Tomos A31988 Workshop Manual

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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

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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

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NUTS, BOLTS, AND TORQUE SPECIFICATIONS

Part

Thread

Torque

Spark plug

M14 x 1.25

18Nm

Cylinder cover

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

15Nm

Crankcase

10Nm

LH engine cover

6Nm

RH engine cover

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

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Classic Cycles Technical Resources

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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)

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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)

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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)

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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)

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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)

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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)

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CHECKING ENGINE PARTS AND ASSEMBLIES

Figure 35

Figure 36

Check both crankcase halves for possible damages or distortions, particularly the joint surfaces, to avoid later leaking of oil from the gearbox.

Check all bearings. If clearance is noticed, the bearings must be replaced.

Check the crankshaft between the center of a horizontal alignment tool and measure out-of-round on all the points indicated in figure 35.

Permissible out-of-round should be within 0.01 mm at check pints 2 and 3 and 0.02 mm at check points 1 and 4. Check if the crankshaft conical part is damaged, inspect the thread on semiaxles and the keyway.

Check piston surfaces for possible damages. With micrometer check piston diameter on points d1, d2, d3 and d4 at right angles to gudgeon pin and compare the reading with the corresponding group on piston and in the table (fig 36)

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Classic Cycles Technical Resources

CYLINDER

D (mm, in)

38.01

+0.01

(1.4964

+0.0024

in)

38.02

+0.01

(1.4968

+0.0024

in)

37.95

+0.01

37.91

+0.01

37.87

+0.01

37.85

+0.01

37.96

+0.01

37.92

+0.01

37.88

+0.01

37.86

+0.01

D (mm, in)

38.51

+0.01

38.52

+0.01

D > D

max 0.012 mm

Ma x permissible bore taper: 0.006mm

PISTON

L = 50 mm L= 52.5 mm L = 55 mm

Piston I. oversize: Ø 38.50mm The cylinder must be bored and honed as shown in the table:

OVERSIZE CYLINDER

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CHECKING, DISMANTLING, AND ASSEMBLING OF THE CLUTCH

Remove the circlip and separate the 1st and 2nd

Dismantle both clutches. The spring is removed

In this manner, brake strips are released, and all

Press pins out of shoes and check brake strips,

Fix the main pin of the clutch spring fitting tool

To assemble the 2nd speed clutch, turn the device

speed clutches (fig 37)

three shoes can be removed (fig 39)

with a screwdriver (fig 38)

spring inside of shoes and 2nd speed clutch gear. At first, assemble the 1

speed clutch as reversed order of dismantling. Particular care should be taken of brake shoes; they must protect each other from falling out (fig 40)

with the thinner part facing upwards. The spring joint must be placed in the middle of one shoe. With the lever of the device, insert the spring into the shoes groove (fig 41)

over. The clutch hub with gear must be placed in the way the gear is on the bottom and the gap between the two shoes fits with the pin. The manner of mounting the spring is the same as mentioned before for the 1

speed clutch (fig 42)

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Classic Cycles Technical Resources

Dismantling of the needle clutch is necessary only in case of replacement. A new needle clutch is pressed with special tool “roller clutch installer.” The needle clutch must be pushed with the signed side towards the center of the clutch drum, or else it may operate in the reverse direction (fig 43)

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DISMANTLING, CHECKING, AND ASSEMBLING OF THE COUNTERSHAFT

Fix the countershaft into a vice and unscrew the nut with a 19mm wrench (fig 44)

Remove the circlip at the shaft’s toothing (fig 46)

Remove the 2nd speed gear (fig 45)

Unfasten the wire spring and separate a small chain sprocket with roller cage (fig 47)

Remove the 1 out (fig 48)

speed gear and shake the rollers

If troubles appear in the self-locking clutch, consisting of rollers with 1

speed gear hub, possible damage of the countershaft may be repaired by grinding the bearing surface for

0.1mm at the most. When most rollers make small hollows in the hub, the latter can be honed. If hollows are rather large, the gear should be replaced.

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Classic Cycles Technical Resources

Reassemble the countershaft in reverse order of

dismantling.

