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RE: Valve cover breather pipe...early MGB engine

To: "''" <>
Subject: RE: Valve cover breather pipe...early MGB engine
From: "Dodd, Kelvin" <>
Date: Tue, 12 Nov 2002 14:50:40 -0800

Some form of breather is absolutely necessary.  The early cars had a
breather built into the oil filler cap.  Many of the alloy covers are
designed to use the original type plastic cap, so you can choose the
breather, or sealed one.

Keeping the fumes from condensing into the oil pan is a very good idea.  

The best way to do it is with some kind of PCV (positive crankcase
ventilation) set up.  I've never taken the time and trouble to do the right
thing, but putting in breather tube with a sized orifice and filter would be
the best way to handle the top end.  A modern PCV valve plumbed into the
intake manifold going to the front breather cover would be the right way to
do the bottom end.  

        Anyone done this with good success?  I set one up once using a
Toyota in-line PCV valve feeding a cross-over pipe above a Weber DCOE
manifold, but never had a chance to do any comparisons on orifice size.  At
least it stopped the blowby from puking oil out of the filler cap.

        In answer to your specific questions.

The breather pipe on the 3M MGB engine hooked to one of the air filters.
The idea was to provide cleanish air to the top of the engine.  Any horrific
blowby was also sucked into the carbs, but that was secondary.  On slightly
later cars the vent was removed and a wire wool stuffed plastic oil filler
cap was supplied as a filtered inlet.

        The bottom end was served by a "road draft tube"  suction was
created as the car whizzed along the road, hopefully sucking the nasty
acidic fumes out of the crank case, and clean filtered air from the air

        This design was superceded by the PCV system which does a better job
of keeping the inside of the motor clean.


> -----Original Message-----
> From: []
> Sent: Tuesday, November 12, 2002 1:59 PM
> To:
> Subject: Valve cover breather pipe...early MGB engine
> Hello All,
> I have a 3 main bearing 63' MGB engine installed in my MGA 
> roadster, and the 
> valve cover that came with the engine has the breather pipe. 
> Is this breather 
> pipe really necessary? Its not connected to anything (were 
> they originally 
> connected to something on the engine?) and I am thinking 
> about replacing the 
> existing cover with one of the aluminum ones. Most of them 
> come without the 
> breather pipe. Am I asking for trouble here by replacing it with a 
> breatherless cover? Any help is appreciated.........and as 
> usual thanks to 
> the fellow MG listers.......and HAPPY HOLIDAYS !!
>          Bill Dillstrom
>   1962 MGA MKII Roadster 

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