Crankcase Breathers

Crank case and gear case breather tube with fitting. Mounts to the gear cover and fits V-models 1934-1936.

Crank case breather tube and fittings for IOE models.

Reproduction of the original breather tube. Oil mist from the crankcases and lubrication from the oil pump are directed to the primary chain through this tube.

Gear case breather tube and fitting or all Sportster models from 1954–1978.

Race track veterans' lore: best running engines have a slight depression in the crankcase. This is easily achieved with a one-way ventilation valve. And what's more, the valve keeps grit and particles from entering the crankcase, additionnally.
The VIP valve has a somewhat larger case that makes use of the Evolution umbrella valve.

Race track veterans' lore: best running engines have a slight depression in the crankcase. This is easily achieved with a one-way ventilation valve. And what's more, the valve keeps grit and particles from entering the crankcase, additionnally.
The SB valve is small-cased and fits better where space is scarce, the valve is not replaceable.

Crankcase breather filter for all Harleys and especially beneficial for models 1975-up if the stock air cleaner has been replaced. Prevents the breather from inhaling impurities into the lower end of the engine.

Crankcase breathers on performance bikes are prone to suck in debris, due to their enhanced respiratory capacity. This nice little filter keeps dirt outside the engine and the oil inside. Fits any 5/16” (8 mm) tube or connector, and - of course - not only racebikes.

Stock replacement breather valves by S&S for all OHV Big Twins 1936–up.

The Evolution style S&S breather reed valve replaces the standard rotary breather valve in 1993→ Evolution Big Twin style engines. Installation is fast and simple. No aligning timing marks, and no rotating parts. There is a +.030“ oversized reed valve for engines with heavily damaged breather bores.
How does it work?
Unlike the rotary breather valve that has been used in Harley-Davidson big twin engines since the 1920‘s, the S&S crankcase breather reed valve is not dependent on the rotation of the crankshaft to make it open and close. Therefore the opening and closing times are not determined by crankshaft position. The functional part of the reed valve consists of three steel reeds that are normally in the closed position. When the pistons travel downward in the cylinders, the air in the crankcase is compressed and pressure in the crankcase below the pistons increases. This pressure causes the reeds to open, allowing the air, oil and oil mist in the crankcase to escape into the cam chest. When the pistons change direction and begin traveling back upward in the cylinders, a vacuum is created in the crankcase. The vacuum causes the reeds to close, preventing air from entering the crankcase. The effect is that a slight vacuum is maintained in the crankcase and oil scavenging is greatly improved. This is most significant at high rpm when the time available to get the air out is the shortest.