Traxxas S-Maxx 5109, S-Maxx Owner's Manual

MODEL 5109

OWNER’S MANUAL

Traxxas
1100 Klein Road
Plano,Texas 75074
Phone: [phone]
Toll-free 1-888-TRAXXAS

Traxxas U.K.
P. O. Box 1128
Winterbourne, Bristol BS17-2SH
England
Phone: [phone]

Internet
www.Traxxas.com
E-mail: [e-mail]

Entire contents ©2004 Traxxas.Traxxas,S-Maxx, TRX 2.5, TQ-3,Top
Fuel, EZ-Start, Ready-To-Race, Ready-To-Win and ProGraphix are
trademarks or registered trademarks of Traxxas. Other brand
names and marks are the property of their respective holders
and are used only for purposes of identification. No part of this
manual may be reproduced or distributed in print or electronic
media without the express written permission of Traxxas.

040401

2

Thank you for purchasing a Traxxas S-Maxx (Stadium Maxx) nitro
monster truck.Traxxas engineers focused on the essentials of
performance by putting plenty of horsepower in a lighter
weight, more agile monster.The new wide Maxx suspension
features multiple shock mounting adjustments, adjustable ride
height, and powerful 4-wheel disk braking. The transmission is
lean and mean with extremely low rotational mass for faster
throttle response, and quicker acceleration. Rear wheel drive
further improves the horsepower-to-weight ratio for exciting
racing action. The S-Maxx is a serious, performance-minded
machine for a new breed of driving enthusiast. Separate
modules for reverse and 4-wheel drive operation allow
customers to add optional performance features to their
Stadium Maxx. A three-channel radio system is already installed
to make upgrades easy. Plus nothing has more accessories and
customization options than a Traxxas Maxx truck!

The S-Maxx’s new TRX 2.5 Racing Engine is the most powerful
engine of its size ever available in a Ready-To-Race

®

truck. Two
years of engineering development and advanced design, along
with thousands of hours of testing, puts the TRX 2.5 in a class by
itself. Each part of the TRX 2.5 - from the air filter on the slide
carburetor,to the tip on the dyno-tuned exhaust system - has
been carefully engineered to provide maximum power over the
broadest RPM range.

Traxxas was the first with standard on-board electric starting.
The new second generation EZ-Start has evolved into an
incredibly advanced and reliable starting solution, featuring
thermal protection for the motor and built-in diagnostics to
monitor the condition of the glow plug.

Obviously,there’s much going on between the wheels of your
S-Maxx. In this manual,we’ll take you step-by-step through all
necessary set-up, break-in, tuning,and operating procedures.

Even if you are an experienced R/C enthusiast,it is
important for you to read and follow the procedures in this
manual. Pay particular attention to the fuel requirements
and break-in procedures. The advanced design of the TRX

2.5 Racing Engine does not follow old-fashioned thinking
regarding fuel and break-in procedures.

4 Before You Proceed

5 Safety Precautions

6 Tools, Supplies

and Required
Equipment

7 Anatomy of the

S-Maxx

8 Quick Start: Getting

Up to Speed

9 Gluing the Tires

10 Decorating

Your S-Maxx

11 The Traxxas TQ-3

Radio System

21 The TRX 2.5

Racing Engine

37 Driving the S-Maxx

38 Adjusting

Your S-Maxx

42 Trouble Shooting

Your S-Maxx

44 Maintaining

and Storing
Your S-Maxx

46 Index

3

Introduction

Before You Proceed

Carefully read and follow all instructions in this and any
accompanying materials to prevent serious damage to your
S-Maxx. Failure to follow these instructions will be considered
abuse and/or neglect.

Before running your S-Maxx, look over this entire manual, and
examine the truck carefully.If for some reason you decide the
S-Maxx is not what you wanted, then do not continue any
further. Your hobby dealer absolutely cannot accept a

S-Maxx for return or exchange after it has been run.

Warnings, helpful hints, and cross-references

Throughout this manual, you’ll notice warnings and helpful
hints, identified by the icons below. Be sure to read them!

An important warning about personal safety or avoiding
damage to your S-Maxx and related components.

Special advice from Traxxas to make things easier and
more fun.

Refers you to a page with a related topic.

Support

If you have any questions about your S-Maxx or its operation,
call the Traxxas Technical Support line toll-free at:
1-888-TRAXXAS (1-888-872-9927)

Technical support is available Monday through Friday from 8:30
am to 9:00pm central time.Technical assistance is also available
at www.Traxxas.com. You may also e-mail customer support
with your question at [e-mail] hundreds of
Traxxas R/C enthusiasts in our online community at Traxxas.com

Traxxas offers a full-service, on-site repair facility to handle any
of your Traxxas service needs. Maintenance and replacement
parts may be purchased directly from Traxxas, or you can save
shipping and handling costs by purchasing them from your
local hobby dealer.

4

All of us at Traxxas want you to safely enjoy your new S-Maxx.
Operate your S-Maxx sensibly and with care, and it will be
exciting, safe, and fun for you and those around you. Failure to
operate your S-Maxx in a safe and responsible manner may
result in property damage and serious injury.The precautions
outlined in this manual should be strictly followed to help
ensure safe operation.You alone must see that the instructions
are followed and the precautions are adhered to.

Important Points to Remember

R/C fuel is dangerous and highly poisonous. Always follow all
directions and precautions printed on the fuel container.

R/C fuel, especially when in a fuel dispensing bottle, may
look like a cool drink to a child. Keep all fuel out of the reach
of children at all times. Do not place fuel containers on the
ground where children can get to them while you are
driving.

R/C fuel is flammable. Never allow smoking, sparks,heat or
flame in the presence of fuel or fuel vapors.

The engine and exhaust system may become extremely hot
during use. Be careful not to touch the parts, especially when
refueling or stopping the engine.

Prolonged exposure to the engine exhaust can be harmful.
Avoid breathing the engine exhaust. Always run your S-Maxx
outdoors, in a well-ventilated area. Never run the engine
indoors.

Don’t operate your S-Maxx at night, or anytime your line of
sight to the model may be obstructed or impaired in any way.

Never operate your S-Maxx in crowds of people or busy
pedestrian areas.The S-Maxx is large and fast, and may cause
injury to those unaware of its presence.

Because the S-Maxx is controlled by radio,it is subject to
radio interference from many sources beyond your control.
Since radio interference can cause momentary loss of
control, always allow a safety margin in all directions around
your model to prevent collisions.

The engine can be loud. If the noise makes you
uncomfortable, wear ear protection. Be considerate of your
neighbors by not running your model early in the morning
or late in the evening.

Most importantly, use good common sense at all times.

▼▼ ▼▼

▼▼▼▼ ▼▼

All instructions and
precautions

outlined in this
manual should be
strictly followed to
ensure safe operation of
your S-Maxx.

The S-Maxx is not

intended for use by

those under 16
years of age without the
supervision of a
responsible and
knowledgeable adult.

5

Safety Precautions

Tools, Supplies, and Required Equipment

Your S-Maxx comes with a set of specialty metric tools.You’ll
need to purchase other items, available from your hobby dealer,
to operate and maintain your model.

For more info on
batteries, see Use

the Right Batteries

on page 13.

A peak-detecting
charger is

recommended for
best performance and
longest battery life. For
more information, see
Use the Right Charger on
page 30.

12 AA alkaline batteries for the radio system

7.2-volt NiCad battery pack for the
EZ-Start starting system

NiCad battery charger

Traxxas Top Fuel

10% quart - #5010 • 20% quart - #5020
10% gallon - #5060 • 20% gallon- #5070

Fuel dispensing bottle (Traxxas part #5001)

TR

AXX

AS

1.5mm hex wrench

2.0mm hex wrench

Glow plug (universal) wrench

Turnbuckle wrenches

Batteries

Fuel

Supplied Tools

Your S-Maxx comes with these specialty metric tools:

Other Required Tools and Supplies

Thin, hobby-quality cyanoacrylate
instant tire glue (often called CA glue)

Safety glasses

#2 Phillips screwdriver

After-run oil (WD-40™) to protect
the engine from corrosion

#1 Phillips screwdriver

Small flat-blade screwdriver (1/8 inch blade)

Filter oil (for the foam air filter)

see page 27 for details

Hobby knife

6

U-Joint wrench

Anatomy of the S-Maxx

Battery

Box

Fuel

Tank

Fuel Tank

Lid

Steering

Servo

Suspension

Arm (upper)

Bumper

(Front)

Bumper

Mount

Skid Plate

(front)

Cross-brace

Shock

(Oil Damper)

Turnbuckle

Throttle/Brake

Servo

Receiver

Box

Transmission

Air

Filter

Pipe

Header

Engine

see pg.20 for details

Pressure Line

Fuel Line

EZ-Start

Motor

EZ-Start

Plug

Bulkhead

Shock
Tow e r

Body

Mount

Spur
Gear

Chassis

7

Slipper

Clutch

Half Shaft

On/Off
Switch

Access Plug

for Receiver Crystal

Antenna

Mount

Pipe

Hanger

The following guide is an overview of the

procedures for getting your S-Maxx running,
from opening the box to breaking in and tuning your engine.
Refer to the pages indicated for details on each step.Look for the
Quick Start logo on the bottom corners of Quick Start pages.

1. Charge the battery pack • See sidebar, page 30

The EZ-Start requires a fully charged 7.2-volt
battery pack (not included).

2. Get the right fuel • See page 26

Use Traxxas Top Fuel™ or consult with Traxxas
before using other fuels.

3. Glue the tires • See page 9

Glue the tires to the rims to prevent the rims
from spinning inside the tires.

4. Install the antenna • See page 15

Install the antenna mast in the S-Maxx.

5. Decal and Install the body • See page 10

You will need to use the body during the break-in
process so it’s best to decal it before you use it on
the truck.

6. Install batteries in the transmitter • See page 13

The S-Maxx requires 8 AA alkaline or rechargeable
batteries for the transmitter.

7. Install batteries in the model • See page 14

The S-Maxx requires 4 AA alkaline or rechargeable
batteries for the receiver.

8. Install the EZ-Start battery • See page 30

Install and connect the 7.2-volt battery pack in
the EZ-Start controller.

9. Turn on the radio system • See page 18

Make a habit of turning the transmitter on first, and off last.

10. Check servo operation • See page 19

Make sure the throttle and steering servos are working
correctly.

11. Range test the radio system • See page 20

Follow this procedure to make sure your radio system
works properly at a distance and that there is no
interference from outside sources.

12. Fill the fuel tank • See page 26

Use your fuel-dispensing bottle to fill the tank.

13. Connect the EZ-Start to the model • See page 31

Learn the proper way to use the EZ-Start electric starting
system

14. Start the engine • See page 32

Learn to use the correct starting procedure for your TRX 2.5.

15. Break-in your engine • See page 32

Follow the break-in instructions exactly to ensure the best­performing, longest-lasting engine.

16. Tune your engine • See page 34

Learn how to set the fuel mixture needles for optimum
engine performance.

17. Drive your S-Maxx • See page 37

Driving tips and adjustments for your S-Maxx

18. Maintaining your S-Maxx • See page 44

Follow these critical steps to maintain the performance
of your S-Maxx and keep it in excellent running
condition.

The Quick Start
Guide is not intended

to replace the full
operating instructions
available in this manual.
Please read this entire
manual for complete
instructions
on the proper use and
maintenance of
your S-Maxx.

Quick Start: Getting up to Speed

8

The tires on your S-Maxx must be glued to the rims using CA
tire glue to prevent the rims from spinning inside the tires.You
can glue the tires without removing the wheels from the truck.
For clarity,these instructions show the process with the wheels
removed.

1. Remove a wheel from the
S-Maxx using the larger
(8mm) end of the glow plug
(universal) wrench.

2. Use your thumb to push the
side of the tire away from the
rim. Place one or two drops of
CA glue into the opening and
release the tire. Capillary
action will draw the glue
around the bead of the tire.

3. Repeat step two at four or five points around the rim, until the
tire is completely secured to the rim.Turn the rim over and
repeat the process for the inside of the rim/tire. Repeat for the
other 3 wheels.

4. Reinstall the wheels, making
sure none of the axle pins
have fallen out from behind
the hex hubs.

Always wear safety
glasses to prevent glue
from splattering into

your eyes.

The acetone in
fingernail polish

remover will
remove excess glue from
your fingers.

For best results while

gluing, clean the bead

of the tires and the
grooves of the wheels with
denatured alcohol before
applying glue. This removes
any mold release agent
residue from the tires and
wheels, providing a better
bond.