Put the chain sprocket in with cage so that the

Use of grease is not suggested because it may impede the function of the self-locking clutch.

beginning of the wire spring is turned 90 degrees left-ward from the spring nose (fig 49). Lock the wire spring to riveted nose on the 1

speed gear

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CHECKING PEDAL SHAFT (kickstart) AND TRANSMISSION CHAIN

If it is necessary to replace the chain sprocket or claw collar on the pedal shaft or kick start, first rmove the protective ring (fig 50/1) and the spring washer (fig 50/2). During assembly, take care that the thinner part of the collar is mounted forward or else the brake spring will slide across the chain sprocket. Check the chain for overtensioning or other damage. In case of damage, the needle bearings in the main shaft should be replaced with a new complete main shaft (fig 51)

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Classic Cycles Technical Resources

CARBURETOR CHECKING

Dismantle the carburetor into component parts (fig 52 Encarwi or 52a Dellorto). Clean the parts with carb cleaner and blow them out with compressed air. Check the parts. In case of wear throttle slide or leakage of float, replace with a new one. When reassembling the carburetor, take care that the float needle fits the float chamber cover. Slightly oil the air filter with light oil.

FIGURE 52 – ENCARWI CARBURETOR

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FIGURE 52a – DELLORTO CARBURETOR

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Classic Cycles Technical Resources

REASSEMBLING THE ENGINE

When reassembling the engine, replace all seals

With the crankshaft bearings fitting tool, press the

Insert the crankshaft into the LH half of the

Place the mainshaft and a washer on the

Join the right crankcase with the left one, acting as

With the crankshaft bearings fitting tool, insert

and gaskets. All parts of the engine should be thoroughly cleaned and lightly oiled. All gaskets should be given a light coat of grease to insure better fit and seal.

crankcase using the splitter. Through the splitter, screw the device on the crankshaft. With an 11mm and a 24mm wrench, place the crankshaft in the crankcase (fit 54)

crankshaft ball bearings into both crankcase halves (fig 53)

mainshaft needle bearing. Insert the fork between the two halves of the crankshaft (fig 55)

follows: (1) Press the two crankcases by hand and then lightly tap them together with a mallet (2) Insert the 6 screws in the inner holes and 2 in the outer holes. Slowly tighten the screws (fig 56)

both crankshaft seal rings.

WARNING: The LH carter seal ring is facing towards the connecting rod, while the RH side is opposite.

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Check that the crankshaft turns freely. Insert pedal

shaft or kick shaft together with countershaft and

The claw collar brake spring must seat in the

chain (fig 57)

recess in the RH half of the crankcase. Place washer 209.005 and bush 209.072 on the crankshaft (fig 58)

Incorporate the clutch drum with mounted 2nd speed clutch (fig 59)

Incorporate 1st speed clutch and protective washer. With the flywheel and clutch holding tool, lock the nut with a 19mm wrench. Torque to 25Nm. Clearance between shoes and clutch drum rim is approx. 0.4 mm. Axial clearance of the clutch drum is from 0.1 mm to 0.3 mm by means of inserting the adjusting thrust washer of 0.3 mm or

0.5mm under the clutch (fig 61)

Handle the roller clutch carefully and if it is necessary, turn the drum only counterclockwise (direction of free rotation). Place the trust washer under the clutch (fig 60)

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Classic Cycles Technical Resources

Before securing the nut with washer, it is

necessary to check the proper function of the

sprocket with the flywheel and clutch holding tool.

assembly. Firmly hold the 2 with the left hand and the clutch drum with the right hand. When the clutch drum rotates counterclockwise, both clutches idle. When it rotates clockwise, the motion is transmitted to the crankshaft (fig 62)

speed driven gear

Fit the gasket and cover and tighten 7 screws with torque of 10Nm (fig 63)

Make sure the piston rings are installed properly by aligning them with the stationary pins mounted in the ring grooves of the piston. Compress the piston rings and mount oiled cylinder (fig 65)

Turn the engine on the stand 90 degrees. Clean residue of crankcase gasket. Mount the piston so that the arrow sign on the top of the piston is facing the exhaust side of the cylinder (fig 64)

Mount the cylinder head, washers, and nuts. Tighten them in an X pattern, torque to 12 Nm. Turn the engine so that the magneto flywheel side is on top. Install the stator base plate. If necessary, slightly oil the felt inset piece of the base plate. When mounting the magneto flywheel, take care when positioning it. The groove on the flywheel hub and the woodruff key on the crankshaft must coincide. Fit the washer and nut, lock the flywheel with the flywheel and clutch holding tool, and tighten the nut to a torque of 30 Nm.

