Where is the engine breather valve on an Evo Sportster?
86-90 engines vent through a valve in the cam cover. 91 and up engines vent through a valve in each rocker box and out the hollow breather bolts in each head to the air cleaner. Factory engine breather valves on all Evo Sportsters are inside the engine.
Where is the air inlet on a Sportster?
On a Sportster motor there’s no air inlet. The engine vents into the intake flow on the upstream side of the carb instead, where there’s much less vacuum. It’s not designed to flow air through it. What’s more, the crankcase volume is constantly changing. There are check valves in line with the breather outlets.
What’s the diameter of an umbrella valve on an Evo?
As a result, the (-89) umbrella valve with its diameter of 1” may not perform correctly as there is likely to be leakage. This looks like a good factory alternative replacement umbrella valve that comes in a replacement kit for Twin Cams.
Which is larger the umbrella valve or the breathing valve?
It’s center inside diameter is slightly larger than the 1.25” OD (-82) umbrella valve. The two ‘C’ shaped slots that do the breathing have an OD of 1“. As a result, the (-89) umbrella valve with its diameter of 1” may not perform correctly as there is likely to be leakage.
86-90 engines vent through a valve in the cam cover. 91 and up engines vent through a valve in each rocker box and out the hollow breather bolts in each head to the air cleaner. Factory engine breather valves on all Evo Sportsters are inside the engine.
On a Sportster motor there’s no air inlet. The engine vents into the intake flow on the upstream side of the carb instead, where there’s much less vacuum. It’s not designed to flow air through it. What’s more, the crankcase volume is constantly changing. There are check valves in line with the breather outlets.
As a result, the (-89) umbrella valve with its diameter of 1” may not perform correctly as there is likely to be leakage. This looks like a good factory alternative replacement umbrella valve that comes in a replacement kit for Twin Cams.
It’s center inside diameter is slightly larger than the 1.25” OD (-82) umbrella valve. The two ‘C’ shaped slots that do the breathing have an OD of 1“. As a result, the (-89) umbrella valve with its diameter of 1” may not perform correctly as there is likely to be leakage.