Rotax 125 MAX DD2 Operating instructions

Repair Manual 125 MAX DD2
Page 1 Issue 01/2006
Repair Manual
for ROTAX®Engine Type 125 MAX DD2
Engine version number 360.125.200
Issued: 01 2006
BRP-ROTAX GmbH & Co. KG
A-4623 GUNSKIRCHEN - Austria
www.rotax.com
www.kart-rotax.com

Repair Manual 125 MAX DD2
Page 2 Issue 01/2006
Foreword
This Repair Manual contains instructions for all the necessary repair and maintenance work on the
Rotax®Engine Type 125 MAX DD2. A special feature of the engine is the chainless and maintenance-free
direct drive, which is coupled to a straight-toothed, two-speed gear box.
This Repair Manual is based on information and the state-of-knowledge of BRP-Rotax of the product current
at the date of issue.
BRP-Rotax reserves the right to make modifications to the engine series without prior notification and to
reflect such changes in this repair manual.
All the work, information and instructions contained in this repair manual satisfy the prerequisite, that they
are presented in accordance with the best knowledge and intent. However, BRP-Rotax accepts no liability
for damages, which arise as a result of information gained from these repair instructions, nor is responsibility
accepted for errors in these instructions.
All rights, including those attached to the reproduction in full or in part of these repair instructions and their
translation are the property of the publisher of the same.
© BRP-Rotax GmbH & Co. KG
Motorenfabrik
A-4623 Gunskirchen - Austria
Tel: [phone]*
Fax: [phone]
www.rotax.com
www.kart-rotax.com
®, TM Protected brand name of Bombardier Recreational Products Inc. (BRP) and / or their subsidiaries
© 2 6 BRP-Rotax GmbH & Co. KG. All rights reserved.

Repair Manual 125 MAX DD2
Page 3 Issue 01/2006
Table of contents
Foreword .....................................................................................................................................................2
IMPORTANT INFORMATION .........................................................................................................5
Attention captions ........................................................................................................................................ 5
General preAttentionary and safety measures ...........................................................................................5
Technical data .............................................................................................................................................8
Visual inspection and servicing intervals of the engine components ...........................................................9
SPECIAL TOOLS, LUBRICATION AND SECURING DEVICES ................................................. 10
Overview of the special tools required ......................................................................................................1
Overview of the lubricants and securing devices ...................................................................................... 11
Location of the engine number ..................................................................................................................12
DISMANTLING THE ENGINE AND GEARBOX .......................................................................... 13
Dismantling the exhaust system ...............................................................................................................13
Dismantling the ignition unit .......................................................................................................................13
Removal of the gear shift .......................................................................................................................... 14
Removal of the radiator hoses ..................................................................................................................14
Removal of carburetor and intake silencer ................................................................................................15
Removal of slipper clutch ..........................................................................................................................15
Removal of the engine from the Kart chassis ...........................................................................................16
Oil draining ................................................................................................................................................16
Removal of the electric starter ..................................................................................................................16
Positioning the engine on the trestle mounting plate .................................................................................16
Exhaust outlet slider function ....................................................................................................................17
Disassembly of the exhaust outlet slider ...................................................................................................17
Removal of the exhaust gas flange ...........................................................................................................18
Removal of the carburetor socket and valve fitting ....................................................................................18
Removal of spark plug............................................................................................................................... 19
Removal of cylinder head cover and combustion chamber insert ............................................................19
Removal of cylinder head cover ................................................................................................................19
Removal of combustion chamber insert ...................................................................................................19
Removal of coolant thermostat .................................................................................................................2
Removal of cylinder ...................................................................................................................................2
Removal of the piston and piston ring .......................................................................................................2
Removal of the water pump shaft .............................................................................................................21
Removal of the gear shift mechanism ......................................................................................................21
Disassembly of the clutch, primary and balance drive ..............................................................................22
Overview of clutch components ................................................................................................................22
Disassembly of the crank and gearbox housing .......................................................................................24
Overview of the crank and gearbox housing components ........................................................................ 24

