Fitments
L77-99 Big Twin (Excl. TC)
Part Description
S&S, steel breather valve. +.030" OD
+.030" oversize steel breather valve. Used to save worn or damaged crankcases. Okay for stock or high performance replacement. Note: JIMS has a +.030" breather hole reamer tool which is available as 978343. Note: that steel breathers require steel breather valve spacers. Plastic breathers require plastic spacers. Do not intermix steel and plastic parts. Note: S&S breather valves come with elongated breather holes to increase the duration of the vacuum, allowing more oil to be drawn from the cylinder heads. This has no disadvantage in any model year, either stock or Big Inch motor. Tech tip: The timing for S&S breather valves, only for late 77-99 Big Twin models, has been changed by S&S in the year 2000. This is done to improve oil scavenging and reduce oil carry-over in high performance / large displacement engines. Old opening was at TDC and closing at 65° after BDC. New opening is 17° after TDC and closing at 82° after BDC. The old timing specification can be obtained by installing the timing mark on the breather gear one tooth clockwise from the timing mark on the cam gear. Also the breather's cavity oil evacuation hole (opposite of the drive gear), which used to be a round hole, has been elongated (made longer) to increase the duration of suction to the crankcase breather 'settling' cavity. The new specifications are not useful in most stock engines, but harmless. Breather windows in S&S cases will typically open at 7° after TDC and close 92° after BDC. Builders using other crankcases may modify crankcase breather opening to obtain these specifications for maximum breather efficiency and performance.
