Piaggio Vespa WORKSHOP MSS Fly 50 4T Workshop Manual

WORKSHOP MANUAL

633212

MSS Fly 50 4T

WORKSHOP

MANUAL

MSS Fly 50 4T

The descriptions and illustrations given in this publication are not binding. While the basic specifications
as described and illustrated in this booklet remain unchanged, PIAGGIO-GILERA reserves the right, at

any time and without being required to update this publication beforehand, to make any changes to

components, parts or accessories, which it considers necessary to improve the product or which are

required for manufacturing or construction reasons.

Not all versions shown in this publication are available in all countries. The availability of single models

should be checked at the official Piaggio sales network.

"© Copyright 2007 - PIAGGIO & C. S.p.A. Pontedera. All rights reserved. Reproduction of this publication

in whole or in part is prohibited."

PIAGGIO & C. S.p.A. - After sales

V.le Rinaldo Piaggio, 23 - 56025 PONTEDERA (Pi)

WORKSHOP MANUAL

MSS Fly 50 4T

This workshop manual has been drawn up by Piaggio & C. Spa to be used by the workshops of Piaggio­Gilera dealers. This manual is addressed to Piaggio service mechanics who are supposed to have a
basic knowledge of mechanics principles and of vehicle fixing techniques and procedures. Any important
changes made to the vehicles or to specific fixing operations will be promptly reported by updates to this
manual. Nevertheless, no fixing work can be satisfactory if the necessary equipment and tools are
unavailable. It is therefore advisable to read the sections of this manual relating to specific tools, along
with the specific tool catalogue.

N.B. Provides key information to make the procedure easier to understand and carry out.

CAUTION Refers to specific procedures to carry out for preventing damages to the vehicle.

WARNING Refers to specific procedures to carry out to prevent injuries to the repairer.

Personal safety Failure to completely observe these instructions will result in serious risk of personal

injury.

Safeguarding the environment Sections marked with this symbol indicate the correct use of the vehicle
to prevent damaging the environment.

Vehicle intactness The incomplete or non-observance of these regulations leads to the risk of serious
damage to the vehicle and sometimes even the invalidity of the guarantee.

INDEX OF TOPICS

CHARACTERISTICS CHAR

TOOLING TOOL

MAINTENANCE MAIN

TROUBLESHOOTING TROUBL

ELECTRICAL SYSTEM ELE SYS

ENGINE FROM VEHICLE ENG VE

ENGINE ENG

SUSPENSIONS SUSP

BRAKING SYSTEM BRAK SYS

CHASSIS CHAS

PRE-DELIVERY PRE DE

TIME TIME

INDEX OF TOPICS

CHARACTERISTICS CHAR

MSS Fly 50 4T Characteristics

Rules

This section describes general safety rules for any maintenance operations performed on the vehicle.

Safety rules

- If work can only be done on the vehicle with the engine running, make sure that the premises are well­ventilated, using special extractors if necessary; never let the engine run in an enclosed area. Exhaust
fumes are toxic.

- The battery electrolyte contains sulphuric acid. Protect your eyes, clothes and skin. Sulphuric acid is
highly corrosive; in the event of contact with your eyes or skin, rinse thoroughly with abundant water
and seek immediate medical attention.

- The battery produces hydrogen, a gas that can be highly explosive. Do not smoke and avoid sparks
or flames near the battery, especially when charging it.

- Fuel is highly flammable and it can be explosive given some conditions. Do not smoke in the working
area, and avoid open flames or sparks.

- Clean the brake pads in a well-ventilated area, directing the jet of compressed air in such a way that
you do not breathe in the dust produced by the wear of the friction material. Even though the latter
contains no asbestos, inhaling dust is harmful.

Maintenance rules

- Use original PIAGGIO spare parts and lubricants recommended by the Manufacturer. Non-original or
non-conforming spares may damage the vehicle.

- Use only the appropriate tools designed for this vehicle.

- Always use new gaskets, sealing rings and split pins upon refitting.

- After removal, clean the components using non-flammable or low flash-point solvents. Lubricate all
the work surfaces, except tapered couplings, before refitting these parts.

- After refitting, make sure that all the components have been installed correctly and work properly.

- For removal, overhaul and refit operations use only tools with metric measures. Metric bolts, nuts and
screws are not interchangeable with coupling members with English measurement. Using unsuitable
coupling members and tools may damage the vehicle.

- When carrying out maintenance operations on the vehicle that involve the electrical system, make
sure the electric connections have been made properly, particularly the ground and battery connections.

CHAR - 7

Characteristics MSS Fly 50 4T

Vehicle identification

VEHICLE IDENTIFICATION

Specification Desc./Quantity

Engine prefix C442M ÷ 1001

Chassis prefix ZAPM44200 ÷ 1001

Dimensions and mass

Specification

Length 1,880

Maximum height 1150 mm

Seat height 785

Width 735

Wheelbase 1,340

Kerb weight 105 kg

WEIGHT AND DIMENSIONS

Desc./Quantity

CHAR - 8

MSS Fly 50 4T Characteristics

Engine

ENGINE

Specification

Engine type Single cylinder 4-stroke Piaggio Hi-PER4

Bore x stroke 39 X 41.8 mm

Cubic capacity 49.93 cm³

Compression ratio 11.5 :1

Timing system single overhead camshaft, driven by a chain to the left side.

Depression carburettor KEIHN CVK 18

CO adjustment 3,2% ± 0,5

Engine idle 1900 ÷ 2000 rpm.

Air filter Sponge, soaked in a mixture (50% SELENIA Air Filter Oil and

Starting system electric starter/kick-starter

Lubrication Engine lubrication with lobe pump (inside the crankcase),

chain-driven, and double filter: mesh and centrifugal.

Fuel supply Gravity feed, with unleaded petrol (with a minimum octane rat-

Max. power (crankshaft) 2,5 KW (3,4 CV) at 6500 rpm.

Cooling system forced coolant circulation system

Valve clearance intake: 0.10 mm discharge: 0.15 mm

Desc./Quantity

50% unleaded petrol).

ing of 95) with carburettor.

CHAR - 9

Characteristics MSS Fly 50 4T

Transmission

TRANSMISSION

Specification Desc./Quantity

Transmission With automatic expandable pulley variator, torque server, V-

belt, automatic clutch, gear reduction unit.

Capacities

CAPACITY

Specification Desc./Quantity

Rear hub oil Quantity: approx. 85 cc

Engine oil Capacity: approx. 850 cm³

Fuel tank capacity approx. 7.2 litres (of which 1.5 l is reserve)

Electrical system

IMPIANTO ELETTRICO

Specification Desc./Quantity

Type of ignition Capacitive discharge type electronic ignition, with incorporated

Ignition advance variable, with microprocessor (before T.D.C.) 10° at 1800-2000 rpm

Spark plug Champion RG 4 PHP

Alternative spark plug DENSO U24ESR-NB

Battery 12V-9Ah

Fuse 10A

Generator single-phase alternating current

high voltage coil

26° at 5000-6000 rpm

Champion RG 4 HC

Frame and suspensions

FRAME AND SUSPENSION

Specification

Type of chassis Welded tubular steel chassis with stamped sheet reinforce-

Front suspension Telescopic mechanical fork, 76-mm travel.
Rear suspension Single hydraulic shock absorber, 72.5-mm travel

Desc./Quantity

ments.

Brakes

CHAR - 10

BRAKES

Specification

Front brake Disc brake (Ø 200 mm) with hydraulic control (lever on the right

end of the handlebar) and floating calliper.

Rear brake drum brake (Ø 140 mm) with mechanical linkage.(l.h. brake

Desc./Quantity

lever).

MSS Fly 50 4T Characteristics

Wheels and tyres

WHEELS AND TYRES

Specification Desc./Quantity

Front wheel rim Die-cast aluminium alloy 3.50 x 12"

Front tyre Tubeless, 120/70-12"

Rear wheel rim Die-cast aluminium alloy: 3.00"x12"

Rear tyre Tubeless, 120/70 - 12"
Front tyre pressure 1.8 bar
Rear tyre pressure 2 bar

Rear wheel pressure (rider and passenger): 2.3 bar

N.B.

CHECK AND ADJUST TYRE PRESSURE WITH TYRES AT AMBIENT TEMPERATURE. ADJUST
PRESSURE ACCORDING TO THE WEIGHT OF RIDER AND ACCESSORIES.

Secondary air

•

The SAS (Secondary air housing) op­erating principle for 50 4T engines is
similar to that for 50 2T engines; the
only difference lies in how air is sucked
in the external and the external side of
the transmission compartment.

•

Air is taken in along tube «A» (to the
cylinder side) and, after been cleaned
through the filter «B», gets into the reed
valve «C» to be directed towards the
head through a flexible pipe and then a
rigid one «D» flanged to the head. In
this way, the air reaches the discharge
pipe to increase the amount of oxygen
in the unburned gases before the cat­alytic converter, thus helping a better
reaction of this device.

Carburettor

50cc Version

CHAR - 11

Characteristics MSS Fly 50 4T

Kehin

KEHIN CARBURETTOR

Specification Desc./Quantity

Type CVK 18

Throttle valve diameter: Ø 18,5

Choke diameter Ø 17

Marking on body: Z61B

Maximum thrust 75

Maximum air thrust (on body) Ø1,1

Marking on conical needle: NGBA

Throttle spring: 100 ÷ 159 gr
Minimum thrust 35

Idle air jet (on body): Ø 1,4

Initial opening - idle mixture screw: 1 3/4

Starter air nozzle (on the body): Ø 1.5

Starter jet 40

Choke needle travel: 11,5 mm

Tightening Torques

FRONT BRAKE

Name

Brake fluid pump - hose fitting 16 ÷20 Nm

Brake fluid pipe-calliper fitting 19 ÷ 24

Calliper tightening screw 24 ÷ 27

Disc tightening screw 8 ÷ 10

Oil bleed screw 7 ÷ 10

Torque in Nm

FRONT SUSPENSION

Name

Lower fork fixing screw 15 ÷ 20

Front wheel axle nut 45 - 50

Torque in Nm

STEERING ASSEMBLY

Name

Upper steering ring nut 35 ÷ 40
Steering lower ring nut 8 ÷ 10
Handlebar fixing screw 50 ÷ 55

Torque in Nm

CHASSIS

Name

Swinging arm - engine pin* 33 ÷ 41

Frame/swing-arm bolt (*) 64÷72

Shock absorber - chassis nut (*) 20 to 25 Nm

shock absorber - engine pin (*) 33 to 41 N·m

Rear wheel axle (*) 104÷126 N·m

Centre-stand mounting bracket bolt 25÷30 N·m

Centre-stand mounting bracket screw 20÷25 N·m

Side stand fixing screw 12 ÷ 20

Side stand bracket fixing screw 15 ÷ 20

Torque in Nm

Overhaul data

Assembly clearances

CHAR - 12

MSS Fly 50 4T Characteristics

Cylinder - piston assy.

CONNECTION PISTON AND CYLINDER

Name

Cylinder (with asso pis-

ton/right way)

Cylinder (with shiram

piston)

Cylinder (with asso pis-

ton/right way)

Cylinder (with shiram

piston)

Asso piston/right way

(with asso cylinder/right

way)
Asso piston/right way
(with shiram cylinder)

Shiram piston (with as-

so cylinder/right way)

Shiram piston (with shir-

am cylinder)
Cylinder 1st oversize A1 39.193 ÷ 39.200 39.154 ÷ 39.161 0.032 ÷ 0.046
Cylinder 1st oversize B1 39.200 ÷ 39.207 39.161 ÷ 39.168 0.032 ÷ 0.046

Piston 1st oversize C1 39.207 ÷ 39.214 39.168 ÷ 39.175 0.032 ÷ 0.046

Piston 1st oversize D1 39.214 ÷ 39.221 39.175 ÷ 39.182 0.032 ÷ 0.046
Cylinder 2nd oversize A2 39.393 ÷ 39.400 39.354 ÷ 39.361 0.032 ÷ 0.046
Cylinder 2nd oversize B2 39.400 ÷ 39.407 39.361 ÷ 39.368 0.032 ÷ 0.046

Piston 2nd oversize C2 39.407 ÷ 39.414 39.368 ÷ 39.375 0.032 ÷ 0.046

Piston 2nd oversize D2 39.414 ÷ 39.421 39.375 ÷ 39.382 0.032 ÷ 0.046
Cylinder 3rd oversize A3 39.593 ÷ 39.600 39.554 ÷ 39.561 0.032 ÷ 0.046
Cylinder 3rd oversize B3 39.600 ÷ 39.607 39.561 ÷ 39.568 0.032 ÷ 0.046

Piston 3rd oversize C3 39.607 ÷ 39.614 39.568 ÷ 39.575 0.032 ÷ 0.046
Piston 3rd oversize D3 39.614 ÷ 39.621 39.575 ÷ 39.582 0.032 ÷ 0.046

Initials Cylinder Piston Play on fitting

A 38,993 ÷ 39,000 38,954 ÷ 38,961 0.032 ÷ 0.046
A 38,993 ÷ 39,000 38,949 ÷ 38,956 0.037 ÷ 0.051
B 39,000 ÷ 39,007 38,961 ÷ 38,968 0.032 ÷ 0.046
B 39,000 ÷ 39,007 38,956 ÷ 38,966 0.037 ÷ 0.051
C 39,007 ÷ 39,014 38,968 ÷ 38,975 0,032 ÷ 0,046

