NACIONAL MOTOR Derbi Euro 3 Instruction manual

moteur derbi
euro 3
documentation atelier
(EN ANGLAIS)

1
DERBI - NACIONAL MOTOR, S.A., manufacturer of DERBI motorcycles and mopeds, has produced this
manual with the aim of documenting and simplifying as much as possible the work you need to do to in dis-
mantling and assembling the 6 speed 50 c.c. engine.
The intention is to provide as much assistance as possible to mechanics working for our brand’s dealers and
sub-dealers.
Due to its constant commitment to improving its products, DERBI - NACIONAL MOTOR, S.A. Sociedad
Unipersonal reserves the right to introduce any modifications it deems fit, without prior warning.
All the information included in this manual is based on the latest data available at the time of its publication.
The drawings and photographs in this manual are for reference purposes only, and may therefore not be
exactly the same as the corresponding parts of the current model itself.
NACIONAL MOTOR, S.A.

3
GENERAL INFORMATION
ENGINE IDENTIFICATION NUMBER
GENERAL TECHNICAL CHARACTERISTICS
DISMANTLING THE CARBURETTOR
DISMANTLING/REASSEMBLING THE REED VALVES
DISMANTLING/REASSEMBLING THE COOLING SYSTEM
DISMANTLING/REASSEMBLING THE OIL PUMP
DIMANTLING/REASSEMBLING THE CYLINDER HEAD
DISMANTLING/REASSEMBLING THE CYLINDER AND PISTON
DISMANTLING/REASSEMBLING THE CLUTCH ASSEMBLY
DISMANTLING/REASSEMBLING THE CRANKSHAFT AND GEAR CHANGE
DISMANTLING THE ALTERNATOR MAGNETO
Page 4
Page 5
Page 6
Page 10
Page 14
Page 16
Page 18
Page 20
Page 22
Page 25
Page 30
Page 38

4
SERVICE RULES
- Use original DERBI parts or parts and lubricants recommended by DERBI. Parts that do not comply with
DERBI design specifications may damage the moped (engine and/or machine).
- Where indicated, use the special tools for this model.
- Always use new seals and gaskets when refitting.
- When tightening a series of nuts or bolts, start with the bolts with the larger diameter or start with the
ones to the inside or centre of the part, and apply the specified tightening torque diagonally in two or three
steps.
- Before removing any component from the engine, clean it carefully to prevent dirt from getting into the
engine.
- Before refitting, lubricate all sliding surfaces.
- After reassembly, and before starting up the moped, check that all the parts are correctly fitted and working
properly.
SERVICE
RULES

5
ENGINE NUMBER
The number is stamped onto the top of the left hand crank-
case (next to the gearbox-clutch oil filler plug).

6
ENGINE
Cycle
Diameter per stroke
Number of cylinders
Total cylinder capacity
Maximum power
Compression ratio
Fuel
Inlet system
Starting system
Lubrication system
Cooling system.
Turn direction
One nickel and silicon carbide coated aluminium cylinder.
95/98 octane lead free petrol (min. 95 octane)
Reed valve direct to the crankcase
11,5:1
Electronic/Kick-start (depending on model)
Liquid with pump, radiator and thermostat
Anticlockwise (looking at the magneto)
Two stroke
N/A
49cc
39,88 x 40mm
Oil pump
TRANSMISSION
Primary transmission
Primary transmission ratio
Clutch
Gears
Gear ratios
Transmission oil volume /
Type
1a
2a
3a
4a
5a
6a
By straight gears
3.7 (21/78)
Multi-disk in oil bath
Constant mesh
650c.c.
SAE 10W40-PIGL-4
11/34
15/30
18/27
20/24
22/23
22/23

