Tomos A31988 Workshop Manual
Tomos A3 1988 Workshop Manual
The following is a modified and English-only version of the A3 manual found at www.classiccycles.org
Please note that this version is NOT guaranteed to be a perfect reproduction of the original; if you have
any doubts as to what you are reading, please check the original to be sure.
CONTENTS
Technical Data ………………………………………………………………………………………………………………………………………..2
Nuts, Bolts, and Torque Specs …………………………………..…………………………………………………………………………..3
Special Tools……………………………………………………………………………………………………………………………………………3
Image..……………………………………………………………………………………………………….………………….….……….4
Engine Removal…………………………………………………………………………………………………….…………………………..……5
Engine Disassembly…………………………….……………………………………………………………….…………………………….…..8
Checking Engine Parts and Assemblies ………………………………………………………………………………………………..11
Checking, Dismantling, and Assembling of the Clutch ……………………………………………………….………………..13
Dismantling, Checking, and Assembling of the Countershaft ………………………….…………………………………..15
Checking Pedal Shaft and Transmission Chain .……………………………………………………………………………….……17
Carburetor Checking……………………………………………………………………..………………………………………………………18
Encarwi Image………………………………………………………..………………………………………………………………..18
Dellorto Image……………………………………………………………………………………………………………………….…19
Reassembling the Engine .……………………………….………………………………………………….……………………………….20
Adjusting the Contact Gap and Ignition Advance ……………………….……………………………………………………….23
Oil Pump……………………………………………………………………………………………………………………………………………….24
Magneto Settings and Electrical Equipment…………………………………….…………………………………………..……..25
Wiring Diagrams (COLOR!)
European without turn signals………………………………………………………………………………………………….26
European with turn signals……………………………………………………………………………………………………….27
U.S. without turn signals…………………………………………………………………………………………………………..28
U.S. with turn signals………………………………………………………………………………………………………….…….29
1
Classic Cycles Technical Resources
TECHNICAL DATA
Engine
Single cylinder, two stroke, air cooled
Bore x stroke
38 x 43 mm (1.496 x 1.693 in)
Piston displacement
49 cm3 (2.990 in3)
Compression ratio
8.5 : 1
Engine output
0.75 -1.5 KW
Gear box
automatic 2-steps, with two centrifugal clutches
Ignition
Flywheel magneto
Ignition advance
1.8-2 mm B.T.D.C.
Contact breaker gap
0.35-0.45 mm (0.014-0.018 inches)
Spark plug gap
0.5 mm (0.020 inches)
Spark plug
NGK B6HS, Champion L86, Bosch W 4 AC
Fuel
Mixture of 86 octane gasoline and two stroke oil (2%, or 50:1)
Gearbox oil/ quantity
Valvomatic type A Suffix A – SAE 10W30 / 220 cm3
Front tire pressure
21 psi
Rear tire pressure
31 psi
Gearbox ratio (I)
17: 74, i = 4.3352
Gearbox ratio (II)
26: 64, i = 2.462
Main shaft
11: 71, i = 6.455
Secondary transmission
chain 90-93 rollers, i = 0.846 – 0.923
Crankshaft out-of-round deflection
max 0.01-0.02 mm
Magneto flywheel deflection
max aksialno 0.1mm
max radialno 0.3mm
Clutch drum axial play
0.1-0.3 mm
2
NUTS, BOLTS, AND TORQUE SPECIFICATIONS
Part
Thread
Torque
Spark plug
M14 x 1.25
18Nm
Cylinder cover
M7
12Nm
Flywheel
M10
30Nm
1st speed clutch
M10 x 1
25Nm
2nd speed driven gear
M14 x 1
80Nm
Mainshaft chain sprocket
M22
60Nm
Cylinder stud bolts
M7
15Nm
Crankcase
M6
10Nm
LH engine cover
M6
6Nm
RH engine cover
M6
7Nm
Engine-frame fastening screws
M8 x 1
25Nm
Swingarm fastening screw
M12 x 1.25
35Nm
Rear shock
M10
25Nm
Top fork lug
M12
35Nm
Front and rear wheel spindle
M11 x 1
32Nm
011.008
Gauge pin
702.856
Crankshaft bearings fitting tool
708.253
Connecting rod bush pulling key
714.011
Repair stand
731.155
Crankshaft bearings puller
