1973 OPEL 1900 bores

DISC BRAKES5B- 11
rLF 5.2. RUBBER FLUID SEALS6.3. HOLLOW PISTONS7.
AL5
3Figure 58.21 Left Front Disc Brake
- Emloded View
the piston circumference by its inherent tension. See
Figure
5B-21. Both pistons are hollow. The open end
of each piston faces the brake disc.
A sheet metal spacer plate with two impressions for
preventing the piston from rotating is installed be-
tween each piston and friction pad and secured by
the friction pad dowel pins. The two friction pads are
positioned on the right and left of the brake disc
recesses in the caliper halves. Each friction pad con-
sists of a backing plate with friction material, which
is abrasive-coated, bonded to it. The friction pad
assemblies are held in position in the brake caliper by
two dowel pins, secured by slit dowel pin retainers,
and by a cross-shaped retaining spring which is pre-
loaded and positioned under the dowel pins, thus
pressing the friction pads and spacer plates firmly
against the pistons. The front brake line leading from
the brake master cylinder attaches to a distribution
tee from which a brake line leads to each front wheel
caliper. The caliper bores are interconnected by fluid
ducts within the caliper halves.
The front wheel disc brakes have self-adjusting pis-
tons. See Figure
5B-22.The adjustment of the pads is effected by the pistons
which push the friction pads ahead towards the
brake disc for a distance equivalent to the amount of
friction pad wear. This means that the greater the
wear the closer the pistons move towards the brake
disc. A running clearance exists between friction
pads and brake disc when the brakes are in “off”
position. This running clearance is provided by the
rubber fluid seals which are positioned in the caliper
half bores and which tightly grip and exert their
pre-load pressure on the pistons. The rubber fluid
seals also prevent the pistons from being pushed into
the caliper half bores more than the distance equiva-
lent to the running clearance. As the friction pads are
adjusted by the pistons, there must be no static pres-
sure in the front brake circuit when the brakes are in“OR position. Non-existence of a static pressure in
the front brake circuit is achieved by eliminating the
check valve in the brake master cylinder on the front
brake circuit. During brake application the pressure
from the brake master cylinder is transferred to the
pistons in the brake caliper. The pistons move ahead
and press the friction pads against both friction
SW-faces of the rotating brake disc. The force exerted on
the brake pedal determines the pressure of the fric-
tion pads against the brake disc. On releasing the
brake pedal, the brake lines of the front brake circuit,
including the caliper half bores, are relieved of
hy-OPERATION

5B- 121973 OPEL SERVICE MANUAL
A = BRAKE ON
THE RUBBER FLUID SEAL TIGHTLY GRIPPING PISTON
IS DEFLECTED IN DIRECTION OF PISTON TRAVELAFRICTION PAD
BRAKE DISCRUBBER FLUID SEALBRAKE
IICALIPER
IPISTON
I
CE BETWEEN RUNNING CLEARAN
FRICTION PAD AND BRAKE DISC
B = BRAKE OFFBTHE PISTON IS RETRACTED BY THE AMOUNT OF
RUBBER FLUID SEAL DEFLECTION. THIS AMOUNT
IS EQUAL TO RUNNING CLEARANCE.SBZZ
Figure 58-22 Rubber Fluid Seal -Automatic Piston Retractiondraulic pressure, and the friction pads and pistonsmove away from the brake disc, leaving a small run-
ning clearance. The brake disc can now rotate freely.
The amount of brake travel is dependent upon the
amount of running clearance. For this reason therunout of the brake disc should be checked, besides
bleeding of the brake system and adjusting the rear
brake shoes, when the pedal free travel is too great.during braking, the rubber seals in the annular
grooves of the brake caliper bores deflect laterally in
the direction of piston movement. See Figure
5B-22,View (A). The seal remains deflected for the duration
of the braking operation. After braking, the caliper
bores are relieved of hydraulic pressure and the rub-
ber seals resume their normal position, thus pulling
or retracting the pistons. The distance traveled by
the pistons is equal to that of the running clearance
between brake disc and friction pads.
