Cylinder and piston
The SST cylinder has bore and stroke mm 56x50. Check the ovalization and the presence of grooves on the inside walls. The cylinder is chromed, bore isn't grindable. It can be buffed by a qualified mechanical workshop. There are five piston sizes with diameters ranging from 5595 to 5599 hundredths of a millimeter. The cylinder-piston tolerance is +/-5 hundredths of a millimeter. It is appropriate to combine the cylinder with its respective piston. The piston has one towards mounting which is indicated by the arrow printed on top and the same must be facing forward.
Spark plug and air filter
Replace air filter and spark plug: during the exercise must be replaced every 3000 and every 5000 km. Screw the spark plug not too enough to avoid breakage of head threads. For correct spark plug type see following references: Champion N3, Magneti Marelli CW7LP; NGK B8ES; BOSCH W3CC. Check that the cover (pipette) not be oxidised inside. Unscrew the contact within the pipette and remove the power cord. Cut the piece of oxidized cable or replace it if necessary. Air filter type is "tall type" for models built until 1983.

Bearings and oil seals

In case of engine opening you should replace all bench bearings, bushings and oil seals. Before disassembling engine you may should check the bearings worn. Shake the axis on which is mounted the pinion, or shake the axis on which clutch is mounted: in both cases there should be no play on the axis. A spill of oil engine from countershaft, pinion side, is index of broken or heavily worn bearings. This situation can lead a gear box block, because misalignment of primary and secondary shafts. Clean the inside of the engine block by oil sludge and impurity deposited at the bottom. The engine can be assembled using a special motor sealant for formation of the seals. Bearing sizes are follows: bench left 6204/C3; bench right 6204/C4; bench right outer 6203/C3. Size of oil seals are follows: bench left 20x35x7/7.5; bench right 17x40x7/7.7; countershaft: 25x37x5.

Crankshaft and connecting rod

One of the possible faults is caused by the fault of the needle bearing located at the foot of connecting rod (more rarely at the head). A loud rattling noise can be felt by running engine. To separate the crankshaft from the connecting rod you will need to use an hydraulic press. Connecting rod, pins and in some case, the piston, must be replaced.


Pictures: (1) cylinder, piston, pin, (2) cylinder, (3) crankshaft with connecting rod, (4) primary and secondary shafts, (5) elements of the gear, (6) clutch springs and cups, (7) hub and clutch cover, (8) clutch disks, (9) oil pumps: long type and short type, (10) anti-vibration rubber, (11) clutch bell, (12) carters.


1   2   3   4

5   6   7   8

9   10  11  12



The carburetor should be cleaned and adjusted. General inspection: bring the bike on the center stand. Start the engine and warm it up, after having done it idle for a few seconds, open the throttle suddenly. The engine must respond immediately. If the engine is turned off or choking is necessary to clean the carburetor, inside and out, and replace all gaskets, sprinklers, and needle valve (the latter are subject to wear). In particular: needle V16, summer jet 82, jet skiing 85 (NB: 90 jet models with electronic ignition motoplat), idle jet 50 of the series (in the case of low resistance can be mounted above a jet, not later than 60). To adjust the minimum turn the screw top (large) to increase the speed screw, unscrew to decrease. The air-fuel mixture is controlled by the lower screw (small): tighten the screw all the way, loosely. Then unscrew making them take a lap and three quarters.


An important control is about carburation that you make when looking at the color of the electrodes of the spark.

If the color is light brown electrodes (hazelnut) carburation is OK.

If the color is white, the mixture is too poor (too much air, overheating, galling).

If the color is black, the mixture is too rich (too much gasoline, electrode plumb, risk of stop and no restart).



If possible, use synthetic 2T oil like Castrol TTS or MOTUL 710. The bike has no oil gauge so you should periodically check the level through the transparent plastic tank, located under the fuel tank. The autonomy of one kg of oil is 700/800 km. Lubrication is left to a pump type Mikuni. With the engine idling, check that the point marked on the butterfly coincides with the mark stamped on it. If so, turn the adjusting screw.

NOTE: the older models are fitted with a "long type" pump (for example, HD-Cagiva models), while the newer models are fitted with a "short type" pump (9). The two pumps are not interchangeable because the casings that house them have the screw holes in different position. If you really want to trade exchange also need housing.

