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Sportster Motorcycle Motor - Top End Discuss Sportster Motorcycle Top End issues. Rockerboxes, Valves, Cylinders, Pistons, Rings, Lift Rods, etc...

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Old 5th June 2020
Hippysmack's Avatar
Hippysmack Hippysmack is offline
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When the engine is off, the crankcase area is at atmosphere (same pressure inside as outside the engine).
When you first start up the bike, the crankcase is purged on the first piston downstoke.
Then the breather closes for the next upstroke which pulls a slight vacuum in the crankcase.
If the breathers are stopped up, the air can't expell and the pressure builds wrecking gaskets.
This could end up being a chain reaction of different gaskets leaking.
(including possible rocker box gaskets, case seals, popping the oil tank cap off and spitting oil from there or the breathers or elsewhere)

It'd be helpful if you'll post some pics of the offending areas.
I think I need it defined "i dont think it works at all".
The breather valves are inside the rocker boxes.
You can't see them unless you remove the box tops.
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