Traxxas TRX 2.5R User manual

OWNERS MANUAL
™
®

TRX 2.5R •2
Traxxas
1100 Klein Road
Plano, Texas 75074
Phone: [phone]
Toll-free 1-888-TRAXXAS
Traxxas U.K.
P.O. Box 1128
Winterbourne, Bristol BS36-2SH, England
Phone: [phone]
Internet
www.Traxxas.com
e-mail: [email protected]
Entire contents ©2004 Traxxas. Traxxas, TRX 2.5R, Top Fuel, and Ready-To-Race 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.
Note: Some photos show the engine equipped with optional accessories, such as the EZ-Start
system, headers, and engine mounts, that are not included in the engine package. See the end
panel of the engine box for exact contents based on your engine model number.

TRX 2.5R •3
Before You Proceed
Carefully read and follow all instructions in this and any accompanying materials to prevent
serious damage to your engine. Failure to follow these instructions will be considered abuse
and/or neglect. Before running your TRX 2.5R Racing Engine, look over this entire manual and
examine it carefully. If for some reason you decide the TRX 2.5R is not what you wanted, do
not continue any further. Your hobby dealer absolutely cannot accept a TRX 2.5R for return
or exchange after it has been run.
Warnings, 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 TRX 2.5R Racing Engine 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 TRX 2.5R Racing Engine 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 8:30am 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 [email protected]. Join thousands of Traxxas R/C
enthusiasts in our online community at www.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.
4Safety Precautions
5Introduction
6TRX 2.5R Racing
Engine Illustrated
7Terms to Know
11 The Fuel
13 The Air Filter
14 The Carburetor
18 Breaking-in Your
TRX 2.5R Racing
Engine
22 Tuning the TRX
2.5R for Best
Performance
27 Troubleshooting
Your TRX 2.5R
Racing Engine
30 Maintaining and
Storing Your TRX
2.5R Racing Engine
33 Index
34 Rebuilding the TRX
2.5R Racing Engine
BEFORE YOU PROCEED

TRX 2.5R •4
All instructions and
precautions outlined in
this manual should be
strictly followed to ensure
safe operation of your
TRX 2.5R Racing Engine.
The TRX 2.5R Racing Engine
is not intended for use by
those under 16 years of
age without the supervision
of a responsible and
knowledgeable adult.
Safety Precautions
All of us at Traxxas want you to safely enjoy your new TRX 2.5R Racing Engine. Operate your TRX
2.5R sensibly and with care, and it will be exciting, safe, and fun for you and those around you.
Failure to operate your TRX 2.5R 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 TRX 2.5R outdoors, in a well-ventilated area. Never run the engine indoors.
•Don’t operate your model at night or anytime your line of sight to the model may be obstructed
or impaired in any way.
•Never operate your model in crowds of people or busy pedestrian areas. The TRX 2.5R makes
models extremely fast and may cause injury to those unaware of its presence.
•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.
SAFETY PRECAUTIONS

TRX 2.5R •5
Introduction
The TRX 2.5R Racing Engine is vastly superior to
typical R/C engines and belongs in the category of
specialty high-performance 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 2.5R 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 2.5R is designed to be tolerant of variations in tuning and running through a
wide range of variable atmospheric conditions, such as changes in temperature, humidity,
and altitude.
The TRX 2.5R 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 2.5R 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 to successfully
break in the TRX 2.5R Racing Engine.
Aroutine maintenance schedule is also required to keep the TRX 2.5R 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 of
the internal engine components (see page 30).
Traxxas strongly
discourages changing or
modifying any part of the
TRX 2.5R Racing Engine.
Old tech tips and tricks
that may have boosted
the power of other
engines could seriously
diminish the performance
of the TRX 2.5R.
There’s more advanced
thinking, development
and testing in the stock
parts of your TRX 2.5R
than in many aftermarket
manufacturer’s so-called
performance parts. The
TRX 2.5R is already one of
the most powerful
engines in its class and
simply will not benefit
from average, low-tech,
aftermarket bolt on
performance items.
INTRODUCTION

TRX 2.5R •6
TRX 2.5R ILLUSTRATED
Air Filter
Base Head Protector
PowerTune™Head
(Cylinder Head)
Pull Starter
Low-Speed
Needle
Throttle Arm
Clutch Bell
Flywheel
Carburetor
Air Intake
Fuel Intake
High-Speed
Needle
Idle Speed
Screw
Crankshaft Crankcase
Air Filter
Housing
TRX 2.5R Racing Engine Illustrated
Optional
Backplate

TRX 2.5R •7
TERMS TO KNOW
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 2.5R is .15 cubic inches or 2.5 cubic
centimeters (cc). The name “TRX 2.5R” 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
achrome-plated brass sleeve. The TRX 2.5R
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
abrand 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 2.5R
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. It is usually characterized by
anoticeable 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 2.5R 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.
Crankcase -The engine “body” that contains all
of the running mechanical components.
Crankshaft -The main shaft of the engine that
holds the reciprocating assembly.

TRX 2.5R •8
TERMS TO KNOW
Cooling fins -The cooling fins are milled 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.
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 engine’s entire
RPM range.
EZ-Start -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.
Filter foam -The oiled foam element inside the
air filter housing. The filter foam in the TRX
2.5R 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, 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, compression will be low and both the
piston and sleeve should be replaced.
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 2.5R 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

TRX 2.5R •9
TERMS TO KNOW
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 (HSN) -Adjusts the
carburetors fuel/air mixture at high RPM.
Idle speed -The speed (RPM) the engine
runs at when the transmitter’s throttle
trigger is at neutral.
Idle speed screw (ISS) -Located on the
carburetor body. This screw adjusts the idle
RPM of the engine.
Lean -Arunning 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 (LSN) -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 nitromethane,
acomponent of model engine fuel that
improves fuel combustion and power
output. Nitro also refers to a class of
R/C powered by model engines instead
of electric.
Nitro content -The amount of nitromethane
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 -Nitromethane 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”.
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.

TRX 2.5R •10
TERMS TO KNOW
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.
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
of 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 -Aterm that refers to how quickly the
model responds to throttle input or how
quickly it accelerates.
Rich -Arunning 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.