WARNING! Pumps "long" and "short" have the inlet/outlet lines inverted. The "long type" pump (13) is fed into the nozzle at the top and emits oil at lower nozzle. The "short type" pump (14) is fed into the lower nozzle and emits oil at the higher nozzle.


13     14



If the battery is old it must be replaced (12 Volt 5/7Ah), the electrolyte level should be checked once a month. Do not reverse the battery poles. Do not start the bike with the battery disconnected from electrical circuit! Always remove the battery during long stops, such as during winter months.


Until V.I.N. 6F-108815 the bike was equipped with a DANSI wiring system (contact breaker, then abandoned and replaced by electronic MOTOPLAT). The flywheels mounted on older models were poor of quality (in particular they were subject to breaking of the magnets). The most recent series of DANSI flywheels is the n. 102222. It can be removed using a puller tool with internal thread 30 mm, pitch 1.5 mm. MOTOPLAT flywheels can be removed using a puller tool with external thread 26 mm, pitch 1.5 mm.

Contact breaker DANSI
Older models were equipped with a DANSI electrical system, contact breaker type. Check the wear of the contacts and replace them if necessary. Replace the condenser also. The capacitors have a life cycle and are destined to end. The typical failure typically occurs when engine is warm: more heat and the bike has more power problems, until to stop. Usually the bike starts again only when engine is cold. To replace the capacitor will be necessary to disconnect the electrical cables green and black and then weld them to the new capacitor. The maximum aperture size of contacts is 0.40 mm. The condenser has capacity of
μF 0,29. 

To recognize the "contact breaker" model, you may look at the dashboard where there are mounted three lights: red "gen", orange "turn", blue "high beam". If while driving the red light stays ON, it means that the controller is not charging the battery. In many cases this is due to blown fuses or at the fuse holder poles that eventually being oxidized. Replace them (16 amperes). If the light stays ON without flashing orange means that the flasher is broken. The bike is fitted with a Lucas flasher, but also works well with a compatible 21W flasher.

Electronic ignition MOTOPLAT

Later models were equipped whit electronic ignition system (do not confuse with "electric start!") provided by the spanish Motoplat. On the dashboard, lights are green "lights", orange "turn",  blue "high beam". The SST 250/350 models are equipped with the same lights with the variant "neutral", green. MOTOPLAT version mount fuses 15 ampere and an "electronic ignition" label is attached on the left crankcase.


Pictures: (15) complete switch, (16) electrical system for contact breaker Dansi.


15  16


Below: (17) ZIP file containg wiring diagrams for electronic ignition Motoplat, contact breaker Dansi and Harley-Davidson.





Contact breaker engines DANSI (flywheel and mechanical switch) (18-19)

a) Disconnect the spark plug and remove left crankcase side cover. Turn the rotor a small amount, untill contact breaker points are opened at the maximum amount (you should see the contacts through the control window). Insert a feeler gauge (mm 0,40) between the contacts and check there is no play in either way. In other words, the gauge must fit perfectly between contacts. In this case no adjustment is required.

If adjusteent is required, then loosen the screw that holds the fixed contact for a small amount. Insert a screwdriver into the control window and with it move in + or - the fixed contact until reaching the maximum aperture size of mm 0,40. Thighten the screw of fixed contact, turn rotor and check the gap again to be sure all is ok.

b) After adjusting the contacts must be checked the ignition timing. Remove the seat and attach to the coil poles a light bulb. Slowly turn the flywheel counterclockwise until the notch "A" engraved on it is close to the notch engraved on left crankcase. Now turn the flywheel slowly until the notches match perfectly. The bulb connected to the coil should light up at this moment. Neither before nor after.