C 39,007 ÷ 39,014 38,963 ÷ 38,970 0,037 ÷ 0,051
D 39,014 ÷ 39,021 38,975 ÷ 38,982 0,032 ÷ 0,046
D 39,014 ÷ 39,021 38,970 ÷ 38,977 0,037 ÷ 0,051

CHAR - 13

Characteristics MSS Fly 50 4T

Piston rings

SEAL RINGS

Name Description Dimensions Initials Quantity

1st Compression ring 39 x 1 A 0.08 ÷ 0.20

2nd Compression ring 39 x 1 A 0.05 ÷ 0.20

Oil scraper ring 39 x 2 A 0.20 ÷ 0.70

1st Compression ring

1st Oversize

2nd Compression ring

1st Oversize

Oil scraper ring 1st

Oversize

1st Compression ring

2nd Oversize

2nd Compression ring

2nd Oversize

Oil scraper ring 2nd

Oversize

1st Compression ring

3rd Oversize

2nd Compression ring

3rd Oversize

Oil scraper ring 3rd

Oversize

39.2 x 1 A 0.08 ÷ 0.20

39.2 x 1 A 0.05 ÷ 0.20

39.2 x 2 A 0.20 ÷ 0.70

39.4 x 1 A 0.08 ÷ 0.20

39.4 x 1 A 0.05 ÷ 0.20

39.4 x 2 A 0.20 ÷ 0.70

39.6 x 1 A 0.08 ÷ 0.20

39.6 x 1 A 0.05 ÷ 0.20

39.6 x 2 A 0.20 ÷ 0.70

CHAR - 14

MSS Fly 50 4T Characteristics

Crankcase - crankshaft - connecting rod

END PLAY BETWEEN DRIVING SHAFT AND CONNECTING ROD

Name

Half-shaft, transmission

side

Flywheel-side half-shaft 16 +0 -0.005 B

Connecting rod 14.8 +0.05 -0 C

Spacer tool 45.00 / Fits and clearan-

Description Dimensions Initials Quantity

14 +0 -0.005 A

E

ces D = 0.15 ÷ 0.30

Slot packing system

N.B.

MEASUREMENT "A" TO BE TAKEN IS A VALUE OF PISTON RE-ENTRY, IT INDICATES BY HOW
MUCH THE PLANE FORMED BY THE PISTON CROWN FALLS BELOW THE PLANE FORMED BY
THE TOP OF THE CYLINDER. THE FURTHER THE PISTON GETS INSIDE THE CYLINDER, THE
THINNER THE HEAD GASKET TO BE APPLIED SHOULD BE (TO RECOVER THE COMPRESSION
RATIO) AND VICE VERSA.

Characteristic

Shimming system to control the compression ratio

CR: 11.1 ÷ 12.9

PISTON PROTRUSION CHECK

Name

shimming_1 0.05 ÷ 0.25 0.35
shimming_2 0.25 ÷ 0.40 0.25

Measure A Thickness

CHAR - 15

Characteristics MSS Fly 50 4T

Products

Product

AGIP ROTRA 80W-90 rear hub oil SAE 80W/90 Oil that exceeds the re­AGIP CITY HI TEC 4T Oil to lubricate flexible transmissions

AGIP FILTER OIL Oil for air filter sponge Mineral oil with specific additives for in-

AGIP GP 330 Grease (brake control levers, throttle

AGIP CITY HI TEC 4T Engine oil SAE 5W-40, API SL, ACEA A3, JASO MA

AGIP BRAKE 4 Brake fluid FMVSS DOT 4 Synthetic fluid

MONTBLANC MOLYBDENUM

GREASE

AGIP GREASE PV2 Grease for the steering bearings, pin

AGIP GREASE SM 2 Grease for odometer transmission gear

TABLE OF RECOMMENDED PRODUCTS

Description Specifications

quirements of API GL3 specifications

(brakes, throttle control and odometer)

grip)

Grease for driven pulley shaft adjusting
ring and movable driven pulley housing

seats and swinging arm

case

Calcium complex soap-based grease

Grease with Molybdenum disulphide

White anhydrous-calcium based grease

to protect roller bearings; temperature

range between -20 C and +120 C; NLGI

Lithium grease with NLGI 2 molybdenum

disulphide; ISO-L-XBCHB2, DIN

Oil for 4-stroke engines

creased adhesiveness

with NLGI 2; ISO-L-XBCIB2

Synthetic oil

2; ISO-L-XBCIB2.

KF2K-20

CHAR - 16

INDEX OF TOPICS

TOOLING TOOL

Tooling MSS Fly 50 4T

TOOLS

Stores code Description

001330Y Tool for fitting steering seats

001467Y008 Pliers to extract 17 mm ø bearings

001467Y009 Driver for OD 42-mm bearings

004499Y Camshaft bearing extractor

005095Y Engine support

008119Y009 Tube to assemble shafts and axles

TOOL - 18

MSS Fly 50 4T Tooling

Stores code Description

020004Y Punch for removing fifth wheels from

020055Y Wrench for steering tube ring nut

020150Y Air heater support

headstock

020151Y Air heater

020162Y Flywheel extractor

020171Y Punch for Ø 17 mm roller case

TOOL - 19

Tooling MSS Fly 50 4T

Stores code Description

020265Y Bearing fitting base

020288Y Fork to assemble piston on cylinder

020291Y Valve fitting/ removal tool

020306Y Punch for assembling valve sealing rings

020329Y MityVac vacuum-operated pump

TOOL - 20

020330Y Stroboscopic light to check timing

MSS Fly 50 4T Tooling

Stores code Description

020331Y Digital multimeter

020332Y Digital rev counter

020333Y Single battery charger

020334Y Multiple battery charger

TOOL - 21

Tooling MSS Fly 50 4T

Stores code Description

020335Y Magnetic support for dial gauge

020340Y Flywheel and transmission oil seals fitting

020358Y 37x40-mm Adaptor
020359Y 42x47-mm Adaptor

020360Y 52x55-mm Adaptor

punch

TOOL - 22

020362Y 12 mm guide

MSS Fly 50 4T Tooling

Stores code Description

020363Y 20 mm guide

020364Y 25-mm guide

020376Y Adaptor handle

020431Y Valve oil seal extractor

020432Y Tool to fit the start-up sector spring

020439Y 17 mm guide

TOOL - 23

Tooling MSS Fly 50 4T

Stores code Description

020448Y Pin lock fitting tool

020449Y Piston position check support

020450Y Camshaft fitting/removal tool

020452Y Tube for removing and refitting the driven

020456Y Ø 24 mm adaptor

020565Y Flywheel lock calliper spanner

pulley shaft

TOOL - 24

MSS Fly 50 4T Tooling

Stores code Description

494929Y Exhaust fumes analyser

TOOL - 25

INDEX OF TOPICS

MAINTENANCE MAIN

MSS Fly 50 4T Maintenance

Maintenance chart

AFTER 1,000 KM OR 4 MONTHS

90'

Action

Hub oil - change
Valve clearance - check
Idle speed (*) - adjustment
Throttle lever - adjustment
Steering - adjustment
Brake control levers - greasing
Brake pads - check condition and wear
Brake fluid level - check
Safety locks - check
Electrical system and battery - check
Tyre pressure - check
Vehicle and brake test - road test

(*) See instructions in «Idle speed adjustment» section

AT 6000 KM OR 12 MONTHS, 18000, 30000, 42000, 54000 AND 66000 KM

60'

Engine oil - replacement
Hub oil level - check
Spark plug / electrode gap - check
Oil filter (net filter) - clean
Variable speed rollers - check or replacement
Brake pads - check condition and wear
Brake fluid level - check
Electrical system and battery - check
Tyre inflation and wear - Check
Vehicle and brake test - road test

EVERY 12000 OR 24 MONTHS AND AT 60000 KM

Engine oil - replacement
Hub oil level - check
Spark plug / electrode gap - check / replacement
Air filter - clean
Oil filter (net filter) - clean
Idle speed (*) - adjustment
Throttle lever - adjustment
Variable speed rollers - check or replacement
Driving belt - replacement
Odometer gear - greasing
Steering - adjustment
Brake control levers - greasing
Brake pads - check condition and wear
Brake fluid level - check
Transmission elements - lubrication
Emergency blockings (°) - Check
Suspensions - check
Electrical system and battery - check
Headlight - adjustment
Tyres condition and wear - Check
Tyre pressure - check
Vehicle and brake test - road test

(*) Refer to rules (Check to CO)
(°) Refer to predelivery operations

Action

Action

MAIN - 27

Maintenance MSS Fly 50 4T

EVERY 24000 KM OR 48000 KM

Action

Engine oil - replacement
Hub oil level - check
Spark plug / electrode gap - check / replacement
Air filter - clean
Oil filter (net filter) - clean
Valve clearance - check
Idle speed (*) - adjustment
Throttle lever - adjustment
Variable speed rollers - check or replacement
Driving belt - replacement
Cylinder ventilation system - check
Odometer gear - greasing
Steering - adjustment
Brake control levers - greasing
Brake pads - check condition and wear
Brake fluid level - check
Transmission elements - lubrication
Emergency blockings (°) - Check
Suspensions - check
Electrical system and battery - check
Headlight - adjustment
Tyres condition and wear - Check
Tyre pressure - check
Vehicle and brake test - road test

(*)Refer to rules (Check to CO)
(°) Refer to predelivery operations.

Engine oil - replacement
Hub oil level - check
Spark plug / electrode gap - check / replacement
Air filter - clean
Oil filter (net filter) - clean
Idle speed (*) - adjustment
Throttle lever - adjustment
Variable speed rollers - check or replacement
Driving belt - replacement
Odometer gear - greasing
Steering - adjustment
Brake control levers - greasing
Brake pads - check condition and wear
Brake fluid hoses - replacement
Brake fluid level - check
Transmission elements - lubrication
Emergency blockings (°) - Check
Suspensions - check
Electrical system and battery - check
Headlight - adjustment
Tyres condition and wear - Check
Tyre pressure - check
Vehicle and brake test - road test

(*)Refer to rules (Check to CO)
(°) Refer to predelivery operations.

EVERY 36000

Action

Engine oil - replacement
Hub oil level - check
Spark plug / electrode gap - check / replacement
Air filter - clean
Oil filter (net filter) - clean

MAIN - 28

EVERY 72000

Action

MSS Fly 50 4T Maintenance

Action

Valve clearance - check
Idle speed (*) - adjustment
Throttle lever - adjustment
Variable speed rollers - check or replacement
Driving belt - replacement
Cylinder ventilation system - check
Odometer gear - greasing
Steering - adjustment
Brake control levers - greasing
Brake pads - check condition and wear
Brake fluid hoses - replacement
Brake fluid level - check
Transmission elements - lubrication
Emergency blockings (°) - Check
Suspensions - check
Electrical system and battery - check
Headlight - adjustment
Tyres condition and wear - Check
Tyre pressure - check
Vehicle and brake test - road test

(*)Refer to rules (Check to CO)
(°) Refer to predelivery operations.

EVERY 2 YEARS

Brake fluid - change

EVERY 3,000 KM

10'

Engine oil - level check/ top-up

Carburettor

- Disassemble the carburettor in its parts, wash all
of them with solvent, dry all body grooves with
compressed air to ensure adequate cleaning.

- Check carefully that the parts are in good condi­tion.

-The throttle valve should move freely in the
chamber. Replace valve in case of wear due to
excessive clearance.

Action

Action

- If there are wear marks in the chamber causing
inadequate tightness or a free valve slide (even if
it is new), replace the carburettor.

- It is advisable to replace the gaskets at every refit.

WARNING
PETROL IS HIGHLY EXPLOSIVE ALWAYS REPLACE THE

GASKETS TO AVOID PETROL LEAKS

MAIN - 29

Maintenance MSS Fly 50 4T

1. Needle valve - 2. Idle speed adjustment screw - 3. Max jet - 4. Accelerating pump - 5. Tapered pin -

6. Jet holder - 7. Float - 8. Chamber - 9. Starter device - 10. Vacuum valve - 11. Cover - 12. Minimum

jet.

Checking the spark advance

The vehicle is provided with a variable spark advance electronic device. Two reference marks for the
timing can be found on the flywheel cover as to find out with more precision the reference mark on the
fan. To check, use a stroboscopic gun Tecnotest 130/P or similar type. Start the engine and let it run
at 1900 revs/min, act on the phase shifter to align the reference mark on the flywheel fan in between
the two reference marks on the casing; at the same time, read the spark advance value on the strobo­scopic gun display. The value should be 10°.
Repeat the above operation with engine running at 5000-6000 revs/min, spark advance should be 26°.

CAUTION

SHOULD THE FLASH INDICATIONS BE UNSTABLE AND THE RPM INDICATION DOES NOT
CORRESPOND WITH THE TRUE ENGINE SPEED VARIATION (FOR EXAMPLE, VALUES SHOWN
ARE HALVED), INSTALL A 10 ÷ 15 KΩ RESISTIVE CABLE CONNECTED IN SERIES TO AN HV
CABLE. IF THE IRREGULAR READING CONTINUES AFTER THIS OPERATION, CHECK THE
COMPONENTS OF THE IGNITION SYSTEM.

