There should be two places crankcase pressurisation should escape from on
all MGB engines. On an 18V there should in any case be a partial vacuum in
the crankcase from suction from the carb(s) applied to the front tappet
cover, and a fresh air inlet from either the charcoal canisters and
anti-runon valve (North American spec) or vented oil filler cap (UK spec).
A North American spec with canisters should have a non-vented cap, but this
has to be replaced with the vented cap if the canister is removed and the
port on the back of the rocker cover sealed. Even if that is not done there
should still be suction from the carbs unless that port has been sealed as
well! Positive harm will be caused to the engine if there is no breathing,
like blowing seals and internal corrosion. And there is no good reason to
remove the canister and anti-runon valve, they have only benefits and no
drawbacks.
PaulH.
----- Original Message -----
From: "Steve Shoyer" <Steve@shoyer.com>
To: <mgs@autox.team.net>
Sent: Tuesday, March 09, 2004 7:08 PM
Subject: Vented oil filler cap for 18V engine
> The last time I tried to get it inspected, there was oil being propelled
out of the dipstick tube. Loosening the oil filler cap "fixed" the problem.
I thought I'd replace the cap with a vented one, at least just to get the
car inspected and legal again. Which cap will fit my engine? It's an 18V,
1980 MGB.
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