The running clearance between brake disc and
fric-tion pads is attained as follows: When the pistons in
the caliper halves are moved towards the brake discThe shifting of the pistons in the direction of the
brake disc due to friction pad wear has no effect on
the running clearance. The running clearance re-mains the same in all piston positions.
DIAGNOSIS
DISC BRAKE TROUBLE DIAGNOSIS
ConditionPulls
Possible Cause
I. Incorrect tire
pressures.Correction1. Inflate evenly on both sides to
the recommended pressures (see
Owner’s Manual).

5B- 19i973 OPEL SERVICE MANUAL
Figure
56-24 Removing Dowel Pins
Figure 56-25 Removing Friction Pads
4. Check rubber seals for wear. If rubber seals are
hardened, brittle or cracked, they must be replaced
as follows:
(a) Remove brake caliper from steering knuckle and
brake disc. Leave hose attached to brake caliper.
(b) Remove seal clamp rings with screwdriver and
remove seal rings from calipers. See Figure
5B-26.(c) Install new rubber seals and clamp rings. Make
sure rubber seal is properly seated. Make sure clamp
ring is correctly positioned on rubber seal,Figure 56-26 Removing or Installing Rubber Seal
Clamp Ring
(d) Attach brake caliper to steering knuckle and
torque bolts to 72
Ib.ft. Prior to installation of
caliper, make sure contacting surfaces of both caliper
and steering knuckle are perfectly clean and free of
any burrs.
CAUTION: This disc brake caliper attachments fas-
tener is an important attaching part in that it could
affect the performance of vital components and sys-
tems, and/or could
result in major repair expense. It
must be replaced with one of the same part number
or with an equivalent part, if replacement
becomes
necessary. Do not use a replacement part of lesser
quality or substitute design. Torque values must be
used as specified during reassembly to assure proper
retention of this part.5. Before installing new friction pads, press both pis-
tons of each caliper to bottom of their bores, using
Return Clamp J-22430.
While pressing piston into
bores, open caliper bleeder valve to prevent excess
brake fluid from overflowing master cylinder con-tainer As soon as pistons are bottomed, tighten
bleeder valve.
6. Check brake disc for lateral runout.
7. Install new friction pads into brake caliper. Fric-
tion pads must be free enough to be easily moved in
their caliper recesses. See
Figure X3-25.If new friction pads are not free, it will be necessary
to remove pads and clean recesses and recess corners
with a wooden spatula and then with denatured al-
cohol and a brush. After cleaning, blow out recesses
with compressed air. Remove any high spots on
edges of friction pads contacting caliper recesses with

58.201973 OPEL SERVICE MANUAL
half, and blow out pistons, carefully regulating air
flow. When removing pistons, proceed with extreme
caution and always keep the fingers ofthe hand hold-
ing the brake caliper away from the piston.
Figure 55.33 Removing Caliper Rim Half Piston
Figure 58-34 Removing Caliper Mounting Half Piston
4. Pry rubber fluid seals out of the annular grooves
in the caliper half bores. See Figure
5B-35.5. Check all parts of the brake caliper for wear. If the
caliper half bores are scored or rusted, use a new
complete brake caliper and friction pads. Small, light
rust spots in the caliper half bores or on the pistons
can be removed with fine emery cloth. If pistons are
damaged, even though the caliper half bores are inFigure 58-35 Removing Rubber Fluid Seal From
Caliper Boresgood condition, the piston must be replaced. The
rubber fluid seals and rubber seals with
clapp rings
for the pistons are to be replaced every time repair
work is carried out on the brake caliper.
6. Thoroughly clean all reusable parts
- complete
brake caliper and pistons
- with denatured alcohol
and dry with compressed air. Prior to cleaning, screw
bleeder valve out of caliper.