Gluing The Tires

9

Hub

Axle Pin

Decorating Your S-Maxx

Applying The Decals

The main decals have
already been applied to
your Revo.The extra decals
provided are die-cut for easy
removal. Use a hobby knife
to lift the corner of a decal
and remove it from the
backing.

Carefully position the decal
over the desired location
and press one side on the
body.Pull the decal tight
and use a finger to gradually
smooth out any air bubbles
as you apply the decal.

Look at the photos on the box for typical decal placement.

10

11

The Traxxas TQ-3 Radio System

Your S-Maxx (model 5109) is equipped with the TQ-3 Radio
System.The TQ-3 is a 3-channel system that provides high-power
output up to a quarter mile and control for up to three servos.
The S-Maxx makes use of two channels for throttle/brake and
steering.The third channel is reserved for future upgrades with
optional reverse module and third shifting servo (available
separately).

CH.3

CH.2

CH.1

Antenna

Throttle Neutral Adjust

Steering Wheel

Throttle Trim

Steering Trim

3rd Channel
Switch*

Power Switch

Power Indicator

Battery Compartment

Servo
Reversing
Switches

Throttle Trigger

S-Maxx Wiring
Diagram

Antenna

On/Off
Switch

Black
Negative

Red
Positive

Receiver

4-Cell

Battery Holder

Channel 1

Steering Servo

Channel 2

Throttle Servo

Channel 3
Channel 2
Channel 1

Battery

*

*Reserved for optional shift servo and reversing module

Your S-Maxx can be
outfitted with full

reversing capability by
installing the optional
reverse module (sold
separately).

Radio System Terminology

Please take a moment to familiarize yourself with these radio­system terms.They will be used throughout this manual.

Channel - The 27 MHz frequency band is divided into 6

channels so that up to six models can be operated
simultaneously.Each channel is referred to by its flag color and
channel number, as shown below.

Clearing your frequency - A routine, verbal check to make sure

nobody else in your area is operating on the same channel.
Always clear your frequency by calling out your channel
number before operating your model.Wait or move to
another area if your channel is already being used.

Crystal (X-tal) - The plug-in device that determines which

channel the radio system will operate on. For each channel,
there are two crystals, one for the receiver and one for the
transmitter.Of those two crystals, the one marked with the
lower number (.455 MHz lower) must be inserted into the
receiver.

Frequency band - The radio frequency used by the transmitter

to send signals to your S-Maxx. All Traxxas RTR models operate
on a 27 MHz frequency band.

Neutral position - The standing position that the servos seek

when the transmitter controls are at the neutral setting.

NiCad - Refers to rechargeable, nickel-cadmium batteries. The

most economical choice, since they may be recharged up to
500 times.

Receiver - The radio unit inside your S-Maxx that receives

signals from the transmitter and relays them to the servos.

Servos - Small motor units in your S-Maxx that operate the

throttle and steering mechanisms.

Three-channel radio system - The TQ-3 radio system,

consisting of the receiver, the transmitter, and the servos.The
system uses three channels: one to operate the throttle, one to
operate the steering, and a third channel which is reserved for
shifting with optional reverse module (sold separately).

Transmitter - The hand-held radio unit that sends throttle and

steering instructions to your S-Maxx.

Tri m - The fine-tuning adjustment of the neutral position of the

servos, made by turning the throttle and steering trim knobs
on the face of the transmitter.

Channel Frequency Band Flag Color Traxxas Part No.

1 26.995 Brown 2031

2 27.045 Red 2032

3 27.095 Orange 2033

4 27.145 Yellow 2034

5 27.195 Green 2035

6 27.255 Blue 2036

Learn terms related
to the TRX 2.5 Racing
Engine beginning on

page 23.

The Traxxas TQ-3 Radio System

12

13

The Traxxas TQ-3 Radio System

Installing Transmitter Batteries

Your TQ-3 transmitter uses 8 AA batteries.The battery
compartment is located at the base of the transmitter.

1. Remove the battery compartment door by pressing the
tab and lifting the door up.

2. Install the batteries in the correct orientation as indicated
in the battery compartment.

3. Reinstall the battery door and snap it closed.

4. Turn on the transmitter and check the power indicator for

a solid red light.

If the power indicator light flashes, then the transmitter
batteries are weak, discharged or possibly installed incorrectly.
Replace with new or freshly charged batteries.The power
indicator light does not indicate the charge level of the
receiver batteries in the model.

Use the Right Batteries

Your transmitter and receiver
use AA batteries. Use new
alkaline batteries, or
rechargeable batteries such as
NiCad or Ni-MH (nickel-metal
hydride) batteries in your
transmitter and receiver. Make
sure rechargeable batteries are
fully charged according to the
manufacturer’s instructions.

If you use rechargeable
batteries in your transmitter, be
aware that when they begin to
lose their charge, they lose
power much more quickly than
regular alkaline batteries.

Caution: Discontinue
running your S-Maxx at the
first sign of weak batteries
(flashing red light) to avoid
losing control.

If the power indicator
doesn’t light red, check

the polarity of the
batteries. Check rechargeable
batteries for a full charge.

CH.3

CH.2

CH.1

Installing Receiver Batteries

The radio receiver in your S-Maxx uses 4 AA batteries.The battery
holder for the receiver batteries is located underneath the battery
cover. The battery cover can be identified by the on/off switch.

1. Remove the battery cover by removing the two 3x10mm
roundhead self-tapping screws from the cover.

2. Remove the battery holder and install 4 AA alkaline batteries.
Make careful note of the battery polarity by comparing
against the diagrams in the battery holder.

3. Insert the battery holder into the battery cover.

4. Reinstall the battery cover and secure with the screws

(see sidebar!).

On/Off
Switch

4-cell
battery
holder

Direct the battery wires
through the slot in the
battery cover. If the

wires are not properly
routed, they may become
broken or shorted, causing
radio system failure and

loss of control. If you use

rechargeable batteries in
your receiver, be aware that
when they begin to lose
their charge, they lose
power much more quickly
than regular alkaline
batteries. Signs of weak
receiver batteries include
sluggish steering response
and shortened radio range.
Caution: Discontinue
running your
S-Maxx at the first sign of
weak batteries to avoid
losing control.

If the radio system
doesn’t appear to

work when the
transmitter and receiver
switches are turned on,
check for correct battery
installation.

The Traxxas TQ-3 Radio System

14

The Traxxas TQ-3 Radio System

15

Spray a little window
cleaner on the antenna

wire to make it easier
to push through the
antenna tube.

Don’t shorten the

length of the antenna

wire. Its length is tuned
to the frequency band;
cutting it could severely
shorten the radio system’s
range.

Don’t push the

transmitter antenna

down from the top. Pull
it down from the bottom,
one segment at a time, to
prevent binding and kinking
the antenna mast.

Setting Up the Antenna

You must install the antenna mast (tube) before you operate
your S-Maxx.You’ll find the plastic antenna tube and tip in the
bag with your manuals and documentation.

1. Locate the black antenna wire that exits the receiver cover.
The S-Maxx receiver cover is mounted on the top of the
chassis, near the front.

2. Pull the wire straight with your fingers and then insert the
end of the wire into one end of the antenna tube. Push the
wire all the way through the antenna tube.

3. Pull the remaining wire through the antenna tube, and then
insert the base of the antenna tube into the molded post on
top of the receiver cover.

4. Fold the remaining antenna wire over the top of the tube
and secure it with the antenna tip.

5. On the transmitter, always fully extend the telescoping
antenna when running your S-Maxx. Make a habit
of holding the transmitter so that the antenna points
straight up.

Antenna Tip

Antenna Tube

The Traxxas TQ-3 Radio System

CH.3

CH.2

CH.1

ACCELERATE BRAKE

L

E

F

T

NEUTRAL

R

I

G

H

T

TQ-3 Radio System Controls

16

Other TQ-3 Radio System Adjustments

In addition to the electronic throttle and steering trim controls,
your radio system features throttle neutral adjustment and
servo reversing switches.

Throttle Neutral Adjustment

The throttle neutral adjustment is located on the transmitter
face and controls the forward/brake travel of the throttle
trigger. Change the adjustment by pressing the button and
sliding it to the desired position.There are two settings
available:

50/50: Allows equal travel for both acceleration and braking.

70/30: Allows more throttle travel (70%) and less

brake travel (30%).

50/50 is the required setting for the S-Maxx with
the TRX 2.5 Racing Engine.

Electronic Throttle Trim

The electronic throttle trim located on the face of the
transmitter adjusts the neutral (center) point of the throttle
servo when the servo is at rest. This control has been preset for
you at the factory. If necessary, adjust the control so that the
carburetor is at idle, and the brakes are not applied (the model

▼▼

The Traxxas TQ-3 Radio System

17

will roll freely). Do not use the throttle trim to raise or lower the
engine idle speed. Make the idle speed adjustment on the
carburetor.

Electronic Steering Trim

The electronic steering trim located on the face of the
transmitter adjusts the neutral (center) point of the steering
servo when the servo is at rest. Adjust this control to make the
model drive straight with no steering input at the wheel.

Servo Reversing Switches

The servo reversing switches are located on the front of the
transmitter,next to the on/off switch. Moving a switch reverses
the direction of the corresponding servo.

Each switch corresponds to a channel, as shown below. For
example, if you turn the steering wheel to the right and your
front wheels turn left, you would move the channel 1 switch to
correct the servo direction. It may be necessary to adjust the
corresponding trim control after moving a switch.

CH.3

CH.2

CH.1

Channel Servo

1Steering
2Throttle and braking
3(Available for future use.)

TQ-3 Radio System Rules

Each time you prepare to run your
S-Maxx, you must clear your frequency
to be sure no one else in the area is
using the same channel as you.

There are six possible channels,
numbered 1 through 6. Each is
represented by a color. Look at the
crystal plugged into the back of your
transmitter to determine which channel
your truck is assigned to.

Always turn your TQ-3 transmitter on first and off last. This
procedure will help to prevent your S-Maxx from receiving
stray signals from another transmitter, or other source, and
running out of control.

Always have the transmitter and receiver turned on before
you start the engine. Never turn the radio system off while
the engine is running.The on/off switch in the model only
turns the receiver on and off.It does not turn off the engine.

Always use new or freshly charged batteries for the radio
system. Weak batteries will limit the range of the radio signal
between the receiver and the transmitter. Loss of the radio
signal can cause you to lose control of your S-Maxx.

▼

▼▼ ▼

Channel 1

Brown

Channel 2

Red

Channel 3

Orange

Channel 4

Yellow

Channel 5

Green

Channel 6

Blue

C

H

.3

C

H

.2

C

H

.1

1

23

Remember, always
turn the TQ-3

transmitter on first
and off last to avoid
damage to your S-Maxx.

18

The Traxxas TQ-3 Radio System

The Traxxas TQ-3 Radio System

Using the TQ-3 Radio System

The TQ-3 Radio System was pre-adjusted at the factory. The
adjustment should be checked, before running the model, in
case of movement during shipping. Here’s how:

1. Fully extend the chrome antenna mast on the transmitter

and turn the switch on.The red indicator light on the
transmitter should be solid red (not flashing).

2. Tu rn on the receiver switch in the model.The switch is

located on the battery cover.

3. Position the S-Maxx so that its front wheels are off the

ground.

4. Tu rn the steering wheel on the transmitter back and forth

and check for rapid operation of the steering servo. Also,
check that the steering mechanism is not loose or binding. If
the steering operates slowly,check for weak receiver
batteries.

5. When looking down at model, the front wheels should be

pointing straight ahead. If the wheels are turned slightly to
the left or right, slowly adjust the steering trim control on the
transmitter until they are pointing straight ahead.

6. Operate the throttle trigger on the transmitter and check for
rapid operation of the throttle servo.When the throttle
trigger is pulled back, the carburetor should open.When the
throttle trigger is pushed all the way forward, the brake
should lock.

7. Once adjustments are made, turn off the receiver on your
S-Maxx, followed by the handheld transmitter.

Throttle/Brake

Servo

Throttle

Brake

Steering

Servo

0° 0°

S-Maxx Servo
Operation

When the engine is
running, don’t use

the throttle trim on
the transmitter to adjust
the engine idle speed.
Instead, use the idle speed
adjustment on the
carburetor.

Because your

S-Maxx features zero-

scrub-radius
suspension and wide tires,
the steering servo will not
fully turn the front wheels
when the vehicle is not
moving.

19

The Traxxas TQ-3 Radio System

Range-Testing the TQ-3 Radio System

Before each running session with your S-Maxx, you should range­test your radio system to ensure that it operates properly.

