General
All mating surfaces must be clean and fit together properly.
Raised threads should be lightly countersunk and pips or
lumps removed by filing or scraping.
Silicone Adhesives
Use
the correct adhesive. Some, such as bath sealant, are not oil resistant and are
corrosive.
Cylinder Block and Crankcase Joint
Remove
all studs from the crankcase and all valve gear from the block. Coat the top of
the crankcase with valve grinding paste and lap the block to the crankcase. For
some obscure reason, all crankcases are high in the middle. Work on this until
the crankcase is an even matt finish. ensure you wash off all grinding paste
afterwards. Lightly countersink the fixing holes in the crankcase. Check that
the cover over the oil pump drive is properly sealed and is below the top of
the crankcase. Place a bead of silicone adhesive around the base of the
cylinder block, do not fit gasket, bolt down tightly, preferably using new
studs and nuts. Don't use too much adhesive as it will ooze out in all the
wrong places. If as a result of omitting the gasket, the pistons protrude above
the cylinder block, then the gasket must be fitted.
Leakage
from the Rear Main Bearing/Flywheel
Oil escaping from here is usually due to a worn oil scroll,
incorrect size oil scroll or the oil-thrower missing. There are several sizes
of oil screw, the correct one is a snug fit to the flywheel boss. The
preference is to fit a modern lip seal. Leakage can also be due to a distorted
rear main bearing housing or cover allowing oil to escape from the joint. The
oil drain hole in the housing does not always line up properly with the hole in
the crankcase. Drill both out to 5/16" to ensure alignment. Seal joint
with silicone adhesive, fitting both gaskets. ensure adhesive does not block
the drain hole.
Front Camshaft Bearing Locating Screw
Leaks
can occur due to poor fitting of this screw. If it is the original square type,
you cannot tighten it without first removing the cylinder block. If you have to
go to all this trouble, then it is probably best to replace it by tapping the
bush 5/16" BSF and fitting a decent screw and fibre washer.
Oil Filler Tube
A
leak sometimes difficult to cure is the thread of the oil filler tube. This
area is vulnerable as the rotation of the crankshaft is continually throwing
oil at it. Seal the thread with a low strength Loctite. Don't be misled - a
poor fitting filler cap will allow oil to run down outside the tube, giving the
impression that the thread is leaking.
Crankcase Pressure
Oil
can be forced out of the crankcase by overfilling or crankcase pressure. The
cure for the former is obvious. The only natural ventilation of the crankcase
is via a few small holes in the valve chest cover. These must be clear. More
ventilation can be provided by fitting a crankcase breather to either the oil
filler tube or the valve chest cover but this should only be necessary on worn
engines.
Sump
Like
all other joints, it is essential that all 14 fixing screws and threads are in good
condition. Fit oval and spring washers. Stripped threads and stretched studs
must be attended to. Seal with silicone adhesive and fit the gasket. Check that
screws are tight after sealant has set.
Leaks from Head Studs
Oil
or water leaking from head studs is nearly always due to a badly fitting head
gasket. Raised threads should be suspected or the gasket binding on the sides
of the head studs. Light countersinking of the holes in the cylinder head can
help. Fix new studs in the block using a low strength Loctite. ensure that both
the top of the block and the cylinder head are ground flat. When fitting the
head gasket, coat both sides with a little grease. It should not be necessary
to use any gasket sealant. Tighten down the head studs in the correct sequence
to 24 ft lbs. If there is a persistent leak from the centre stud - the cylinder
block is probably cracked in that area.
Conclusion
I expect that after going to all the trouble of fixing the above leaks, it will leak somewhere else!
VINCE LEEK