On Thu, 21 Sep 1995, Russ Wilson wrote:
> Denise related:
> >At a recent San Diego MG Club meeting, Mike Haines (sp?) and his nepwhew
> >from across the pond, described driving a TC from San Diego to New York
> >and back again. He said it leaked three quarts of oil on the way there
> >and then they figured out what the problem was and it didn't need any oil
> >on the way back.
>
> Only a quart per thousand miles in a TC!! I wouldn't even mention it. My
> seal-less B dumps twice that.
A well-built T-Type engine can do a _lot_ better than that. Either Haines
was going awfully fast, or his engine was awfully loose!
> >I don't understand his explanation and I don't know if
> >it relates to an early MGB, but Mike said that the oil slinger on the crank
> >(front? back?) would sling oil if the car was turned off immediately after
> >stopping. Once they started letting it idle for a minute (maybe two?) it
> >stopped slinging oil entirely.
>
> I can imagine the slinger working *better* at crusing rpm than at idle but
> the "on or off" behavior of the leak rate you describe seems odd.
It's a function of the oil slinger design coupled with the oil flow
characteristics at speed and at idle. When the engine is running, any oil
that escapes from the rear of the rear main bearing hits the oil slinger.
The slinger throws it off into a cavity behind the rear main, from which
it flows down a tube into the sump. Any oil that attempts to escape
rearward from the cavity is forced forward by the oil return threads on
the rear of the crank.
If the rear bearing clearance is fairly tight (about 0.001 to 0.0015 or
so), relatively little oil escapes from the rear of the bearing so the
slinger and screw arrangement works surprisingly well as long as the
engine is running. However, when the engine is shut down, there is
nothing to stop any oil left in the cavity from draining out into the
flywheel housing. That's why the XPAG/XPEG engines in the T-Types have a
drain hole at the lowest point of the flywheel housing, complete with
loose split pin to rattle around and keep dirt from clogging the hole.
The reason more oil drips out if the engine is shut down immediately after a
high-speed run is simply that there is more oil in the cavity around the
slinger. If you let the engine idle for a bit before shutting down,
there is less oil, so less dripping.
All bets are off when the bearings get worn and loose. No matter what
the engine speed, there is too much leakage out of the rear main for the
slinger and screw arrangement to deal with, especially at high engine
speeds, so you can lose a _lot_ of oil out into the flywheel housing.
Fresh engine or not, keep that drip hole clear of dirt. The XPAG was not
meant to have a wet clutch!
In the late 1960's and early 1970's when a lot of us still drove our
T-Types daily, at local club events we would put a piece of typing paper
under each car's drip hole as soon as it pulled in. The one with the
smallest puddle of oil on the paper won a little prize. And there was
_always_ at least a drop or two, no matter how recent the engine rebuild.
-----------------------------------------------------------------------
Chip Old 1948 M.G. TC TC6710 NEMGTR #2271
Cub Hill, Maryland 1962 Triumph TR4 CT3154LO (daily driver)
fold@mail.bcpl.lib.md.us
If cars had evolved as fast as computers have, by now they'd cost a
quarter, run for a year on a half-gallon of gas, and explode once a day.
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