S&S Cycle Change in S&S Breather Gears User Manual
Page 2
S&S
®
breather gears for late 1977-up big twin engines have been changed to improve oil scavenging and reduce oil carry-over in high-
performance engines.
These changes apply to breather gears 33-4241, 33-4242, 33-4250 and 33-4260 (formerly 33-4236, 33-4240, 33-4251 and 33-4261) and
are as follows:
1.
Oil evacuation hole has been elongated to increase duration of suction to breather settling cavity.
2.
Opening and closing specifications have been changed for same reason. Old and new specification are shown below for reference.
Old:
Opening: TDC (+/- 10°)
New:
Opening: 17° after TDC (+/- 10°)
Closing: 65° after BDC (+/- 10°)
Closing: 82° after BDC (+/- 10°)
NOTES:
●
S&S crankcases are machined for maximum breather timing. When 33-4241, 33-4242, 33-4250 and 33-4260 breather gears are
installed in S&S crankcases, breather window will typically open at 7° after TDC and close at 92° after BDC. Builders using other
crankcases may modify crankcase breather opening to obtain these specifications for maximum performance.
●
Change in breather gear is primarily to facilitate oil scavenging in large displacement engines. New specifications are harmless but
not useful in most older engines.
●
New gears can easily be identified by elongated hole on end of gear opposite drive teeth. See picture below.
2
Old Style
New Style
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