1. Tu rn on the radio system and check its operation as described
in the previous section (Using Your Radio System, pages 17- 19).

2. Have friend hold the model with the engine off.

3. Make sure your transmitter antenna is fully extended, and then

walk away from the model with the transmitter until you reach
the farthest distance you plan to operate the model.

4. Operate the controls on the transmitter once again to be sure
that the model responds correctly.

5. Do not attempt to operate the model if there is any problem
with the radio system or any external interference with your
radio signal at your location.

Don’t attempt to
operate your

S-Maxx if there are
any problems with your
radio system or radio
interference at your
location.

20

Introduction

There’s nothing like the TRX 2.5 Racing Engine in your new
S-Maxx. The TRX 2.5 Racing Engine is vastly superior to typical
R/C engines and belongs in the category of specialty high­performance racing engines. It’s the result of years of focused
engineering development, and thousands of hours of
controlled testing and rigorous real-world running.It offers
unprecedented power and performance that turns ready-to-run
into Ready-To-Race

®

.

The TRX 2.5 Racing Engine takes a total-system approach.Each
part of the engine, from the air filter to the exhaust tip, is
carefully engineered to work in harmony with other engine
components. Each part complements the next, to extract
maximum power.The TRX 2.5 is designed to be tolerant of
variations in tuning, and to run successfully through a wide
range of variable atmospheric conditions, such as changes in
temperature, humidity, and altitude.

The TRX 2.5 is manufactured to exacting tolerances and requires
a specially-designed break-in procedure to accomplish the final
precision fitting of the internal engine components. It is very
important that you follow the new break-in procedure as closely
as possible to achieve the best performance and longest life
from your TRX 2.5 Racing Engine.Old style break-in procedures,
such as simply running the engine with a very rich fuel mixture
for the first 4 tanks of fuel, will not achieve the best results.
Follow the steps in this manual.

A routine maintenance schedule is also required to keep the
TRX 2.5 in top running condition. Cleaning the air filter after
each hour of running is particularly important. Also it is
extremely important to perform after-run maintenance on the
engine to prevent corrosion from building up on the internal
engine components (see page 45).

Traxxas strongly
discourages changing

or modifying any part
of the TRX 2.5 Racing
Engine. Old tech tips and
tricks that may have
boosted the power of other
engines could seriously
diminish the performance
of the TRX 2.5.

There’s more advanced
thinking, development and
testing in the stock parts of
your TRX 2.5 than in many
aftermarket manufacturer’s
so-called performance
parts. The TRX 2.5 is already
the most powerful engines
in its class and simply will
not benefit from average,
low-tech, aftermarket bolt
on performance items.

The TRX 2.5 Racing Engine

21

The TRX 2.5 Racing Engine

TRX 2.5 Illustrated

Air

Filter

Head Protector

Head (Cylinder head)

EZ-Start

Drive Unit

EZ-Start

Motor

Engine
Mount

Low-Speed

Needle

Throttle

Arm

Clutch

Bell

Flywheel

Carburetor

Air Intake

Fuel Intake

High-Speed Needle

Idle Speed

Screw

EZ-Start

Plug

Positive

Wire

Negative

Wire

Fuel Line

Fuel Tank

Pipe

Exhaust

Tip

Pressure

Line

Ground

Wire

Glow Plug

Wire

EZ-Start

Controller

22

Crankshaft

Crankcase

The TRX 2.5 Racing Engine

Terms to Know

You’ll find these Nitro R/C engine terms throughout this
section of the manual.

.15 - .15 or “15”refers to the size of the engine. The TRX 2.5 is .15

cubic inches or 2.5 cubic centimeters (cc).The name “TRX 2.5”
is derived from the cc measurement.

ABC - Abbreviation for aluminum, brass,and chrome. Refers to

engine construction that consists of an aluminum piston that
slides in a chrome-plated brass sleeve.The TRX 2.5 uses ABC
construction.

Air filter - The air filter sits atop the carburetor and prevents

harmful dust and dirt from entering the engine. Dirt ingestion
is the number one cause of premature engine failure so the
engine should never be run without the air filter in place.

Big Block .15 - A .15 (2.5) engine that uses a larger crankcase

size and longer stroke than typical .15 engines. Generally only
used for specific racing classes.

Break-in - Break-in is the procedure for running a brand new

engine according to specific instructions.This correctly
prepares the engine for normal running.The break-in
procedure can be different for different makes of engines.
Follow the Traxxas directions for break-in exactly.

Carb - Abbreviation for carburetor.
Carburetor - The carburetor atomizes (mixes) the fuel with the

air so that the engine can burn it. There are two types of
carburetors, slide carbs and barrel carbs. The TRX 2.5 uses the
superior slide carburetor design.

Clean-out - Cleaning-out is a condition that occurs when the

engine is accelerating and the fuel mixture becomes
sufficiently lean to allow the engine to continue into its upper
RPM power band. Usually characterized by a noticeable
decrease in blue exhaust smoke and a dramatic increase in
engine speed.

Combustion chamber - The combustion chamber is machined

into the bottom of the cylinder head.This is where the glow

plug ignites the fuel.The shape of the combustion chamber is
designed to promote more efficient burning of the fuel.

Connecting rod - The connecting rod transfers the piston

motion to the crankshaft.The TRX 2.5 Racing Engine uses a
“knife-edged” connecting rod. The aerodynamic, sharpened
edges allow it to “slice”through the pressurized air/fuel
mixture inside the crankcase.

Cooling fins - The cooling fins are molded into the cylinder

head and crankcase and cause heat to be drawn away from
the engine. Heat is removed when it dissipates into the air
passing across the cooling fins. It is important to keep the fins
clean of dirt and debris for maximum cooling efficiency.

Crankcase - The engine “body” that contains all of the running

mechanical components.

Crankshaft - The main shaft of the engine that contains the

rotating assembly.

Cylinder head (head) - The finned aluminum part on top of the

engine that is responsible for dissipating most of the engine’s
heat. The combustion chamber is machined into the bottom of
the head.

Dyno - Abbreviation for dynamometer. A precise piece of

testing equipment that accurately measures engine power
and torque output over the engines entire RPM range.

EZ-Start - Second generation Traxxas on-board electric starting

system.The system consists of a hand held starter control unit
and an on-board gearbox with an electric motor to spin the
engine.The new EZ-Start contains many performance and
reliability improvements over the first generation EZ-Start.

Filter foam - The oiled foam element inside the air filter

housing.The filter foam in the TRX 2.5 must be thoroughly
cleaned and re-oiled after every hour of run time.

Fit - Usually refers to the fit of the piston and sleeve. If the fit is

tight, then the piston will feel very tight at top of the sleeve
and the engine will have good sealing and compression. If the
fit is loose, then compression will be low and the piston and
sleeve should be replaced.

Learn terms related
to the TQ-3 Radio
System on page 12.

23

The TRX 2.5 Racing Engine

Flame-out - Occurs when the engine stops running at high

RPM. Usually the fault of an excessively lean fuel mixture or
glow plug failure.

Fuel - (10% 20%) The TRX 2.5 must have model engine fuel to

run. Traxxas Top Fuel is recommended.Fuel is sold in quarts
and gallons from hobby dealers.The 10 and 20% labeling
refers to the percentage amount of nitromethane contained in
the fuel (see “nitro percentage” definition).

Fuel mixture - The ratio of fuel to air as determined by the

needle settings of the carburetor.

Fuel tubing (fuel line) - The thick silicone tubing that carries

fuel from the fuel tank to the carburetor.

Glow plug - The glow plug is located in the cylinder head at the

top of the combustion chamber.It contains a platinum
element that glows red hot when voltage is applied.When the
engine is being started, the heat from the glow plug ignites
the fuel mixture and starts the combustion process.

Glow plug driver - This tool clips onto the glow plug and

supplies the required voltage to light the glow plug element. It
is also called an igniter.EZ-Start equipped engines do not
require this separate tool.

Header - The aluminum tube that connects the exhaust system

to the engine exhaust port. The length and diameter of the
header must be carefully selected to extract the most power
from the engine.

High-speed needle - Adjusts the carburetors fuel/air mixture at

high RPM.

Idle speed - The speed (RPMs) the engine runs at when the

transmitter’s throttle trigger is at neutral.

Idle speed screw - Located on the carburetor body.

Thi screw adjusts the idle RPM of the engine.

Lean - A running condition where the engine is not getting

enough fuel (for the available air). Symptoms include engine
overheating, or the engine runs for a short time and then

stalls, particularly at high speed. This is a dangerous
condition that should be corrected immediately or it can
ruin your engine.

Leaning the mixture - Turning either the high speed and/or

low-speed needle(s) clockwise to decrease the amount of fuel
the engine receives.

Low-speed needle - Needle valve that controls the low-speed

fuel mixture.

Needle valve - Valve consisting of a tapered needle that closes

against a corresponding seat to regulate fuel flow.

Nitro - Abbreviation for nitro methane, a component of model

engine fuel that improves fuel combustion and power output.
Nitro also refers to a class of RC powered by model engines
instead of electric.

Nitro content - The amount of nitro methane used in the fuel.

Usually measured as a percentage of the total fuel volume.
Traxxas engines are optimized to use 10-20% nitro. 30% nitro
may be used for racing.

Nitromethane - Nitro methane is a component in the fuel that

increases power from the combustion process up to a point.
Engines are generally optimized to use a range of nitro
content for the best power.

O-ring - Rubber “O”-shaped ring used as a sealing gasket.
Pipe - Abbreviation for the tuned exhaust pipe on a nitro

engine. See “Tuned Pipe” definition.

Piston - The piston is the internal engine part that is attached to

the upper end of the connecting rod and moves up and down
in the cylinder sleeve.The precise fit between the piston and
the sleeve creates a seal that allows engine to have the
required compression for combustion.

Port - Ports are openings in the sleeve that allow atomized fuel

to enter the combustion chamber and burned exhaust gasses
to exit. The shape and location of the ports are a large factor in
controlling the engine timing and power output.

24

Priming - Manually causing fuel to move from the fuel tank up

to the carburetor.This is sometimes necessary after the engine
has been sitting for a long period of time and all the fuel has
drained back to the tank. On a Traxxas model this is done by
holding your finger over the exhaust tip for one or two
seconds while the engine is starting.

Punch - A term that refers to how quickly the model responds

to throttle input or how quickly it accelerates.

Rich - A running condition where the engine is getting too

much fuel for the available air. It is better to run an engine
slightly rich to increase engine life. Excessively rich mixtures
cause the engine to have sluggish performance with
exaggerated blue smoke and unburned fuel coming from the
exhaust.

RPM - Abbreviation for revolutions per minute (how many times

the engine crankshaft spins in a minute).

Sleeve - Internal engine part that contains the piston. The

precise fit between the sleeve and the piston creates a seal
that allows engine to have the required compression for
combustion.The sleeve in a TRX engine is made of brass and is
then hard-chrome plated.

Slide carburetor - The throttle on a slide carburetor closes and

opens by sliding a barrel in and out of the carburetor body.
This type of carburetor is preferred for performance use
because it provides a less restrictive “straight-through” air path
than the barrel carburetor design.

Stall - When the engine stops running, usually due to an

incorrect fuel mixture setting or running out of fuel.

Tuned pipe - The tuned exhaust pipe usually consists of a

specially-shaped metal or composite chamber with baffles
that is designed to enhance the power output of the engine.

Wear-in - Fitment process that occurs during engine break-in

where internal engine parts develop an even more precise
matched fit through actual use under controlled
circumstances.

WOT - Abbreviation for wide-open throttle.

The TRX 2.5 Racing Engine

25

The TRX 2.5 Racing Engine

The Fuel

Use the Right Fuel

It’s imperative that you use the correct fuel in
your TRX 2.5 for maximum performance and
engine life.Traxxas Top Fuel should be used
to ensure correct engine lubrication,
performance, and ease of tuning. Traxxas Top
Fuel has been proven in thousands of engines,
so you can count on it every day for great
performance.

Top Fuel is the only fuel which is 100% certified for use in
Traxxas engines.
Traxxas Top Fuel is made with just the right balance of the
highest grade natural and synthetic lubricants to allow
excellent throttle response and the best top-end
performance, without sacrificing long-term durability.
All of the components in the fuel are carefully selected from
the best materials available and then custom blended to
match the metallurgy and temperature characteristics of
Traxxas engines.

You may use 10% or 20% nitro-content fuel. Use the same
percentage all the time; don’t switch back and forth between
10% and 20% fuel. If you break-in your engine on 20% fuel, then
always use 20% fuel.