7
ELECTRICAL SYSTEM
Generator
Voltage /Generating power
Ignition type
Ignition advance
Spark plug gap
Alternator magneto
12v / according to model
DIU
1.2 mm. Before T.D.C.
See machine specifications table
MAINTENANCE PROGRAMME
CHECKS
Gearbox/clutch oil
Spark plug
Carburettor
Cylinder/cylinder head/piston
Complete piston (including segments)
Air filter
Inlet reeds
Engine coolant
Fuel and oil pipes
Oil pump draught
1000 / 2
Replace
Check
Adjust and
clean
Check
Check
5000 / 12
Replace
Adjust and
clean
Clean
Check
Check
10000 / 24
Replace
Replace
Adjust and
clean
Clean
Check
Replace
Replace
Check
15000 / 36
Check
Replace
Adjust and
clean
Replace
Clean
Check
Check
20000 / 48
Replace
Replace
Adjust and
clean
Clean
Check
Replace
Replace
Check
25000 / 60
Check
Replace
Adjust and
clean
Clean
Check
Check
SPARK PLUGS USED IN DERBI 50c.c. 6 SPEED ENGINES
See machine specifications table.
KMS / MONTHS (whichever comes first)
Clean
(every 15.000km)

8
TORQUE TIGHTENING TABLE
M1 4x125 spark plug-cylinder head securing device
M6x100 cylinder head cover-cylinder sec.dev.
M7x100 cylinder head nut sec.dev.
M1x100 magneto-crankshaft sec.dev.
M5x80 base plate-crankcase sec.dev.
M6x100 right cover-crankcase sec.dev.
M1 0x100 engine pinion-crankshaft sec.dev.
Kick-start lever bush – starter shaft sec.dev. M6x100
M6x100 crankcases sec.dev.
M3x0.5 reeds –support sec.dev.
M6x100 carburettor nozzle-crankcase sec.dev.
M5x80 oil pump-crankcase sec.dev.
M6x100 starter motor-crankcase sec.dev.
M6x100 Bendix cap -crankcase sec.dev.
M5x80 pump runner-pump shaft sec.dev.
M6x100 pump cover-crankcase sec.dev.
M1 4x150 thermistor –cylinder head sec.dev.
M4x70 thermostat—cylinder head cover sec.dev.
M1 2x150 clutch bell housing – primary shaft sec.dev.
M5x80 clutch spring – bell housing sec.dev
M6x100 left cover-crankcase sec.dev.
M5x80 primary shaft bearing seal – crankcase sec.dev.
M5x80 (10.9) drum control head – drum sec.dev.
M1 0x150 oil drain screw – crankcase sec.dev.
M6x100 starter stop – crankcase sec.dev.
M1 0x100 counterweight pinion – counterweight shaft sec.dev.
Release lever-release shaft sec.dev. M6x100
M5x80 seal – change output pinion sec.dev.
M6x100 gear sec. lever -crankcase sec.dev.
M8x125 selector stop – crankcase sec.dev.
M5x80 oil pump cover - right cover sec.dev.
M6x100 gear lever – selector shaft sec.dev.
M1 0x100 (PA6) neutral indicator – crankcase sec.dev.
2 ÷ 4
0,8 ÷ 1
1,9 ÷ 2,2
3,5 ÷ 4,5
0,25 ÷ 0,35 Sealed
0,8 ÷ 1
3,5 ÷ 4,5
0,8 ÷ 1
0,8 ÷ 1
0,1 ÷ 0,2
0,8 ÷ 1
0,35 ÷ 0,45
0,8 ÷ 1
0,8 ÷ 1
0,35 ÷ 0,45
0,8 ÷ 1
3,2 ÷ 3,8
0,1 ÷ 0,15
3,5 ÷ 4,5
0,35 ÷ 0,45
0,2 ÷ 0,35
0,35 ÷ 0,45
0,5 ÷ 0,7
1,5 ÷ 1,8
0,8 ÷ 1
3,5 ÷ 4,5
0,8 ÷ 1
0,35 ÷ 0,45 Sealed
0,8 ÷ 1 Sealed
1,5 ÷ 1,9
0,35 ÷ 0,45
0,8 ÷ 1
0,25 ÷ 0,35
20 ÷ 40
8 ÷ 10
19 ÷ 22
35 ÷ 45
2,5 ÷ 3,5 Sealed
8 ÷ 10
35 ÷ 45
8 ÷ 10
8 ÷ 10
1 ÷ 2
8 ÷ 10
3,5 ÷ 4,5
8 ÷ 10
8 ÷ 10
3,5 ÷ 4,5
8 ÷ 10
32 ÷ 38
1 ÷ 1,5
35 ÷ 45
3,5 ÷ 4,5
2 ÷ 3,5
3,5 ÷ 4,5
5 ÷ 7
15 ÷ 18
8 ÷ 10
35 ÷ 45
8 ÷ 10
3,5 ÷ 4,5 Sealed
8 ÷ 10 Sealed
15 ÷ 19
3,5 ÷ 4,5
8 ÷ 10
2,5 ÷ 3,5
TIGHTENING TORQUE
(N.m.) TIGHTENING TORQUE (m•kg)
SECURING DEVICE DESCRIPTION