7. Lightly coat new rubber fluid seals with brake
fluid and insert fluid seals into grooves of brake
caliper bores.
8. Place brake caliper into vise to install pistons.
After installing one piston, change position of brake
caliper in vise to install second piston. The piston to
friction pad spacer plates should be used as a gauge
to locate relieved edge of piston at 20 degrees to
horizontal during piston installation. See Steps
9-IO-
11-12.9. Place caliper mounting half in vise and coat its
bore and piston lightly with brake fluid. Then push
piston, with hollow end towards brake disc, into the
caliper bore. Turn piston so that the relieved edge
faces downwards at an angle of 20 degrees and facing
in brake disc direction. The guide surface in the
caliper half recess at the brake pipe connection side,
will properly align the piston. Push piston into
caliper bore up to the stop.
10. Change position of brake caliper and install sec-
ond piston in the same manner.
11. Install new rubber seals with clamp rings. Make
sure that the rubber seals are properly seated on the

6A- 121973 OPEL SERVICE MANUALINTAKE AND EXHAUST MANIFOLD REMOVAL
AND
INSTALLATION
Removal1. Disconnect battery.
2. Remove air cleaner.
3. Disconnect throttle linkage at carburetor.
4. Disconnect vacuum advance line at carburetor.
5. Remove fuel line at carburetor inlet.
6. Remove positive crankcase ventilation hose at
rocker arm cover.
7. Disconnect E.G.R. lines from carburetor and in-
take manifold.
8. Disconnect exhaust pipe.
9. Remove six bolts attaching manifold assembly to
cylinder head and remove manifold and carburetor
as an assembly. Discard manifold gasket.
To separate intake and exhaust, manifold, remove
carburetor and four bolts using Tool J-23016, attach-
ing intake manifold to exhaust manifold. Always in-
stall a new manifold intermediate gasket when the
manifolds are separated.
Installation1. Install new manifold gasket and place manifold in
position.
2. Install manifold bolts. New manifold to cylinder
head gasket must be installed whenever a manifold
is removed.
3. When installing the manifold, start with the No.
1 and No. 2 bolts. See Figure 6A-16. Gradually
tighten both bolts until snug. Then continue with the
rest of the bolts in the sequence illustrated in Figure6A-16. Torque bolts to 33 lb. ft.
Figure 6A-16 Manifold
Bolt Tightening Sequence4. Connect parts removed in Steps 1 thru 8 above.
CYLINDER HEAD REMOVAL AND INSTALLATION
Removal1. Drain coolant from radiator and block. Loosen
drain plug on right side of engine to avoid coolant
entering into cylmder bores. Drain plug is located onthe right rear of cylinder block above oil pressure
switch.2. Remove hoses from thermostat housing. Collect
coolant as it contains anti-freeze.
3. Remove 6 intake and exhaust manifold attaching
bolts and swing assembly aside.
4. Remove spark plug wires from plugs.
5. Remove bracket bolt holding spark plug wires
away from cylinder head.
6. Remove rocker arm cover.
7. Remove 10 cylinder head bolts using 12 MM ser-
rated drive J-22915, and 2 cylinder head to timing
chain cover bolts with a 6MM hex head wrench. See
Figure 6A- 17.
Figure 6A-17 Serrated Bits
8. Remove three bolts attaching plate to front of
cylinder head.
9. Remove plastic screw from end of camshaft.
10. Remove 3 bolts attaching camshaft sprocket to
cylinder head. Slide sprocket off of camshaft and
remove head. Place head on bench supported at each
end by a block of wood to prevent damage to valves.
Installation1. Install in reverse procedure to removal, paying
particular attention to the following:

6A. 141973 OPEL SERVICE MANUAL
wire brushes for removing carbon, avoid scratching
valve seats and valve faces. A soft wire brush such as
J-8089 is suitable for this purpose.