What about Other Fuels?

Can other brands of fuel be used besides Top Fuel? There are
other fuels that can provide satisfactory performance; however
there could be long-term costs in the form of decreased engine
performance, loss of tuning ease, and shorter engine life.

Everyone has an opinion or a claim to make about fuel. The
engineering team at Traxxas spent over 2-years developing the
TRX 2.5 Racing Engine. No one knows more about the specific
fuel requirements of Traxxas engines, than Traxxas engineers.We
strongly urge you not to take chances with your engine
investment and use the Traxxas fuel made for the TRX 2.5.

Handling the Fuel

Follow all directions and warnings on the fuel can.

Keep the fuel tightly capped at all times. Some components
in the fuel can evaporate very quickly and upset the balance
of the fuel.
Do not store unused fuel in the fuel dispenser.Immediately
return fresh unused fuel back into the fuel can.
Do not mix old and new fuel. Never mix different brands of
fuel together.
Store the fuel in a cool dry location, away from any source of
heat, ignition,or combustion.
Read and follow the safety precautions on page 5
in this manual.

Filling the Fuel Tank

Use a fuel dispensing bottle (Traxxas Top
Fueler, part# 5001) to put fuel into the
S-Maxx’s fuel tank.To fill the fuel bottle,
squeeze the air out, insert the dispenser
tip into the fuel can, and release your grip
on the bottle. As the bottle
expands, fuel will be
drawn into it.

To fill your model flip up
the spring-loaded cap on
the fuel tank, insert the tip
of the fuel bottle, and
squeeze to dispense the
fuel. Fill the tank until the
fuel level reaches the base of the filler neck. Close the fuel tank
lid, making sure it closes tightly.

Fuel Tank Seal Adjustment

The rubber seal on the fuel tank is important to the function of
the engine.The fuel tank is pressurized by the exhaust system to
provide reliable fuel flow.If the tank lid does not seal properly,
an air leak will be created that can cause your engine to run
erratically and be difficult to start. If necessary, the rubber O-ring
tank seal can be adjusted for improved sealing by tightening
the screw on the underside of the tank lid.

▼▼▼▼ ▼▼

▼▼▼

You may use higher
nitro percentages than

20% in certain
circumstances. Call 1-888­TRAXXAS for more
information.

26

The Air Filter

The TRX 2.5 air filter is carefully designed to deliver maximum
performance while protecting your engine from dust and dirt.
Use only the supplied filter.You will not improve engine
performance by switching to an aftermarket filter, and you
may risk engine damage due to poor filtration.

The TRX 2.5 air filter assembly consists of 3 pieces:

1. A rubber filter base

2. A plastic housing consisting of a permanently assembled

mesh cap and body

3. An oiled foam element

You must clean the filter after every hour of runtime, even if the
filter looks clean. Dust (which is often too fine to see) and dirt
constantly move through the filter anytime the engine is
running. Even if you can’t see dirt on the filter,it is present inside
the foam after any amount of runtime. If you exceed the
recommended cleaning intervals, your engine will be damaged.
Engine damage or wear due to dirt ingestion is easy to detect,
and one of the top causes of premature engine failure.

Air Filter Cleaning Instructions

1. Remove the air filter from the

carburetor bore by pulling
the entire filter firmly to the
side to release it. Do not pull
straight up.

2. Disassemble the filter.Pull the

rubber base out of the filter
body.With the base removed, the foam element is visible in
the bottom of the filter body.Pull out the foam element.

3. Clean the filter parts by thoroughly washing all three pieces of
the filter assembly in hot soapy water (dishwashing detergent
works well). Repeat twice.

4. Thoroughly dry the parts with a clean towel or compressed air.
Remember to wear your safety glasses when working with
compressed air.

5. Oil the foam element by saturating it with foam filter oil.Use
the supplied Traxxas filter oil (part# 5263) or a high-quality,
special-purpose foam filter oil like what is used for high­performance motorcycle and ATV engines.This type of filter oil
is available at motorcycle pro-shops.If foam filter oil is not
available, clean 30-40 weight motor oil can be substituted, but
is not preferred.Never run the engine without a properly
oiled filter! Apply 30 drops of the Traxxas filter oil evenly to
the top, bottom and sides of the filter element (30 total drops
divided among the 3 surfaces). Squeeze the filter element
repeatedly to help spread the oil throughout. Squeeze the
excess oil from the foam.The filter element should be evenly
colored by the oil. Even color indicates that the oil is evenly
distributed. Note: Do not use the air filter oil for anything

other than the air filter. It is not meant to be a lubricant.

6. Reassemble the filter and install it on the engine,making sure
the rubber base fits securely on the carburetor with no gaps or
air leaks.

The TRX 2.5 Racing Engine

Clean your air filter
after every hour of

runtime to avoid
engine damage, even if the
filter looks clean.

If you use compressed

air to dry your air filter

assembly, wear safety
glasses and avoid directing
compressed air toward
your skin.

27

The TRX 2.5 Racing Engine

The Carburetor

Understanding the Carburetor adjustments

The carburetor performs several functions. It controls the
engine’s speed by restricting the intake of air and fuel into the
engine. It atomizes the fuel (suspends the fuel droplets in the
air) and also controls the air/fuel ratio of the mixture entering
the engine (how much air for a given amount of fuel).

To help provide a better understanding of engine tuning and
why it’s necessary, the following is a brief explanation of the
air/fuel combustion process that takes place inside the engine.

In order to create the cylinder pressure that results in power, the
engine burns the air/fuel mixture. Both air and fuel,in correct
amounts, are needed for proper combustion. It is the
carburetor’s job to mix the air and fuel together (atomize the
fuel), in the correct proportion for the best possible combustion.
This is the ideal air/fuel ratio.The ideal air/fuel ratio required for
the engine remains roughly constant. Due to variations in
atmospheric conditions (temperature, humidity, altitude etc.)
fuel flow adjustment valves (called fuel mixture needles) are
required to meter the fuel and maintain the ideal air/fuel ratio in
these ever-changing conditions. For example, colder air is more
dense (more air molecules) for a given volume of air and
therefore requires more fuel (more fuel molecules) to maintain

the correct air/fuel ratio.Warmer air is less dense (fewer air
molecules) and therefore needs less fuel to maintain the correct
air/fuel ratio.The tuning needles are there to adjust how much
fuel is made available for the carburetor to mix with the
available air (atomization).

The Fuel Mixture Needles

The amount of fuel metered and atomized by the carburetor is
controlled by the two mixture needles, the high-speed needle
and the low-speed needle.The low-speed needle is used to
meter the fuel used by the engine at idle and low RPM (part­throttle) engine speed.The high-speed needle is used to meter
the fuel when the throttle is open from part throttle to wide­open throttle (WOT).Two needles on the TRX 2.5 provide precise
control of the air/fuel ratio across the engine’s entire RPM range.

The maximum possible fuel flow is always controlled by the
high-speed needle. It works like the main water valve on a
garden hose.Turn it clockwise to close the valve,counter­clockwise to open it. When the throttle is at idle or partially
open, the low-speed needle again meters the fuel flow at the
outlet (needle seat) where the fuel enters the carburetor venturi.
This second valve acts like the spray nozzle at the end of the
garden hose in our example.When you accelerate from idle, the
throttle opens and the low-speed needle is pulled away from
the needle seat. This allows more fuel to flow with the increased
air flow.As the throttle is increased, the low-speed needle is

28

See page 35 for
more information on
how air density

affects engine tuning.

Air

Fuel

Dense Air Less Dense Air

pulled completely away from the needle seat leaving it fully
open. At that point, fuel metering is entirely controlled by the
high-speed needle. Again, using our water hose example,when
the spray nozzle at the end of our garden hose is fully open,
then the main water valve can be used to adjust how fast the
water flows.

The engine’s performance is directly linked to the fuel
mixture. Richening the fuel mixture increases the amount of
fuel in the air/fuel mixture ratio and leaning the fuel mixture
decreases the amount of fuel in the air/fuel mixture ratio.

Slightly lean fuel mixtures deliver stronger,more efficient
combustion and more power, but with less lubrication.

Slightly rich fuel mixtures deliver cooler running and more
lubrication but with slightly less power.

Tuning the engine means finding the perfect balance between
the two; excellent power to meet your needs while maintaining
good lubrication for long engine life. The optimal fuel mixture
setting is rich to provide a safety margin against having a lean
condition if some variable changes (such as the temperature
from one day to the next).

General fuel mixture settings are measured by the number of
turns the needles are turned out from fully closed.The fuel
mixture settings have been pre-set from the factory to typical
break-in settings. Do not readjust your carburetor from the
factory settings until after the engine is started and running,
and you have been able to observe the engine running to
assess what minor adjustments may be required to compensate
for fuel, temperature, and altitude.Adjustments are usually
made in 1/8 or 1/16-turn increments.

The Idle Speed Adjustment

The idle speed screw controls the closed position of the throttle
slide.When the throttle servo is in its neutral position, the
throttle slide should be stopped against the idle adjustment
screw.Always use the idle speed adjusting screw to control
engine idle. Do not use the throttle trim on the transmitter to
adjust idle speed. The idle speed should be set as low as
possible and still maintain reliable running.

▼▼

The TRX 2.5 Racing Engine

Water Valve

(Controls Overall Flow)

High Speed Needle

Water Nozzle

(Controls Fine Flow)

Low Speed Needle

See Tuning the TRX 2.5
for Best Performance

on page 34 for
complete information on
adjusting the air/fuel
mixture and idle speed.

29

Lean

Rich

TRX 2.5 Factory
Needle Settings

If your factory preset
carburetor adjustments
have been tampered with,
use the following settings:

• Set the high-speed needle

to 4 turns out from closed.

• Set the low-speed needle

so the screw head (red in
Fig. A) is flush (even) with
the end of the slide (yellow
in Fig. A).

Always use the factory
settings for initial starting.
Only use these settings
when the factory settings
have been lost.

Low Speed

Needle Adjustment

Fig. A

The TRX 2.5 Racing Engine

30

The Traxxas EZ-Start Electric Starting System

The Traxxas EZ-Start brings the convenience of push-button
electric engine starting to your S-Maxx. The EZ-Start consists of
a handheld control unit and an on-board motorized starter.

Power for the EZ-Start system comes from a 7.2-volt
rechargeable NiCad battery pack installed in the handheld
control unit (battery not included).
The engine glow plug is heated automatically by the
EZ-Start system, eliminating the need to keep up with a
separate glow plug igniter.
The voltage to the glow plug is kept constant, regardless of
the load placed on the starter by the starter motor.
The “Glow Plug”LED (light emitting diode) on the control
unit indicates the condition of the glow plug.
The “Motor” LED indicates the status of the EZ-Start electric
starter motor.
The cush drive mechanism in the drive unit prevents
damage to the gears caused by engine kickback.
Smart Start™protection circuitry prevents damage to the
motor by cutting power if the load on the motor or other
electronics exceeds safe limits.

Installing the EZ-Start Battery

The EZ-Start system requires a fully charged 7.2-volt NiCad
battery pack (not included). Use a charger (not included)
designed for 7.2-volt battery packs. Charge the battery
according to the charger manufacturer’s directions.

1. Press the tab in the end of the battery compartment door
to open

2. Plug a fully charged 7.2-volt NiCad battery pack into the
connector inside.

3. Twist the battery 2 or 3 times to twirl the battery plug wires.
This helps hold the wire and battery in place when the
battery is placed in the compartment

4. Place the battery into the compartment and press the wires
securely into place.

5. Slide the battery compartment door back on and lock the
end tab.

▼▼▼▼▼ ▼ ▼

Use the
Right Charger

The most convenient
type of charger is an AC peak­detecting charger that plugs
directly into an AC wall
outlet. It contains special
peak-detection circuitry that
automatically shuts the
charger off when the battery
is fully charged.

If you’re using a 15-minute
timed charger, always fully
discharge the battery pack
before each charge. Some
high mAh battery packs
(1500 mAh or higher) require
more than the standard 15
minutes of charge time. If the
battery pack is cold after 15
minutes of charging, add
another 5 minutes of charge
time. Closely monitor the
battery pack and stop
charging it when it begins to
feel warm to the touch. Never
leave a battery charging
unattended. Always follow
charger manufacturer’s
instructions.