N.B.

WHEN THE INDUCTION CLAMP READS THE SIGNAL CORRECTLY, A READING CAN BE CAR­RIED OUT AT OVER 6000 RPM.

RPM LIMITER

Specification

1 spark out of 7 8200 Revs/min
1 spark out of 3 8300 Revs/min

Suppression of all sparks 8500 Revs/min

Desc./Quantity

MAIN - 30

MSS Fly 50 4T Maintenance

Spark plug

Detach the spark plug cap and then remove the
spark plug.

- Carefully examine the spark plug, and replace it
if the insulator is damaged or chipped.

- With the aid of a feeler gauge, measure the spark
gap and, if necessary, adjust by bending outer
electrode with care.

- Ensure the sealing washer is in good conditions.

- Refit the spark plug by engaging the thread man­ually and then tightening it to the prescribed torque
using the box-spanner provided.

Characteristic

Electrode gap

0.7 ÷ 0.8 mm

Spark plug

NGK CR 8EB

Alternative spark plug

DENSO U24ESR-NB

Locking torques (N*m)

Spark plug 10 ÷ 15 Nm

The central electrode of the above spark plug is treated with silicone oil that acts as an antioxidant
agent. If the silicone oil is in excess, crystals tend to form and, by causing hot fire points to preignition
phenomena, tend to reduce the spark plug performance. This results in difficulties for vehicles to reach
the maximum speed and anomalous noises.
If the above situation should occur, replace the spark plug before performing any other intervention.
Before installing the new spark plug, blow with air to remove the silicone oil in excess.

MAIN - 31

Maintenance MSS Fly 50 4T

Direct the jet of compressed air into the round groove between the threaded metal part and the ceramic
part of the inner electrode while turning the spark plug to allow removal of the oil in excess.

Hub oil

Check

Rest the vehicle on its centre stand on an even
surface.

- Unscrew the oil dipstick "A", dry it with a clean
cloth and reinsert it, screwing it in thoroughly.

- Pull out the dipstick and check that the oil level is
above the "middle" notch (dipstick with 3 notches).
For dipsticks with 2 notches, the oil level must re­main in the lower half of the dipstick.

-Screw up the oil dipstick again and make sure it
is locked properly into place.

Recommended products

AGIP ROTRA 80W-90 rear hub oil

SAE 80W/90 Oil that exceeds the requirements of
API GL3 specifications

Replacement

Remove the oil filler cap/dipstick "A".

- Unscrew the oil drainage plug "B" shown in the
figure and drain out all the oil.

- Screw the drainage plug back and fill up the hub
with the required oil (about 100 cm³)

MAIN - 32

MSS Fly 50 4T Maintenance

Air filter

- Remove the l.h.s. fairing.

- Remove the air-box cover after removing the 6
fixing screws shown in the figure, and then extract
the filtering element.
Cleaning:

- Clean with water and neuter soap;

- Dry with a clean cloth, without squeezing, and
with light jets of air;

- Immerge in a 50% oil-petrol mixture;

- Let it drip and then compress it with your hands,
without squeezing.

- Refit all components in the reverse order.

CAUTION
IF THE VEHICLE IS MOSTLY USED ON DUSTY ROADS,

THE AIR FILTER NEEDS TO BE CLEANED AT SHORTER
INTERVALS THAN INDICATED IN THE SCHEDULED MAIN­TENANCE TABLE.
DO NOT RUN THE ENGINE WITH THE AIR FILTER DISAS­SEMBLED OR EXCESS WEAR OF CYLINDER AND PISTON
WILL RESULT.

Recommended products

AGIP FILTER OIL Oil for air filter sponge

Mineral oil with specific additives for increased ad­hesiveness

Engine oil

-The oil decanting system is a labyrinth type so it
does not require servicing.

N.B.
IN THE EVENT OF LONG ROUTES OR LACK OF SERVIC-

ING, ADEQUATELY CLEAN THE LABYRINTH BY REMOV­ING THE FOUR SCREWS AND SHEET METAL COVER.

Replacement

Loosen the oil filler plug.

- Unscrew the gauze strainer drain plug on the flywheel side and allow the oil to drain completely.

- Retighten the drain plug and pour in approximately 600-650 cc of oil.

MAIN - 33

Maintenance MSS Fly 50 4T

- Start the engine, let it idle for about a minute and then switch it off.

- Wait for at least ten minutes and then top up by adding oil to the «MAX» level.

Check

Check oil level every time the vehicle is used, with
the engine cold. The level should be between the
MAX and MIN marks on the oil level dipstick shown
in figure; the stand should be firm on an even sur­face during the check.
If the check is carried out after the vehicle has
been used, i.e. the engine is hot, the level line will
be very low; for an adequate check, wait at least
10 minutes after the engine stops in order to have
the correct level.
Check by pushing the dipstick all the way into the
hole.

CAUTION

USING THE ENGINE WITH INSUFFICIENT LUBRICATION
OR WITH THE WRONG LUBRICANTS MAY INCREASE
WEAR AND TEAR ON THE MOVING PARTS AND MAY
CAUSE SERIOUS DAMAGE.

Characteristic

Engine oil

Capacity: ~ 850 cc

Engine oil filter

- Change oil when the engine is hot.

- Place a container under the oil sump and remove
the oil drainage cap.

- After draining the oil, clean the mesh filter with a
specific solvent and then blow it with compressed
air.

- The filter can be reached after removing cap
"A" (see figure).

- After this operation, refit the filter and screw the
oil cap at the prescribed torque using a new O­Ring

MAIN - 34

MSS Fly 50 4T Maintenance

- Refill the engine with oil through the oil filling hole
located in the oil sump.

- Engine oil capacity: ~ 850 cc.

- Lock the cap manually.

N.B.

Run the engine for a couple of minutes and check the oil level
when the engine is cold. The level should always be below the
MAX mark

N.B.

For the first top-up or when servicing, add 850 cm³ of engine
oil; for any other case, add 650 cm³ and top-up, if required.

Recommended products

AGIP CITY HI TEC 4T Engine oil

SAE 5W-40 Synthetic oil that exceed the require­ments of API SL, ACEA A3, JASO MA specifica­tions

Locking torques (N*m)

Engine oil pre-filter cover 25 ÷ 28 Nm

Checking the ignition timing

- Turn the flywheel clockwise until its 2nd notch
coincides with the Pick-up reference mark as
shown in the figure.
Make sure that the reference point on the camshaft
command crown is aligned with the reference point
on the head as shown in the second figure.
If the reference is opposite the indicator on the
head, turn the crankshaft once more as the piston
must be at the TDC of the bursting phase.

N.B.
TIME THE TIMING SYSTEM UNIT AS DESCRIBED IN CHAP-

TER 6 IF IT IS NOT IN PHASE

MAIN - 35

Maintenance MSS Fly 50 4T

Checking the valve clearance

- Remove the spark plug access cover, undo the
4 fixing screws indicated in the figure and remove
the tappet cover.

- To check valve clearance, centre the reference
marks of the timing system point as described
above.

- Use an adequate thickness gauge to check that
the clearance between the valve and the register
corresponds with the indicated values.
Should the valve clearance values, intake and
drainage respectively, be different from the ones
indicated below, adjust them by loosening the lock
nut and operate on the register with a screwdriver
as shown in the figure.

Characteristic

Inlet (with cold engine)

0.10 mm

Outlet (with cold engine)

0.15 mm

Headlight adjustment

Proceed as follows:

1. Place the vehicle, in running order and with the
tyres inflated to the prescribed pressure, on a flat
surface 10-m away from a white screen situated in
a shaded area, making sure that the longitudinal
axis of the scooter is perpendicular to the screen;

2. Turn on the headlight and check that the bor­derline of the projected light beam on the screen
is not lower than 9/10 of the distance from the
ground to the centre of vehicle headlamp and high­er than 7/10;

3. If otherwise, adjust the right headlight with screw
«A».

N.B.
THE ABOVE PROCEDURE COMPLIES WITH THE EURO-

PEAN STANDARDS REGARDING MAXIMUM AND MINI-

MAIN - 36

MSS Fly 50 4T Maintenance

MUM HEIGHT OF LIGHT BEAMS. REFER TO THE STATU­TORY REGULATIONS IN FORCE IN EVERY COUNTRY
WHERE THE VEHICLE IS USED.

CO check

The check may be necessary in the event of irreg­ularities in the engine performances, or when ad­justing the engine idle speed.

- The test must be carried out only after having
carefully cleaned all carburettor components with
the air filter clean and the spark plug in good con­ditions.

1) Warm up the engine by riding the vehicle for
about 5-10 minutes, as this is the time required for
the choke device to disengage.

2) Shut down the engine only for the time required
to carry out operations 3) and 4).

3) Remove the RH side fairing and the SAS box
cover by loosening the 3 screws shown in the fig­ure. Interpose a plastic sheet between the secon­dary air one-way valve and its housing on the
cover. Ensure the valve gasket seals properly. Re­fit the SAS box cover.

4) Fit the special tool for the collection of exhaust
gases as shown in the picture. Pay attention in en­suring the seal between the exhaust pipe and the
collection tube. Insert the gas analyser and the ex­haust tube.

5) Insert the multimetre thermometer inside the
sump, through the oil filler hole.

6) Start up the engine and, before adjusting the
idle speed, ensure the oil temperature is between
70 and 80 °C.

7) Wait for a few minutes to let the temperature
stabilise.

8) Without ever activating the throttle and
through the idle screw, bring the engine speed to
1,950 ± 50 rpm.

MAIN - 37

Maintenance MSS Fly 50 4T

9) Adjust the flow screw so to obtain a "CO" read­ing of 3.2 % ± 0.5 %.

10) Slowly twist the throttle handgrip, bringing the
engine up to a speed of 4,000 rpm and then re­lease it; check the idle speed is the same as be­fore, otherwise repeat the operations starting from
point (3).

Specific tooling

020332Y Digital rev counter
494929Y Exhaust fumes analyser
020331Y Digital multimeter

SAS filters inspection and cleaning

After taking out the plug spark cover, unscrew the
three screws «A» and remove the right fairing. Un­screw the three screws «B» and remove the hous­ing cover of the secondary air system. Detach the
housing cover and remove the filtering element
«C» made of sponge. Wash the sponge with water
and neutral soap, then dry with a clean cloth and
short blasts of compressed air. While cleaning the
filter, check the condition of the reed valve «D»,
and mount it back in place on the housing.
Before closing the cover of the SAS housing,
check the good condition of the sealing O-ring; re­place it if damaged or deformed.

N.B.
The reed valve can be inserted in only one direction on the

SAS housing

MAIN - 38

MSS Fly 50 4T Maintenance

MAIN - 39

INDEX OF TOPICS

TROUBLESHOOTING TROUBL

MSS Fly 50 4T Troubleshooting

This section makes it possible to find the solutions to use in troubleshooting.
For each breakdown, a list of the possible causes and respective interventions is given.

Engine

Poor performance

POOR PERFORMANCE

Possible Cause Operation

The carburettor is dirty; vacuum operated cock failure Dismantle, wash with solvent and dry with compressed air or

Excess of encrustations in the combustion chamber Descale the cylinder, the piston, the head and the valves

Incorrect timing or worn timing system elements Time the system again or replace the worn parts

Muffler obstructed Replace

Automatic starter failure Check: mechanical movement, electric connection and fuel

supply, replace if required.

Oil level exceeds maximum Check for causes and fill to reach the correct level

Lack of compression: parts, cylinder and valves worn Replace the worn parts

Transmission belt worn Replace

Inefficient automatic transmission Check the rollers and the pulley movement, replace the dam-

aged parts and lubricate the driven pulley moveable guide with

Montblanc Molybdenum Grease

Clutch slipping Check the clutch system and/or the bell and replace if neces-

Overheated valves Remove the head and the valves, grind or replace the valves

Wrong valve adjustment Adjust the valve clearance properly

Valve seat distorted Replace the head assembly

Air filter blocked or dirty. Dismantle the sponge, wash with water and shampoo, then

soak it in a mixture of 50% petrol and 50% of specific oil (Se­lenia Air Filter Oil), then hand dry without squeezing, allow to

drip dry and then reassemble.

Defective floating valve Check the proper sliding of the float and the functioning of the

replace

sary

valve

Rear wheel spins at idle

REAR WHEEL

Possible Cause

Idling rpm too high Check the idling speed and, if necessary, adjust the C.O.

Clutch fault Check the spring/friction mass and the clutch bell

Air filter housing not sealed Correctly refit the filter housing and replace it if it is damaged

Purifier-carburettor fitting damaged Replace

Starting difficulties

STARTING PROBLEMS

Possible Cause

Altered fuel characteristics Drain off the fuel no longer up to standard; then, refill

Rpm too low at start-up or engine and start-up system dam-

aged

Incorrect valve sealing or valve adjustment Inspect the head and/or restore the correct clearance

- Engine flooded. Try starting-up with the throttle fully open. If the engine fails to

Operation

Operation

Check the starter motor and the system.

start, remove the spark plug, dry it and before refitting, make

the motor turn so as to expel the fuel excess taking care to

connect the cap to the spark plug, and this in turn to the ground.

If the fuel tank is empty, refuel and start up.