Repair Manual 125 MAX DD2
Page 4 Issue 01/2006
DISASSEMBLY , INSPECTION AND ASSEMBLY OF SPECIFIC COMPONENTS .................... 26
Carburetor .................................................................................................................................................26
Crank and gearbox housing ......................................................................................................................27
Shaft seal, water pump .............................................................................................................................27
Other shaft seals .......................................................................................................................................28
Needle and ball bearings ...........................................................................................................................28
Gear box ....................................................................................................................................................29
Crankshaft .................................................................................................................................................31
Conrod set - Repair set .............................................................................................................................32
Piston and piston ring ................................................................................................................................33
Piston pin, needle bearing and retaining rings ...........................................................................................34
Cylinder .....................................................................................................................................................35
Piston and cylinder sizing ..........................................................................................................................35
Centrifugal clutch and starter crown wheel ...............................................................................................36
Clutch drum with drive gear ......................................................................................................................37
Gear transmission .....................................................................................................................................38
Electric starter ...........................................................................................................................................38
Radiator .....................................................................................................................................................4
Overload clutch .........................................................................................................................................41
ASSEMBLY OF GEARBOX AND ENGINE ................................................................................ 42
Installation of the crankshaft and gearbox housing ....................................................................................42
Overview of crank and gearbox housing components .............................................................................. 43
Installation of the water pump shaft ...........................................................................................................45
Installation of the clutch, primary and balance drive ..................................................................................46
Overview of clutch components ................................................................................................................46
Installation of the piston and piston pin ...................................................................................................... 49
Installation of the cylinder ..........................................................................................................................5
Installation of the combustion chamber insert and cylinder head cover .................................................... 51
Installation of the spark plug ...................................................................................................................... 52
Installation of the outlet slider ....................................................................................................................52
Installation of the exhaust gas port ............................................................................................................54
Installation of the valve fitting and carburetor socket ................................................................................. 54
Installation of the overload clutch...............................................................................................................55
Installation of the carburetor ...................................................................................................................... 55
Installation of the ignition box .....................................................................................................................55
Installation of the engine on the chassis ....................................................................................................56
Installation of the fuel pump .......................................................................................................................56
Installation of the intake silencer ................................................................................................................57
Installation of the gear shift ........................................................................................................................57
Installation of the exhaust system .............................................................................................................58
Installation of the radiator ...........................................................................................................................59
Installation of the radiator hoses ................................................................................................................6

Repair Manual 125 MAX DD2
Page 5 Issue 01/2006
IMPORTANT INFORMATION
Attention captions
Throughout this Repair Manual emphasis is placed on specific information, which the user must unconditionally
adhere to, through the use of the following captions:
▲ Warning: Signifies information, which if not followed, could result in injury to the driver, the technician
or other persons and ultimately in their death.
■ Attention: Signifies information, which if not followed, could result in major damage to the engine.
Likewise, a risk to the health of the driver, the technician or other persons, cannot be excluded.
◆ Note: Useful information designed to provided assistance in the execution of a work instruction or
inspection/test step.
➩Signifies a work instruction
✔Signifies an inspection/test step
General preAttentionary and safety measures
▲ Warning: The ROTAX Engine Type 125 MAX DD2 has been designed and developed exclusively for
use in a Kart. Any other use renders the BRP-ROTAX factory limited warranty null and void.
■ Attention: The information provided in this repair manual is based on the experience of experts over
many years.This information also applies to the specialist under regular operating conditions.
The guidelines are sensible and necessary. However, they cannot take the place of expert
theoretical and practical instruction.
■ Attention: All spare parts used must satisfy the technical requirements specified by BRP-ROTAX.
This condition can only be guaranteed by using original ROTAX spare parts. In the event of
the use of non-approved spare parts the BRP-ROTAX limited warranty is rendered null and
void.
■ Attention: Non-approved modifications to the engine and associated components likewise releases
BRP-ROTAX from its warranty obligations.
■ Attention: A routine repair can only be guaranteed provided the prescribed special tools, devices,
securing means, seals and sealing agents and lubricants are used.
■ Attention: The prescribed tightening torques must be unconditionally adhered to.
■ Attention: When repairing engine components and undertaking engine maintenance work, dismantled
seals and retaining rings must always be replaced by the prescribed and BRP-ROTAX
approved new parts.