The TRX 2.5 Racing Engine

Using the EZ-Start

Your EZ-Start controller plugs into a 4-prong receptacle in the
center of the pickup bed on your S-Maxx. When the red button
on the controller is depressed, the EZ-Start motor begins to spin
the engine, and power from the control unit heats the glow
plug. Assuming all settings and preparations are correct, the
engine should start almost immediately.

Each of the two status indicator
LEDs on the handheld control unit,
the Motor LED and the Glow Plug
LED, should light green while
starting. If either LED fails to light
while starting, there is a fault
indicated with that function:

If the Glow Plug LED fails to
light, the glow plug may be bad,
or the glow plug wire may be
damaged or disconnected.

If the Motor LED fails to light
and the starter fails to operate,
then the EZ-Start is in
protection mode.

Protection Mode

The EZ-Start uses Smart Start™technology to monitor the
condition of the system and detect failures.The controller
monitors the load being placed on the EZ-Start motor. If the
load becomes excessive,the system shuts off power to the
motor to prevent costly damage to the motor and the
controller.This may occur, for example, if the engine floods with
fuel during starting. The starter spins at first but when excessive
fuel in the combustion chamber begins to lock up the engine,
the starter motor slows under the heavier load.This causes the
protection circuit to shut off the power to the motor. Allow at
least 3 minutes for the starter motor to cool and the circuit to
automatically reset before continuing.Use the time to find and
eliminate the condition that caused the excessive load on the
starter motor.

▼▼

When the EZ-Start
controller is in protection

mode, wait at least three
minutes before attempting to
start the engine, to give the
starter motor time to cool.

It’s normal for your

EZ-Start controller

to become warm

after repeated use.

See page 43
for information
on clearing a
flooded engine.

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

Motor

Glow

Plug

31

The TRX 2.5 Racing Engine

32

See Important Points
to Remember on page

5 for other

precautions.

Never run your
S-Maxx indoors. Since

the TRX 2.5 Racing
Engine exhaust fumes are
harmful, always run your
S-Maxx outdoors, in a well
ventilated area.

Your TRX 2.5 Racing

Engine doesn’t usually

require priming. If you
do need to prime your
engine, watch the fuel line
carefully to avoid flooding
your engine. See page 43
for information on clearing
a flooded engine.

Your carburetor is

pre-set at the factory

to give the correct air­to-fuel ratio and idle speed
for engine break-in. Do not
adjust the carburetor
unless you observe a poor
running condition that
requires correction.

Breaking-in Your TRX 2.5 Racing Engine

The TRX 2.5 uses a ringless,aluminum-brass-chrome (ABC)
piston/sleeve construction.This type of engine design relies on a
very precise running fit between the piston and sleeve for cylinder
sealing. Engine break-in is necessary to allow the piston and

sleeve to develop an extremely precise fit and optimum cylinder
sealing. Therefore, proper engine break-in is critical to achieving
the fastest, most reliable engine performance.

Allow yourself about 1 to 11/2hours to complete the break-in
procedure.The engine break-in period will take 5 tanks of fuel in a
S-Maxx.The break-in time is not the time to impress your friends
with your new S-Maxx. You must wait until the engine is fully

broken in before attempting sustained high speed running.

Patience and careful attention during break-in will reward you with
the best-performing TRX 2.5 possible.

During break-in, your engine may appear to malfunction with
symptoms like stalling, inconsistent performance, and fouled glow
plugs.These are simply the normal “break-in pains”engines
sometimes go through.They will disappear once your engine is
fully broken in. Many owners report not experiencing any of these
symptoms with the TRX 2.5. We recommend replacing the glow

plug with a new one after the engine break in procedure.

Engine Break-in Procedure

The focus during break-in is to vary and limit the engine speed.
This will be accomplished by accelerating and stopping at different
rates for the first 5 tanks of fuel. As the engine begins to break-in,
the duration and intensity of the acceleration will gradually
increase. Sustained high-speed running is not permitted until the
6th tank of fuel. Perform the initial break-in on a large,flat, paved
surface. Apply all throttle and braking actions gently. Abrupt

acceleration or braking could cause the engine to stall
unnecessarily.

Special break-in fuels are not recommended.Use the same fuel
you plan to use everyday.
If possible, avoid breaking-in the engine on extremely hot or
cold days.
Pay careful attention to the fuel level. Do not allow the fuel tank

to run completely empty. An extremely low fuel level causes
the mixture to run too lean.This could result in a burned glow
plug or extremely high engine temperatures.
Keep extra glow plugs handy (Traxxas part #3231). The break-in
process can cause deposits to form on the plug leading to plug
failure.

Follow the instructions exactly for each of the first 6 tanks of fuel.

Starting Your TRX 2.5 Racing Engine for the First Time

Before you start your TRX 2.5 Racing Engine for the first time,make
sure you have read all instructions and precautions in this manual.

Pay close attention to the tank-by-tank break-in instructions in
the next section, and make sure you have read and understood
them before you run your engine.

Your engine must be at room temperature (70°F or 21° C) or
above the first time you start it.If it’s cooler than room

temperature outside,keep your S-Maxx indoors until you’re ready
to start it, then take it outside.

1. Turn on the radio system according to the instructions
on page 18.

2. Make sure the throttle is in the idle position.

3. Connect the EZ-Start controller according to the instructions on

page 31.

4. Press the starter button and watch for fuel moving through the
fuel line up to the carburetor.Watch closely! The fuel moves very
fast. If the fuel doesn’t move through the line within 5 seconds,
prime the engine by briefly (one or two seconds) covering the
exhaust outlet until the fuel is just visible in the carburetor fuel
line. Watch carefully! If the engine is primed too long, it will

flood with fuel and stop turning.

5. Once fuel reaches the carburetor, the engine should quickly start
and idle.

6.Disconnect the EZ-Start controller from the model.

7.Proceed with the engine break-in.

If your engine doesn’t start, see Troubleshooting Your S-Maxx
on page 42.

▼

▼▼▼

The TRX 2.5 Racing Engine

33

As you gain
experience in the

hobby, you may
discover that many people
have differing opinions on
what is the proper
procedure to break-in a
model engine. Only use the

Traxxas break-in procedure.
Other break-in procedures
could result in a weak,
damaged, or otherwise poor
performing engine. The

procedure outlined here
was extensively tested and
proven to yield better
performing engines than
other “common” break-in
methods. Even if you have
years of experience using
model engines, please do
not ignore this caution!

Tank 1

1. Drive the model with the body off.

2. Driving procedure: Gently pull the throttle trigger to 1/4

throttle over a 2-second count. Then gently apply the brake to
stop.Count the two seconds out while accelerating: one

thousand one, one thousand two, and then stop. Operate the
throttle trigger as smoothly as you can. Repeat this starting and

stopping procedure until the first tank of fuel is nearly empty.

3. Look for thick blue smoke exiting the exhaust outlet. If there is
no smoke, richen the high-speed needle 1/4 turn, by turning the
needle counterclockwise.

4. When the fuel tank is nearly empty,shut off the engine by
pinching the fuel line connected to the carburetor.

5. Let the engine cool for 15 minutes.

Note: If at any point the engine cuts out or stalls during gentle
acceleration, richen the high-speed needle 1/4 turn by turning the
needle counterclockwise.

Tank 2

1. From tank 2 forward, the S-Maxx should be driven with the

body on.

2. Driving procedure: Gently pull the throttle trigger to 1/2
throttle over a 2-second count. Then gently apply the brake to
stop. Count the two seconds out while accelerating: one
thousand one, one thousand two, and then stop. Repeat this
starting and stopping procedure until the second tank of fuel
is nearly empty.

3. When the fuel tank is nearly empty, shut off the engine and let it
cool for 15 minutes.

Tank 3

1. Driving procedure: Gently pull the throttle trigger to 1/2

throttle over a 3-second count. Then gently apply the brake
to stop. Count the three seconds out while

accelerating: one thousand one, one
thousand two,one thousand three, and then
stop. Repeat this starting and stopping

procedure until the third tank of fuel is
nearly empty.

2. As the engine loosens, the idle speed may
increase and cause the model to try to creep
forward when stopped.Reduce the idle

speed by turning the idle adjustment (see page 22) on the
carburetor counterclockwise.

3. When the fuel tank is nearly empty, shut off the engine and
refuel. From here on, you do not need to let the engine cool
between tanks.

Tank 4

1. Driving procedure: Gently pull the throttle trigger to full

throttle over a 3-second count. Then gently apply the brake to
stop. Count the three seconds out while accelerating: one

thousand one, one thousand two, one thousand three, and then
stop. Repeat this starting and stopping procedure until the

fourth tank of fuel is nearly empty.

2. Apply the throttle gradually! Your finger should not reach full
throttle until the end of the three-second count.

3. Keep your driving smooth and consistent.

4. When the fuel tank is nearly empty, shut off the engine and

refuel.

Tank 5

1. Driving procedure: Gently pull the throttle trigger to full

throttle over a 3-second count, hold for 2 more seconds, and
then gently apply the brake to stop. Count the five seconds out
while accelerating.Repeat this starting and stopping
procedure until the fifth tank of fuel is nearly empty.

2. When the fuel tank is nearly empty, shut off the engine and
refuel.

Tank 6

During the sixth tank of fuel, the engine can be tuned for general
performance use. Proceed to the next section in this manual.

Tank

1
2
3
4
5

Throttle

1/4
1/2

1/2
Full
Full

Time

2 Seconds
2 Seconds
3 Seconds
3 Seconds
5 Seconds

Cool

15 Minutes
15 Minutes

-

-

-

Body

Off
On
On
On
On

Notes

Apply throttle gradually.
Apply throttle gradually.
Reduce idle speed if necessary.
Keep your driving consistent.
Accelerate over 3 second count,

hold for 2 seconds.

34

The TRX 2.5 Racing Engine

When adjusting the
low-speed fuel mixture,

it is very important to
make several high-speed
runs with the S-Maxx
between adjustments to
clear out any excess fuel.
Perform the pinch test
immediately after. If the
engine is allowed to idle for
a long period of time, it
could “load up” with fuel and
give you an inaccurate
measurement from your
pinch test.

For your convenience,

the low-speed needle

has a positive stop that
prevents it from being over
tightened and damaging the
needle and seat. This also
provides an easy way to
gauge how many turns out
from closed the low-speed
needle adjustment is set to.

When tuning for

performance, watch

closely to notice when
there is no longer any
increase in speed or power
when the high-speed
mixture is lean. If you lean
the high-speed mixture to
the point that the engine
cuts-out, hesitates, or stalls,
you are well into the danger
zone and engine damage is
likely. Richen the high-speed
needle 1/4 turn and retune.

Tuning the TRX 2.5 for Best Performance

The engine’s performance depends on the fuel mixture. Turn the
mixture needles clockwise to lean the fuel mixture and
counterclockwise to richen it. Leaning the fuel mixture will
increase engine power up to the engine’s mechanical limits.

Never run the engine too lean (not enough fuel flow). Never
lean the engine until it begins to cut-out or stall. Leaning the
engine beyond the safe allowable limits will result in poor
performance and almost certain engine damage. Indications

of an overly lean mixture include:

Cutting out or sudden loss of power during acceleration.

Overheating (temperature beyond 270° F at the glow plug)
Little or no blue smoke coming from the exhaust.

If any of these conditions are present, stop immediately and
richen the high speed mixture 1/4 turn. The engine will
probably be slightly rich at that setting and you can then retune
for performance. Always tune for performance by starting rich
and moving leaner toward the ideal setting.Never try to tune
from the lean side.There should always be a light stream of blue
smoke coming from the exhaust.

Before you begin tuning,the engine should be warmed up to its
normal operating temperature and running slightly rich. All final
tuning adjustments must be made to the engine at its normal
operating temperature.You can tell the engine is running rich
by noting any of the following:

Sluggish acceleration with blue smoke coming from
the exhaust.
There is unburned fuel spraying from the exhaust tip
Leaning the high-speed fuel mixture increases performance

High-Speed Fuel Mixture Adjustment

With the engine warm and running at a rich setting, gradually
lean the high-speed fuel mixture in 1/16 turn increments. Make
several high-speed passes with Revo after each adjustment to
clear out the engine and note any change in performance.The
TRX-2.5 is extremely powerful. Remember to apply the throttle
gradually to prevent wheelies or loss of control. Continue this
procedure until there is no longer any performance
improvement.

If any one of the following conditions occurs, the fuel mixture
is already past the maximum safe lean setting:

1. There is no longer any performance improvement

2.

The engine begins to cut out at high speed

(Danger!)

3.

There is a sudden loss of power during acceleration

(Danger!)

4.

