Jerry,
On the TR4A closed system, there is supposed to be a slight vacuum
inside the engine at all times. The oil cap has a hole of just the
right size to allow in the right amount of air.
However, my engine has a long breather pipe on that hole, and
it APPEARS to have the original PCV system as well. So, it can run well
with an open system. I do not know what needles the carbs have, however.
It seems to me that if you allow more air into the crankcase than expected
by the breather system, then you will be allowing more
air into the intake manifold than expected, which will result in a leaner
mixture since the breather meets the manifold on the engine side of the carbs.
Now, you can re-tune the carbs to compensate for the "air leak".
That being said, the Smiths diaphragm unit for the breather has some sort of
spring in it, so I never understood exactly how it was supposed to work. The
diaphragm and spring might limit the volume of air (pressure differential) that
the breather will allow....
My advice os to plug the hole back to original spec. But why is it open???
Too much blow-by on a well used engine?
At least you should install a proper breather tube on the hole to minimize
oil leakage.
-Tony
ARhodes@compuserve.com
>Date: Tue, 01 Jun 1999 19:41:33 -0700
From: Jerry Oliver <slantws@home.com>
Subject: TR4A Breather plug
Does anyone have an idea what effect not having the breather plug in the
block on a closed system engine would have? I was under my car (66 TR4A
nearly finished restoration) this evening, and noticed some oil. The
hole in the block where the breather would be on an open system car is
plugged on the closed system. I just have the hole. I haven't driven the
car yet. The engine was rebuilt several years ago, but the car isn't
quite finished. I've started the engine periodically and let it warm up,
and it seems fine. I suppose I should install a plug???
Jerry Oliver
Olympia, WA
66TR4A 61
MGA 58
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