Place the distance bush, chain sprocket, and protective washer on the main shaft and tighten the nut with a 30 mm wrench. Lock the chain

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ADJUSTING THE CONTATCT GAP AND IGNITION ADVANCE

These two operations are interrelated and proceed as follows.

-Screw the dial gauge support tool and the dial gauge into the spark plug hole.

-By rotating the flywheel, put the piston at TDC and set the dial gauge to zero.

-The breaker points are fully open at TDC. Check and if necessary, reset the gap between 0.35 and 0.45 mm (fig 66)

-Rotate the flywheel in the clockwise direction until the breaker points connect. With a test light, buzzer or Ohm meter, determine when a connection is made. The testing device must be connected to the short circuit (black) wire and to the ground of the engine (fig 67)

-At the moment of connection of the points, the test battery light will glow brightly, the buzzer will change the acoustic frequency, or the Ohm meter will show approximately zero Ohms. On the dial gauge, read off the value in mm of the ignition advance which must be from 1.8 to 2 mm BTDC.

-In case of excessive advance, the stator base plate should be rotated in the direction of engine rotation (see arrow on flywheel). In case of insufficient advance, turn the plate in the opposite direction.

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Classic Cycles Technical Resources

OIL PUMP

Note: When fitting the magneto cover on oil pump

cut off, which may lead to breakdown of the unit.

After assembly or repair of models with oil pump, you must keep to the following instructions

The pump is connected to the magneto nut on the crankshaft by a special clutch (fig 68)

Pour approximately 1 liter gas mixture in the ratio of 50:1 (2% oil) into the fuel tank and start the engine. Let the engine run for about 5 minutes so as to make the oil pump push oil into the engine.

Fill up the tank with regular gas.

Unscrew the bleed screw on the oil pump and wait until oil from the tank under the seat flows to the pump. The screw is then screwed on (fig 69)

Ensure that the oil level in the oil tank does not fall under the marking MIN (fig 70). Pay special attention to the routing of the oil lines to and from the oil pump. If the outflow line is crimped, oil will not reach the carburetor, causing engine damage.

models, make sure the oil pump seat axis lines up with the crankshaft axis. Use the centering pin attached to the magneto cover (fig 71) for this purpose. When the center has been found, push the cover by hand onto the crankcase (which is made possible by the spring in the centering tool) and fix the cover by screwing it down.

Major deviations from the center result in the clutch damage, and this, in turn, causes the oil pump drive stoppage. The lubrication of the cylinder, piston, and crankshaft of this unit is thus

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MAGNETO SETTINGS AND ELECTRICAL EQUIPMENT

The voltage regulator should be checked when bulbs blow frequently. During the check, the engine should be operating and the lights switched off-on, alternatively. The voltage should always read 12+/-

0.5 V. Before replacing the regulator, make sure the improper operation is not due to bad grounds.

The direction indicator relay should be checked within the wiring system. Previously check the bulbs and direction indicators switch.

The STOP switch should be checked by a pilot bulb or OHM-meter. When replacing the switch, make sure the new one is identical to the replaced one wince there are two types of STOP switches (those that are switched on in neutral position, and those that are switched off in neutral position)

Electric wiring and combination switches are checked according to the wiring diagram. Check the magneto components both within the wiring system and separately.

The flywheel should be checked by visual inspection for mechanical damage and proper cone fit. Check deflection by help of the crankshaft. The maximum permissible axial deflection amounts to 0.1 mm and radial deflection to 0.3 mm.

To check the capacitor it should be separated from other electrical components of the magneto. Check the capacitor capacitance by means of a capacitance meter and the ability of the capacitor to retain an electric charge.

NOTE: Caution is recommended in handling the non-insulated parts since there is a possibility of an electric shock. The capacitor should, therefore, be discharged by connecting the two contacts.

Contact breaker: check the contacts and the cam nose for wear. Insert insulating mass between the two breaker contacts and by an OHM-meter make sure the parts are electrically disconnected (there exists a possibility of uncture on the bearing bush or fixing bolt insulation)

The ignition coil both external and internal can only be checked if a special mototester is available. The checking procedure is laid down by the manufacturer of this device. If this is not available, a possible fault can be established by replacing a truly good sample coil for the existing coil.

The lighting coil should be checked with engine in operation (2000-3000 RPM). To check the coil, use a voltmeter and an approximate bulb of the same rated power (W) as the magneto.

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