Figure 6A-21 Removing Valve Cap Retainers5. Clean carbon and gum deposits from valve guide
bores.6. Inspect valve faces and seats for pits, burned spots
or other evidences of poor seating. If a valve head
must be ground until the outer edge is sharp in order
to true up the face,discard the valve because the
sharp edge will run too hot.
J-22917-1 .0030” O.S.
J-22917-2 .0059”
05.J-22917-3 .Ol 18” OS.
Figure 6A-22 Reaming Valve Guide
CORRESPONDINGVALVE STEM DIA.
SIZE IN.VALVE GUIDE
PRODUCTION.3553.
.3562.3538..3543.3524.3528PRODUCTION
AND SERVICE
.3582.3592.3567.3572.3553.3559.3615.
.3622.3597.3602.3583.3588
.3671.3681.3656..3661.3642.3647
6A-2:Figure 6A-23 Valve Guides and Corresponding Valves

ENGINE MECHANICAL AND MOUNTS6A- 19
sion. When replacing flywheel use new bolts and
torque to 43 lb.ft.
PISTON, RINGS AND CONNECTING RODS
Removal and Disassembly of Piston
and Rod Assemblies
1. Drain oil.
2. Remove oil pan. 3. Remove cylinder head.
4. Examine the cylinder bores above the ring travel.
If bores are worn so a ridge exists, remove the ridges
with a ridge reamer to avoid damaging rings or
cracking ring lands in pistons during removal.
5. Mark the cylinder number on all pistons, connect-
ing rods and caps. Starting at the front end of the
crankcase, the cylinders are numbered l-2-3-4,
6. Remove cap and bearing shell from number 1
connecting rod.
7. Push the piston and
rod assembly up and out of
top cylinder. Then reinstall cap and bearing shell on
rod.
0
-J-23436-4
J-23436-2+
J-6047
Figure
6A-3 1 Piston Pin Removal Tool Layout - 1 .S
Engine
8. Remove other rod and piston assemblies in the
same manner.
9. Remove compression rings and oil rings.
10. Remove piston pin in following manner:
a. Position base support J-6047 on hydraulic press.
b. Place tool J-23436-2 in base support with large
diameter bore facing upward. See Figure
6A-31.
c. Position piston and rod assembly on tool
J-
23436-2 making certain the pin is aligned on tool.
d. Position tool J-23436-4 in opposite end of piston
pin and press pin out.
Inspection of Cylinder Bores
Inspect cylinder walls for scoring, roughness, or
ridges which indicate excessive wear. Check cylinder
bores for taper and out-of-round with an accurate
cylinder gage at top, middle and bottom
ofbore, both
parallel and at right angles to the centerline of the
engine. The diameter of the cylinder bores at any
point may be measured with an inside micrometer or
by setting the cylinder gauge dial at “0” and measur-
ing across the gauge contact points with outside mi-
crometer while the gauge is at the same “0” setting.
If a cylinder bore is moderately rough or slightly
scored but is not out-of-round or tapered, it is possi-
ble to repair the bore by honing to accept a standard
service piston. If cylinder bore is very rough or deeply scored, it may be necessary to rebore the cyl-
inder to fit an oversize piston in order to insure satis-
factory results.
If a cylinder bore is tapered
.ooO5” or more, or is
out-of-round
.0005” or more, it is advisable to hone
or rebore for the smallest possible oversize piston and
rings.
Visual Inspection of Pistons, Rings, and Pins
Clean carbon from piston surfaces and under side of
piston heads. Clean carbon from ring grooves with a
suitable tool and remove any gum or varnish from
piston skirts with suitable solvent.
Carefully examine pistons for rough or scored bear-
ing surfaces, cracks in skirt, head cracked or broken
ring lands, and chipping or uneven wear which
would cause rings to seat improperly or have exces-
sive clearance in ring grooves. Damaged or faulty
pistons should be replaced.
