On Wed, 6 Mar 1996, Mark Jurras wrote:
> >
> > I'd renew the oil filler cap once a year or so. The factory
> > recommendation is once every 12 000 miles. >
> As I am still learning
>about MG's I wondering why this needs to be done. Can anyone help?
>-Mark = =o&o
>
On some cars (My Midget leaps to mind), blowby and other gases and
pressure are eliminated from the crankcase through a breather in (for
instance) the front timing cover or tappet cover. The breather is
connected to the carbs or intake manifold, and the vacuum there draws out
the bad stuff, which is burned off along with the fuel. As air is
practically guaranteed to enter the crankcase when it is under vacuum, the
oil filler cap is designed to allow air to enter. Inside the cap is a
filter (apparently made out of the same stuff that's in a fractionating
column, for any other organic chemistry students out there). Presumably
the filter becomes clogged, and the cap then needs replacement.
BTW, having vacuum on an A-Series crankcase is a very good idea; on mine,
blowby pressure will otherwise drive copious amounts of oil out through
the rear "seal."
Michael Chaffee
mchaffee@ux1.cso.uiuc.edu
CCSO's secretary has officially disavowed any knowledge of my actions.
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