TROUBL - 41

Troubleshooting MSS Fly 50 4T

Possible Cause Operation

Automatic starter failure Check: mechanical movement, electric connection and fuel

Air filter blocked or dirty. Dismantle the sponge, wash with water and shampoo, then

soak it in a mixture of 50% petrol and 50% of specific oil (Se­lenia Air Filter Oil), then hand dry without squeezing, allow to

Faulty spark plug or incorrect ignition advance Replace the spark plug or check the ignition circuit components

The carburettor is dirty; vacuum operated cock failure Dismantle, wash with solvent and dry with compressed air or

Battery flat Check the charge of the battery, if there are any sulphur marks,

replace and use the new battery following the instructions

Intake coupling cracked or clamps incorrectly tightened Replace the intake coupling and check the clamps are tight-

Defective floating valve Check the proper sliding of the float and the functioning of the

Carburettor nozzles clogged Dismantle, wash with solvent and dry with compressed air

supply, replace if required.

drip dry and then reassemble.

replace

shown in the chapter

ened
valve

Excessive oil consumption/Exhaust smoke

EXCESSIVE OIL CONSUMPTION / EXHAUST SMOKE

Possible Cause Operation

Worn valve oil guard Replace the valve oil guard

Oil leaks from the couplings or from the gaskets Check and replace the gaskets or restore the coupling seal

Worn or broken piston rings or piston rings that have not been

fitted properly

Worn valve seat Check and if necessary replace head assembly

Replace the piston cylinder unit or just the piston rings

Insufficient lubrication pressure

POOR LUBRICATION PRESSURE

Possible Cause

By-Pass remains open Check the By-Pass and replace if required. Carefully clean the

Oil pump with excessive clearance Perform the dimensional checks on the oil pump components

Oil filter too dirty Replace the cartridge filter

Oil level too low Restore the level using the recommended oil type (Selenia HI

Engine tends to cut-off at full throttle

ENGINE TENDS TO CUT OUT AT FULL THROTTLE

Possible Cause

DEFECTIVE CIRCUIT OF FEEDING Check and possibly replace the automatic vacuum tap, check

Incorrect float level Restore the level in the tank by bending on the float the thrust-

Water in the carburettor Empty the tank through the appropriate bleed nipple.

Maximum nozzle dirty - lean mixture Wash the nozzle with solvent and dry with compressed air

Engine tends to cut-off at idle

Operation

By-Pass area.

Scooter 4 Tech)

Operation

the vacuum intake and the conduit seal

ing reed of the petrol inlet rod so as to have the float parallel to

the tank level with the carburettor inverted.

TROUBL - 42

ENGINE TENDS TO CUT-OFF AT IDLE

Possible Cause

Incorrect timing Time the system and check the timing system components

Operation

MSS Fly 50 4T Troubleshooting

Possible Cause Operation

Incorrect idle adjustment Adjust using the rpm indicator

Pressure too low at the end of compression Check the thermal group seals and replace worn components

Faulty spark plug or incorrect ignition advance Replace the spark plug or check the ignition circuit components

The starter remains on Check: electric wiring, circuit not interrupted, mechanical

Minimum nozzle dirty Wash the nozzle with solvent and dry with compressed air

Excessive exhaust noise

EXCESSIVE EXHAUST NOISE

Possible Cause Operation

Depression intake pipe of the secondary air device disconnec-

ted or dented
Reed valve of the secondary air device does not close correctly
and wears out the rubber coupling between the device and the

head pipe

High fuel consumption

movement and power supply; replace if necessary

Replace the pipe

Replace the device and the coupling

HIGH FUEL CONSUMPTION

Possible Cause Operation

Float level Restore the level in the tank by bending on the float the thrust-

Loose nozzles Check the maximum and minimum nozzles are adequately

Starter inefficient Check: electric wiring, circuit continuity, mechanical sliding and

Air filter blocked or dirty. Dismantle the sponge, wash with water and shampoo, then

SAS malfunctions

ANOMALIES IN THE SECONDARY AIR DEVICE

Possible Cause

Depression intake pipe of the secondary air device disconnec-

ted or dented
Reed valve of the secondary air device does not close correctly
and wears out the rubber coupling between the device and the

head pipe

Transmission and brakes

ing reed of the petrol inlet rod so as to have the float parallel to

the tank level with the carburettor inverted.

fixed in their fittings

power supply

soak it in a mixture of 50% petrol and 50% of specific oil (Se­lenia Air Filter Oil), then hand dry without squeezing, allow to

drip dry and then reassemble.

Operation

Replace the pipe

Replace the device and the coupling

Clutch grabbing or performing inadequately

IRREGULAR CLUTCH PERFORMANCE OR SLIPPAGE

Possible Cause

Faulty clutch Check that there is no grease on the masses. Check that the

clutch mass contact surface with the casing is mainly in the
centre with equivalent characteristics on the three masses.

Check that the clutch casing is not scored or worn in an anom-

Operation

alous way

TROUBL - 43

Troubleshooting MSS Fly 50 4T

Insufficient braking

INSUFFICIENT BRAKING

Possible Cause Operation

Inefficient braking system Check the pad wear (1.5 min). Check that the brake discs are

Fluid leakage in hydraulic braking system Failing elastic fittings, plunger or brake pump seals, replace

not worn, scored or warped. Check the correct level of fluid in
the pumps and change brake fluid if necessary. Check there is
no air in the circuits; if necessary, bleed the air. Check that the

front brake calliper moves in axis with the disc.

Brakes overheating

BRAKES OVERHEATING

Possible Cause Operation

Rubber gaskets swollen or stuck Replace gaskets.

Compensation holes on the pump clogged Clean carefully and blast with compressed air

Brake disc slack or distorted Check the brake disc screws are locked; use a dial gauge and

Defective piston sliding Check calliper and replace any damaged part.

a wheel mounted on the vehicle to measure the axial shift of

the disc.

Electrical system

Battery

Possible Cause

Battery This is the device in the system that requires the most frequent

Turn signal lights malfunction

TURN INDICATOR NOT WORKING

Possible Cause

Electronic ignition device failure With the key switch set to "ON" jump the contacts 1 (Blue -

BATTERY

Operation

attention and the most thorough maintenance. If the vehicle is
not used for some time (1 month or more) the battery needs to
be recharged periodically. The battery runs down completely in
the course of 3 months. If the battery is fitted on a motorcycle,

be careful not to invert the connections, keeping in mind that

the black ground wire is connected to the negative terminal

while the red wire is connected to the terminal marked+.

Operation

Black) and 3 (White) on the voltage regulator connector. If by

operating the turn indicator control the lights are not steadily

on, replace the control unit; otherwise, check the cable harness

and the switch.

Steering and suspensions

TROUBL - 44

MSS Fly 50 4T Troubleshooting

Rear wheel

REAR WHEEL ROTATES WITH ENGINE AT IDLE

Possible Cause Operation

Idling rpms too high Adjust the engine idle speed and the CO%, if necessary.

Clutch fault Check the springs / clutch masses

Controls

STEERING CONTROLS AND SUSPENSIONS

Possible Cause Operation

Torque not conforming Check the tightening of the top and bottom ring nuts. If irregu-

Steering hardening Check the tightening of the top and bottom ring nuts. If irregu-

Malfunctions in the suspension system If the front suspension is noisy, check: the efficiency of the front

Seal fault or breakage Replace the shock absorber Check the condition of wear of the

larities continue in turning the steering even after making the
above adjustments, check the seats in which the ball bearings
rotate: if they are recessed or if the balls are squashed, replace

them.

larities continue in turning the steering even after making the
above adjustments, check the seats in which the ball bearings
rotate: if they are recessed or if the balls are squashed, replace

them.

shock absorber; the condition of the ball bearings and relevant

lock-nuts, the limit switch rubber buffers; and the movement

bushings. In conclusion, check the tightening torque of the

wheel hub, the brake calliper, the shock absorber disc in the

attachment to the hub and the steering tube.

steering covers and the adjustments.

TROUBL - 45

INDEX OF TOPICS

ELECTRICAL SYSTEM ELE SYS

MSS Fly 50 4T Electrical system

ELECTRICAL SYSTEM

Specification

1 Front left turn indicator
2 Front turn indicator bulbs Front turn indicator bulbs 12V-10W x 2
3 Horn button
4 Indicators switch
5 Light switch
6 Rear stop switch
7 Headlight bulb 12V-35/35W
8 Front tail light bulb Type: All glass

9 Right turn indicator warning light 12V - 2W
10 Low fuel warning light 12V - 1.2W
11 Left turn indicator warning light 12V - 2W
12 High-beam warning light 12V - 1.2W
13 Instrument panel light bulbs Type: All glass

14 Headlight warning light 12V 1.2W
15 Odometer with warning lights and level indicator
16 Front headlight

Desc./Quantity

Power: 12V 5W

Quantity: 1

Power: 12V 1.2W

Quantity: 2

ELE SYS - 47

Electrical system MSS Fly 50 4T

Specification Desc./Quantity

17 Front brake stop button
18 Starter button
19 Key switch
20 front right turn indicator
21 Fuel level transmitter
22 Automatic starter
23 Starter remote control
24 rear right turn indicator
25 Rear light assembly
26 Stop and tail light bulb Type: Spherical

27 Battery 12V - 9Ah
28 Electronic ignition device
29 Magneto flywheel
30 Starter motor
31 Fuse carrier (N° 1 fuse to 10 A)
32 rear left turn indicator
33 Rear turn indicator bulbs Two, 12V-10W, spherical
34 Voltage regulator
35 Claxon in c.c.
36 Resistance 6,8 Ohm - 10W

Power: 12V 21/5W

Quantity: 1

Colours of the electrical cables:
B = White, Bl = Blue, G = Yellow, Mr = Brown, N = Black, Gr = Grey,
Rs = Pink, R = Red, Vi = Purple, V = Green

Conceptual diagrams

Ignition

ELE SYS - 48

MSS Fly 50 4T Electrical system

IGNITION

Specification Desc./Quantity

1 Magneto flywheel
2 Pick - up
3 Key switch contacts
4 Electronic ignition device
5 Fuse 10 A
6 Voltage regulator
7 Battery 12V-9Ah

Headlights and automatic starter section

HEADLIGHTS

Specification

1 Magneto flywheel
2 Voltage regulator
3 Light switch
4 Headlight bulb 12V-35/35W
5 High-beam warning light 12V - 1.2W
6 Rear light bulb 12V - 5W
7 Headlight warning light 12V - 1.2W
8 Front position light filament 12V - 5W
9 Instrument panel light bulbs Type: All glass

10 Instrument panel lighting bulbs 12V - 2W

Desc./Quantity

Power: 12V 1.2W

Quantity: 2

ELE SYS - 49

Electrical system MSS Fly 50 4T

Battery recharge and starting

BATTERY RECHARGE AND START-UP SECTION

Specification

1 Voltage regulator
2 Magneto flywheel
3 Automatic starter
4 Battery 12V-9Ah
5 Remote starter switch
6 Starter motor
7 Start up button
8 Brake light filament 12V-21W
9 Front and rear brake light button
10 Key switch
11 Main fuse 10A
12 Resistance 6,8 Ohm - 10W

Desc./Quantity

ELE SYS - 50

MSS Fly 50 4T Electrical system

Level indicators and enable signals section

START PERMISSIVE BUTTONS AND LEVEL INDICATORS

Specification

1 Voltage regulator
2 Fuel gauge
3 Fuel level sender
4 Low fuel warning light 12V - 1.2W
5 Front and rear brake light button
6 Fuse 10 A
7 Battery 12V-9Ah
8 Brake light filament 12V-21W
9 Key switch contacts

Desc./Quantity

ELE SYS - 51

Electrical system MSS Fly 50 4T

Turn signal lights

TURN INDICATORS AND HORN

Specification

1 Indicators switch
2 Horn button
3 Horn
4 Two (2) turn signal warning light bulbs 12V - 2W
5 4 Turn indicator bulbs 12V-10W
6 Voltage regulator
7 Key switch contacts
8 Fuse 10 A
9 Battery 12V-9Ah

Desc./Quantity

Checks and inspections

In case the cause of ignition failure or malfunction
cannot be easily identified at sight, first of all re­place the control unit by another one in operating
conditions.
Remember that the engine must be off to discon­nect and replace the control unit.
If after replacement the vehicle starts properly, the
control unit is failing and must be replaced.

ELE SYS - 52

MSS Fly 50 4T Electrical system

If the failure persists, check the generator and the
stator components as follows:
After visually checking the electrical connections,
use a specific tester to measurement the stator
winding and the pickup (see table).
If any failure is found after checking the loading coil
and the pick-up, replace the stator and the dam-

aged parts.

Disconnect the connector on the flywheel cover
and measure the resistance between either con­tact and the earthing.

Specific tooling

020331Y Digital multimeter

PICK-UP CHECK

Specification Desc./Quantity

1 1) Brown cable and earth ~ 170 Ω

STATOR WINDING CHECK

Specification

1 1) Black cable and earth ~ 1 Ω

Desc./Quantity

Ignition circuit

All the control operations of the system that require
the disconnection of cables (checks of the con­nections and the devices making up the ignition
circuit) must be done with the engine off: if this is
not done, the controls might be irretrievably dam­aged.

ELE SYS - 53

Electrical system MSS Fly 50 4T

Stator check

- Using a tester, check the resistance between the
brown-earth and black-earth terminal.