The engine begins to overheat.Symptoms of
overheating include:

Steam or smoke coming from the engine (not exhaust)
Hesitation or stalling during acceleration
Popping or clattering sound when decelerating
(detonation)
Fluctuating idle speed
Temperature measurement above

270° F

at the glow plug

Richen the fuel mixture to the optimum setting by richening the
high-speed needle at least 1/8 turn counterclockwise and retest.
This setting will extend engine component life.

▼▼ ▼▼▼

▼▼ ▼ ▼▼▼

The TRX 2.5 Racing Engine

35

Low-Speed Fuel Mixture Adjustment

The low-speed mixture is always set after the high-speed needle
is correctly adjusted.The low-speed mixture will be set using the
pinch test.

1. Once the engine is warm, do several high-speed runs to

confirm that the high-speed needle is set correctly.

2. Bring the vehicle in and pinch closed the fuel line going into

the carburetor.The engine should run for 2-3 seconds, speed
up, and then die.

3.

If the engine runs longer than 3 seconds, then lean the
low-speed needle 1/16 turn, make several more high­speed runs, and retest.

4. If the engine dies immediately without speeding up, then

richen the low-speed needle 1/8 turn, make several more
high-speed runs, and retest.

When the low-speed needle is set correctly,the engine’s throttle
response should be very quick, possibly even to the point of
making it difficult to keep the S-Maxx from doing a wheelie
when you accelerate!

Idle Speed Adjustment

Once the high and low-speed mixtures have been set, reduce
the idle speed to the minimum reliable idle speed. Remember,
this adjustment should be made while the engine is running at
normal operating temperature.

1. Turn the throttle trim on the transmitter so that the brakes

are applied.This ensures that the throttle slide is resting
against the idle adjustment screw.

2.

If necessary, remove the air filter to gain access to the idle
adjustment screw.

3.

Turn the screw counterclockwise to reduce the idle
speed, or clockwise to increase it. The idle speed should
be set as low as possible while still maintaining reliable
running characteristics.

4.

Reset the throttle trim on the transmitter

Fine-Tuning the Carburetor

After fine-tuning your TRX 2.5 Racing Engine at the end of the
break-in procedure, no major adjustments to the fuel mixture
are usually necessary. Make note of the temperature, humidity,
and barometric pressure at the time you finished fine tuning
your carburetor.Current weather conditions can be found
online from national websites, local TV news websites, and
Television.This information will be considered your baseline
setting.You may need to adjust your carburetor needles to
compensate for changes in temperature and barometric
pressure (air density) from day to day. Generally, you’ll need to
richen the fuel mixture when the weather is colder than your
baseline temperature and the air density is higher.Lean the fuel
mixture when weather is warmer than your baseline
temperature and the air density is lower.The chart below
provides general guidelines on how weather conditions affect
air density when they move higher or lower than your baseline
setting (see page 28 for detailed info on how air density affects
mixture settings).

If the...

Humidity

Pressure (barometer)

Temperature

Altitude

Nitro %

is..

Lower
Higher
Lower
Higher
Lower
Higher
Lower
Higher
Lower
Higher

then the air density is...

Slightly more dense
Slightly less dense
Less dense
More dense
More dense
Less dense
More dense
Less dense

adjust (correct) the fuel mixture to be...

Slightly richer
Slightly leaner
Leaner
Richer
Richer
Leaner
Richer
Leaner
Leaner
Richer

36

Tuning The Engine By Temperature

The following procedures require an
optional infrared temperature probe
or on-board temperature gauge
(Traxxas on-board digital
temperature gauge, part#4090).
Engine temperature can be used as
an effective tuning aid when you understand the relationship
between engine temperature and ambient temperature.

The engine operating temperature,when tuned for maximum
performance, will vary according to atmospheric conditions. The
atmospheric condition that has the most influence on engine
temperature is air temperature. Expect the engine temperature
to vary almost in direct proportion to atmospheric temperature.
Assuming you tuned the engine for the same maximum
performance each day,the engine will run about twenty
degrees hotter when it’s ninety degrees outside than it would in
seventy-degree weather.For this reason, we cannot give you a
definitive temperature range that indicates the best possible
engine tuning.

The temperature gauge can aid you in tuning by giving you a
relative indication of how your adjustments are affecting the
engine and by preventing you from exceeding maximum
engine temperature. For example, as you lean the fuel mixture,
the engine performance will increase along with the
temperature. If you continue to lean the fuel mixture and
the temperature increases but the engine performance
does not change, then you have exceeded the maximum safe
lean setting.

Even if it’s 100°F outside,you should be able to tune for
maximum performance. Try to keep your engine from exceeding
270°F when measured at the glow plug. If tuning for maximum
performance results in engine temperature exceeding 270°F,
try to increase airflow to the engine by cutting out the rear
of the body,windshield, and front valance. If the engine
temperature still cannot be kept below 270°F, richen the
high-speed needle slightly.

The TRX 2.5 Racing Engine

37

Driving the S-Maxx

Introduction

Your TRX 2.5 Racing Engine is broken in, the fuel mixture is
balanced, and the idle is set…now it’s time to have some fun!
This section contains instructions on driving and making
adjustments to your S-Maxx. Before you go on, here are some
important precautions to keep in mind.

Don’t run your S-Maxx in water, mud, snow, or wet grass.

It’s t empting,but water and mud are easily drawn through
the air filter and will severely damage the engine. Small
amounts of moisture can cause electronics to fail and loss of
control over your S-Maxx.
The TRX 2.5 is extremely powerful. Remember to apply the
throttle gradually to prevent wheelies or loss of control.
Don’t hold the S-Maxx off the ground and rev the engine
excessively with no load on the engine.This practice could
result in internal engine damage. Avoid over-revving the
engine when the S-Maxx is airborne after a jump.
Avoid excessive high-speed running for extended periods of
time or over long distances.This could cause the engine to
build up enough speed to exceed maximum safe RPM limits.
Don’t drive your S-Maxx with drive train damage of any kind.
The engine could be damaged due to overloads on the
engine caused by drivetrain friction, or over-revving caused
by loose or missing parts.
Don’t tow anything with your S-Maxx.The engine is cooled
by airflow created by speed. Towing creates a high load on
the engine, and at the same time limits cooling of the engine
due to low vehicle speed.
If your S-Maxx gets stuck, stop driving immediately. Move
the vehicle and then continue driving.

Driving Tips

Monster trucks by design have a high center of gravity that
requires a different driving technique.To prevent rollovers,
slow down as you approach turns and then apply strong
throttle through the turns.This technique will help the
S-Maxx grab the surface and turn sharper.
Do not apply brakes and turn the wheel at the same time.
You could tip the truck over.
When jumping, apply some throttle while the S-Maxx is in
the air to keep the truck’s nose up and land level on all 4
wheels. Be careful not to over-rev the engine or land at full
throttle. Either could seriously damage your S-Maxx. If the
nose of the truck is too high, then quickly tap the brake to
level the truck in the air..
Drive over large obstacles (such as curbs and rocks) at an
angle, instead of head on. This will allow the suspension to
articulate and absorb the impact much easier.

▼▼▼▼

▼▼▼▼▼▼ ▼

Once you become familiar with driving your S-Maxx, you might
need to make adjustments for better driving performance.

Adjusting the Slipper Clutch

The S-Maxx features an adjustable slipper clutch on the spur
gear to help protect the drive train from sudden shock loads
(such as landing off of jumps with the engine at full throttle).
Under normal conditions the slipper clutch should not slip.
Before adjusting the slipper clutch, turn the model off. Do
not adjust the slipper clutch while the engine is running.

Use the supplied glow plug (universal) wrench to tighten the
slipper nut (clockwise) until it stops, and then back the nut out
1/4 of a turn. If you notice any decrease in performance after
making changes to the slipper clutch adjustment, then it may
be too loose.The slipper must not be allowed to slip during
normal acceleration or the slipper could be damaged.

Adjusting the Toe-in

Your S-Maxx comes from the factory with zero degrees of toe-in
in the front, and one degree of toe-in in the rear.You can adjust
the toe-in on the front and rear of the truck. Set the steering trim
on your transmitter to neutral.Now, adjust your steering

turnbuckles so that
both front wheels
are pointing
straight ahead and
are parallel to each
other (0 degrees
toe-in).This will
ensure the same
amount of steering
in both directions.
Adjust the rear toe
control links so
that the rear
wheels have 1˚ of
toe-in.

Adjusting the Camber

Two pivot balls are accessible through
the spokes of each of the wheels on
your S-Maxx. From the factory, the
pivot balls are completely tightened
into the suspension arms, which give
each of the wheels –1˚ of camber.
Unscrewing the bottom camber pivot
ball with a 2.5mm hex wrench will
increase the wheel’s negative camber.
You should not adjust the top pivot ball; unscrewing it will
increase positive camber and will also change the wheel’s toe-in.

Adjusting the suspension

The S-Maxx has adjustable suspension so that it may be
optimized for different kinds of terrain and driving styles.

Fine Tuning the Shocks

The eight shocks (oil dampers) on your S-Maxx have
tremendous influence on its handling.Whenever you rebuild
your shocks, or make any changes to the pistons, springs or oil,
always do it carefully and in sets (front or rear). Piston head
selection depends on the range of oil viscosities that you have
available. For example, using a two-hole piston with lightweight
oil will give you the same damping as a three-hole piston with
heavier oil.We recommend using two-hole pistons with a range
of oil viscosities from 10W to 40W (available from your hobby
shop). The thinner viscosity oils (30W or less) flow with less
resistance and provide less damping,while thicker oils provide

38

Adjusting Your S-Maxx

0°

1°

1°

0°

-1°

-1°

Factory toe-in settings

can be achieved by

installing the rod ends
on the turnbuckles until
they bottom out against
the shoulder. If you desire
more toe-out, the tips of
the rod ends must be
trimmed to allow them to
screw down further onto
the turnbuckle threads.

more dampening. Use only 100% pure
silicone shock oil to prolong seal life.
From the factory, the S-Maxx uses
30W oil.

The ride height for the S-Maxx can be
adjusted by adding or removing the clip­on spring pre-load spacers. Note that
changes in ride height will occur when
changes in shock angle or spring rates
are made.You can compensate for ride
height changes by changing the pre-load
spacers on the shocks

Caster Adjustment

The S-Maxx offers the ability to adjust the
caster angle of the front suspension.
Caster adjustment may be used to influence the understeer/
oversteer handling characteristics of the S-Maxx. Increasing the
caster angle will increase the tendency of the truck to oversteer
(less traction on the rear tires, more traction on the front tires),
while decreasing the caster angle will cause the truck to have a
tendency to understeer (push in the turns). This effect becomes
more pronounced at higher steering angles and higher spring
rates. Caster is adjusted by repositioning the shims on the pivot
point of the upper suspension arms.

The stock caster setting is 7-degrees with one shim at each end
of the arm. Reduce the caster angle to 4-degrees by removing
the rear shim and inserting it next to the front shim. The caster
angle can be increased to 10-degrees by removing the front
shim and inserting it next to the rear shim.

Shock Mounting Positions

Big bumps and rough terrain require a softer suspension with
the maximum possible suspension travel and ride height.
Racing on a prepared track or on-road use requires a lower ride
height and firmer,more progressive suspension settings.The
more progressive suspension
settings help reduce body roll
(increased roll stiffness), dive
during braking, and squat
during acceleration.
Upper shock mounting
position (A) should generally
be used with lower shock
mounting positions 1 and 2.
Upper shock mounting
position (B) should be generally
be used with lower shock
mounting positions 3 and 4.
The innermost upper shock
mounting position (0) can be used for tuning with the inner pair
of lower shock mounting positions on the arm (1,2). It is not
compatible with lower shock mounting positions 3 and 4. Other
combinations may be used to achieve individualized suspension
settings.

LowerShock Mounting Positions

In the out-of-the-box configuration, the shocks are installed in
position (A) on the shock tower and position (3) on the lower
suspension arm. This setting allows for firm suspension and low
ride height, increasing the spring force (at the wheel). This
setting improves high-speed cornering on smoother terrain by
lowering the center of gravity. Body roll,brake dive, and squat
are also reduced.

The inner pair of holes on the lower suspension arm should
be used to increase the ride height of the S-Maxx.The more
vertical position of the shocks will allow for lower shock
progression and the soft, plush feel that’s characteristic of a
Traxxas Maxx Truck.

