Before reassembly of the engine unit is commenced, the various
component parts should be cleaned thoroughly and placed on a sheet of
clean paper, close to the working area.
Make sure all traces of old gaskets have been removed and that the
mating surfaces are clean and undamaged. Great care should be taken when
removing old gasket compound not to damage the mating surface. Most
gasket compounds can be softened using a suitable solvent such as methylated
spirits, acetone or cellulose thinner. The type of solvent required
will depend on the type of compound used. Gasket compound of the
non-hardening type can be removed using a soft brass-wire brush of
the type used for cleaning suede shoes. A considerable amount of
scrubbing can take place without fear of harming the mating
surfaces. Some difficulty may be encountered when attempting to
remove gaskets of the self-vulcanizing type, the use of which is becoming widespread,
particularly as cylinder head and base gaskets. The gasket should be
pared from the mating surface using a scalpel or a small chisel with a
finely honed edge. Do not, however, resort to scraping with a sharp
instrument unless necessary.
Gather together all the necessary tools
and have available an oil can filled with clean engine oil. Make sure
that all new gaskets and oil seals are to hand, also all replacement parts required. Nothing is more
frustrating than having to stop in the middle of a reassembly sequence
because a vital gasket or replacement has been overlooked. As a general
rule each moving engine component should be lubricated thoroughly as it
is fitted into position.
Make sure that the reassembly area is clean and that there is adequate
working space. Refer to the torque and clearance setting wherever they
are given. Many of the small bolts are easily sheared if over tightened.
BMW now recommend the use of Three Bond 1207 B silicone sealant
(formerly Loctite 574) for all mating surfaces which require the use of
jointing compound and emphasize that careful work is necessary to
prevent oil leaks. All mating surfaces must be cleaned of all traces of
old gaskets or of old jointing compound and must be absolutely flat and
unmarked. Using a clean, fluff-free cloth soaked in fresh high
flash-point solvent wipe over the mating surfaces to remove all traces
of old oil or grease. Apply a thin, continuous coat of sealant to the
mating surfaces and assemble the parts immediately; tighten the
retaining nuts, bolts or screws evenly and progressively to the
specified torque settings, where available. Allow the sealant to harden
for one hour before running the engine and peel off any surplus sealant
from the outside of the joint.
Remember that if the mating surfaces are in good condition there
should be no need for a thick film of sealant; the thinnest smear will
usually prove sufficient to seal a joint. Sealant is wasted that is
pushed out to form a bead on each side of the joint; note that while the
bead on the outside is merely annoying and unsightly, proclaiming
amateurish work, the bead on the inside is free to break off and block oilways or cause other similar problems.