Contents - Volkspage

2A.4 Engine in-car repair procedures
manufacturer. Note the lower compression
ratio of the supercharged G40 model (engine
code PY).
9 If the pressure in any cylinder is low, carry
out the following test to isolate the cause.
Introduce a teaspoonful of clean oil into that
cylinder through its spark plug hole, and
repeat the test.
10 If the addition of oil temporarily improves
the compression pressure, this indicates that
bore or piston wear is responsible for the
pressure loss. No improvement suggests that
leaking or burnt valves, or a blown head
gasket, may be to blame.
11 A low reading from two adjacent cylinders
is almost certainly due to the head gasket
having blown between them: the presence of
coolant in the engine oil will confirm this.
12 If one cylinder is about 20 percent lower
than the others and the engine has a slightly
rough idle, a worn camshaft lobe could be the
cause.
13 If the compression reading is unusually
high, the combustion chambers are probably
coated with carbon deposits. If this is the
case, the cylinder head should be removed
and decarbonised.
14 On completion of the test, refit the spark
plugs and restore the ignition system.
General information
1 The primary function of the toothed timing
belt is to drive the camshaft(s), but it is also
used to drive the coolant pump. Should the
belt slip or break in service, the valve timing will
be disturbed and piston to valve contact may
occur, resulting in serious engine damage.
2 For this reason, it is important that the
timing belt is tensioned correctly and
inspected regularly for signs of wear or
deterioration.
Removal
3 Disconnect the battery negative cable and
position it away from the terminal.
4 With reference to Section 2, remove the
timing belt outer cover and set the engine to
TDC on cylinder No1 .
5 If the timing belt is relatively new and is to
be refitted later, check to see if it has
manufacturers markings to indicate the
correct direction of rotation. If none are
present, make your own using a dab of paint
or typists correction fluid.
Caution: If the belt is refitted differently,
accelerated wear leading to premature
failure may occur.
6 With reference to Chapter 3, loosen the
water pump retaining bolts, then turn the
pump body clockwise to relieve the tension
from the timing belt. Slide the timing belt from
the camshaft sprocket (see illustration).
4.6 Releasing the timing belt from the
camshaft sprocket
7 Using an Allen bit, unbolt the auxiliary belt
pulley from the crankshaft sprocket. Remove
the screws, lift off the timing belt lower cover,
then remove the timing belt.
Inspection
8 Examine the belt for evidence of
contamination by coolant or lubricant. If this is
the case, identify the source of the
contamination before progressing any further.
Check the belt for signs of wear or damage,
particularly around the leading edges of the
belt teeth. Renew the belt if its condition is in
doubt; the cost of belt renewal is negligible
compared with potential cost of the engine
repairs, should the belt fail in service.
Similarly, if the belt is known to have covered
more than 60,000 miles, it is prudent to renew
it regardless of condition, as a precautionary
measure.
9 If the timing belt is not going to be refitted
for some time, it is a wise precaution to hang
a warning label on the vehicles’ steering
wheel, to prevent others from attempting to
start the vehicle.
Refitting
10 Loop the timing belt under the crankshaft
sprocket loosely, observing the direction of
rotation markings.
11 Bolt the lower timing belt cover in
position, then refit the auxiliary belt pulley to
the crankshaft sprocket and tighten the
retaining bolts to the specified torque.
12 Engage the timing belt teeth with the
crankshaft sprocket, then manoeuvre it into
position over the coolant pump and camshaft
sprockets - avoid bending the belt back on
itself or twisting it excessively as you do this.
Ensure that the ‘front run’ of the belt is taught
- ie all the slack should be in the section of the
belt that passes over the coolant pump pulley.
13 With the belt fitted, ensure that the timing
marks on the crankshaft pulley and camshaft
sprocket are exactly aligned with their
corresponding reference marks on the timing
belt inner cover; refer to the illustrations in
General information for details.
14 Insert a stout screwdriver between the
lugs on the coolant pump casting, then using
the screwdriver as a lever, turn the coolant
pump so that the slack in the belt is taken up
(see illustration).
4.14 Adjusting the timing belt tension by
rotating the coolant pump
15 Test the belt tension by grasping it
between the fingers at a point mid-way
between the coolant pump and camshaft
sprockets and twisting it; the belt tension is
correct when it can just be twisted through
90° (quarter of a turn) and no further (see
illustration).
16 When the correct belt tension has been
achieved, tighten the coolant pump mounting
bolts to the specified torque.
17 Using a spanner or wrench and socket on
the crankshaft sprocket centre bolt, rotate the
crankshaft through two complete revolutions
and reset the engine to TDC on cylinder No1 ,
with reference to Section 2. Re-check the belt
tension, adjusting it if necessary.
18 Refit the timing belt cover and fasten the
retaining clips securely.
Camshaft sprocket
Removal
1 With reference to Section 2 remove the
timing belt cover, set the engine to TDC on
cylinder No1 and remove the timing belt.
2 The camshaft sprocket must be held
stationary whilst its retaining bolt is
4.15 Testing the timing belt tension