To: dakota@csclub0.cs.fredonia.edu@INTERNET; jlindsay@oharamfg.com@INTERNET
From: Clement_D on Fri, Jul 12, 1996 8:16 AM
Subject: RE: Breather hose
From: jlindsay@oharamfg.com@INTERNET on Fri, Jul 12, 1996 1:37 AM
> I dunno..... I think there may be more to this breather thing. On a stock
>setup, the breather is put under a vacuum. Small amount yes, but it's there.
>Open up the air cleaner housing & you lose that.
>
> I remember back in my high school days, (mid '70s) the cool thing to do
was
>to turn your air cleaner lid upside down, opening up the chamber. I
>definitely remember GM products blowing the oil filter right off the block
>from the crankcase pressure buildup.
>
> Don't ask me why or how, but it was common. I think it had to do with the
>PCV valve in the breather hose.
I too played the Upside Down air cleaner lid trick in High School (late
60's) and never have heard of the the oil filter blowing of the block as a
result. Having down some engineering work for Lee Filters years ago, oil
filters have burst pressures in excess of 300 psi so I doubt crank case
pressure anything to do with the incidences you recall. You would blow out
oil pan, valve cover and main seals long before you could ever build up
enough crank pressure to even exceed the pressure generated by the oil pump.
I would say that something else was causing the oil filter problem and it
was just a coincedence that the air filter lid had been flipped.
On all engines I have seen, the breather hose attached to the air filter is
to allow air into the engine so that a vacuumn is not created in the
crankcase by what is being drawn through the PCV valve. Prior to the PCV
valve, engines were vented to atmosphere (ususally through the oil filler
cap). The PCV valve was added as an emmissions control device to draw off
fumes from the crankcase and recirculate them through the engine (the other
end of the PCV is connected to the intake manifold). The breather hose was
added to the air filter housing so that the make up air was clean. Some
vehicles it is inboard of the filter element on others there is a small
filter in the filter housing just for the breather. Because of the way the
PCV works you will get some back flow at times through the breather that is
why you normally see some oil residue around it.
There is no reason to worry about having the breather not connected to the
air filter housing other than from an emmisions inspection stand point and
doing something to filter the air drawn in (see my post yesterday).
Dave Clement
89 4x4 LE
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