If the bulb lights up before, the ignition time is to early; If the bulb lights up after, the ignition timing is delayed. Adjustment is necessary.

c) Adjustment instructions: dismount the flywheel and loosen the three small screws that lock the stator to the engine, that be enough to afford, forcing slightly, the rotation of the stator. Mount the flywheel does not lock it. Spin the flywheel counterclockwise and verify the ignition timing as above. If the bulb goes lights up before that the notch "A" doesn't match with the notch engraved on crankcase engine, (ignition too early), you will have to rotate the stator counterclockwise, giving him small shots with a screwdriver through the control window of flywheel. Conversely, if the bulb lights up after (ignition timing delayed) you will have to rotate the stator clockwise. Reached and controlled the exact point of ignition, carefully remove the flywheel without moving the stator. Tighten the three screws of stator, reassemble the flywheel and lock it.


18  Click per ingrandire19


Below: (20) ZIP file containing wiring scheme for stator Dansi 101511 and 102222.





Electronic ignition engines MOTOPLAT (21-22)

For inspecting flywheel alternator remove left crankcase cover. To check the ignition timing proceed as follows.

a) Assemble the stator plat on engin without fully tighten it.

b) Assemble the rotor and insert a pivot (2 mm diameter) in the hole; turn the rotor until the pivot come in the stator plate hole.

c) Turn until the rotor mark is in line with the crankcase reference mark.

d) Remove the rotor, lock the statoric plate; then assemble and lock the rotor.

21  22


The transmission group (sprocket, pinion, chain) are subject to normal wear and tear of exercise. A worn chain, during the march, undergo deformations with variable speed that brought in contact with some parts of the chassis, creating a noisy burst effect. The phenomenon is felt particularly in fifth gear. The new chain must adhere to the sprocket, without any swing. A worn chain can derail while driving. Tighten the chain, without bringing it live, using the chain tensioner to the rear wheel nut. The free-swinging vertical chain should be about 2 cm. Periodically lubricate the group catena. The group pinion, sprocket and chain must be replaced every 10,000 km, whereas at 5,000 km a change must be made of single chain. The pinion has 14 teeth, while the sprocket has 62 teeth (both models: integral and spokes wheel). Up to the chassis number 6F-91938 the integral wheel was supplied with a sprocket of 59 teeth.

You can purchase the kit provided by PBR (only through authorized dealers).

Kit PBR for spoke wheels = EK205 (pinion 14 - sprocket 62)

Kit PBR for integral wheels = EK267 (pinion 14 - sprocket 62)


Below: (23) sprocket 62 teeth and pinion 14 teeth.


The bike mount a Lafranconi muffler serie (DGM 30229S). The muffler is plated with connections to 3 springs and support bracket. At the time, there were also other expansion mufflers produced by third parties (the famous Giannelli, Figaroli, Proma). The expansion muffler requires the replacement of maximum
jet (largest 5-7 points) and a greater ignition timing. The expansion provide higher performance than the original, even if very quickly presents the inconvenience of silencer obstruction.


Pictures: (24) Lafranconi muffler sierie; (25) racing muffler Giannelli.


24   25



Lafranconi is a muffler type with diaphragms. 

One of the drawbacks of this is that of the muffler clogged. If running the bike "stuttering" and fails to pick up speed, most likely the muffler is clogged. The unburnt oils form with time carbon deposits which are deposited on the conduits. Sometimes escape from the muffler black solid debris. Regular cleaning prevents this phenomenon.
The muffler of Lafranconi series has a removable
spak arrestor. To repeat the process must first obtain a rugged hook and hook the exhaust pipe from the inside. With the help of an extractor it will be possible to extract the spark arrestor without ruin the terminal part of the muffler.

Pictures: (26) Step of spark arrestor removal; (27) spark arrestor pulled out, the image shows the position of the hook.


26   27


Internal cleaning

Once you extracted the spark arrestor will be possible to proceed to the cleansing of the muffler with use of sodium hydroxide (NaOH), commonly known as caustic soda. Caustic soda is a strong base, hygroscopic and in contact with water produces an exothermic reaction.
CAUTION: caustic soda is
a dangerous chemical mixture; Avoid any contact with eyes and skin because it can bring severe burns. Caustic soda should be handled with care, using appropriate protections: nitrile gloves, mask and goggles.
To prepare the solution
will be necessary about 50 grams of caustic soda every 1 liter of water (50 g / liter). This proportion will produce a pH 14 solution. Pour the crystals of sodium hydroxide in a flask and pour hot water. Mix the solution with an iron rod. The crystals begin to melt, the chemical reaction produce a lot of heat.
The cleaning can be
performed using one of these two different systems:
a) pouring caustic soda
directly into the muffler. With this system, it will be necessary about 3 liters of solution.
b) pouring the caustic soda inside a container, usually a
PVC tube placed in vertical position (height cm 100, diameter cm 10), which houses the muffler. The tube will have a lower end cap, sealed with Teflon. With this system, it will be necessary about 6 liters of solution.
ave the solution from 2 hours to 24 hours. At the end it will be necessary to empty the muffler from the solution and rinse the inside with water. Will come from the muffler debris and fouling. If necessary, repeat the operation several times.

