Telewest (PH) (paul.hunt1@blueyonder.co.uk) wrote:
> 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.
That all sounds reasonable, and is basically what I suspected, but wasn't
sure.
The Doug Jackson side plate does not, in fact, have any suction on the
tappet cover. The instructions for said plate have you directing the line
from the PCV or both carbs via a 1/2" line to one of two places. On a B
with a 70+ rocker cover and charcoal canister removed, to the vent elbow at
the rear of the cover, enlarging the vent bleed hole in said elbow to
5/32", or to a new 1/2" hole drilled in the side of the cover and a plastic
K&N hose fitting, vented oil cap required.
I think I can see now, based on your description, that Doug's setup does,
in fact provide a path for gas to be vented, the vent elbow and the vented
cap. That path was what was confusing to me.
Here's what I don't grasp though. The carbs are a lower pressure, so the
gasses are drawn from the engine back into the carbs. Are these flammable
gasses? does drawing these gasses into the carbs not throw them right back
into the cylinders? I guess I'm assuming these are post combustion gasses,
and throwing them back into the cylinders is just going affect the mixture
in ways you don't want.
_______________________________
Chris Thompson
1974 MGB Chrome Bumper Roadster
/// or try http://www.team.net/cgi-bin/majorcool
/// Archives at http://www.team.net/archive
|