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re oval vent

Subject: re oval vent
From: Geoff Love <>
Date: Sat, 14 Dec 1996 17:48:30 -0500
I've been giving some deep thought to your comments re the pressurising
of the bell housing through the oval vent helping to prevent oil leaks.
I need further clarification, please.  I don't understand how the action
of the rotating flywheel can cause either a partial vacuum or a partial
pressure within the bellhousing (depending upon which way the oval vent
is fitted), if the housing is open to ambient air pressure as would
appear to be the case, via both the opening through which the starter's
Bendix drive passes, or the small drain hole at the bottom of the
bellhousing. Surely, any possible flywheel effects must be so marginal
that they are more than overcome by the previously mentioned holes?  I
can understand the effect appearing if the bellhousing were a sealed
unit, and certainly a pressure differential between the housing and the
crankcase would help or hinder oil leaks if that were the case, so are
you saying that the pressure differential generated in the bell housing
by the flywheel/oval vent relationship is so strong as to overcome the
effects of the leaks around the Bendix and/or the drain hole? Please
elaborate. Thank you.

Geoff Love, The English Connection

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