fold seats BMW 3 SERIES 1988 E30 Workshop Manual

24Repeat the procedure for the remaining
valves. Remember to keep all the parts for
each valve together, so they can be refitted in
the same locations.
25Once the valves and related components
have been removed and stored in an
organised manner, the head should be
thoroughly cleaned and inspected. If a
complete engine overhaul is being done,
finish the engine dismantling procedures
before beginning the cylinder head cleaning
and inspection process.
9 Cylinder head and
components-
cleaning and inspection
4
1Thorough cleaning of the cylinder head(s)
and related valve train components, followed
by a detailed inspection, will enable you to
decide how much valve service work must be
done during the engine overhaul. Note: If the
engine was severely overheated, the cylinder
head is probably warped (see paragraph 10).
Cleaning
2Scrape all traces of old gasket material and
sealing compound off the cylinder head,
intake manifold and exhaust manifold sealing
surfaces. Be very careful not to gouge the
cylinder head. Special gasket removal
solvents are available at motor factors.
3Remove all built-up scale from the coolant
passages.
4Run a stiff brush through the various holes
to remove deposits that may have formed in
them.
5Run an appropriate-size tap into each of the
threaded holes, to remove corrosion and
thread sealant that may be present. If
compressed air is available, use it to clear the
holes of debris produced by this operation.
Warning: Wear eye protection
when using compressed air!
6Clean the cylinder head with solvent, and
dry it thoroughly. Compressed air will speed
the drying process, and ensure that all holesand recessed areas are clean. Note:
Decarbonising chemicals are available, and
may prove very useful when cleaning cylinder
heads and valve train components. They are
very caustic, however, and should be used
with caution. Be sure to follow the instructions
on the container.
7Clean all the rocker shafts/arms/followers,
springs, valve springs, spring seats, keepers
and retainers with solvent, and dry them
thoroughly. Clean the components from one
valve at a time, to avoid mixing up the parts.
Caution: DO NOT clean the
hydraulic tappets of the M40
engine; leave them completely
immersed in oil.
8Scrape off any heavy deposits that may
have formed on the valves, then use a
motorised wire brush to remove deposits from
the valve heads and stems. Again, make sure
the valves don’t get mixed up.
Inspection
Note: Be sure to perform all of the following
inspection procedures before concluding that
machine shop work is required. Make a list of
the items that need attention.
Cylinder head
9Inspect the head very carefully for cracks,
evidence of coolant leakage, and other
damage. If cracks are found, check with an
machine shop concerning repair. If repair isn’t
possible, a new cylinder head should be
obtained.
10Using a straightedge and feeler gauge,
check the head gasket mating surface for
warpage (see illustration). If the warpage
exceeds the limit listed in this Chapter’s
Specifications, it may be possible to have it
resurfaced at a machine shop, providing the
head is not reduced to less than the specified
minimum thickness.
11Examine the valve seats in each of the
combustion chambers. If they’re badly pitted,
cracked or burned, the head will require
servicing that’s beyond the scope of the home
mechanic.12Check the valve stem-to-guide clearance
by measuring the lateral movement of the
valve stem with a dial indicator (see
illustration). The valve must be in the guide
and approximately 2.0 mm off the seat. The
total valve stem movement indicated by the
gauge needle must be divided by two, to
obtain the actual clearance. After this is done,
if there’s still some doubt regarding the
condition of the valve guides, they should be
checked by a machine shop (the cost should
be minimal).
Valves
13Carefully inspect each valve face for
uneven wear, deformation, cracks, pits and
burned areas (see illustration). Check the
valve stem for scuffing and the neck for
cracks. Rotate the valve, and check for any
obvious indication that it’s bent. Look for pits
and excessive wear on the end of the stem.
The presence of any of these conditions
indicates the need for valve service as
described in the next Section.
14Measure the margin width on each valve
(see illustration). Any valve with a margin
narrower than specified will have to be
replaced with a new one.
Valve components
15Check each valve spring for wear on the
ends. The tension of all springs should be
checked with a special fixture before deciding
2B•10 General engine overhaul procedures
9.14 The margin width on each valve must
be as specified (if no margin exists, the
valve cannot be reused)
9.13 Check for valve wear at the points
shown here
9.12 A dial indicator can be used to
determine the valve stem-to-guide
clearance (move the valve as indicated by
the arrows)
9.10 Check the cylinder head gasket
surface for warpage by trying to slip a
feeler gauge under the straightedge (see
this Chapter’s Specifications for the
maximum warpage allowed, and use a
feeler gauge of that thickness)
1 Valve tip
2 Collet groove
3 Stem (least-worn
area)4 Stem (most-worn
area)
5 Valve face
6 Margin