3
2. Lower Oil Return Holes
Sportster cylinder oil return holes must be lowered in
those stroker conversions where oil ring crosses stock
oil return hole. This is necessary to prevent oil from
returning above oil ring which will cause engine to
smoke. Several lowering methods have been used
successfully but rather than give them all, we decided
to provide the one that requires the fewest special tools
and materials.
NOTES
●
Oil rings will usually touch and/or cross oil return
holes with installation of stroke 4
7
⁄
16
” or longer. Strokes
shorter than 4
7
⁄
16
” do not require this step.
●
Method given below was tried as an experiment when
we installed an S&S 4
5
⁄
8
” stroker kit in our 1972 test
Sportster. All steps axcept 8 and 9 were performed.
Object was to see if engine would smoke and use
excessive oil which it did not. Several customers have
also reported similar successes when leaving stock holes
open. Based upon our test results and these customer
reports, we feel relatively confident in recommending
that stock oil return holes be left open even though we
have tried it on only one test engine and cannot
guarantee that it will work in all instances. If you decide
to try leaving the stock oil return holes open, perform all
of the following steps except 8 and 9.
For strokes 4
7
⁄16” and longer, perform following steps:
A. Place cylinder with head gasket surface down on
bench. Lay out lines “A” on cylinder base gasket
surface so they are directly above centers of old
oil return holes which exit into cylinder bore. See
Figure 1.
B. Lay piece of
1
⁄8” thick material against cylinder
spigot 90° to lines A and scribe lines "B".
C. Centerpunch points where lines A and B
intersect.
D. Drill
3
⁄16” diameter hole at each point
perpendicular to gasket surface to meet
passage coming from cylinder head. Be careful
not to break drill when breaking into existing
passage as holes may be slightly misaligned
and drill may tend to grab.
E. Centerpunch corners where lines A intersect
spigot. See Figure 2.
F. Drill
3
⁄32” diameter hole at each point at 60° angle
into cylinder bore.
G. Enlarge
3
⁄32” holes from inside cylinder bore with
3
⁄16” diameter drill.
H. Braze or weld old oil return holes shut.
Centerpunch, then
rill
3
⁄
32
" diameter hole
Figure 2
Centerpunch, then
drill
3
⁄32" diameter hole
Picture 2 Picture 3
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