quick technical ? about breathers
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quick technical ? about breathers
I am wondering where the engine gets the air that circulates in the crankcase...do the breathers in the heads allow air in and out of the crankcase?? I noticed there are valves(??) in the breathers in the heads and I thought (think) they only allow air out of the engine (when the pistons go down they push the air out, when they go back up they have to suck the air from somewhere)...
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I am wondering where the engine gets the air that circulates in the crankcase...do the breathers in the heads allow air in and out of the crankcase?? I noticed there are valves(??) in the breathers in the heads and I thought (think) they only allow air out of the engine (when the pistons go down they push the air out, when they go back up they have to suck the air from somewhere)...
When someone experiences excessive oil blow from the breathers, once the obvious is ruled out (oil level), I suggest a leak-down test. I've seen new rings eliminate the problem without having to do a breather bypass.
Last edited by Weavr99FLHT; Nov 21, 2014 at 02:17 PM.
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The motion of air and oil inside the engine is a fascinating subject! The pistons create a mild pressure in the crankcase as they both travel down the cylinders, which is used to assist the oil pump to evacuate oil to the oiltank. As the pistons travel back up the cylinders they create a partial vacuum, which is used to draw oil from the rocker boxes back down into the crankcase, where it can be evacuated to the oiltank.
There is a breather valve in the camshaft chest on Evos, to relieve crankcase pressure, but I can't find a similar part on the twincams, which I suspect is incorporated into the cam plate. That valve does indeed allow air in and out of the engine breather (one reason it is connected to the air filter!). I no longer own a twincam, but expect the lubrication system is described in detail in the factory service manual.
There is a breather valve in the camshaft chest on Evos, to relieve crankcase pressure, but I can't find a similar part on the twincams, which I suspect is incorporated into the cam plate. That valve does indeed allow air in and out of the engine breather (one reason it is connected to the air filter!). I no longer own a twincam, but expect the lubrication system is described in detail in the factory service manual.
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