39

Adjusting Your S-Maxx

7°

Caster adjustment shims (1 Front, 1 Rear)

Vertical

Ground plane

Vertical

4°

Caster adjustment shims (2 Front)

Ground plane

Vertical

Caster adjustment shims (2 Rear)

Ground plane

10°

Adjusting Your S-Maxx

Spring rate (at the wheel) increases as the lower shock

mounting position is moved from position (1) to position (4).
This is equivalent to using stiffer springs.Use higher spring rate
settings for flatter terrain with smaller and fewer bumps,and
lower spring rate settings for bigger bumps.

Ride height decreases as the lower shock mounting position is
moved from position (1) to position (4). Each pair of lower shock
mounting holes (1,2 and 3,4) has equal ride height. Use lower
ride height for high-speed cornering and flat terrain, and when
racing on relatively smooth tracks. Increase the ride height for
rougher terrain and tracks.

Upper Shock Mounting Positions

The upper shock mounting positions will have suspension
effects opposite from the lower shock mounting positions.

Spring rate (at the wheel), increases as the upper shock

mounting position is moved from position (A) to position (B).

Ride height is not affected by changes in the upper shock

mounting position.

Use the chart below to see the effect of the various shock
mounting positions. The horizontal length of the lines indicates
the amount of suspension travel. The angle or slope of the lines
indicates the spring rate (at the wheel).

40

For easier access to the
rear-most shock
mounting screw,

remove the one end of the
rear turnbuckle. In the front,
remove the suspension pin
from the lower front
suspension arm to gain
easier access to the lower
shock mounting screws.

2.5

2

1.5

1

0.5

0

010203040 6070809010

0

50

Wheel Force (lb)

Wheel Travel (mm)

Wheel Force vs. Wheel Travel

Lower Mount 1, Upper Mount 0
Lower Mount 2, Upper Mount 0
Lower Mount 1, Upper Mount A
Lower Mount 2, Upper Mount A
Lower Mount 3, Upper Mount A
Lower Mount 4, Upper Mount A
Lower Mount 1, Upper Mount B
Lower Mount 2, Upper Mount B
Lower Mount 3, Upper Mount B
Lower Mount 4, Upper Mount B

Less Firm

More Firm

Lower Mount 4

Lower Mount 3

Lower Mount 2

Lower Mount 1

41

Adjusting the Two-Speed Transmission

The S-Maxx comes equipped with a two-speed transmission.
When the shift point on the transmission is adjusted correctly,it
will maximize acceleration and improve drivability. If necessary,
use the supplied 2.0mm hex wrench to adjust the shift point.

1. Stop the engine.

2. Remove the large rubber plug from the transmission housing.

3. Look into the hole in the transmission housing and rotate

the spur gear until the access hole in the aluminum drum
is visible.

4. Once the access hole is
visible, hold the spur gear
and use your finger to
turn the primary gear
shaft which extends from
the transmission housing.
Turn it clockwise. Note
that you will see two set
screws pass under the
access hole. As you slowly turn
the primary gear shaft
counterclockwise, the first set
screw that becomes visible
holds the two-speed
mechanism on to the shaft. Do
not loosen this screw.The
second set screw is the
adjustment screw.

5. Insert the 2.0 hex wrench
through the clutch drum and
into the adjustment set screw.

6. Tu rn the adjustment screw 1/8
turn clockwise to raise the shift
point (later shifts). Be careful not
to over tighten the adjustment
screw or you may damage the
tension spring.Do not make
constant adjustments or you will
loosen the screw’s locking
device.

7. Tu rn the adjustment screw 1/8
turn counter-clockwise to lower
the shift point (earlier shifts). Be careful not to loosen the
adjustment screw too much or you may cause the screw and
spring to fall out (requiring major disassembly and repair).

8. Use 1/8 turn increments to find the approximate,
desired shift point.

9. Check performance by running a test lap after each
adjustment.

10. Use 1/16 turn increments to fine-tune the shift point.

11. Be sure to reinstall the access plug to prevent dirt from

entering the transmission.

HOLD

Adjusting Your S-Maxx

42

The following section addresses some very basic engine and
radio questions you may have about your S-Maxx.Most questions
arise from simple user errors or minor adjustments that are easy
to correct. If you can’t find a solution for your S-Maxx here, then
visit our Web site at www.Traxxas.com and click on the Customer
Support menu. There you will find a much more extensive and
detailed online troubleshooting area. In addition, you may call
Traxxas Customer Service at 1-888-TRAXXAS (outside the US call
972-265-8000).

Radio system does not work properly:

If the power light on the transmitter does not come on, check
for proper battery installation and that the batteries are new
and/or fully charged. If the power light is blinking, then the
transmitter batteries are weak and should be replaced.See
page 13 for more details.
If the transmitter light is on but the radio is still not
responding,check for proper installation of the receiver
batteries and that the batteries are new and/or fully charged.
Check to make sure the on/off switch on the model is in the
on position. Finally,if there is still no response check the red
and black wires that connect the battery pack to the “batt”
terminal on the receiver (you will have to remove the receiver
cover). Make sure the wires are not pinched or damaged and
that the plug is secure in the receiver. See page 14 for more
details.

Short radio range:

If the radio range appears short, then first check to make sure
the transmitter antenna is fully extended and that the
antenna in the S-Maxx is in place and has not been cut or
damaged. Next, make sure the batteries are all fully charged.
Finally, if you are still experiencing short range,try a different
location. Sometimes there can be interference from various
sources that can cause your radio to malfunction.

Engine will not spin (EZ-Start will not turn the engine):

If neither LED on the controller lights, the EZ-Start battery
could be discharged or improperly connected.Inspect and
recharge if necessary.

If the glow plug LED lights and the motor LED does not, then
the EZ-Start controller is in protection mode. Allow the
controller to cool for at least three minutes.The circuitry
should automatically reset.
Check to make sure the wires are connected to the EZ-Start
motor in the S-Maxx.The red wire should connect to the
positive motor terminal, indicated by a red dot next to the
terminal.
The engine could be flooded. If too much fuel accumulates in
the combustion chamber at start up, the engine will
hydraulically lock. Follow the procedure on page 43 for
clearing a flooded engine.
Check for binding at the engine flywheel. If you are not able to
turn the engine by hand, the engine could be flooded, there
could be binding in the clutch system, or there could be
internal engine damage. (Note: It is normal for the engine to
be extremely tight and hard to turn when the piston reaches
the top of the compression stroke.)

Engine extremely sluggish, hard to start, and will not idle
during tank 1 of the break in:

It is possible that the factory adjusted break-in settings on
your carburetor are too rich for your geographic location,
atmospheric conditions, or fuel brand. Extremes in
temperature,humidity,barometric pressure, and altitude can’t
always be accounted for with a single high-speed needle
setting.The symptoms described above can occur when the
air density is very low such as in high mountainous elevations,
and extremely cold temperatures. Under these conditions,
lean the fuel mixture slightly,1/8 turn, to see if there is any
improvement in starting and idling. Only lean the fuel mixture
just until the engine will run and idle reliably and then
proceed with the break in.

The contents of different brands of fuel (other than Traxxas
Top Fuel) in combination with extreme atmospheric
conditions can also make the factory preset break-in settings
too rich and cause the symptoms described above.Again, try
leaning the fuel mixture slightly,1/8 turn, to see if there is any
improvement in starting and idling.

▼▼▼▼▼▼

▼▼ ▼▼

Troubleshooting Your S-Maxx

Engine spins but will not start:

If the engine is spinning but will not start, first check to make
sure that both the motor and glow plug LEDs on the EZ-Start
controller light when the button is depressed. If the glow
plug LED does not light, make sure the blue glow plug wire is
tightly connected and is not damaged in any way.If the wire
is good, then replace the glow plug. It is normal for glow
plugs to require periodic replacement. Only use Traxxas
heavy-duty long glow plugs (part #3231).
Check to make sure the fuel is getting to the carburetor.
Remove the fuel line where it connects to the carburetor to
see if there is fuel in it. If not, you may need to prime the
engine. Reconnect the fuel line and then refer to page 32 for
instructions on priming the engine.
Check your fuel mixture settings. It may be necessary to
adjust the fuel mixture if the outside temperature or
barometric pressure has changed significantly since
the last time the engine was run (see Fine Tuning the
Carburetor on page 36). Turn the high-speed needle out
(rich/counterclockwise) 1/4 turn, hold the throttle trigger at
about 1/2 throttle and try again to start the engine. Once
started, retune the engine for performance (see page 35).
The engine could be worn. If the fit between the piston and
sleeve is loose, compression is reduced and the engine will be
difficult to start when it is warm, and may tend to stall when
running and when the throttle is closed suddenly to idle.
Engine life depends on many factors including fuel type, air
filter maintenance, needle settings, and how the engine was
used. For example, if the engine was allowed to ingest dirt
from lack of air filter maintenance or running through water,
then the internal engine components could wear out
extremely fast.

Engine performance sluggish:

Engine performance depends mostly on the fuel mixture
settings and how they compensate for the current
atmospheric conditions. Before you suspect other failures with
the engine, richen the high-speed needle at least 1/4 turn and
then retune the engine for performance (see page 35).

If the fuel mixture seems to be set correctly,make sure the
fuel is fresh. If the fuel is old, or was left uncapped for a long
period, then some of the important fuel components could
have evaporated.Try new, fresh, Traxxas Top Fuel
Try a new Traxxas 3231 glow plug.Sometimes a glow plug
will work well enough to start the engine but not be able to
deliver the engine’s full performance potential.
Check to make sure there is no binding in the driveline that
would cause excessive loads on the engine.

Clearing a Flooded Engine:

If the engine is primed for too long during startup, then it can
become flooded with fuel.When the engine is flooded it will no
longer turn due to excess fuel in the combustion chamber
preventing upward movement of the piston.Use the following
procedure to clear a flooded engine.

1. Remove the blue glow plug wire.

2. Remove the glow plug and gasket with the glow plug
wrench supplied with your model. A 5/16 nut driver will also
work.

3. Turn the model upside down and plug in the
EZ-Start controller.

4. Push the EZ-Start button for several seconds to clear the
engine of excess fuel

5. Turn the model over and reinstall the glow plug and gasket.

6. Reconnect the blue glow plug wire to the glow plug.

7. Reconnect the EZ-Start controller

8. Do not prime the engine. Pull the throttle to 1/2 throttle and
push the EZ-Start button. The engine should start
immediately.

▼▼ ▼

▼▼▼▼▼

43

Troubleshooting Your S-Maxx

44

If the engine is worn or
damaged enough to

require replacing the
piston, sleeve, or
connecting rod, consider
exchanging your old
engine for a brand new
engine under the terms of
the Traxxas Lifetime Engine
Replacement Plan (ERP). It
could save you time and
effort. Details are in your
model’s documentation
package.

The TRX 2.5 is

designed to be easy to

rebuild. Critical engine
components such as the
crankcase, crankshaft, and
engine bearings are made
to extremely high quality
standards and should
under normal
circumstances outlast
multiple sets of pistons,
sleeves, connecting rods,
and wrist pins
(reciprocating assemblies).
It could be more
economical for you to
continue to use your good
bearings and crankshafts,
and simply replace the
reciprocating assembly as
needed. Engine assembly is
not difficult and replacing
the reciprocating assembly
does not require any
special tools or skills.

Your S-Maxx requires timely maintenance in order to stay in top
running condition. Neglecting the maintenance could allow dirt,

deposits, and moisture to build up inside the engine leading to
internal engine failure. The following procedures should be

taken very seriously.

After each hour of running:

Clean and re-oil the air filter.The instructions for this
procedure are on page 27. We cannot stress enough the

value of cleaning your air filter at the scheduled intervals.

Do not neglect your air filter maintenance!

Clean the outside of the engine of accumulated dirt, oil,and
grime. Accumulated grime will decrease the engine’s ability to
cool itself.

After each running session:

Perform after-run maintenance on the engine.This clears the
engine of destructive moisture and other corrosive deposits.

This is extremely important for the life of the engine. See
page 45 for after-run maintenance procedures.

I

nspect the vehicle for obvious damage or wear.Look for:

1. Loose or missing screws

2. Cracked, bent, or damaged parts

3. Cut or loose wiring

4. Cut or kinked fuel lines

5. Signs of fuel leakage

Inspect the gears for wear,broken teeth, or debris lodged
between the teeth.

Other periodic maintenance:

Slipper clutch pegs (friction

material):The slipper clutch
pegs will wear over time and
require replacement.The life of
the pegs depends on how the
slipper clutch was adjusted and
how the S-Maxx was used. If
the slipper will not tighten or you are seeing signs of wear on
the face of the gear,then the pegs should be replaced.

