Hello,

I keep seeing videos on external breathers. They say blow by and movement of huge piston increases crankcase pressure and they vent it. Oil comes out too and into air filter. Cool, got it.

Never had an engine apart myself and I’m curious, how is the oil getting from the crankcase to the header? Is it through the push rod covers? Probably a stupid question as in 10-15 videos no one explained that part.

Many thanks.

 

Read and learn.

 

Oil it pumped through the lifters and pushrods to lubricate the rocker arms and valve stems and help cool the top end of the engine. Most of the oil drains back to the oil pan, but mist is blown out by crankcase pressure into the air cleaner and into the throttle and pulled into the combustion chamber where it can be burned, rather than dumped to the atmosphere or ground. Much the way a PCV valve on a typical automotive engines works.

Paul

 

on the evo engine, you have umbrella valves in each head that act like one way check valves that allow c/c vapors to exit to the air cleaner as mandated by big brother. the system is simple but not without problems. if the valves are old or non pliable, they leak and prevent the oil from returning to the lower engine case on the up stroke where c/c vacuum is made. right before the valve, there is a maze or separation chamber that supposedly removes the oil. the c/c vapors are mostly water but oil does attach itself so there is always some that escapes. as a side note, as rpm goes up, the vacuum level drops till you have a positive c/c pressure which will force more vapors out the valves and since the engine needs diff'l pressure to move oil around, oil will start to pool.
the biggest issue with the system is lazy flow. look at rice, they have a more robust way of getting rid of the vapors, but alass, hd is cheap-a$$.
when the vapors enter the air cleaner, it relies on air flow through the media to carry the vapors to the throat of the carb or throttle body. there are several reasons why the oil collects one being decel reduces flow through the media and another c/c vapor volume past designed parameters. another could be lack of maintenance, aka, restricted media. just as well to throw in modified breathers as people change for the looks.
when flow becomes lazy, heavier particles will drop out thanks to gravity. also, when the vapor leaves the head port, and it hits the cleaner wall, it is like a coalescer, small droplets collect and form bigger drops which drops out. the cure is to put the flow in the area of the most flow and not inches away. but people are lazy and just drop it to the ground, not epa friendly for sure. a lot say this is bad for the engine but billions of running engines say they are wrong. if you have a slobbering engine, it is time for a fix that runs deeper than dropping it to the ground.

Attachment 611098

modified 01 sport run hard and put up wet too many times to count and yet zero issues with oil in the cleaner as the vapors are sent to the highest flow area.

 

Thanks for the replies everyone. I had no idea pushrods were hollow. Also with the terminology I picked up here I was able to better search for information on specific engines and found some old posts that would have explained. Thanks again.