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27.3a Undersize crankshaft bearings are
indicated by a spot and/or line on the front
counterweight
3 Note that undersize bearings may already
have been fitted, either in production or by a
previous repairer. Check the markings on the
backs of the old bearing shells, and if in doubt
take them along when buying new ones (see
illustrations). Production undersizes are also
indicated by paint marks as follows:
White line on main bearing cap - parent bore
0.40 mm oversize
Green line on crankshaft front counterweight
- main bearing journals 0.25 mm undersize
Green spot on counterweight - big-end
bearing journals 0.25 mm undersize
4 If the crankshaft endfloat is more than the
maximum
specified
amount,
thrustwashers should be fitted to the centre
main bearings. These are usually supplied
together with the main and big-end bearings
on a reground crankshaft.
5 An accurate method of determining bearing
wear is by the use of Plastigage. The
crankshaft is located in the main bearings (and
big-end bearings if necessary) and the
Plastigage filament located across the journal
which must be dry. The cap is then fitted and
the bolts/nuts tightened to the specified
torque. On removal of the cap the width of the
filaments is checked against a scale which
shows the bearing running clearance. This
clearance is then compared with that given in
the Specifications (see illustration).
6 If the spigot bearing in the rear of the
crankshaft requires renewal extract it with a
suitable puller. Alternatively fill it with heavy
29.1 Weight class mark (arrowed) on
connecting rod
27.3b Main bearing cap marks (arrowed)
denote oversize parent bore
grease and use a close fitting metal dowel
driven into the centre of the bearing. Drive the
new bearing into the crankshaft with a soft
metal drift.
28 Cylinder block and bores -
examination and renovation
1 The cylinder bores must be examined for
taper, ovality, scoring and scratches. Start by
examining the top of the bores; if these are
worn, a slight ridge will be found which marks
the top of the piston ring travel. If the wear is
excessive, the engine will have had a high oil
new
consumption rate accompanied by blue
smoke from the exhaust.
2 If available, use an inside dial gauge to
measure the bore diameter just below the
ridge and compare it with the diameter at the
bottom of the bore, which is not subject to
wear. If the difference is more than 0.152 mm
(0.006 in), the cylinders will normally require
reboring with new oversize pistons fitted.
3 Proprietary oil control rings can be obtained
for fitting to the existing pistons if it is felt that
the degree of wear does not justify a rebore.
However, any improvement brought about by
such rings may be short-lived.
4 If new pistons or piston rings are to be fitted
to old bores, deglaze the bores with abrasive
paper or a "glaze buster" tool. The object is to
produce a light cross-hatch pattern to assist
the new rings to bed in.
29.2 Relationship of piston crown arrow and
connecting rod oil splash hole (arrowed)
SOHC engines 2A•13
27.5 Checking the width of the Plastigage
filament against the scale on the packet
5 If there is a ridge at the top of the bore and
new piston rings are being fitted, either the top
piston ring must be stepped ("ridge dodger"
pattern) or the ridge must be removed with a
ridge reamer. If the ridge is left, the piston ring
may hit it and break.
6 Thoroughly examine the crankcase and
cylinder block for cracks and damage and use
a piece of wire to probe all oilways and
waterways
to
ensure
that
unobstructed.
29 Pistons and connecting rods
- examination and renovation
1 Examine the pistons for ovality, scoring and
scratches. Check the connecting rods for wear
and damage. The connecting rods carry a
letter indicating their weight class; all the rods
fitted to one engine must be of the same class
(see illustration).
2 The gudgeon pins are an interference fit in
the connecting rods, and if new pistons are to
be fitted to the existing connecting rods the
work should be carried out by a Ford garage
who will have the necessary tooling. Note that
the oil splash hole on the connecting rod must
be located on the right-hand side of the piston
(the arrow on the piston crown faces forwards)
(see illustration).
3 If new rings are to be fitted to the existing
pistons, expand the old rings over the top of
the pistons. The use of two or three old feeler
blades will be helpful in preventing the rings
dropping into empty grooves. Note that the oil
control ring is in three sections.
4 Before fitting the new rings to the pistons,
insert them into the cylinder bore and use a
feeler blade to check that the end gaps are
within the specified limits (see illustrations).
5 Clean out the piston ring grooves using a
piece of old piston ring as a scraper. Be
careful not to scratch the aluminium surface of
the pistons. Protect your fingers - piston ring
edges are sharp. Also probe the groove oil
return holes.
6 Fit the oil control ring sections with the
spreader ends abutted opposite the front of the
piston. The side ring gaps should be 25 mm
they
are
2A
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