N.B.
VALUES ARE STATED AT AMBIENT TEMPERATURE. A

CHECK WITH THE STATOR AT OPERATING TEMPERA­TURE LEADS TO VALUES HIGHER THAN THOSE STATED.

Electric characteristic

Stator : Brown-earth

approx. 170 Ω (Pick-Up)

Stator : Black-earth

~ 1 Ω (Stator)

Voltage regulator check

A malfunction in the voltage regulator might cause the following problems depending on the type of
fault:

1) Bulbs burned out (regulator in short circuit).

2) Malfunction of the lighting system and the electric starter (regulator interrupted).

3) Battery not recharging.

4) Turn indicators not working.
The regulator is earthed through the electrical system, so the regulator body does not earth the circuits
inside the regulator.
There must be insulation between each regulator terminal and the regulator body (use the tester to
check electric resistance).

1) BURSTING LIGHT BULBS
Replace the voltage regulator as this is definitely
faulty.

2) HEADLIGHTS AND CHOKE NOT-OPERA­TIONAL
In order to leave the AC free from absorptions, so
to carry out voltage checks, please proceed as fol­lows. Remove the handlebar covers. Detach the
connections from the headlight and the 5 PIN con­nector from the dashboard. Remove the taillight
bulb. Remove the automatic choke connector from
the system.
Access the voltage regulator, start the engine and
let it run at idle.

ELE SYS - 54

MSS Fly 50 4T Electrical system

Insert the positive terminal from the tester (setting
the tester on AC mode) on terminal no. 1 (yellow­black wire) and the negative terminal on terminal
no. 2 (black wire); check for voltage (see figure).
If voltage is present, check the wiring from the
headlight to the voltage regulator, and the opera­tion of the light switch.
If no voltage is found, put the negative terminal to
earth; if this provides voltage readings, check the
earth wire (terminal no. 2) on the regulator (black
wire); otherwise, replace the regulator as certainly
faulty.
As a last test it is possible to check the output volt­age from the stator:

-Detach the regulator connector and interpose the
tester in AC mode, between the Gray-Blue wire (4)
and earth (see figure).

-The voltage output at 2,000 rpm must be approx.
25 - 35V
If this test also gives no voltage, replace the reg­ulator as certainly faulty.

N.B.
TO MEASURE THE ABOVE VOLTAGE USE AN ANALOGUE

TESTER THAT CAN MEASURE ALTERNATING VOLTAG­ES AND KEEP THE ENGINE AT IDLE TO HAVE AN ALTER­NATING VOLTAGE OF A FREQUENCY AS CLOSE AS
POSSIBLE TO 50HZ SO AS TO DETECT THE EFFICIENT
VOLTAGE VALUE SUPPLIED BY THE REGULATOR
(ABOUT 12V).

Recharge system voltage check

3) BATTERY DOES NOT RECHARGE
The fault in the DC section of the voltage regulator
may cause, depending on the type of failure, the
following faults:

a) Bursting of protection fuse due to exces­sively high voltage (regulator short-circuited)
and resulting in the battery not recharging.
b) Battery not recharging (regulator circuit in­terrupted).
Interventions

ELE SYS - 55

Electrical system MSS Fly 50 4T

a) Bursting of protection fuse (regulator short­circuited).
Check the wiring running from the fuse to the ig­nition key-switch is not damaged, as this may cre­ate a short-circuit with earth (thus excluding
possible regulator failures); if the protection fuse
bursts only after the ignition key-switch is turned
to "ON", and with the regulator connector detach­ed, it is then necessary to check the wirings and
systems downstream the key-switch are not short­circuited with earth.
Proceed by measuring the resistance between
contacts 3 (White) and 2 (Black) from the voltage
regulator (with the connector detached).
If the reading differs excessively from the figures
shown, replace the regulator as short-circuited.
b) Battery not recharging (regulator circuit inter­rupted).
To check for the presence of faults on the recharg­ing section of the voltage regulator, it is necessary
to initially operate on the battery, using two testers
(one for voltages and one for currents), as shown
in the second figure, and follow the operations giv­en below:
Start the engine (connecting, temporarily, the red
wire to the positive terminal of the battery, so to
avoid damaging the instrument measuring the cur­rent).
Check the voltage at idle is at least 13V (charged
battery) and the recharge current is 1.5 - 2A with
the lighting system and the choke device exclu­ded, as described in the chapter "CHECKING THE
VOLTAGE REGULATOR".
As the engine speed increases, so do the recharge
current and voltage, and at speeds above 4,000
rpm, a recharging current of approx. 4.5A must be
observed; reactivating the lighting system and
choke device, and operating the stop light and

ELE SYS - 56

MSS Fly 50 4T Electrical system

horn, current values of ≥ 5A may be found, with
voltage readings of 14 - 14.5V (regulator threshold
voltage).

If the readings do not match the above figures,
replace the regulator; otherwise check wiring
and connections.

Electric characteristic

Voltage regulator resistance

~ 8 MΩ

Sealed battery

INSTRUCTIONS FOR REFRESHING THE
STOCK CHARGE OF AN OPEN CIRCUIT

1) Voltage check

Before installing the battery on the vehicle, check
the open circuit voltage with a normal tester.

- If the voltage exceeds 12.60 V, the battery may
be installed without any renewal recharge.

- If voltage is below 12.60 V, a renewal recharge
is required as explained in 2).

2) Constant voltage battery charge mode

-Constant voltage equal to 14.40÷14.70V

-Initial charge voltage equal to 0.3÷0.5 for nominal
capacity

-Duration of the charge: 10 to 12 h recommended
Minimum 6 h
Maximum 24 h

3) Constant current battery charge mode

-Charge current equal to 1/10 of the nominal ca­pacity of the battery

-Duration of the charge: 5 h

WARNING

-WHEN THE BATTERY IS REALLY FLAT (WELL BELOW

12.6V) IT MIGHT BE THAT 5 HOURS OF RECHARGING ARE
NOT ENOUGH TO ACHIEVE OPTIMAL PERFORMANCE.
IN THESE CONDITIONS IT IS HOWEVER ESSENTIAL NOT
TO EXCEED EIGHT HOURS OF CONTINUOUS RECHARG­ING SO AS NOT TO DAMAGE THE BATTERY ITSELF.

1 Hold the vertical tube
2 Look at the level

ELE SYS - 57

Electrical system MSS Fly 50 4T

3 The float must be freed

Dry-charge battery

The battery is an electrical device which requires careful monitoring and diligent maintenance. The
maintenance rules are:

1) Check the level of the electrolyte

The electrolyte level must be checked frequently and must reach the upper level. Only use distilled
water, to restore this level.
If it is necessary to add water too frequently, check the vehicle's electrical system: the battery works
overcharged and is subject to quick wear.

2)Load status check

After restoring the electrolyte level, check its density using an appropriate densitometer (see the figure).
When the battery is charged, you should detect a density of 30 to 32 Bé corresponding to a specific
weight of 1.26 to 1.28 at a temperature of no lower than 15° C.
A density reading of less than 20° Bé indicates that the battery is completely flat and it must therefore
be recharged.
After charging the battery, check each element electrolyte level and density. If the scooter is not used
for a given time (1 month or more) it will be necessary to periodically recharge the battery.
The battery runs down completely in the course of three months.
If it is necessary to refit the battery in the vehicle, be careful not to reverse the connections, remembering
that the earth wire (black) marked (-) must be connected to the - negative terminal while the other two
red wires marked (+) must be connected to the terminal marked with the + positive sign.
Regular bench charging must be carried out with the specific battery charger, (single) or (multiple),
setting the battery charger selector to the type of battery to be recharged. Connections to the power
supply source must be implemented by connecting the corresponding poles (+ to+ and - to -).

4) Cleaning the battery

The battery should always be kept clean, especially on its top side, and the terminals should be coated
with Vaseline.

WARNING

- Before recharging the battery, remove the plugs of each cell. Keep the battery away from naked flames
or sparks when charging.
Remove the battery from the vehicle removing the negative clamp first.

CAUTION

NEVER USE FUSES WITH A CAPACITY HIGHER THAN THAT RECOMMENDED.
USING A FUSE OF UNSUITABLE RATING MAY SERIOUSLY DAMAGE THE VEHICLE OR EVEN
CAUSE A FIRE.

CAUTION

DRINKING WATER CONTAINS MINERALS THAT CAN BE EXTREMELY HARMFUL TO THE BAT­TERY: USE DISTILLED WATER ONLY.

CAUTION

TO ENSURE MAXIMUM PERFORMANCE THE BATTERY MUST BE CHARGED BEFORE USE.

ELE SYS - 58

MSS Fly 50 4T Electrical system

INADEQUATE CHARGING OF THE BATTERY WITH A LOW ELECTROLYTE LEVEL BEFORE IT
IS FIRST USED SHORTENS THE LIFE OF THE BATTERY.

Specific tooling

020333Y Single battery charger
020334Y Multiple battery charger

WARNING

- Battery electrolyte is toxic and it may cause serious burns. It contains sulphuric acid. Avoid contact
with eyes, skin and clothing. In case of contact with eyes or skin, flush abundantly with water for about
15 minutes and seek immediate medical attention.
In the event of accidental ingestion of the fluid, immediately drink large quantities of water or milk. Follow
with milk of magnesia, beaten egg or vegetable oil. Seek immediate medical attention
Batteries produce explosive gases; keep clear of free flames, sparks or cigarettes; ventilate the area
when recharging the battery indoors.
Always protect your eyes when working close to batteries.

Keep out of the reach of children.

1)- Remove the short closed tube and the caps, then pour sulphuric acid into the cells using the type
specified for batteries, with a specific gravity of 1.26, corresponding to 30° Bé, at a minimum temperature
of 15°C until the upper level is reached.

2) - Leave to rest for at least 2 hours; then, restore the level with sulphuric acid.

3)- Within the following 24 hours, recharge with the specific battery charger (single) or (multiple) at a
density of about 1/10 of the battery nominal capacity and until the acid density is about 1.27, corre­sponding to 31º Bé, and these values are stabilised.

4) - Once the charge is over, level the acid (by adding distilled water). Close and clean carefully.

5)- Once the above operations have been performed, install the battery in the vehicle ensuring the
connections between the wiring and the battery terminals are correct.

WARNING

- ONCE THE BATTERY HAS BEEN INSTALLED IN THE VEHICLE IT IS NECESSARY TO REPLACE
THE SHORT TUBE (WITH CLOSED END) NEAR THE + POSITIVE TERMINAL WITH THE CORRE­SPONDING LONG TUBE (WITH OPEN END), THAT YOU FIND FITTED TO THE VEHICLE, TO
ENSURE THAT THE GASES THAT FORM CAN ESCAPE PROPERLY.

Specific tooling

020333Y Single battery charger
020334Y Multiple battery charger

ELE SYS - 59

INDEX OF TOPICS

ENGINE FROM VEHICLE ENG VE

MSS Fly 50 4T Engine from vehicle

Exhaust assy. Removal

- Remove the 2 fixing nuts from the manifold to the
head

- Undo the 2 screws fixing the muffler to the hous­ing; then remove the whole muffler paying atten­tion to the interference between its supporting
bracket and the cooling cover.

Removal of the engine from the vehicle

Removing the engine from the frame

-Disconnect the battery.

-Remove the muffler assembly.

- Remove the rear wheel.

- Remove the rear brake mechanical transmission.

-Disconnect the electric terminals.

-Remove the throttle grip transmission.

- Disconnect the tubing (petrol-vacuum operated cock control).

- Disconnect the swinging arm on the engine side

- Disconnect the rear shock absorber lower clamping

WARNING

Be very careful when handling fuel.

CAUTION

When installing the battery, first attach the positive cable and then the negative cable.

WARNING

Wear safety goggles when using hitting tools.

ENG VE - 61

INDEX OF TOPICS

ENGINE ENG

MSS Fly 50 4T Engine

Automatic transmission

Transmission cover

- Remove the 12 fixing screws.

- Remove the oil filling cap and then slide out the
cover.
If this operation is carried out directly on the vehi­cle, it is necessary to remove the transmission
cooling coupling and the air filter housing retain­ers.

N.B.
USE A MALLET ON THE APPROPRIATE COUPLINGS TO

REMOVE THE COVER.

Kickstart

-To remove the start up pinion push the starter
lever to facilitate extracting the pinion.

-Remove the kick-start screw and lever.

-Remove the Seeger ring and the washer indica­ted in the figure.

-Pull out the toothed sector.

WARNING
THE SECTOR KEEPS THE SPRING SET, BE CAREFUL SO

AS NOT TO CAUSE ANY ACCIDENTS

Air duct

- To remove the intake throat on the transmission
cover, just remove the three fixing screws indica­ted in the figure.

ENG - 63

Engine MSS Fly 50 4T

Removing the driven pulley shaft bearing

- Slightly heat the crankshaft from the inside side
to avoid damaging the coated surface and use the
driven pulley shaft or a pin of the same diameter
to remove the bearing.

N.B.
IN CASE OF DIFFICULTY A STANDARD 8MM-INSIDE DI-

AMETER EXTRACTOR CAN BE USED.

Refitting the driven pulley shaft bearing

Refit the bearing with the aid of a bushing with the same diameter as the external plate of the bearing
after slightly heating the crankcase from the inside.