9
SPECIAL USES
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
00H05400451
00H05400581
00H05401561
00H05300041
00H05600241
00H05300151
00H05600351
00F05300021
00G05300011
00D05310091
Herramienta standard
00H05600421
00H05600431
00H05100101
00H05401451
00H05400461
00H05601261
00H05301841
Crankshaft oil seal fitting tool
Starter shaft oil seal fitting tool
Selector shaft oil seal fitting tool
Clutch bell housing securing tool
Primary shaft needle bush fitting tool
Engine opening pusher
GPR secondary shaft oil seal guide pivot
Alternator magneto extractor
Alternator magneto turn locker
Senda engine pinion
GPR engine pinion
Water pump exterior oil seal
Water pump interior oil seal
Engine pinion fastening tool
Counterweight shaft cage
Counterweight shaft oil seal
Water pump shaft guide pivot
Crankshaft journal oil seal guide pivot
NAME REFERENCE
NUMBER

10
CARBURETTOR
- Loosen the clamps securing the carburettor to the inlet
nozzle and the air filter nozzle. Disconnect the fuel, oil and
fuel tap depressor pipes, and extract the carburettor.
- Loosen the carburettor cover screw and dismantle it to-
gether with the throttle cable assembly, gas valve and ta-
pered dosage needle(1).
-Compress the gas valve return spring against the cover
and extract the throttle cable terminal through the gas
valve channel.
- Dismantle the cold start (choke) system piston valve
securing clamp and extract the assembly (1).
- Before removing the idling circuit air quantity regula-
ting screw (“compensator”), check its position by counting
the number of turns needed to screw it right in (without
forcing).
Make a note of this measurement and then unscrew and
remove it. - (In case of doubt, consult the machine specifi-
cations table to determine the factory set position for this
screw).
CARBURETTOR

11
- Extract the screws from the carburettor bowl and extract
the bowl itself, thereby gaining access to the bores: the
maximum(1), minimum(2) and cold start bores, as well as
the float and its needle valve.
REASSEMBLING THE CARBURETTOR
- Clean all the components of the carburettor with solvent
(take care not to damage the carburettor bowl gasket or
the cold start valve O-ring).
- With the aid of compressed air, blow meticulously through
all of the orifices through which air, oil and fuel pass.
- With the aid of scales, check the weight of the float. This
is engraved on it (3.5 grams). If it exceeds this weight,
renew it.
- Check that the tapered needle controlling the flow of
petrol to the bowl, together with the spring on its stem
connecting it to the float, are in good condition. Should
this not be the case, renew them.
- Check the condition of the cold start system piston valve.
In the event of the vulcanised closing seat or the metal
body of the piston being damaged (scratches and/or co-
rrosion that exceed 25% of its total area), renew it.
- Check the size of the bores based on the numbers etched
onto them. Fit suitable ones (see adjustments table). Fa-
ilure to do so will result in the performance of the engine
being affected.
REASSEMBLING
THE
CARBURETTOR

