Contents - Volkspage

2B.12 Engine removal and overhaul procedures
7.6 Clear out threaded holes using the
correct size of tap
5 If the castings are not very dirty, you can do
an adequate cleaning job with hot, soapy
water and a stiff brush. Take plenty of time,
and do a thorough job. Regardless of the
cleaning method used, be sure to clean all oil
holes and galleries very thoroughly, and to dry
all components well. Protect the cylinder
bores as described above, to prevent rusting.
6 All threaded holes must be clean, to ensure
that fixings are tightened to the correct
torque during reassembly. To clean the
threads, run the correct-size tap into each of
the holes to remove rust, corrosion, thread
sealant or sludge, and to restore damaged
threads (see illustration). If possible, use
compressed air to clear the holes of debris
produced by this operation. Note: Take extra
care to exclude all cleaning liquid from blind
tapped holes, as the casting may be cracked
by hydraulic action if a bolt is tightened in a
hole containing liquid.
7 Apply suitable sealant to the new oil gallery
plugs, and insert them into the holes in the
block. Tighten them securely.
8 If the engine is not going to be reassembled
immediately, cover it with a large plastic bag
to keep it clean; protect all mating surfaces
and the cylinder bores as described above, to
prevent rusting.
Inspection
9 Visually check the casting for cracks and
corrosion. Look for stripped threads in the
threaded holes. If there has been any history of
internal water leakage, it may be worthwhile
having an engine overhaul specialist check the
cylinder block/crankcase with professional
equipment. If defects are found, have them
repaired if possible, failing this the cylinder
block should be renewed.
10 Check the cylinder bores for scuffing or
scoring. Any evidence of this kind of damage
should be cross-checked with an inspection
of the pistons: see Section 5 of this Chapter. If
the damage is in its early stages, it may be
possible to repair the block by reboring it.
Seek the advice of an engineering workshop
before you progress.
11 To allow an accurate assessment of the
wear in the cylinder bores to be made, their
diameter must be measured at a number
of points, as follows. Insert a bore gauge
into cylinder bore No 1 and take three
measurements in line with the crankshaft axis;
one at the top of the bore, roughly 10 mm
below the bottom of the wear ridge, one
halfway down the bore and one at a point
roughly 10 mm the bottom of the bore. Note:
Stand the cylinder block squarely on a
workbench during this procedure, inaccurate
results may be obtained if the measurements
are taken when the engine mounted on a stand.
12 Rotate the bore gauge through 90°, so
that it is at right angles to the crankshaft axis
and repeat the measurements detailed in
paragraph 11 (see illustration). Record all six
measurements and compare them with the
data listed in the Specifications Section. If the
difference in diameter between any two
cylinders exceeds the wear limit, or if any one
cylinder exceeds its maximum bore diameter,
then all four cylinders will have to be rebored
and oversize pistons will have to be fitted.
Note that the imbalances produced by not
reboring all the cylinders together would
render the engine unusable.
13 Use the piston diameter measurements
recorded earlier (see Section 5) to calculate
the piston to cylinder clearances. Compare
these with the specified maximum and
determine whether reboring and oversize
pistons are required.
14 Place the cylinder block on a level work
surface, crankcase downwards. Use a straight
edge and a set of feeler blades to measure the
distortion of the cylinder head mating surface
in both planes, A maximum figure is not
quoted by the manufacturer, but use the
figure of 0.05 mm as a rough guide. If the
measurement exceeds this figure, repair may
be possible by machining - consult your
dealer for advice.
15 Before the engine can be reassembled, the
cylinder bores must be honed. This process
involves using an abrasive tool to produce a
fine, cross-hatch pattern on the inner surface of
the bore. This has the effect of seating the
piston rings, resulting in a good seal between
the piston and cylinder. There are two types of
honing tool available to the home mechanic,
both are driven by a rotary power tool, such as
a drill. The ‘Bottle Brush’ hone is a stiff,
cylindrical brush with abrasive stones bonded
to its bristles. The more conventional surfacing
hone has abrasive stones mounted on spring
loaded legs. For the inexperienced home
mechanic, satisfactory results will be achieved
more easily using the Bottle Brush hone. Note:
If you are unwilling to tackle cylinder bore
honing, an engineering workshop will be able to
carry out the job for you at a reasonable cost.
16 Carry out the honing as follows; you will
need one of the honing tools described
above, a power drill/air wrench, a supply of
clean rags, some honing oil and a pair of
safety glasses.
17 Fit the honing tool in the drill chuck.
Lubricate the cylinder bores with honing oil and
insert the honing tool into the first bore,
compressing the stones to allow it to fit. Turn
on the drill at its slowest speed and as the tool
rotates, move it up and down in the bore at a
rate that produces a fine cross-hatch pattern
on the surface. The lines of the pattern should
ideally cross at about 50-60” (see illustration).,
although some piston ring manufacturers may
quote a different angle; check the literature
supplied with the new rings.
A
Warning:
!
Wear safety glasses to
pro tact your eyes from debris
flying off the honing tool.
16 Use plenty of oil during the honing
process. Do not remove any more material
than is necessary to produce the required
finish. When removing the hone tool from the
bore, do not pull it out whilst it is still rotating;
maintain the up/down movement until the
chuck has stopped, then withdraw the tool
whilst rotating the chuck by hand, in the
normal direction of rotation.
19 Wipe out the oil and swarf with a rag and
proceed to the next bore. When all the bores
have been honed, thoroughly clean the whole
cylinder block in hot soapy water to remove
all traces of honing oil and debris. The block
can be considered clean when a clean rag,
moistened with new engine oil does not pick
up any grey residue when wiped along the
bore.
7.12 Bore measurement points 7.17 Cylinder bore honing pattern