N.B.

WHEN REFITTING, ALWAYS REPLACE THE BEARING WITH A NEW ONE.

CAUTION

WHEN REMOVING/REFITTING THE BEARING, TAKE CARE NOT TO DAMAGE THE COVER
PAINTED SURFACE.

Removing the driven pulley

- Lock the clutch bell housing with the specific tool.

- Remove the nut, the clutch bell housing and the
whole of the driven pulley assembly.

N.B.
THE UNIT CAN ALSO BE REMOVED WITH THE DRIVING

PULLEY MOUNTED.

Specific tooling

020565Y Flywheel lock calliper spanner

ENG - 64

MSS Fly 50 4T Engine

Inspecting the clutch drum

- Check that the clutch bell is not worn or damaged.

- Measure the inner diameter of the clutch bell.

Characteristic

Clutch bell diameter/standard value

Ø 107+0.2 +0 mm

Clutch bell diameter/max. value allowed after
use

Ø 107.5 mm

Eccentricity measured /max.

0.20 mm

Removing the clutch

- Equip the tool with long pins screwed into position
«A» from the outside, insert the entire driven pulley
in the tool and have the central screw make con­tact.

CAUTION
THE TOOL WILL BE DEFORMED IF THE CENTRAL SCREW

IS TIGHTENED UP TOO FAR.

- Using a 34 mm socket wrench remove the clutch
locking nut.

- Loosen the central screw by undoing spring of
the driven pulley unit

- Separate the components.

Specific tooling

020444Y Tool for fitting/ removing the driven
pulley clutch

ENG - 65

Engine MSS Fly 50 4T

Inspecting the clutch

- Check the thickness of the clutch mass friction
material.

- The masses must not show traces of lubricants;
otherwise, check the driven pulley unit seals.

N.B.
UPON RUNNING-IN, THE MASSES MUST EXHIBIT A CEN-

TRAL FAYING SURFACE AND MUST NOT BE DIFFERENT
FROM ONE ANOTHER.
VARIOUS CONDITIONS CAN CAUSE THE CLUTCH TO
TEAR.

CAUTION
DO NOT OPEN THE MASSES USING TOOLS TO PREVENT

A VARIATION IN THE RETURN SPRING LOAD.

Characteristic

Check minimum thickness

1 mm

Pin retaining collar

- Remove the collar with the aid of 2 screwdrivers.

- Remove the three guide pins and the mobile half
pulley.

ENG - 66

MSS Fly 50 4T Engine

Removing the driven half-pulley bearing

- Remove the roller bearing with the special ex­tractor inserted from the bottom of the fixed half­pulley.

CAUTION
POSITION THE HOLDING EDGE OF THE EXTRACTION PLI-

ERS BETWEEN THE END OF THE BEARING AND THE
BUILT IN SEALING RING.

Specific tooling

001467Y029 Bell for bearings, O.D. 38 mm

- Remove the ball bearing retention snap ring.

- Expel the ball bearing from the side of the clutch
housing by means of the special tool.

N.B.
PROPERLY SUPPORT THE HALF-PULLEY SO AS NOT TO

DEFORM THE SLIDING SURFACE OF THE DRIVING BELT

Specific tooling

020376Y Adaptor handle
020363Y 20 mm guide

Inspecting the driven fixed half-pulley

- Check that there are no signs of wear on the work
surface of the belt. If there are, replace the half­pulley..

- Make sure the bearings do not show signs of un­usual wear.

- Measure the external diameter of the pulley bush­ing.

Characteristic

Stationary driven half-pulley/Standard diame­ter

Ø 33.965 to 33.985 mm

Stationary driven half-pulley / Minimum diam­eter admitted after use

Ø 33.96 mm

ENG - 67

Engine MSS Fly 50 4T

Inspecting the driven sliding half-pulley

- Remove the 2 inner sealing rings and the two O­rings.

- Measure the inside diameter of the mobile half­pulley bushing.

Characteristic

Mobile driven half-pulley/ Maximum diameter
allowed

Ø 34.08 mm

- Check the belt contact surfaces.

- Insert the new oil seal and O-rings on the mobile
half-pulley.

- Fitting the half-pulley on the bushing.

Recommended products

AGIP GREASE SM 2 Grease for the tone wheel
revolving ring

Soap-based lithium grease containing NLGI 2 Mo­lybdenum disulphide; ISO-L-XBCHB2, DIN
KF2K-20

- Make sure the pins and collar are not worn, reassemble the pins and collar.

- Use a greaser with a curved spout to lubricate the driven pulley unit with around 6 g of grease. This
operation must be done through one of the holes inside the bushing until grease comes out of the
opposite hole. This procedure is necessary to prevent the presence of grease beyond the O-ring.

Recommended products

AGIP GREASE SM 2 Grease for the tone wheel revolving ring

Soap-based lithium grease containing NLGI 2 Molybdenum disulphide; ISO-L-XBCHB2, DIN KF2K-20

Refitting the driven half-pulley bearing

- Fit a new ball bearing with the specific tool.

- Fit the ball bearing retention snap ring.

- Fit the new roller bearing with the wording visible
from the outside.

CAUTION
PROPERLY SUPPORT THE HALF-PULLEY TO PREVENT

DAMAGE TO THE THREADED END WHILE THE BEARINGS
ARE BEING FITTED.

Specific tooling

020376Y Adaptor handle

ENG - 68

MSS Fly 50 4T Engine

020456Y Ø 24 mm adaptor
020362Y 12 mm guide
020171Y Punch for Ø 17 mm roller case

Inspecting the clutch spring

- Check that the contrast spring of the driven pulley
does not show signs of deformation

- Measure the free length of the spring

Characteristic

Standard length

118 mm

Minimum length allowed after use

XXXX

- Check the thickness of the clutch mass friction
material.

-The masses must not show traces of lubricants;
otherwise, check the driven pulley unit.

N.B.
UPON RUNNING-IN, THE MASSES MUST EXHIBIT A CEN-

TRAL CONTACT SURFACE AND MUST NOT BE DIFFER­ENT FROM ONE ANOTHER. VARIOUS CONDITIONS CAN
CAUSE THE CLUTCH TO TEAR.

CAUTION
DO NOT OPEN THE MASSES USING TOOLS SO AS TO

PREVENT A VARIATION IN THE RETURN SPRING LOAD.

Characteristic

Minimum thickness permitted:

1 mm

Refitting the clutch

- Preassemble the driven pulley group with spring,
sheath and clutch.

- Position the spring with the sheath

- Insert the components in the tool and preload the
spring being careful not to damage the plastic
sheath and the end of the threaded bar.

ENG - 69

Engine MSS Fly 50 4T

- Reassemble the nut securing the clutch and tight­en to the prescribed torque.

CAUTION
SO AS NOT TO DAMAGE THE CLUTCH NUT USE A SOCK-

ET WRENCH WITH SMALL CHAMFER.
CAUTION
POSITION THE NON-CHAMFERED SURFACES OF THE

NUT IN CONTACT WITH THE CLUTCH

Locking torques (N*m)

Nut locking clutch unit on pulley 55 ÷ 60 Nm

Refitting the driven pulley

-Refit the driven pulley assembly, the clutch bell
and the nut, using the specific tool.

Specific tooling

020565Y Flywheel lock calliper spanner

Locking torques (N*m)

Driven pulley shaft nut 40 to 44 Nm

Drive-belt

- Make sure the driving belt is not damaged and
does not have cracks in the toothed grooves.

- Check the width of the belt.

Characteristic

Transmission belt/Minimum width

17.5 mm

ENG - 70

MSS Fly 50 4T Engine

Removing the driving pulley

- Lock the driving pulley using the appropriate tool.

- Remove the central nut with the related washer,
then remove the drive and the plastic fan.

- Remove the stationary half-pulley.

- Remove the belt, washer and remove the mobile half-pulley with its bushing, being careful that the
rollers and contrast plate fitted loosely on it do not come off.

Specific tooling

020451Y Starting ring gear lock

Inspecting the rollers case

1) Check that the bushing and the sliding rings of
the mobile pulley do not show signs of scoring or
deformation.

2) Check the roller running tracks on the contact
pulley; there must not be signs of wear and check
the condition of the contact surface of the belt on
the half-pulleys (mobile and stationary).

3) Check that the rollers do not show signs of
marked facetting on the sliding surface and that
the metallic insert does not come out of the plastic
shell borders.

4) Check the integrity of the sliding blocks of the
contact plate.

- Check that the internal bushing shown in the fig­ure is not abnormally worn and measure inside
diameter «A».

- Measure outside diameter «B» of the pulley slid­ing bushing shown in the figure.

CAUTION
DO NOT LUBRICATE OR CLEAN THE BUSHING.

Characteristic

Driving pulley / Maximum diameter:

ENG - 71

Engine MSS Fly 50 4T

20.12 mm

Driving pulley/ Standard diameter:

20.021 mm

Driving pulley bushing/ Diameter maximum:

XXX mm

Driving pulley bushing/ Standard diameter:

20 -0.020/-0.041mm

Refitting the driving pulley

- Manually move the movable driven half-pulley
away by pulling it towards the clutch unit and insert
the belt observing the direction of rotation of the
first fitting.

N.B.
IT IS GOOD PRACTICE ALWAYS TO FIT THE BELT SO

THAT THE WORDS CAN BE READ IN CASE IT DOES NOT
SHOW A FITTING SIDE.

- Refit the components of the assembly (roller con­tainer assembly with bushing, limiting washer, sta­tionary half-pulley, cooling fan belt with drive,
washer and nut).

- With the specific tool, tighten the lock nut to 20
Nm and then perform a final 90° locking in order to
prevent the rotation of the driving pulley.

N.B.
REPLACE THE NUT WITH A NEW ONE AT EVERY REFIT
CAUTION
UPON FITTING THE DRIVING PULLEY UNIT IT IS OF UT-

MOST IMPORTANCE THAT THE BELT IS FREE INSIDE IN
ORDER TO AVOID WRONG TIGHTENING AND CONSE­QUENTLY DAMAGING THE CRANKSHAFT KNURLING.

Specific tooling

020451Y Starting ring gear lock

Locking torques (N*m)

Crankshaft pulley nut 18 to 20 + 90° Nm

ENG - 72

MSS Fly 50 4T Engine

Refitting the transmission cover

- Check the following for wear: toothed section,
toothed section shaft, cover seat bushing, pinion
shaft and its seating in the crankcase and the re­turn spring.

- Remove the damaged components.

- Grease the spring.

- Remove the toothed sector and load the spring
with an appropriate tool.

- Refit the washer, the Seeger and the Kick-start
lever.

Recommended products

AGIP GREASE MU3 Grease for odometer
transmission gear case

Soap-based lithium grease with NLGI 3; ISO-L­XBCHA3, DIN K3K-20

- Insert the pinion in its seating by pushing the starter lever.

- Fit the intake throat and tighten the 3 screws.

-Make sure the oil sump presents centring dowels
and sealing gaskets.

- Replace the cover tightening the 12 screws to the
prescribed torque.

-Refit the oil filling cap.

Locking torques (N*m)

Transmission cover screws 11 ÷ 13 Nm

End gear

ENG - 73

Engine MSS Fly 50 4T

Removing the hub cover

- Drain the rear hub oil

- Remove driven pulley

- Remove the rear brake shoes

- Remove the 5 screws fixing the cover to the
crankcase

- Remove the cover with the wheel axle and pull it
out

- Remove the intermediate gear with the appropri­ate shim washers

Removing the wheel axle bearings

- Remove the oil seal and the seeger ring.

- Fix the hub cover properly to avoid damaging the
sealing surface with the housing

- Remove the wheel axle bearing using the specific
tool

Specific tooling

020363Y 20 mm guide
020376Y Adaptor handle
020477Y Adaptor 37 mm

ENG - 74

MSS Fly 50 4T Engine

Removing the driven pulley shaft bearing

- Remove the seeger ring

- Heat the engine crankcase but do not direct the
hot air towards the bearing

- Extract the driven pulley shaft together with the
bearing with a few mallet blows

- Remove the bearing off the driven pulley shaft
using the specific tool and a press

N.B.
USE THE SPECIFIC TOOL ON THE SIDE WITH THE SMALL-

ER INTERNAL DIAMETER

Specific tooling

020452Y Tube for removing and refitting the
driven pulley shaft

ENG - 75

Engine MSS Fly 50 4T

Inspecting the hub shaft

- Check the three shafts for wear or distortion of
the toothed surfaces, the bearing housings, and
the oil seal housings.

- In case of anomalies, replace the damaged com­ponents.

- Check capacity ( A ) of the transmission gear
(wear, deformations, etc.)

- Check the pulley shaft seating: Superficial wear
( B ) may indicate irregularities in the crankcase
seatings or in the pulley shaft capacities

Inspecting the hub cover

- Check that the fitting surface is not dented or dis­torted.

- If faults are found, replace the hub cover.

Refitting the wheel axle bearing

- Support the hub cover on a wooden surface

- Heat up the hub cover using the thermal gun.