Repair Manual 125 MAX DD2
Page 6 Issue 01/2006
■ Attention: Dismantled nuts, bolts and other fixing elements must be reassembled in a cleaned and
rust-free condition or replaced by new parts of equivalent quality.
■ Attention: Correct observance of the prescribed maintenance interval and careful attention to the
technical documentation is decisive for the life and serviceability of the engine.
■Attention: A fundamental requirement is that on removal of the engine for repair or maintenance purposes
it should be secured on the Special Tools No. 876 762 (Trestle support) and No. 676 052
(Trestle adapter) obtainable from BRP-ROTAX.
■Attention: After assembly of the engine, inspect all components for correct seating, tightness and
correct function.
■Attention: Eliminate small defects as soon as they are discovered, in order to avoid the possibility of
major engine damage.
■Attention: Adhere unconditionally to the safety recommendations of the Kart manufacturer.

Repair Manual 125 MAX DD2
Page 7 Issue 01/2006

Repair Manual 125 MAX DD2
Page 8 Issue 01/2006
Technical data
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Repair Manual 125 MAX DD2
Page 9 Issue 01/2006
Visual inspection and servicing intervals of the engine components
▲W arning: All repair and maintenance work must only be carried out by a qualified technician.
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Repair Manual 125 MAX DD2
Page 10 Issue 01/2006
SPECIAL TOOLS, LUBRICATION AND SECURING DEVICES
Overview of the special tools required
Fig. 1
Pos. ROTAX Part No. Description Use
1 277 380 Locking tool Locking the crankshaft
2 676 022 Installation tool Shaft seal, hollow shaft
3 676 030 Installation tool Bearing sleeve, E-Starter
4 676 032 Installation tool Clamping sleeve WP impeller
5 676 021 Installation tool Shaft seal, water pump
6 676 190 Locating/locking device for primary gear wheels 34, 35, 36 teeth
7 676 192 Locating/locking device for primary gear wheels 32, 33, 37, 38 teeth
8 676 035 Installation tool Piston pin circlips
9 676 200/202 Locking device assy. for locking starter toothed ring
10 876 762 Trestle support assy. Engine support device for servicing and repair
work
11 676 052 Trestle adapter for ROTAX engine FR 125 MAX DD2
12 251 680 Spring hook Engine
13 297 040 ROTAX logo with registered serial number
Table 3

Repair Manual 125 MAX DD2
Page 11 Issue 01/2006
Fig. 2
Overview of the lubricants and securing devices
Item ROTAX Part No. Description Use
14 297 434 Loctite Antiseize 15387
15 899 788 Loctite 648 Screw locking
16 899 785 Loctite 221 Screw locking
17 897 161 Molykote 111
18 297 386 Silastic 732 Sealing
19 897 330 Lithium base grease Roller bearing grease
20 897 651 Loctite 243 Screw locking
Table 4
111
111
SILASTIC
732 RTV
18
16 20
17
19
14
15

Repair Manual 125 MAX DD2
Page 12 Issue 01/2006
Fig. 3
Location of the engine number
The engine number is stamped on the clutch side
housing half, see Fig. 3.This information is required
for the unambiguous ordering of spare parts and for
enquiries.

Repair Manual 125 MAX DD2
Page 13 Issue 01/2006
DISMANTLING THE ENGINE AND GEARBOX
◆ Note: Adhere to the operating and installation instructions of the Kart
manufacturer. The following basics apply: First allow the engine to cool
adequately and switch off all electrical power to the Kart.
◆ Note: Remove the leads from the battery terminals.
▲Warning: When disconnecting the battery leads proceed as follows - first free the
negative pole, then the positive pole. Remember, that the ignition unit is
under a high voltage (25KV) during operation, therefore removal of the
spark plug connector during operation is not permissible.
Dismantling the exhaust system
➩Free the exhaust system attachments in
accordance with the instructions of the Kart
manufacturer. See also Fig. 104 and the
installation manual.
➩Detach the exhaust springs, loosen the nuts on
the shock mountings and remove the exhaust
system.
Dismantling the ignition unit
➩Pull the spark plug connector (Item 1) from the
spark plug.
➩Detach the plug connections on the ignition
transformer (Item 4), on the spark generator (Item
3) and on the electric starter (Item 2) by pressing
the respective catch on the wiring harness.
■Attention: Always pull on the connector, not on
the cable.
➩Free the ground cable for the spark generator (Item
7) on 2 nuts (Item 15).
➩Free the starter ground cable fixing (Item 12) from
the nut (Item 14) and washer (Item 13).
➩Loosen and remove the ignition transformer (Item
6) on the nut (Item 14), washer (Item 13) and 2
rubber mountings (Item 9).
➩Free the guard plate (Item 8) on the spark
generator (Item 7) at the 2 screws (Item 10).
➩Loosen and remove the starter motor (Item 5) on
the 2 screws (Item 11).
Fig. 4
Fig. 5

