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This photo is before working the case window to match the S&S Breather valve..
Note the elongated top end return vacuum hole in their valve .. Oem does not have that, it gives more time to pull oil out of the top end = Less oil up there, less oil leaks .. !
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.
This photo shows the case window after the work was done for matching the gear case window ...
This procedure increases the area that air and oil have to pass from breather gear cavity to cam chest ...
Photo below shows checking the valve's open and closing timing..
This work maximizes the efficiency of scavenging oil from flywheel cavity
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 past piston rings.
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