MG Car Club of South Australia
TeChnical TopiC REAR CRANK LEAKS
by Bob Schapel
T
-Type engines are notorious for
dripping oil from the rear of the
crankshaft. It wasn’t such a problem
when the cars were young, because
most driveways were gravel, but nowa-
days we don’t like little black pools on
the concrete. I believe that a common
oversight during assembly can cause or
increase this leakage, whether the rear
seal is original or modified.
Sometimes, the original scroll system
works really well. This rare phenome-
non probably only occurs when the
main bearings and scroll have optimum
clearances, and crank-case pressure is
minimal.
Dad’s Y-Tourer leaked virtually no oil
from the rear of the crank. However,
when things are not right, getting the
scroll perfect can be an expensive addi-
tion to a rebuild. Fitting a modern seal
kit is probably more likely to yield suc-
cess. However, oil might still find its
way to the outside world, despite all
these efforts, unless special care is
taken during assembly.
but this has the side-effect of providing
channels for oil to escape. Using silicon
(or similar) to seal the areas marked
with grey shading, will prevent oil taking
these routes. It applies to all systems,
whether original or modified.
The diagram originated from the instruc-
tions I supplied with the seal kits I made
between 1988 and 2000, so ignore the
additional bit at the back if you have not
fitted a modification.
I made about 300 and sent a lot to
Europe. I only sent a couple to the USA
and UK before Moss started offering kits
based on the same idea. I have seen
the fitting instructions for the Moss seal
kit and noticed there was no mention of
sealing the area in question.
I am not suggesting that sealing these
areas will cure ALL those annoying
leaks, but it will certainly eliminate one
possible cause.
The diagram shows how oil might seep
out, between the block and rear cap,
even if none escapes through the scroll
(or seal) itself. Blue arrows show how
oil might escape by seeping, perhaps
with a little help from crank-case pres-
sure. Red arrows show where oil might
be pushed out by oil pressure.
The faces between the main-bearing
caps and the block are accurate but are
not perfect. They usually display ma-
chine marks, which are potential oil
pathways. The edges of the cap re-
cesses in all engine blocks are relieved
to ensure that the caps fit home snugly,
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