Piston/sleeve:

The life of the piston and
sleeve will vary greatly with how the
engine was used and maintained.The
piston and sleeve should be replaced
when they no longer seal effectively
(loss of compression). Symptoms include
the engine being difficult to start when
warm, stalling when warm,and stalling
when throttle is suddenly closed to idle.
Replace the wrist pin and G-clip
whenever the piston and sleeve are
replaced.

Connecting rod:

The connecting rod
should be replaced when the piston and
sleeve are replaced or after three gallons
of fuel, whichever comes first. Also
replace the piston wrist pin and G-clip
whenever the connecting rod is replaced.As with other
internal engine components, connecting rod life depends
engine’s usage and the quality and frequency of the
engine maintenance.

EZ-Start:

The cush drive elements in the EZ-Start drive
unit should be inspected after 3-gallons of fuel. If the cush
drive elements appear deformed or hardened they should
be replaced. Inspect the EZ-Start gears for any signs of
wear.Damaged gears should be replaced. Coat the gears
with a thin layer of white lithium grease.

▼▼ ▼

▼▼ ▼ ▼ ▼▼

Maintaining and Storing Your S-Maxx

Maintaining and Storing Your S-Maxx

After-run Procedure

You must perform after-run maintenance on your Traxxas
engine whenever the model will be stored for longer than a few
hours.Taking the time to prepare your engine for storage will
reward you with longer engine life, easier starting, and better
performance.

When a nitro engine is shut off, some excess unburned fuel
remains in the engine.The methanol in model engine fuel is
hygroscopic, which means it easily attracts and absorbs
moisture.This moisture can cause rust and corrosion on the
steel engine parts (crankshaft, bearings, wrist pin and starter
shaft) if the fuel is not removed from the engine.There are after
run oil products available from your hobby dealer or you can
use WD-40™,a common household lubricant. To ensure your TRX

2.5 Racing Engine is protected from internal corrosion, use the
following procedure:

1. Whenever possible, shut off the engine by pinching the fuel
line closed.This allows most of the excess fuel to be
consumed by the engine. Be sure the throttle is in the idle
position.You may have to pinch the fuel line closed for
several seconds before the engine stops.

2. Completely empty the fuel tank. Use your fuel-dispensing
bottle to suck out the old fuel. Do not mix the old fuel with
your fresh fuel supply.If you leave fuel in the tank,
transporting or handling your S-Maxx may cause fuel to run
into the engine.

3. With the fuel tank empty and the throttle at the idle
position, try to start the engine.The engine will most likely
start and run for a few seconds as it uses up any fuel
remaining in the engine and fuel lines.

4. Once the engine stops, clean the outside of the engine with
compressed air or spray motor cleaner. Once the engine is
clean and dry, remove the glow plug power wire, glow plug,
and air filter.

5. Open the throttle fully and spray a one-second burst of
WD-40 into the carburetor and into the glow plug hole
(Caution! Wear safety glasses to prevent spray from getting
into your eyes).

6. Place a rag or paper towel over the engine to catch any
WD-40 that may come out the carburetor or glow plug hole.

7. Connect the EZ-Start controller to the model and spin the
engine for 10 seconds.

8. Remove the rag or paper towel and repeat steps 5–7 two
more times.

9. Clean and re-oil the air filter so it will be ready for use next
time. See page 27 for air filter maintenance instructions.

10. Replace the glow plug, reconnect the glow plug power wire,
and reinstall the air filter.

Denatured alcohol
(available from home

centers and paint
supply stores) in a spray
bottle is an extremely
effective cleaner. Be sure to
wear safety glasses and
gloves when working with
denatured alcohol.

Fun fact: WD-40

™

stands
for “water displacement
attempt #40.” The WD-

40

™

product used today was
the successful 40th attempt
at creating a water­displacing lubricant.
WD-40

™

was the lab test

label.

Be sure to follow
proper maintenance

and storage procedures
to avoid damage to your
engine and other
components of your S­Maxx.

Don’t put the fuel from

your tank back into

your fuel jug. Dispose
of it properly, following city
or county regulations.

Always wear eye

protection when using

compressed air or spray
cleaners and lubricants.

45

46

Index

ABC, 23
After-run maintenance, 21, 43, 44
After-run procedure, 44
Air density, 28, 35
Air Filter 7, 22, 23, 27, 35, 43, 44

Cleaning, 21,27
foam, 23
maintenance, 42
oil, 6

Air Intake, 22
Air temperature, 36, 42
Air/fuel mixture, 28
Air/fuel ratio, 28, 29, 32
Airflow, 36
Ambient temperature, 36
Antenna (receiver), 11, 15, 41

tip, 15
tube, 15
wire, 15

Antenna (transmitter), 11, 15, 41
Antenna Mount, 7
Atmospheric conditions, 28, 36, 42
Axle pins, 9
Barometric pressure, 35, 42
Baseline setting, 35
Batteries, 6, 12, 13, 14, 41

charging, 30
receiver,13, 14
rechargeable, 13,14
transmitter,13

Batteries, Ni-MH (nickel-metal
hydride), 13
Batteries, NiCad (nickel-cadmium),
6, 12, 13, 30
Battery box, 7
Battery compartment (Transmitter),
11, 13
Battery holder, 11, 14
Bearings, 44
Big Block .15, 23
Binding, 42

Body mount, 7
Brake, 19
Bulkhead, 7
Bumper, 7
Bumper mount, 7
CA glue, 9
Camber, 38
Carb, see also Carburetor 23
Carburetor, 22, 23, 28, 42

adjustments, 28
barrel, 23
fine-tuning, 35
slide, 25
venturi, 28

Caster, 39
Channel, 11, 12, 17, 18
Channel number, 12
Charger, 6, 30

peak-detecting, 30
timed, 30

Chassis, 7
Clean-out, 23
Cleaning, 43
Clearing your frequency, 12
Clutch bell, 22
Combustion, 28
Combustion chamber, 23
Compression, 24, 42, 43
Connecting rod, 23, 43
Cooling fins, 23
Crankcase, 22, 23
Crankshaft, 22, 23, 44
Cross-brace, 7
Crystal, 12, 18

Access Plug, 7

Curbs, 37
Customer service, 4, 41
Cylinder sealing, 32
Decals, 10
Differential, 7
Drivetrain friction, 37

Driving Tips, 37
Dyno, 23
E-mail, 4
Engagement pawls, 41
Engine, TRX 2.5, 7, 22, 26

"cutting out", 34
break-in, 21, 23,32

driving procedure, 33
cooling, 36, 43
damage, 27
detonation, 34
failure, 27,43
flooding, 31,41, 42
hesitation, 34
life, 42,43
maintenance, 43
mount, 22
overheating, 34
performance, 29
priming, 25,32, 42
revving, 37
shut off,44
sluggish acceleration, 34
stalling, 25,32, 34, 42, 43
temperature, 34,36
terms, 23
tuning, 28,34

by temperature, 36

Exhaust, 5, 22
Exhaust fumes, 32
EZ-Start, 6, 23, 24, 30, 41

“glow plug”LED, 30, 31,41
“motor” LED,30, 31, 41
battery, 30,41
controller, 22,31, 41, 42, 44
cush drive, 30
drive unit, 22
motor, 7,22,31,41
plug, 7,22
Protection Mode, 31,41
Smart Start

™

,30,31

Fit, 23
Flag color, 12
Flame-out, 24
Flooding, see Engine; flooding
Flywheel, 22, 41
Frequency band, 12, 15
Fuel, 5, 6, 24, 26, 42, 44

break-in fuel, 32
fuel dispensing bottle, 6,26

Traxxas Top Fueler,26
Traxxas Top Fuel, 24, 26,42
unburned, 44

Fuel flow, 28
Fuel intake, 22
Fuel line (fuel tubing), 7, 22, 24, 42
Fuel mixture adjustment, 35

high-speed fuel mixture, 34
low-speed mixture, 35

Fuel mixture, see also air/fuel
mixture, 24, 34, 35, 42
Fuel tank, 7, 22, 26, 44

emptying, 44
filling, 26
fuel level, 32
tank lid, 7,26
tank seal, 26

Glow plug, 24, 30, 31, 32, 34, 41-42

driver,24
fouled, 32
igniter, 30
power wire, 22,42, 44

Ground wire, 22
Half shaft, 7
Head (cylinder head), 22, 23
Head Protector, 22
Header, 7, 24
Hex hubs, 9
Humidity, 35
Idle adjustment screw, 35
Idle speed, 17, 24, 29, 32, 33, 34, 35
Idle Speed Adjustment, 29, 33, 35

Idle Speed Screw, 22, 24, 29
Jumping, 37
Lean, 24, 29

leaning the mixture, 24
maximum safe lean setting, 34-35,
36

Lubrication, 29
Maintenance, 43
Maintenance schedule, 21
Methanol, 44
Mixture needles, 34

high-speed needle, 22,24, 28, 35,42
low-speed needle, 22,24, 28, 35

Moisture, 43, 44
Needle seat, 28
Needle settings, 42
Needle valve, 24
Negative wire, 22
Neutral (center) point, 16-17
Neutral position, 12
Nitro, 24

content, 24,26
percentage, 26

compensating for,35

Nitromethane, see also Nitro, 24
O-ring, 24
Oil, 6

after-run, 6, 44
filter, 6
WD-40

™

,6,44

Oil Dampers, see Shocks
On/Off switch, 7, 11, 14, 18, 41
Over revving, 37
Peak detection, see Charger
Pinch test, 35
Pipe (tuned), 7, 22, 24, 25
Pipe hanger, 7
Piston, 24, 32

wrist pin, 43,44

Piston and Sleeve, 42, 43
Pivot balls, 38

Port, 24
Positive Wire, 22
Power Switch, 11
Pressure Line, 7, 22
Priming, see Engine; priming
ProGraphix, 10
Punch, 25
Quick Start, 8, 9, 10, 13, 14, 15, 18,
19, 20, 26, 30, 31, 32, 34, 37, 43
Radio interference, 5, 20
Radio System, 11, 12, 19, 41

adjustments, 16
controls, 16
range-testing, 20
rules, 18
terminology, 12
terms, 12

Range, 14, 15, 18, 20, 41

short, 41

Receiver, 11, 12, 41

cover (box), 7,15, 41

Required equipment, 6
Rich, 25, 29
Ride height, 39, 40
Rollovers, 37
RPM, 25

limits, 37

Safety, 5
Servo reversing switches, 11, 16
Servos, 7, 11, 12

reversing, 11,17
steering, 7,11, 17,19
throttle/brake, 7,11, 16-17, 19

Shipping, 4
Shock Mounting Positions, 39, 40

Lower, 39
Upper, 40

Shock progression, 39
Shock Tower, 7
Shocks, 7, 38

Fine Tuning,38

Shuddering, 41
Skid Plate, 7
Sleeve, 25, 32
Slipper Clutch, 7, 38, 43

adjusting, 38
pegs, 43

Smoke, 34
Spring rate, 40
Spur Gear, 7
Stalling, see Engine; stalling
Starter shaft, 44
Starting, see Engine; starting
Steering mechanism, 19
Steering Trim, Electronic, 11, 12, 17,
19
Steering Wheel, 11, 19
Storage, 44
Supplies, 6
Support, 4, 41
Suspension

adjusting 39, 40

Suspension Arms, 7
Tank 1, 33
Tank 2, 33
Tank 3, 33
Tank 4, 33
Tank 5, 33
Tank 6, 33
Temperature, see Engine;

temperature

Temperature gauge, 36

digital temperature gauge, 36
infrared temperature probe,36

Throttle Arm, 22
Throttle Neutral Adjustment, 11, 16
Throttle response, 35
Throttle slide, 35
Throttle Trigger, 11, 16, 19
Throttle Trim, Electronic, 11, 12, 16,
19, 35
Toe-in, 38

Tools, 6
TQ-3, see also Radio System 11
Transmission, 7
Transmitter, 12, 18, 41

indicator light, 19
power indicator,11, 13

Traxxas Lifetime Engine
Replacement Plan, 43
Trim, see also Throttle Trim
and Steering Trim, 12
Troubleshooting, 41
Turnbuckle, 7
Turns, 37, 39
Two-Speed, 41

access hole, 41
adjusting, 41

Understeer, 39
Water, 42
Wear-in, 25
Weather conditions, 35
Wheelies, 34
Wheels, 9
Wiring diagram, 11
WOT, 25, 28
X-tal see also Crystal, 12
Zero-scrub-radius, 19

47

Index

1100 Klein Road, Plano Texas 75074

1-888-TRAXXAS