Pictures: (28) flask containing sodium hydroxide solution; (29-30) 1st method with filled muffler, correct position of the muffler; (31-32) 2nd method with vertical tube, muffler filling.


28   29   30  31  32



The rupture of the rope is a major cause of the failure of the speedometer. The rope breaks generally to the wheel. More rarely may have broken the beveled gear odometer that postponement must be periodically greased. It is recommended not to tighten the screw ever strong national odometer because in future could prove unable to unlock it.

The SST 125 tachometer is electronic, having free field from 0 to 7000 rpm, a threshold of attention (yellow) from 7,000 to 7,500 rpm and an area of overload (red) from 7,500 to 10,000 rpm. NOTE: the counter of the models with "power pins DANSI" and model with "electronic ignition MOTOPLAT", although the same outside and inside, are not compatible. The difference is that the calibration has been set by the factory at the time of production. To recognize with which model the tachometer is compatible is necessary to observe the plate attached on the back: the parameter 20000 is compatible with the DANSI model, the parameter 30000 is compatible with the MOTOPLAT model.



Check the wear of the pads and the state of the brake disk. The disc is 260 mm with 6 holes for the screws and a thickness of 4.5 mm. The central hole has a diameter of mm 80 for the model with integral wheels and a diameter of mm 60 for the model with spoke wheels. The brake caliper is a Brembo P28N-RH, with a mm 28 piston and spaced of the fork coupling by mm 88. Older models mounted a Brembo P04 universal caliper, with a mm 32 piston. Pad and piston are welded as one piece. To replace the brake fluid and do the complete cleaning, proceed as follows.

a) Slightly loosen the bleed valve on the caliper.

b) Attach a rubber tube on the end of the valve and make it end in a container of raccolta.

c) Spill the old liquid by repeatedly pressing on the brake lever, until the empty impianto.

d) Loosen the inlet pipe on the caliper with a 14 wrench.

e) Loosen the screws holding the caliper half. The screws are very hard and it's easy to damage them. The Kit Brembo contains new screws.

f) Finally remove the caliper from the fork and disassemble it by removing the bolts loosened in step "e".

g) Remove the cylinders on both sides of the caliper half. To do this blow compressed air in the ducts.

h) Clean communicating vessels of any debris. Use Kit Brembo package to change all rubber seals and grease the cylinders.

i) Fit the caliper with new screws taken from the kit.

j) Install the caliper on the fork by tightening the screws. Let loose only the purge valve with a tube connected as point "b".

k) Fill the system by pouring new oil into the bowl located at the righ side of handlebar, repeatedly pumping on brake lever.

l) When oil comes out of the tube previously connected, you must tighten the bleed valve to close the circuit.

m) Pour more oil into the bowl and act on the lever until the system enter into pressure.

Use only DOT 4 brake oil.


Below: (33) caliper Brembo P04, (34) caliper Brembo P28N, (35) pad mm 51,5 x 35,2 x 6,3 maximum, (36) disassembled caliper

33 34  35 36

Always change tires during the restoration. The old tires are subject to cracking and breaking along the furrows. The old tires tend to stiffen and lose grip on the road. Replace bearings too. The bearings are broken when there is clearance between the wheel and the axis on which it is mounted.

The model with spokes have the following characteristics: front rim size 19 x 1.60 and rear rim size 18 x 1.85. The spokes are of three different types: those for the front wheel are of a single type and have a diameter of 3.5 mm, while those of the rear wheel are of two different types (internals and externals to the hub) and they have a diameter of 3 mm.

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