- Preassemble the bearing on the specific punch
using grease and then insert the bearing in its
seating

- Refit the seeger ring and the oil seal using the 42
x 47 mm adaptor

N.B.
POSITION THE OIL SEAL WITH THE SEALING LIP FACING

THE HUB INTERNAL SIDE

Specific tooling

020150Y Air heater support
020151Y Air heater
020376Y Adaptor handle

ENG - 76

MSS Fly 50 4T Engine

020363Y 20 mm guide
020359Y 42x47-mm Adaptor

Refitting the hub bearings

- Remove the wheel axle on the cover and pay at­tention not to damage the sealing lip of the oil seal

- Apply a thin layer of grease on the two shim
washers of the intermediate gear and fit one on the
cap so that it does not interfere with the wheel axle
gear when placing the transmission shaft

Refitting the ub cover

- Apply product recommended for surfaces on the
hub cap and refit cap on the crankcase

- Fit the 5 screws and tighten them to the specified
torque.

N.B.
CLEAN THE CONTACT SURFACES OF THE HUB COVER

AND THE HALF CRANKCASE OF RESIDUE FROM PREVI­OUS GASKETS BEFORE APPLYING A NEW ONE.

Recommended products

Loctite 510 Liquid sealant

ENG - 77

Engine MSS Fly 50 4T

Gasket

Locking torques (N*m)

hub cap screws 24 - 26

Flywheel cover

Cooling hood

- Remove the manifold and the carburettor undo­ing the 2 fixing screws on the head

- Remove the fastening clamp of the secondary air
pipe and disconnect it

- Remove the 4 front coupling screws (1 of them is
a knob) and the side fixing screw at the crankcase
base.

- Remove the 4 side screws

- Extract the 3 covers - Remove the cover sealing
gaskets on the head

- For refitting, repeat the removal steps but in re­verse order

CAUTION
TAKE CARE TO CORRECTLY POSITION THE FLYWHEEL

CONNECTOR.
N.B.
WHEN REFITTING THE COVER, TAKE CARE NOT TO DAM-

AGE THE STATOR WIRING.

ENG - 78

MSS Fly 50 4T Engine

Cooling fan

- Remove the cooling fan by undoing the 3 screws
fixing it to the rotor

- When refitting the fan, pay attention that the
screw holes in the fan and the rotor coincide, then
tighten screws at the specified torque.

Removing the stator

- Remove the 2 Pick-Up screws and the 2 stator
fixing screws indicated in the figure.

- Remove the stator and its wiring.

Refitting the stator

- Refit the stator and flywheel carrying out the re­moval procedure in reverse, tightening the retain­ers to the specified torque.

N.B.
THE PICK-UP CABLE MUST BE POSITIONED ADHERING

TO THE FUSION TONGUE ON THE CRANKSHAFT IN SUCH
A WAY AS TO AVOID BEING CRUSHED BY THE FAN COV­ER ASSEMBLY.

Locking torques (N*m)

Pick-up screws 3 ÷ 4 Stator screws 3 ÷ 4

Flywheel and starting

ENG - 79

Engine MSS Fly 50 4T

Removing the starter motor

- Undo the screw on the power positive contact
and disconnect the cable

- Undo the 2 screws fixing the starter motor to the
crankcase and recover the power wiring.

Removing the flywheel magneto

- Lock the rotation of the flywheel using the calliper
spanner.

- Remove the nut.

CAUTION
THE USE OF A CALLIPER SPANNER OTHER THAN THE

ONE SUPPLIED COULD DAMAGE THE STATOR COILS

- Extract the flywheel with the extractor.

Specific tooling

020565Y Flywheel lock calliper spanner
020162Y Flywheel extractor

ENG - 80

MSS Fly 50 4T Engine

Inspecting the flywheel components

- Check that the flywheel internal magnets are in
good conditions.

- Check that the flywheel splines exhibit no loos­ening.

- Check there are no deformations that may cause
rubbing on the stator and the Pick-Up.

- Check that the stator winding, its ferromagnetic
support and the pick-up are in good conditions.

Starter gear rim

- Check the toothing is level and in good conditions

Intermediate gear

- Check that the keying toothing on the crown and
the starter motor are in good conditions.

- Check that the Bendix opens and returns ade­quately.

ENG - 81

Engine MSS Fly 50 4T

Refitting the flywheel magneto

- Refit the stator and the pick-up being careful to
pass the wiring through the appropriate crankcase
couplings.

- Refit the flywheel to the crankshaft being careful
to respect the keying, then lock rotation with the
specific tool and tighten the nut to the prescribed
torque.

N.B.
A VARIATION OF THE AIR GAP DISTANCE CAN LEAD TO

A VARIATION IN THE IGNITION ADVANCE SUCH AS TO
CAUSE PINGING, KNOCKING ETC.

Specific tooling

020565Y Flywheel lock calliper spanner

Locking torques (N*m)

Flywheel nut 52 ÷ 58

Refitting the starter motor

- Install the starter motor in its seating in the crank­case.

- Tighten the screw on the head side but do not
lock it, screw the second screw inserting the earth
cable (black), then tighten the 2 screws at the pre­scribed torque.

- Tighten the locking screw of the positive cable
(red) on the side contact.

N.B.
REFIT THE REMAINING PARTS AS DESCRIBED IN THE

CYLINDER HEAD, TIMING, LUBRICATION, FLYWHEEL
AND TRANSMISSION CHAPTERS.

Locking torques (N*m)

Starter motor screws 11 ÷ 13

Cylinder assy. and timing system

ENG - 82

MSS Fly 50 4T Engine

Removing the rocker-arms cover

- Remove the cooling covers

- Remove the 4 retainers of the tappet cover

- Remove the cover and the O-ring

- Remove the 4 screws and then remove the Blow­by cover

- Clean the nozzle labyrinth and the membrane
(replace it, if necessary), then remove the cover
unit.

See also

Cooling hood

Removing the timing system drive

- Temporarily loosen the tensioner central screw
and remove it together with the spring.

- Unscrew the 2 retainers indicated in the figure
and remove the chain tightener support being
careful to recover the sealing gasket.

N.B.
SHOULD THE GASKET NOT BE IN GOOD CONDITIONS,

REPLACE IT AFTER CAREFULLY CLEANING THE FAYING
SURFACE IN ORDER TO AVOID ENGINE OIL LEAKS

ENG - 83

Engine MSS Fly 50 4T

- Remove the driving pulley

- Remove the oil pump chain

- Remove the tappet cover

- Remove the central screw and the belleville
washer indicated in the figure and lock the cam­shaft crown with the specific tool.

N.B.
TO FACILITATE REMOVING THE HEAD COMPONENTS,

SET THE CRANKSHAFT TO THE TIMING POINT (TDC OF
THE COMPRESSION END).

Specific tooling

020565Y Flywheel lock calliper spanner

- Remove the camshaft control pulley and the washer below.

- Remove the pinion of the crankshaft timing control

- To remove the chain lower guiding pad, remove the head by pulling it upwards

N.B.

IT IS ADVISABLE TO MARK THE CHAIN IN ORDER TO ENSURE THAT THE DIRECTION OF RO­TATION IS MAINTAINED.

See also

Removing the rocker-arms cover
Removing the driving pulley
Removal

Removing the cam shaft

- Remove the bearing clamping screw indicated in
the figure.

- Remove the entire camshaft with bearing using
the specific tool shown in the figure.

- Take out the camshaft bearing with the aid of the
specific tool, being careful to mount a screw on the
camshaft in order to protect its thread.

N.B.
IF A BEARING SEPARATES FROM THE CAMSHAFT, IT IS

ESSENTIAL TO FIT A NEW BEAR.

Specific tooling

ENG - 84

MSS Fly 50 4T Engine

020450Y Camshaft fitting/removal tool
004499Y Camshaft bearing extractor
004499Y001 Bearing extractor bell
004499Y002 Bearing extractor screw
004499Y006 Bearing extractor ring
004499Y027 Bearing extractor part

- Pull out the rocking lever bolt operating on the
flywheel hole and remove the rocking levers at the
same time.

N.B.
MARK THE ASSEMBLY POSITION OF THE ROCKING LEV-

ERS IN ORDER TO AVOID MISPLACING THE INTAKE AND
DISCHARGE ENDS.

Removing the cylinder head

- Remove the cooling covers, the timing control,
the camshaft and the rocking levers.

- Remove the spark plug.

- Remove the 2 side fixings shown in the figure.

- Loosen the 4 head-cylinder fastening nuts in two
or three stages and in criss-cross fashion.

- Remove the head, the two centring dowels and
the gasket.

N.B.
IF NEEDED, THE HEAD MAY BE REMOVED WITH THE

CAMSHAFT, PINS AND ROCKING LEVERS WITHOUT RE­MOVING THE DRIVING PULLEY UNIT. REMEMBER TO
HOLD THE TIMING CHAIN WITH A PIECE OF METAL CA­BLE AND TO ADJUST THE CHAIN TIGHTENER UPON RE­FITTING.

ENG - 85

Engine MSS Fly 50 4T

Removing the valves

- Using the specific tool fitted with the element
shown in the figure, remove the cotters, the plates
and the spring between the valves.

- Remove the oil seals with the appropriate tool.

- Remove the lower spring supports.

Specific tooling

020431Y Valve oil seal extractor

Removing the cylinder - piston assy.

- Remove the cylinder paying attention to the 2
cylinder centring dowels in the housing.

- Remove the cylinder base gasket.
To avoid damaging the piston, keep it fixed while
removing the cylinder.

- Remove the two stop rings, the wrist pin and the
piston.

- Remove the 3 piston rings.

N.B.
BE CAREFUL NOT TO DAMAGE THE PISTON RINGS DUR-

ING REMOVAL.

ENG - 86

MSS Fly 50 4T Engine

Inspecting the small end

- Measure the internal diameter of the small end
using an internal micrometer.

N.B.
IF THE DIAMETER OF THE ROD SMALL END EXCEEDS

THE MAXIMUM DIAMETER ALLOWED, SHOWS SIGNS OF
WEAR OR OVERHEATING REPLACE THE CRANKSHAFT
AS DESCRIBED IN THE "CRANKCASE AND CRANK­SHAFT" CHAPTER".

Characteristic

Max. diameter admitted: check the small end

13.030 mm

Standard diameter: check the small end

13 +0.025+0.015mm

Inspecting the wrist pin

- Measure the outer diameter of the gudgeon pin.

Characteristic

Standard diameter: gudgeon pin

13 -0-0.004mm

Minimum admissible diameter gudgeon pin

12.990 mm

Inspecting the piston

- Calculate the piston pin coupling clearance.

Fitting clearance

Pin coupling clearance 13 +0.010+0.005mm 0.005 ÷

0.014 mm

- Measure the outside diameter of the piston, perpendicular to the gudgeon pin axis.

- Carry out the measurement at 27 from the piston crown as shown in the figure.

- Carefully clean the sealing rings housings with the aid of an old piston ring.

ENG - 87

Engine MSS Fly 50 4T

- Measure the coupling clearance between the sealing rings and the piston grooves using a thickness
gauge, as shown in the figure.

- If the clearances detected exceed the limits specified in the table, the piston and the piston rings should
be replaced.

PISTON

Name Description Dimensions Initials Quantity

Top piston ring 0.030 ÷ 0.065 mm 0.080 mm

Middle piston ring 0.020 ÷ 0.055 mm 0.070 mm

oil scraper 0.040 ÷ 0.160 mm 0.20 mm

Inspecting the cylinder

- Using a bore meter, measure the inner cylinder
diameter at three different points according to the
directions shown in the figure.

- Check that the coupling surface with the head is
not worn or misshapen.

- Pistons and cylinders are classified into catego­ries based on their diameter. The coupling is car­ried out in pairs (A-A, B-B, C-C, D-D).

Characteristic

Maximum allowable run-out:

0.05 mm

- The cylinder rectifying operation should be car­ried out with a surfacing that respects the original
angle. at 120° crossed.

- The cylinder surface roughness should be of
R.A.= 0.30 ÷ 0.50.

- This is indispensable for a good seating of the
sealing rings, which in turn minimises oil consump­tion and guarantees optimum performance.

ENG - 88

MSS Fly 50 4T Engine

- The pistons are oversized due to cylinder rectifi­cation and are subdivided into two categories 1st
and 2nd with 0.2-0.4mm oversize. They are also
classified into 4 categories A-A, B-B, C-C, D-D.

Inspecting the piston rings

- Alternately insert the three sealing rings into the cylinder, in the area where it retains its original di­ameter. Using the piston, insert the rings perpendicularly to the cylinder axis.

- Measure the opening, see figure, of the sealing rings using a thickness gauge.

- If any measurements are greater than specified, replace the piston rings.

N.B.

BEFORE REPLACING ONLY THE PISTON RINGS, ENSURE THAT THE CLEARANCE BETWEEN
THE PISTON RINGS AND THE PISTON RING GROOVES, AND BETWEEN THE PISTON AND THE
CYLINDER, IS AS SPECIFIED. IN ANY CASE, NEW PISTON RINGS USED IN COMBINATION WITH
A USED CYLINDER MAY HAVE DIFFERENT BEDDING CONDITIONS THAN THE STANDARD.

SEALING RINGS

Name

Top piston ring 0.08 ÷ 0.20 mm 0.35 mm

Middle piston ring 0.05 ÷ 0.20 mm 0.30 mm

oil scraper 0.20 ÷ 0.70 mm 0.80 mm

Description Dimensions Initials Quantity

ENG - 89

Engine MSS Fly 50 4T

Removing the piston

- Install piston and wrist pin onto the connecting
rod, aligning the piston arrow the arrow facing to­wards the exhaust.

