Adam writes:
>Why do some rocker covers have a breather pipe and some not?
>
>What's the purpose of a breather?
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Adam,
ALL piston engines have a breather or crankcase vent of some kind. The
combustion process causes blow by, no matter how good your piston rings
are, some gasses get by, as well as the reciprocating motion creates
pumping inside the crankcase, and the heat generated inside the engine
would cause the air to expand and when cool to contract. These crankcase
fumes have to have someplace to go otherwise they would blow out the seals,
the dipstick tube, or any other place that was available. The valve cover
provides a convenient place, usually being high on the engine, it will have
less oil to deal with, and a small flame trap can be incorporated to
prevent any small explosions cause by an intake backfire igniting the
crankcase vapors. Very early engines, before the advent of positive
crankcase ventilation (PVC), used what was commonly called a draught tube,
which was simply a tube from the crankcase (usually on the push rod covers
on the side of the block, when engines had these) to a point under the car,
directly in the air-stream, with the bottom cut or exit angled so that the
air rushing under the vehicle caused a low pressure area at the tube exit,
and would draw the vapors out.
Barry Schwartz (San Diego) bschwart@pacbell.net
72 V6 Spitfire (daily driver)
70 GT6+ (when I don't drive the Spit)
70 Spitfire (project)
73 Ford Courier (parts hauler, rain vehicle)
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