S&S Cycle Sidewinder 3 5/8 Big Bore Cylinders for 1936–1999 Big Twins - Manual (Page 10)

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Piston to Piston Clearance
A. Perform steps A through C in “Connecting Rod Clearance” on page 8
B. Rotate flywheel to position where pistons are closest to each other. See Picture 4, page 9.
C. Check clearance between pistons.
NOTE: A minimum of 1⁄16" clearance is required.
D. Disassemble cylinders and pistons, and carefully file edge of piston skirts until clearance is obtained.
E. Reassemble and check clearance.
Piston to Flywheel Clearance
A. Perform steps A through C in “Connecting Rod Clearance” on previous page.
B. Rotate flywheel to position where front piston is closest to flywheel. See Picture 5, page 9.
C. Check clearance between piston and flywheel.
NOTE: A minimum of 1⁄16" clearance is required.
D. Disassemble cylinder and piston, and carefully file piston skirt until clearance is obtained.
E. Reassemble and check clearance.
F. Repeat procedure for rear piston.
8. Breather Timing (All)
To maximize efficiency when scavenging oil from flywheel cavity in big twin engines, it is necessary to check and usually modify crankcase
breather timing.
NOTES:
• Breather timing can be checked after other crankcase clearancing is done or during initial disassembly.
• Early crankcase breather opening is a rough cast elliptical hole. Later vintage crankcases have a breather opening that is square.
• Objective of this step is to modify cases so that hole in cases is located in same position as hole in breather gear with opening and closing
sides of hole in case in correct location for proper breather timing.
• S&S Part #53-0020, Degree Wheel Kit, was designed to aid in checking breather timing. Procedures below assume an S&S degree wheel is
used.
• S&S recommends grinding hole to maximum timing specifications. If there is any doubt and timing falls within specs, leave breather
opening alone. See Figure 3 for breather timing specifications.
Figure 3