Mike,

It sounds like a crack in the water jacket, which, of course, is cast as
an integral part of the case.  The only long term fix to have a
specialist weld the crack properly.  You might check with one and see if
they can do it "in situ," but I doubt it. You will probably have to
bring them the case half.

If you want to try to patch it, drill the stress relief hole you
discussed, and go ahead and fill the crack with JB Weld.  Then I would
put a patch over the crack on the inside to withstand the pressure of
the coolant.  Check with marine stores for a good epoxy system and use a
piece of Fiberglas mesh.  Put three or four coats of epoxy on, an cover
the crack by an inch or so on all sides with the mesh.

Might work for quite awhile, is a cheap fix, and won't harm anything.
If you weld it later they can burn the epoxy off.

Good luck, and that is definitely a weird one! That area is not subject
to any particular stress, so it is hard to guess why it cracked.

Mike Conlon wrote:
>
> After replacing both the cylinder heads on my '86
> Syncro Westy, I was most annoyed to note that the
> right hand cylinder still leaks coolant.  After
> removing the offending cylinder head (a new AMC unit
> on the right hand/passenger side here in the USA), I
> was depressed to see a crack in the block that
> originates right where the cylinder head faces up to
> the block and extends about 1&1/4 inches towards the
> center of the engine.  If peering into the engine
> compartment, the crack originates at the top right
> rear edge of the block and extends along the top edge
> in a straight line along the rounded edge of the
> block.  The crack does indeed go all the way through
> the aluminum and is quite visible from both inside the
> block and outside.