731.798
Clutch spring fitting tool
732.193
Dial gauge support tool
732.202
Flywheel and clutch holding tool
732.268
Roller clutch installer
732.746
Iskra flywheel puller
735.753
Fork
735.888
Case splitter
736.533
CEV flywheel puller
737.080
Centering pin
975.709
Dial gauge
SPECIAL TOOLS
3
Classic Cycles Technical Resources
4 5
ENGINE REMOVAL
Drain the oil from the gearbox (fig 1)
With 11mm wrench, unscrew the nut and drive
out lever pin (fig 3)
Unscrew the footrest screw with 17mm wrench
(fig 2)
For pedal versions, refer to figures 3a and 4a
Remove the hub, cups and springs (fig 4)
Unscrew the three screws of LH and RH shield
each and detach shields from frame (fig 5)
Classic Cycles Technical Resources
Unscrew three screws of magneto cover and
detach cover (fig 6)
For oil pump injection refer to chapter OIL PUMP
Remove the chain by removing master link (fig 7)
Unscrew the crown nut and extract control cable
along with throttle piston (fig 8)
Detach all electrical leads (fig 10)
Unscrew bottom screw on control cable cover and
release the spark plug cable (fig 9)
Remove fuel supply line. Remove the two exhaust
manifold bolts, the fixing screw, and remove the
exhaust silencer (fig 11)
6
Unscrew all three engine screws with two 13mm
wrenches (fig 12)
Take the intake silencer out of the frame (fig 14)
Hold the engine by hand. Extract top screw (3) and
remove the engine out of the frame (fig 13)
7
Classic Cycles Technical Resources
ENGINE DISASSEMBLY
Rotate the engine placed on the stand so that the
Place the engine on the repair stand (special tool).
Remove the carburetor and spark plug (fig 15)
Detach clutch drum and sintered bush (fig 18)
Remove the standard washers on the crankshaft
and on the mainshaft (fig 20)
The pedal shaft and the countershaft are
connected by a starter chain, so both shafts will
have to be taken out together (fig 19)
flywheel magneto is on top. Using the flywheel
and clutch holding tool to hold the flywheel, use a
17mm socket to remove the flywheel nut (fig 21)
8
The flywheel is removed with the flywheel puller,
a 19mm, and a 32mm wrench (fig 22)
Make a scriber mark across the bottom of the
stator plate and the crankcase in order to facilitate
the re-timing. Remove the 3 screws and lift the
stator assembly from the engine (fig 23)
Slacken the chain sprocket nut. Using the flywheel
and clutch holder tool and a 30mm wrench,
remove the sprocket nut (fig 24)
With pointed nose pliers, remove the gudgeon pin
spring circlips (fig 26)
Using an 11mm socket, unscrew the 4 cylinder
head nuts. Remove the washers, cylinder head,
cylinder, and base gasket (fig 25)
Press out the gudgeon pin and remove the piston
(fig 27)
9
Classic Cycles Technical Resources
If the brass bushing in connecting rod needs to be
replaced, use the connecting rod bush pulling key,
and replace with a new one using same tool
(fig 28)
Upon installing the new bushing, drill two
lubrication holes according to the holes in the
connecting rod.
The bush as a spare part has inner diameter 9.80
+/- 0.1 mm and it is necessary to ream it out to
increase the inner diameter to 10mm.
Remove the crankshaft and gasket and knock out
the mainshaft (fig 31)
If the ball bearing remains on the crankshaft, use
the crankshaft bearings puller (fig 33)
In case the crankshaft ball bearing remains in the
RH crankcase, use the crankshaft bearings fitting
tool (fig 32)
The mainshaft sealing ring and ball bearing are
pressed out by using a suitable socket (fig 34)
10
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