> I was thinking that the head and crankcase were connected enough that
> the
> pressure was equalized. Through the pushrod passages?
Exactly so; although if the rings are in really bad shape, there may be
enough blowby to develop some pressure against the restriction of the
pushrod tubes.
But the OP said he had a TR4A with a PCV valve, which means it also at least
had a sealed filler cap.
Triumph's idea of "positive crankcase ventilation" was to seal up the
crankcase (and rocker shaft area), with the only exit being through a tiny
orifice in the PCV valve to the intake manifold. This arrangement totally
fails to address what happens at full throttle, when blowby is maximum and
there is no manifold vacuum to speak of. The answer of course, is that the
pressure blows oil out through any tiny gap, like that in the labyrinth rear
main seal (and typically the rocker gasket as well).
-- Randall
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