I disassembled my 318 Magnum and
found this on the rear main [see pix,
below -Ed.], is this a casting flaw or did
something bad happen? I know it has a
small hole, but I have never seen a rear
main with a hole that big, is it safe to
It is difficult to tell from the photo with
any certainty, but to me it looks like an
OEM defect (foundry flaw). I don’t like it
one bit, I’d certainly not use it in any performance
application. Since you didn’t
mention any kind of failure associated
with the defect, I have to assume that the
engine ran OK, so, maybe for a deadstock
rebuild, put on dark sunglasses
and bolt it together.
Problem: It will cost more to fix this
properly (find another cap, mill it undersize,
then align-bore the block) than a
complete core engine would cost. Me?
I’d have a 360 in there ASAP. Note that
the cap is marked “360”, that’s because
the rear main seal area on 318 Magnums
was increased in diameter to be common with 360s.