- Fit the pin stop ring onto the appropriate tool.

Specific tooling

020448Y Pin lock fitting tool

- With the opening in the position indicated on the
tool, set the lock ring into position in the tool with
the punch.

- Rest the tool on the piston paying attention that
the 90°chamfered side faces upwards as indicated
in the figure.

- Fit the gudgeon pin stop using the plug.

CAUTION
USING A HAMMER TO POSITION THE RINGS CAN DAM-

AGE THE LOCKING HOUSING.

Choosing the gasket

N.B.

MEASUREMENT "A" TO BE TAKEN IS A VALUE OF PISTON RE-ENTRY, IT INDICATES BY HOW
MUCH THE PLANE FORMED BY THE PISTON CROWN FALLS BELOW THE PLANE FORMED BY
THE TOP OF THE CYLINDER. THE FURTHER THE PISTON GETS INSIDE THE CYLINDER, THE
THINNER THE HEAD GASKET TO BE APPLIED SHOULD BE (TO RECOVER THE COMPRESSION
RATIO) AND VICE VERSA.

Characteristic

Shimming system to control the compression ratio

CR: 11.1 ÷ 12.9

PISTON PROTRUSION CHECK

Name

shimming_1 0.05 ÷ 0.25 0.35
shimming_2 0.25 ÷ 0.40 0.25

Measure A Thickness

ENG - 90

MSS Fly 50 4T Engine

- Provisionally fit the piston into the cylinder, without any base gasket.

- Fit a dial gauge on the specific tool, then rest both on a stop surface.

- Zero set the dial gauge on the stop surface. Keeping the zero position, assemble the tool on the cylinder
and lock it with 2 nuts as shown in the figure.

- Rotate the crankshaft until TDC (the inverted point of the dial gauge rotation)

- Measure piston protrusion compared with the head plane and determine the gasket thickness to be
used according to the table below. By correctly identifying the cylinder base gasket thickness, an ade­quate compression ratio is maintained.

- Remove the specific tool and the cylinder.

Characteristic

Standard compression ratio

C.R. 11.5 ÷ 12 ÷ 1

CYLINDER BASE GASKET THICKNESS

Specification

Cylinder height 56.45 ± 0.05

Head gasket thickness (fibre) 0.95 ± 0.06

Measure detected 0.9 ± 0.05

Base gasket thickness 0.4

Measure detected 1 ± 0.05

Base gasket thickness 0.5

Desc./Quantity

ENG - 91

Engine MSS Fly 50 4T

CYLINDER BASE GASKET THICKNESS

Specification Desc./Quantity

Cylinder height 57.15 ± 0.05

Head gasket thickness (steel) 0.3 ± 0.05

Measure detected 0.20 ± 0.05

Base gasket thickness 0.4

Measure detected 0.30 ± 0.05

Base gasket thickness 0.5

This engine is manufactured with two different head gasket solutions:

- Fibre gasket drw. 969244 0.95 mm thick.

- Steel gasket drw. 969393 0.3 mm thick.
In order to guarantee an adequate compression ratio, the gaskets match cylinders with different heights:

- Fibre gaskets with cylinder 56.45 mm high

- Fibre gaskets with cylinder 57.15 mm high

In order to carry out the revision both gaskets should be present on the spare parts.
All pin-piston-cylinder units supplied with the spare parts present cylinders 57.15 mm high

ENG - 92

MSS Fly 50 4T Engine

Refitting the piston rings

- Fit the oil scraper ring starting from the spring,
taking care that the spring ends do not superim­pose. Fit the two piston rings so that their gaps and
that of the oil scraper ring are never aligned.

- Fit the 2nd sealing ring with the identifying letter
«T» facing towards the piston crown.

- Fit the 1st sealing ring with the reference letter
«T» facing towards the piston crown.

- Misalign the lining openings at 120° as shown in
the figure.

- Lubricate the components with engine oil.

N.B.
IN ORDER TO OBTAIN A GOOD BEDDING, THE 2 SEALING

PISTON RINGS ARE MADE OF CONE SHAPED CONTACT
SECTION TO THE CYLINDER. AS A RESULT IT IS IMPOR­TANT TO RESPECT THE FITTING INSTRUCTION TO AS­SEMBLY THE RINGS WITH THE "T" MARK FACING
UPWARDS.

- Alternately insert the three sealing rings into the
cylinder, in the area where it retains its original di­ameter. Using the piston, insert the rings perpen­dicularly to the cylinder axis.

- Measure the opening, see figure, of the sealing
rings using a thickness gauge.

- If any measurements are greater than specified,
replace the piston rings.

N.B.

BEFORE REPLACING ONLY THE PISTON
RINGS, ENSURE THAT THE CLEARANCE BE­TWEEN THE PISTON RINGS AND THE PISTON
RING GROOVES, AND BETWEEN THE PISTON
AND THE CYLINDER, IS AS SPECIFIED. IN ANY
CASE, NEW PISTON RINGS USED IN COMBI-

ENG - 93

Engine MSS Fly 50 4T

NATION WITH A USED CYLINDER MAY HAVE
DIFFERENT BEDDING CONDITIONS THAN
THE STANDARD.

SEALING RINGS

Name DescriptionDimensionsInitials Quantity

Top piston

ring

Middle pis-

ton ring

oil scraper 0.20 ÷

0.08 ÷

0.20 mm

0.05 ÷

0.20 mm

0.70 mm

0.35 mm

0.30 mm

0.80 mm

Refitting the cylinder

If the four cylinder stud bolts should be replaced in this kind of engine, it is necessary to tighten the
head nuts strictly following the procedure below.
The procedure is different from that indicated in the vehicle manuals:
Head nuts tightening (only for stud bolts replacement) 6÷7 N*m +90° + 90° + 90°
The 45° rotation reduction of the key is necessary to avoid stud bolt stretching.

- Fit the base gasket of the chosen thickness, pre­viously determined.

- Fit the cylinder as shown in the figure

- The piston can be kept out of the housing plane
using the appropriate tool.

N.B.
BEFORE FITTING THE CYLINDER, CAREFULLY BLOW

OUT THE LUBRICATION DUCT AND OIL THE CYLINDER
BARREL.

Specific tooling

020288Y Fork to assemble piston on cylinder

Inspecting the cylinder head

- Using a trued bar check that the cylinder head
surface is not worn or distorted.

- Check that the camshaft and rocking lever pin
bearings show no signs of wear.

- Check that the cylinder head cover surface, the
intake manifold and the exhaust manifold are not
worn.

Characteristic

Maximum admitted unevenness: Head check

ENG - 94

MSS Fly 50 4T Engine

0.05 mm

HEAD CHECK

Specification Desc./Quantity

Standard diameter (mm) A Ø 32.015 ÷ 32.025 mm
Standard diameter (mm) B Ø 16.0 ÷ 16.018
Standard diameter (mm) C Ø 11.0 ÷ 11.018

Inspecting the timing system components

- Check that the guide shoe and the tensioner shoe
are not worn out.

- Ensure that the camshaft drive pulley, the chain
assembly and the sprocket wheel are not worn.

- If sings of wear are found, replace the parts. if the
chain, pinion or pulley are worn, replace the whole
assembly.

- Remove the central screw and the tensioner
spring. Check that the one-way mechanism is not
worn.

- Check the condition of the tensioner spring.

- If examples of wear are found, replace the whole
assembly.

Inspecting the valve sealings

- Measure the width of the sealing surface on the
valve seats.

Characteristic

Sealing surface width: Intake

1.5 mm

Sealing surface width: Drainage

ENG - 95

Engine MSS Fly 50 4T

1.6 mm

- Insert the valves into the cylinder head.

- Test the 2 valves alternatively.

- The test is carried out by filling the manifold with
petrol and checking that the head does not ooze
through the valves when these are just pressed
with the fingers.

Inspecting the valve housings

- Remove any carbon formation from the valve
guides.

- Measure the inside diameter of each valve guide.

- Take the measurement at three different heights
in the rocker arm push direction.

Characteristic

Discharge guide: Standard diameter

5 +0+0.012mm

Discharge guide: Wear limit

5.022 mm

Intake guide: Standard diameter

5 +0+0.012mm

Intake guide: Wear limit

5.022 mm

- If the width of the impression on the valve seat or the diameter of the valve guide exceed the specified
limits, replace the cylinder head.

- Check width of the impression on the valve seat «V»

Characteristic

Wear limits:

Max. 1.6 mm.

ENG - 96

MSS Fly 50 4T Engine

Inspecting the valves

- Measure the diameter of the valve stems in the
three positions indicated in the diagram.

- Calculate the clearance between the valve and
the valve guide.

Characteristic

Minimum diameter allowed: Intake

4.970 mm

Minimum admissible diameter drainage

4.960 mm

Fitting clearance

Standard clearance: Intake 0.015 ÷ 0.042 mm
Standard clearance: drainage 0.025 ÷ 0.052 mm

- Check that there are no signs of wear on the
contact surface with the articulated register termi­nal.

- If the sealing surface on the valves is wider than
the specified limit, damaged in one or more points
or curved, replace the valve with a new one.

Characteristic

Valve standard length: Intake

70.1 mm

Valve standard length: drainage

69.2 mm

Fitting clearance

Max. clearance allowed: Intake 0.052 mm Max.
clearance allowed: drainage 0.062 mm

- If the checks above give no failures, you can use the same valves. For best sealing results, it is
advisable to grind the valves. Grind the valves gently with a fine-grained lapping compound. During
grinding, keep the cylinder head in a horizontal position. This will prevent the lapping compound resi­dues from penetrating between the valve stem/guide coupling.

CAUTION

TO AVOID SCORING THE CONTACT SURFACE, DO NOT KEEP ROTATING THE VALVE WHEN
NO LAPPING COMPOUND IS LEFT. CAREFULLY WASH THE CYLINDER HEAD AND THE
VALVES WITH A SUITABLE PRODUCT FOR THE TYPE OF LAPPING COMPOUND BEING USED.

ENG - 97

Engine MSS Fly 50 4T

Inspecting the springs and half-cones

- Check that the upper spring caps and the cotter
halves show no signs of abnormal wear.

Refitting the valves

- Lubricate the valve guides with graphite grease.

- Place the lower plates of the valve spring on the
head.

- Use the punch to fit the 2 sealing rings one at a
time.

Specific tooling

020306Y Punch for assembling valve sealing
rings

- Fit the valves, the springs and the upper caps.

- Using the appropriate tool, compress the springs
and insert the cotters in their seats.

Inspecting the cam shaft

- Inspect the cam shaft for signs of abnormal wear
on the cams.

Characteristic

Standard diameter - Bearing A:

Ø 12 +0.002 +0.010

mm Standard diameter - Bearing B:

Ø 16-0.015 -0.023 mm

Minimum diameter allowed - Bearing A:

ENG - 98

MSS Fly 50 4T Engine

Ø 11.98 mm

Minimum diameter allowed - Bearing B:

Ø 15.96 mm

- If any of the above dimensions are outside the
specified limits, or there are signs of excessive
wear, replace the defective components with new
ones.

N.B.
A BALL BEARING IS FITTED ON BEARING «A»; CONSE-

QUENTLY, BEARING «B» IS THE MOST IMPORTANT AS IT
WORKS DIRECTLY ON THE HEAD ALUMINIUM

Characteristic

Standard height - Intake:

25.935 mm

Standard height - Discharge:

25.935 mm

Fitting clearance

Maximum admissible axial clearance: 0.5 mm

- Check there are no signs of scoring or wear on
the rocking lever bolt.

- Measure the diameter «A».

- Measure the internal diameter of each rocking
lever. level «B».
Check there are no signs of wear on the pad from
contact with the cam and on the jointed adjustment
plate.

- In case of anomalies, replace the damaged com­ponents.

Characteristic

Minimum admissible diameter

Ø 10.970 mm

Maximum diameter allowed:

Ø 11.030 mm

ENG - 99

Engine MSS Fly 50 4T

Refitting the head and timing system components

- Fix the head on a workbench.

- Screw the tool to fit the camshaft fully down on
the bearing's inner track.

- Fit the camshaft fully into its seating together with
the bearing with the aid of a mallet.

- Remove the tool.

- Fit the head gasket after cleaning the faying sur­face carefully.

- Insert the head in the cylinder stud bolts and
tighten the 4 fixing nuts to the prescribed torque.

Specific tooling

020450Y Camshaft fitting/removal tool

Locking torques (N*m)

Head-cylinder stud bolt nuts: 6 ÷ 7 +135° +90° Nm

first fitting, upon refitting tighten again at 6 ÷ 7 90° +90° Nm

- Loosen the rocking lever registers.

- Fit the pin, the intake rocking lever and the dis­charge rocking lever.

- Lubricate the 2 rocking levers through the holes.

N.B.
IF A BEARING SEPARATES FROM THE CAMSHAFT, IT IS

ESSENTIAL TO FIT A NEW BEARING.

- Screw the limit screw for the pin and the camshaft
with the washer indicated in the figure and tighten
it to the prescribed torque.

Locking torques (N*m)

Rocking lever axle and camshaft bearing
screw 3 ÷ 4 Nm

ENG - 100