
53-0007 and 53-0008 spacers to space cases away
from boring fixture.
See Picture 4.
NOTE: Be careful not to damage studs. Do not lift cases by studs
and avoid knicking, scratching or denting studs.
Damaged studs may cause stress risers which can lead to stud
failure and possible damage to engine components.
F. Center boring bar head in cylinder spigot bore in
crankcases, not hole in plate. Refer to manufacturer’s
instructions supplied with boring bar for correct
procedure.
G. Bore hole to diameter of 3.878" to 3.880" by 1
5
⁄8" deep.
Measure depth perpendicular from cylinder base
gasket surface.
4
Picture 2
Pictur
e 3
Picture 4
CAUTION
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