Repair Manual 125 MAX DD2
Page 14 Issue 01/2006
Fig. 8
Removal of the gear shift
➩Cut through the cable ties around the Bowden
cables.
➩Unhook the gear shift actuator Bowden cables.
Removal of the radiator hoses
➩Unscrew the radiator hose for the water pump
from the connector component at the clamp
shown in Fig. 7.
➩Collect the coolant in a suitable vessel and use
again, if possible, on reassembly of the engine.
➩Detach the radiator hose from the mounting on
the cylinder head cover, after first unscrewing
the clamp, as shown in Fig. 8.
Fig. 6
Fig. 7

Repair Manual 125 MAX DD2
Page 15 Issue 01/2006
Removal of carburetor and intake silencer
▲ Warning: Any spilt and overflowing gasoline
must be immediately absorbed with
the aid of a binding agent and
correctly disposed of. Do not work
with open flames or other sources
of ignition. Gasoline must not be
allowed to contact hot engine and
assembly components - Risk of fire
and explosion!
➩Detach the hose to the carburetor (Item 7), if
necessary, unfasten the fuel hose.
➩Remove the impulse pipe (Item 8).
➩Dismount the fuel pump (Item 9).
▲W arning: Fuel may spill out when removing the
carburetor.
➩Release the intake silencer fixing on the Kart
frame, see also Fig. 101, page 57.
➩Release the intake screw hose clamp (Item 10)
and remove the carburetor, complete with air filter
box (Item 11).
Removal of overload clutch
➩Loosen the retaining ring Allen screws (Item 1).
➩Loosen all four slipper clutch socket head
screws (Item 2) uniformly.
➩Remove the overload clutch from the hollow
shaft by moving it towards the left.
Fig. 9
Fig. 10
Fig. 11

Repair Manual 125 MAX DD2
Page 16 Issue 01/2006
Fig. 14
Removal of the engine from the Kart chassis
➩Free the engine support following the Kart manufacturer’s instructions.
➩Lift the engine from the Kart chassis using a suitable hoist.
Oil draining
➩Remove the oil drain screw (Item 1) with sealing
(Item 2) from the crank and gearbox housing.
Drain the oil into a suitable vessel and dispose
of it in the correct manner.
Removal of the electric starter
➩Detach the electric starter (Item 1), complete,
from the crank and gearbox housing (Item 3) by
removing the 2 Allen screws (Item
2).Disassembly and inspection of the electric
starter is described from page 38. Free the
ground cable (Item 4) from the housing.
Positioning the engine on the trestle mounting
plate
➩Loosen the Hall probe fixing screws and remove
the Hall probe from the engine housing.
➩Unscrew the base plate from the engine, position
the engine on the trestle mounting plate, see Fig.
14, and fix it securely with the 4 fixing screws.
◆ Note: Special tool – ”Trestle support,
complete with trestle adapter
mounting plate” ROTAX-No. : 876
762, 676 052.
Fig. 12
Fig. 13

