Pressure will build up inside the valve cover/cam cover from combustion
blow-by in the crankcase. Remember there's an oil drain from the head to
the crankcase. Oil goes down, gasses come up. The old mesh filters in oil
fill tubes and road draft tubes connected to the block were early venting
solutions. Later the open vents were sealed and a vent tube was run to the
air cleaner from the valve cover. Since there is a slight vacuum in the air
cleaner, blow-by gasses plus oil vapor were drawn into the intake.
Even later, "positive crankcase ventilation" or PCV valves were added. I
think these were only check valves, but, it they got gummed up (which they
did), it affected emissions. Since blow-by gasses were drawn into the
intake anyway, I'm not sure why PCV valves were required or what they
accomplished. If Bubba is reading this, he probably knows.
To Eddie's question: Yes, you need that thing, or some sort of crankcase
vent to relieve combustion pressure in the crankcase/valve cover.
Otherwise, it will quickly itself through the weakest joint -- probably the
valve cover gasket or the oil pan gasket.
Those who have the Nissan (original or Clymer reprint) shop manual can see
the road draft tubes used on early cars in the photos of 1600 engine
removal/replacement. It was a metal tube bolted to the block at the
driver's side in the back, and curved down around the block to a point about
by the joint with the oil pan. Some later cars still had the holes in the
blocks, but they were blanked off.
Gary
----- Original Message -----
From: <fairlady1964spl310@yahoo.com>
To: "Eddie" <eddietude@socal.rr.com>
Cc: "All list" <datsun-roadsters@autox.team.net>
Sent: Saturday, May 23, 2009 12:03 PM
Subject: Re: [Roadsters] Valve Cover discovery...
>I may know a little about this....
> It is my understanding, that there were a couple different configurations
> for
> the crankcase ventilation on the early 1500 roadsters. The earlier (63,
> 64)
> have a breather tube that goes from the engine backing plate to the upper,
> left, rear corner of the block. These used a breathable oil cap like on
> the
> 1000 and 1200s....an odd looking, painted cap containing metal mesh as a
> filter. There was no rear hole in the valve cover. The other
> configuration,
> is a two piece oil cap (usually chrome) with a tube that connects to the
> air
> cleaner. Again, no hole in the valve cover. The 1965, R16, I believe,
> was
> when it changed to the vented valve cover we all know and love. Regarding
> the
> mechanical purpose of "crankcase ventilation", I've no clue.
> Patti
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