S&S Cycle Bore Big Twin Stroker Kit 1936–1999 3 7/16 - 3 1/2 - Manual (Page 17)

17
Improper breather timing causes poor oil scavenging from flywheel cavity and incorrect crankcase air pressure. These conditions may
cause unwarranted engine oil leaks around gaskets and seals and probable oil burning due to oil blow by past piston rings. Removal of
excessive material from breather gear opening is irreversible and damage to crankcases may result.
To check and modify breather timing perform following steps:
A. Bolt degree wheel pointer to drive side crankcase half using center case stud and nut. Position pointer towards sprocket shaft.
B. Install degree wheel assembly on sprocket shaft. Rotate flywheel assembly so front piston is at TDC, top dead center. Position degree
wheel on sprocket shaft so pointer indicates 0° TC, top center, and tighten set screw.
C. Rotate flywheels in normal direction of travel to 10° before TC as in Picture 10, below left. Observe breather gear and hole in crankcase
through tappet block opening to determine hole in breather gear and hole in case relationship.
D. Rotate flywheels to 7° after TC. Again note relationship. If edge of hole in gear appears in hole in crankcases during this span of degrees,
then cases have proper opening specs. If not, then opening side of hole in cases must be ground. Grind hole to 7° before TC, maximum
timing specifications.
E. Rotate flywheels to 55° after BC, bottom center. Observe breather gear and hole in crankcase to note their relationship.
F. Rotate flywheels to 92° after BC and note relationship. See Picture 11, above right. If back edge of hole in gear disappears from view
during this span of degrees then cases have proper closing specs. If not, then closing side of hole in cases must be ground. Grind hole to
92° after BC, maximum timing specifications.
G. Note location of hole in gear as opposed to hole in crankcases. See Figure 7, previous page. Grind hole in cases so location matches holes
in gear with respect to where toothed portion of gear hits cases. Picture 12, below, shows finished breather gear opening.
H. Optional Step
NOTE: To further maximize breather efficiency some engine builders modify or remove screen in breather gear.
Breather gear screen stops foreign material from getting into gear side cavity where material could possibly stop oil pump and/or
damage other parts. No oil to engine will result in damage to engine components.
To modify screen:
a. Early gears - Remove clip that holds screen in place.
b. Early gears - Turn screen so it covers hole made by removing clip.
c. Early gears - Spot weld screen in place.
d. All gears - Drill all holes in screen as large as possible without weakening screen.
CAUTION
Picture 10 Picture 11
Picture 12
CAUTION