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Steel Rotary Breather Gears for 1936–'84 Big Twins

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Product Reviews

S&S steel rotary breather gears have better dimensional stability than plastic gears, especially at high temperatures. Abrasive particles are less likely to get embedded in a steel gear body— embedded particles can damage the crankcase breather gear cavity. A screen provides better protection than a slotted gear— small particles are stopped from getting to the gear cavity where they may damage the gears and oil pump. S&S steel rotary breather gear features a welded-in screen and larger diameter holes, providing improved air flow/oil scavenging from the flywheel cavity. Crankcase flywheel cavity vacuum and oil scavenging are further improved by optimized breather window timing. Breather oil trap scavenging is significantly improved by increased scavenge port duration. S&S steel rotary breather gears are available for all OHV engines from 1936–'84 in standard and +.030" oversize for repair jobs where the cases have been damaged.


S&S® High Evacuation Breather Gears For 1936–'47 Big Twins. With the new high evacuation breather gear for knucklehead engines, we applied the same principle to the cylinder head return oil suction passage as we did to the breather pocket scavenge port on our other breather gears. By elongating that hole in the gear, the duration of vacuum on the passage is increased. That allows more oil to be drawn from the "tins" and returned to the gearcase and ultimately to the oil tank. Getting more oil out of the tins reduces one of the most common problems with knuckle engines – leaky tins.

  • All steel construction—superior dimensional stability, abrasion
  • Welded-in screen
  • Higher flow than stock
  • Elongated breather pocket scavenge hole for increased suction

  • Standard diameter for replacement or new builds
  • +.030" diameter for damaged engines
S&S® Breather Gears Only for 1936–'99 Big Twins
Year of Camshaft   Standard Size   +.030" Oversize
1936-Early '47   106-5070   106-6012
1948-Early '77   33-4246*  33-4247 
Late 1977-'99   33-4241**  33-4242 
*S&S Cycle 33-4246 is a service part replacement for Harley-Davidson® part number 25313-73.
**S&S Cycle 33-4241 is a service part replacement for Harley-Davidson® part numbers 25310-82A, 25313-77B, & 25311-90)
Note: All reference to H-D® part numbers is for identification purposes only. We in no way are implying that any of S&S Cycle's products are original equipment parts or that they are equivalent to the corresponding H-D® part number shown.


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