Contents - Volkspage

2B.10 Engine removal and overhaul procedures
5.18 Checking the piston ring
side clearance
5.20a Big end bearing cap and connecting
rod markings
A identification (cylinder number) markings
B Orientation recesses
5.20b Orientation arrow on piston crown
(highlighted)
11 Use a section of old piston ring to scrape
the carbon deposits out of the ring grooves,
taking care not to score or gouge the edges of
the groove.
12 Carefully scrape away all traces of carbon
from the top of the piston. A hand-held wire
brush (or a piece of fine emery cloth) can be
used, once the majority of the deposits have
been scraped away. Be careful not to remove
any metal from the piston, as it is relatively
soft. Note: Take care to preserve the piston
number markings that were made during
removal.
13 Once the deposits have been removed,
clean the pistons and connecting rods with
paraffin or a suitable solvent, and dry
thoroughly. Make sure that the oil return holes
in the ring grooves are clear.
14 Examine the piston for signs of terminal
wear or damage. Some normal wear will be
apparent, in the form of a vertical ‘grain’ on
the piston thrust surfaces and a slight
looseness of the top compression ring in its
groove. Abnormal wear should be carefully
examined, to assess whether the component
is still serviceable and what the cause of the
wear might be.
15 Scuffing or scoring of the piston skirt may
indicate that the engine has been overheating,
through inadequate cooling, lubrication or
abnormal combustion temperatures. Scorch
marks on the skirt indicate that blow-by has
occurred, perhaps caused by worn bores or
piston rings. Burnt areas on the piston crown
are usually an indication of pre-ignition,
pinking or detonation. In extreme cases, the
piston crown may be melted by operating
under these conditions. Corrosion pit marks in
the piston crown indicate that coolant has
seeped into the combustion chamber and/or
the crankcase. The faults causing these
symptoms must be corrected before the
engine is brought back into service, or the
same damage will recur.
18 Check the pistons, connecting rods,
gudgeon pins and bearing caps for cracks.
Lay the connecting rods on a flat surface and
look along thelength to see if it appears bent
or twisted. If you have doubts about their
condition, get them measured at an
engineering workshop. Inspect the small end
bush bearing for signs of wear or cracking.
17 Using a micrometer, measure the
diameter of all four pistons at a point 10 mm
from the bottom of the skirt, at right angles to
the gudgeon pin axis. Compare the
measurements with those listed in the Specifications.
If the piston diameter is out of the
tolerance band listed for its particular size,
then it must be renewed. Note: If the cylinder
block was re-bored during a previous
overhaul, oversize pistons may have been
fitted. Record the measurements and use
them to check the piston clearances when the
cylinder bores are measured, later in this
Chapter.
18 Hold a new piston ring in the appropriate
groove and measure the side clearance using
a feeler blade (see illustration). Note that the
rings are of different widths, so use the
correct ring for the groove. Compare the
measurements with those listed; if the
clearances are outside of the tolerance band,
then the piston must be renewed. Confirm this
by checking the width of the piston ring with a
micrometer.
19 Using internal/external vernier callipers,
measure the connecting rod small end internal
diameter and the gudgeon pin external
diameter. Subtract the gudgeon pin diameter
from the small end diameter to obtain the
clearance. If this measurement is outside its
specification, then the piston and connecting
rod bush will have to be resized and a new
gudgeon pin installed. An engineering
workshop will have the equipment needed to
undertake a job of this nature.
20 The orientation of the piston with respect to
the connecting rod must be correct when the
two components are reassembled. The piston
crown is marked with an arrow (which can
easily be obscured by carbon deposits); this
must point towards the timing belt end of the
engine when the piston is installed in the bore.
The connecting rod and its corresponding
bearing cap both have recesses machined into
them close to their mating surfaces - these
recesses must both face in the same direction
as the arrow on the piston crown (ie towards the
timing belt end of the engine) when correctly
installed (see illustrations). Reassemble the
two components to satisfy this requirement.
21 Lubricate the gudgeon pin and small end
bush with clean engine oil. Slide the pin into
the piston, engaging the connecting rod small
end. Fit two new circlips to the piston at either
end of the gudgeon pin, so that their open
ends are facing 180° away from the removal
slot in the piston. Repeat this operation for the
remaining pistons.
Removal
1 Note: If no work is to be done on the
pistons and connecting rods, then removal the
cylinder head and pistons will not be
necessary. Instead, the pistons need only be
pushed far enough up the bores so that they
are positioned clear of the crankpins. The use
of an engine stand is strongly recommended.
2 With reference to Chapter 2A, carry out the
following:
a) Remove the crankshaft timing belt
sprocket.
b) Remove the clutch components and
flywheel.
c) Remove the sump, baffle plate, oil pump
and pickup.
d) Remove the front and rear crankshaft oil
seals and their housings.
3 Unbolt the pistons and connecting rods
from the crankpins, as described in Section 5
(refer to the Note above).
4 Carry out a check of the crankshaft endfloat,
as follows. Note: This can only be
accomplished when the crankshaft is still
installed in the cylinder block/crankcase, but is
free to move. Set up a DTI gauge so that the
probe is in line with the crankshaft axis and is
in contact with a fixed point on end of the
crankshaft. Push the crankshaft along its axis
to the end of its travel, and then zero the