Repair Manual 125 MAX DD2
Page 17 Issue 01/2006
Exhaust outlet slider function
◆ Note: The engine has a pneumatic exhaust outlet control to optimize the
performance characteristics. Air pressure controls the slider bellows via
the impulse bore. The slider piston pulls up the exhaust outlet slider and
thus provides a longer outlet control time.The fuel throughput and therefore
also the power is increased.
◆ Note: Adjustment to determine the optimum opening of the outlet slider can only
take place under load - on the track, during actual operation. The exhaust
gas temperature has a decisive influence on the opening behavior of the
outlet slider.The temperature curves during driving operation are completely
different to those obtained on the engine test stand and during idling.
Therefore the adjustment and changes to the adjustment of the outlet slider
during idling are not suitable for predicting performance behavior during
actual driving operation.
Disassembly of the exhaust outlet slider
➩Release the spring clip (Item 1).
➩Remove and store the slider cover (Item 3), complete with adjuster screw (Item 2)
and pressure spring (Item 4).
➩Lift away the outer tubular spring (Item 7).
➩Unscrew the slider piston (Item 5) using a T-spanner.
➩Remove the inner tubular spring (Item 8) from the slider bellows (Item 6), push out the
slider bellows from the slider piston.
➩Free the slider guide, lower portion (Item 9) from the cylinder (Item 16) by undoing the
2 screws (Item 11). Remove the gasket (Item 10) and washer (Item 12).
➩Remove the outlet slider (Item 15) with o-ring (Item 14) and stud bolt (Item 13).
◆ Note: If the outlet slider or the stud bolt is replaced, on installation these must be
secured with Loctite 221.
Fig. 15

Repair Manual 125 MAX DD2
Page 18 Issue 01/2006
Fig. 17
Removal of the exhaust gas flange
➩Free the flange (Item 1) at the 2 Allen screws
(Item 2) from the cylinder (Item 3) and remove
the gasket (Item 4).
◆ Note: A leaking connection between the
outlet port and the exhaust system
leads to a loss of performance.
Removal of the carburetor socket and valve
fitting
➩Free the carburetor socket (Item 1) with the
screw hose clamp (Item 3) from the cylinder
(Item 2) by removing the 5 screws (Item 6).
➩Remove the valve fitting (Item 4) and gasket
(Item 5) from the cylinder.
✔Inspect the rubber parts for porosity.
✔Check the reed valve (Item 8) for secure seating.
✔Check the reed valve (Item.7) for damage and
cracks.
Fig. 16

Repair Manual 125 MAX DD2
Page 19 Issue 01/2006
Removal of spark plug
➩Unscrew the spark plug from its threaded
socket with the spanner SW 16.
✔Visual inspection of the spark plug for
carbonization, oil fouling and discoloration of the
electrode.
Fig. 18 shows the most frequently found examples
of spark plug unserviceability, leading to
replacement.
1 = normal
2 = fouled
3 = insulator breakage
4 = melted electrode
5 = oil carbon / deposits
Removal of cylinder head cover and combustion
chamber insert
◆ Note: If only the components in the
crankcase are to be replaced or
inspected, then the cylinder can be
removed, complete with the
peripheral components:The exhaust
socket, carburetor socket and outlet
slider remain installed.
Removal of cylinder head cover
➩Free the cylinder head cover (Item.1) on
removing the 4 screws (Item 5) from the cylinder
(Item 2).
➩Lift away the cylinder head cover, complete with
the shaped gasket (Item 3).
Removal of combustion chamber insert
➩Free the combustion chamber insert (Item 6),
complete with spring washers, on removing the
5 hexagon head bolts (Item 8).
➩Lift away the combustion chamber insert with
lower o-ring (Item 7) and upper o-ring (Item 10).
Fig. 18
Fig. 19

Repair Manual 125 MAX DD2
Page 20 Issue 01/2006
Fig. 22
Removal of coolant thermostat
➩Remove the coolant thermostat (Item 13) from
the cylinder head cover on removing the 2
screws (Item 17) on the metal mounting bracket
(Item 16).
➩Remove the thermostat from the support plate
(Item 14).
➩Remove the coil spring (Item 15).
Removal of cylinder
➩Release the cylinder by unscrewing the 4 flanged
nuts (Item 11) from the crank and gearbox
housing.
➩Remove the cylinder with base gasket (Item 12)
from the crank and gearbox housing.
➩Only loosen the screw plug (Item 4) if it is not
sealing or is damaged.
■Attention: Do not damage the piston, piston
ring and cylinder wall when
dismantling these components.
Removal of the piston and piston ring
➩Push out the piston pin retainer ring with a
suitable tool.
■Attention: In order to protect the piston pin
retainer ring from unintentional loss
in the crankcase, a suitable clean
cloth should be used to cover the
open cylinder bore.
■■
■■
■Attention: Always support the piston with the
hand in order to avoid a bending
moment on the connecting rod.
Fig. 20
Fig. 21