12
- Check the position of the tapered dosing needle.
- Moving the circlip on the needle upwards results in a
leaner mixture, and moving it downwards results in a ri-
cher mixture. This allows adjustments to be made for ex-
treme climatic conditions.
- Renew the tapered dosing needle if damage is visible on
its circumference.
- Check for the absence of scratches on the minimum cir-
cuit air regulator screw cone. These would affect its per-
formance.
- Check for the absence of scratches on the sliding valve.
In the event of these exceeding 25% of its total area, re-
new it.
- Be sure to install one with the same characteristics (see
markings on its base).

13
- Completely reassemble the carburettor. Refit the carbu-
rettor to the engine, making sure to connect the fuel, oil
and fuel tap depressor activation pipes properly.
- Check that the idling circuit air quantity regulating screw
(“compensator”) is in a similar position to that before dis-
mantling (in case of doubt, consult the machine specifica-
tions table to determine the factory set position).
- Check that the throttle control run is correct and is not
blocked or hardened at any point.
- Set the free play adjustment of the throttle cable sleeve
tensioner on the throttle twist-grip to give a free play of
3 to 5 mm.
- Extract the foam air filter, wash it in soapy water, then
wring it out and dry it completely. Next, soak it in special
oil for filters and refit it.
- Then adjust idle speed, using the following procedure:
1. Start the engine.
2. Screw in the screw regulating the sliding valve at rest
position until the engine is about to stall.
3. Then slowly screw in or unscrew the screw regulating
the sliding valve at rest position until an idle speed of
1600 ± 200 rpm is achieved (with the help of an exter-
nal rev-counter).
4. Turn the throttle twist-grip sharply to cause a rapid
increase in engine revs, and check that it accelerates
and decelerates smoothly and quickly, without missing.
Should this not be the case, adjust the position of the
minimum air regulating screw (AS) ¼ of a turn and go
back to point 3. Screwing in the AS will obtain a richer
mixture (with more petrol), while unscrewing the AS will
lead to a leaner mixture (less petrol).

14
DISMANTLING THE REED VALVE
- Remove the carburettor from the engine.
- Extract the inlet nozzle closing bolts and the inlet nozzle.
The reed valve can then be accessed and extracted
- Check that there are no cracks, distortions or breakages
on the reed petals. If there are, renew them.
- Remove the securing screws from the height limiter and
from the inlet valve petals and check that there are no
cracks in the petals’ securing base. If there are, renew the
reeds.
REFITTING THE REED VALVE
- To refit the reed valve, proceed in the reverse order to
dismantling, paying special attention to the correct posi-
tioning of the height limiter and the reed (with the bevels
matching). The elimination of the height limiter and the
type of reed used will modify the performance of the en-
gine and may make it less reliable.
- Check the reed cage O-ring and replace it if damaged.
Fit a new seal.
DISMANTLING
THE
REED
VALVE

15
DISMANTLING THE COOLING SYSTEM
- Completely drain the coolant from the engine by deta-
ching the hoses connecting the pump to the radiator.
- Drain the engine oil and extract the transmission cover.
- Remove the bolts from the water pump cover and extract it.
- Loosen the water pump runner securing nut and extract
the latter by unscrewing it.
- Extract the circlip, top washer, pump driving pinion, its
key and the bottom washer. Then gently tap the shaft from
the inside outwards, pulling with it the two seals.
- Change the water seals at the first sign of coolant or oil
leaking from the breather bore. Also renew the shaft if it
shows signs of wear at the circumference where the seals
are positioned.
REFITTING THE COOLING SYSTEM
- Fit the circlip (1) onto the shaft stem (2), inserting it into
the cover from the outside with the 8.3 x 14 x 1 washer (3)
under the circlip.
REFITTING
THE
COOLING
SYSTEM
DISMANTLING
THE
COOLING
SYSTEM