Fitting Pistons to Cylinders
The pistons are cam ground, which means that the

6A. 201973 OPEL SERVICE MANUAL
diameter at the right angle to the piston pin is greater
than the diameter parallel to the piston pin. When a
piston is checked for size, it must be measured with
micrometers applied to the skirt at ,points 90 degrees
to the piston pin. See Figure
6A-32. The piston
should be measured (for fitting p&poses) 2
l/2 in-
ches below the top of piston.
MEASURE AT
Figure 6A-32
Measuring,PistonInspect bearing surfaces of piston pins. Check for
wear by measuring worn and unworn surfaces with
micrometers. Rough or worn pins should be re-
placed. Check fit of piston pins in piston bosses.
Occasionally pins will be found tight due to gum or
varnish deposits. This may be corrected by removing
the deposit with a suitable solveni. If piston bosses
are worn out-of-round or oversize, the piston and pin
assembly must be replaced. Oversize pins are not
practical because the pin is a press fit in the connect-
ing rod. Piston pins must tit the piston with
0X4”to
.OCHl7” clearance.
Examine all piston rings for scores, chips or cracks.
Check compression rings for tension by comparing
with new rings. Check gap of compression rings by
placing rings in bore at bottom of ring travel. Meas-
ure gap with feeler gage. Gap should be between
,011” and .02.1”. If gaps are excessive (over .021”) it
indicates the rings have worn considerably and
should be replaced.
No attempt should be made to cut down oversize
pistons to fit cylinder bores. This practice
will de-
stroy the surface treatment and affect the weight.
The
sma/Jest possible oversize service pistons shouId
be used and the cylinder
bores should be honed to
size for proper clearance.1. Before installing piston, piston rings, or reboring
cylinders, observe the following:Cylinder bores may not be the same size. Standard
replacement piston sizes are in the midpoint of the
cylinder bore size range. Therefore, it may be neces-
sary to hone cylinders for correct piston tit. Out-of-
round on cylinder bore must not exceed
.ooO5”maximum with a taper of not over
.OilO5”.Before the honing or reboring operation is started,
measure all new pistons with micrometer contacting
at points exactly 90 degrees to piston pin (Figure6A-32) then select the smallest piston for the first
fitting. The slight variation usually found between
pistons in a set may provide for correction if the first
piston has excessive clearance.
If wear of cylinder does not exceed
.005” honing is
recommended for truing the bore. If wear or
out-of-round exceeds these limits, the bore should be trued
up with a fly cutter boring bar and then finish honed.
When reboring cylinders, all crankshaft bearing caps
must be in place and tightened to proper torque to
avoid distortion ofbores in final assembly. Always be
certain the crankshaft is out of the way of the boring
cutter when boring each cylinder. When making thefinal cut with boring bar, leave
,001 w on the diameter
for finish honing to give the required clearance speci-
fied.When honing cylinders, use clean sharp stones of
proper grade for the required amount of metal to be
removed, in accordance with instructions of the hone
manufacturer. Dull or dirty stones cut unevenly and
generate excessive heat. When using coarse or
medium grade stones use care to leave sufficient
metal so that all stone marks may be removed with
the fine stones used for finishing in order to maintain
proper clearance.
When finish honing, pass the hone through the entire
length of cylinder at the rate of approximately 60
cycles per minute. This should produce the desired
45 degree cross hatch pattern on cylinder walls
which will insure maximum ring life and minimum
oil consumption.
It is of the greatest importance that refinished cylin-
der bores have not over
.0005” out-of-round or ta-
pered. Each bore must be final honed to remove all
stone or cutter marks and provide a smooth surface.
During final honing, each piston must be fitted in-
dividually to the bore in which it will be installed and
should be marked to insure correct installation.
After final honing and before the piston is checked
for fit, each cylinder bore must be thoroughly
washed to remove all traces of abrasive and then
dried. The dry bore should then be brushed clean
with a power-driven iibre brush. If all traces of abra-
sive are not removed, rapid wear of new pistons and
rings will result. Fit new pistons in the following
manner: