A 73 with all emissions plumbing present and correct should have a sealed
oil filler cap, the crankcase venting via a restricted port on top of the
rocker cover and the charcoal canister. Without emissions plumbing it
should have a vented oil filler cap and if present the rocker cover vent
should be sealed. The crankcase has to have two ports to be vented
properly. Usually the carbs are connected to the front cover to provide the
suction, drawing filtered and restricted (to prevent upsetting the mixture)
either via the vent on top of the rocker cover (non-vented oil filler cap)
and charcoal canister on smogged cars or via a vented and restricted oil
filler cap on unsmogged. If you apply carb or manifold suction to the
rocker cover you must have a filtered, restricted vent somewhere on the
crankcase or it isn't going to be scavenged properly. If the front tappet
cover is solid where is air going to be drawn from? BMC engines used to
have a relatively ineffective scavenging system using a hose from the air
cleaner to the rocker cover, and an open but filtered vent on the front
tappet cover. Applying carb suction to this cover and having a filtered and
restricted vent elsewhere (vented oil filler cap or charcoal canister) is
far superior. The PCV is an unnecessary complication that was ditched by
the factory for all cars.
----- Original Message -----
From: "Chris Thompson" <ct-mg@cthompson.com>
To: <mgs@autox.team.net>
Sent: Thursday, April 10, 2003 3:38 PM
Subject: Rebirth
> Should a 74 18V (actually, it's a 73, long story) have a vented cap? The
> curved tube out the top of the valve cover goes to a T fitting, one arm
> goes to the charcoal canister, the other branch is plugged. The front
> tappet cover is connected to a Y fitting, with each of those branches
> attaching to the intake manifold on the DGV.
...
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