16
- Use tool number 13 (see special tools list) to insert the in-
ner oil seal (4) with the spring downwards. Use tool num-
ber 12 to fit the top oil seal (5) with the spring upwards.
Both seals should be lightly greased.
- Fit the 5.25 x 15 x 1 washer (6), the pump runner (7)
and the securing nut (8). Tighten to a torque of 0.35-0.45
m.kg.
- Through the inside of the cover fit the 8.3 x 14 x 1 washer
(9), the key (10), the pump driving pinion (11), the 8.3 x 14
x 1 washer (12) and the circlip (13).
- Fit the transmission cover with a new gasket and refill
the engine crankcase with 650 c.c. of SAE 10W40 API GL-
4 type oil.
- Fit a new water pump cover gasket.
- The cooling system should then be refilled and pur-
ged according to the following procedure:
1. Prepare an external feed tank with -18ºC freezing
point coolant positioned at a height of approximately
2m from the ground, with the aim of filling the cooling
system from the expansion tank.
2. Start up the engine and keep it ticking over.
3. Open the feed tank tap and let the coolant flow fre-
ely until it reaches the minimum level in the cooling
system expansion tank.
Close the tap.
4. Close the expansion tank valve cap.
Warm up the engine until the thermostat opens.
5. Check that the body of the radiator warms up. If it
fails to do so, this is an indication that the thermostat
has not opened or that there are air locks inside the
cooling system circuit.
6. Turn off the engine and allow to cool.

17
7. Replenish the expansion tank with coolant until the
minimum level is reached in the expansion tank (on
warming up, the level will rise due to expansion in the
circuit).
8. Check the electric circuit of the overheating warning
indicator on the instrument panel, by disconnecting the
temperature sensor connector and connecting its ter-
minal to earth using a length of wire, and then turning
on the ignition. The instrument panel indicator light
should light up.
9. To check the cylinder head temperature sensor, as
well as the fan activating thermo-contact (only in the
versions where this is fitted) submerge their active part
in a container filled with water and heat this up. Con-
nect a multi-meter set to read resistances between its
metal body and connection terminal and check that as
the water temperature rises, the sensor’s resistance
value decreases. If this is not the case, renew the sen-
sor.
- The thermostat should be suspended submerged in a
container of water without touching the container, and
the water heated up. Use a thermometer to check when
the thermostat begins to open and when it stops opening
(completely open).
SENSOR
CYLINDER HEAD COOLANT TEMP.
ELECTRO-FAN THERMO-CONTACT
ON
124 ± 3°C
97 ± 3°C
OFF
114 ± 3°C
85 ± 3°C
OPENING STARTS
60°C±2°C
TRAVEL
3.5 ÷ 5 A 70°C ± 2°C

18
DISMANTLING THE OIL PUMP
- Remove the inspection cover situated on the clutch half-
housing.
- Free the securing clamps on the pump input and output
oil pipes. Plug the input pipe to prevent the oil tank from
draining.
- Dismantle the pump control cable, freeing it first from
the control cam and then from the sleeve stop on the clu-
tch half-housing.
- Remove the two Allen screws securing the pump to the
clutch half-housing and extract the pump. Turn the pump
shaft manually and check that it turns smoothly.
- Check the condition of the O-ring and the shaft oil seal.
Renew them if they are damaged.
- The oil pump is an essential unit for the proper safe func-
tioning of the engine. In the event of faults, it should be
renewed not dismantled.
REFITTING THE OIL PUMP
- Refit by carrying out the removal procedure in reverse
up to this point.
- Take special care to ensure that the shaft movement
transmission notches mesh correctly with the gearing on
the clutch half-housing.
REFITTING
THE
OIL
PUMP
DISMANTLING
THE
OIL
PUMP