trx 25r owners manual - rczone.biz

OWNERS MANUAL

™

®

TRX 2.5R • 2

Traxxas1100 Klein RoadPlano, Texas 75074Phone: 972-265-8000Toll-free 1-888-TRAXXAS

Traxxas U.K.P.O. Box 1128Winterbourne, Bristol BS36-2SH, EnglandPhone: 44-117-956-1002

Internetwww.Traxxas.come-mail: [email protected]

Entire contents ©2004 Traxxas. Traxxas, TRX 2.5R, Top Fuel, and Ready-To-Race are trademarksor registered trademarks of Traxxas. Other brand names and marks are the property of theirrespective holders and are used only for purposes of identification. No part of this manual maybe reproduced or distributed in print or electronic media without the express writtenpermission of Traxxas.

Note: Some photos show the engine equipped with optional accessories, such as the EZ-Startsystem, headers, and engine mounts, that are not included in the engine package. See the endpanel of the engine box for exact contents based on your engine model number.

TRX 2.5R • 3

Before You ProceedCarefully read and follow all instructions in this and any accompanying materials to preventserious damage to your engine. Failure to follow these instructions will be considered abuseand/or neglect. Before running your TRX 2.5R Racing Engine, look over this entire manual andexamine it carefully. If for some reason you decide the TRX 2.5R is not what you wanted, donot continue any further. Your hobby dealer absolutely cannot accept a TRX 2.5R for returnor exchange after it has been run.

Warnings, hints, and cross-referencesThroughout this manual, you’ll notice warnings and helpful hints, identified by the iconsbelow. 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.

SupportIf you have any questions about your TRX 2.5R Racing Engine or its operation, call the TraxxasTechnical 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 customersupport with your question at [email protected]. Join thousands of Traxxas R/Centhusiasts 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 saveshipping and handling costs by purchasing them from your local hobby dealer.

4 Safety Precautions

5 Introduction

6 TRX 2.5R Racing Engine Illustrated

7 Terms to Know

11 The Fuel

13 The Air Filter

14 The Carburetor

18 Breaking-in Your TRX 2.5R RacingEngine

22 Tuning the TRX2.5R for BestPerformance

27 TroubleshootingYour TRX 2.5RRacing Engine

30 Maintaining andStoring Your TRX2.5R Racing Engine

33 Index

34 Rebuilding the TRX2.5R Racing Engine

BEFORE YOU PROCEED

TRX 2.5R • 4

All instructions andprecautions outlined in this manual should bestrictly followed to ensuresafe operation of your TRX 2.5R Racing Engine.

The TRX 2.5R Racing Engineis not intended for use bythose under 16 years of age without the supervisionof a responsible andknowledgeable adult.

Safety PrecautionsAll of us at Traxxas want you to safely enjoy your new TRX 2.5R Racing Engine. Operate your TRX2.5R 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 damageand serious injury. The precautions outlined in this manual should be strictly followed to helpensure safe operation. You alone must see that the instructions are followed and the precautionsare 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 allfuel out of the reach of children at all times. Do not place fuel containers on the ground wherechildren 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 touchthe 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 obstructedor impaired in any way.

• Never operate your model in crowds of people or busy pedestrian areas. The TRX 2.5R makesmodels 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. Beconsiderate 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

IntroductionThe TRX 2.5R Racing Engine is vastly superior totypical R/C engines and belongs in the category ofspecialty high-performance racing engines. It’s theresult of years of focused engineering development,and thousands of hours of controlled testing andrigorous real-world running. It offers unprecedentedpower and performance that turns ready-to-run into Ready-To-Race®.

The TRX 2.5R Racing Engine takes a total-systemapproach. Each part of the engine, from the air filterto the exhaust tip, is carefully engineered to work inharmony with other engine components. Each partcomplements 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 isvery important that you follow the new break-in procedure as closely as possible to achievethe best performance and longest life from your TRX 2.5R Racing Engine. Old style break-inprocedures, such as simply running the engine with a very rich fuel mixture for the first 4tanks of fuel, will not achieve the best results. Follow the steps in this manual to successfullybreak in the TRX 2.5R Racing Engine.

A routine maintenance schedule is also required to keep the TRX 2.5R in top runningcondition. Cleaning the air filter after each hour of running is particularly important. Also it isextremely important to perform after-run maintenance on the engine to prevent corrosion ofthe internal engine components (see page 30).

Traxxas stronglydiscourages changing ormodifying any part of theTRX 2.5R Racing Engine.Old tech tips and tricksthat may have boostedthe power of otherengines could seriouslydiminish the performanceof the TRX 2.5R.

There’s more advancedthinking, developmentand testing in the stockparts of your TRX 2.5Rthan in many aftermarketmanufacturer’s so-calledperformance parts. TheTRX 2.5R is already one ofthe most powerfulengines in its class andsimply will not benefitfrom average, low-tech,aftermarket bolt onperformance items.

INTRODUCTION

TRX 2.5R • 6

TRX 2.5R ILLUSTRATED

Air FilterBase Head Protector

PowerTune™ Head (Cylinder Head)

Pull Starter

Low-SpeedNeedle

Throttle ArmClutch Bell

Flywheel

Carburetor

Air Intake

Fuel Intake

High-SpeedNeedle

Idle SpeedScrew

Crankshaft Crankcase

Air FilterHousing

TRX 2.5R Racing Engine Illustrated

OptionalBackplate

TRX 2.5R • 7

TERMS TO KNOW

Terms to KnowYou’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 cubiccentimeters (cc). The name “TRX 2.5R” isderived from the cc measurement.

ABC - Abbreviation for aluminum, brass, andchrome. Refers to engine construction thatconsists of an aluminum piston that slides ina chrome-plated brass sleeve. The TRX 2.5Ruses ABC construction.

Air filter - The air filter sits atop the carburetorand prevents harmful dust and dirt fromentering the engine. Dirt ingestion is thenumber one cause of premature enginefailure so the engine should never be runwithout the air filter in place.

Big Block .15 - A .15 (2.5) engine that uses alarger crankcase size and longer stroke thantypical .15 engines. Generally only used forspecific racing classes.

Break-in - Break-in is the procedure for runninga brand new engine according to specificinstructions. This correctly prepares theengine for normal running. The break-inprocedure can be different for differentmakes of engines. Follow the Traxxasdirections for break-in exactly.

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

the fuel with the air so that the engine canburn it. There are two types of carburetors;slide carbs and barrel carbs. The TRX 2.5Ruses the superior slide carburetor design.

Clean-out - Cleaning-out is a condition thatoccurs when the engine is accelerating andthe fuel mixture becomes sufficiently lean toallow the engine to continue into its upperRPM power band. It is usually characterized bya noticeable decrease in blue exhaust smokeand a dramatic increase in engine speed.

Combustion chamber - The combustionchamber is machined into the bottom of thecylinder head. This is where the glow plugignites the fuel. The shape of the combustionchamber is designed to promote moreefficient 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 allowit to “slice” through the pressurized air/fuelmixture inside the crankcase.

Crankcase - The engine “body” that contains allof the running mechanical components.

Crankshaft - The main shaft of the engine thatholds the reciprocating assembly.

TRX 2.5R • 8

TERMS TO KNOW

Cooling fins - The cooling fins are milled intothe cylinder head and crankcase and causeheat to be drawn away from the engine. Heatis removed when it dissipates into the airpassing across the cooling fins. It is importantto keep the fins clean of dirt and debris for maximum cooling efficiency.

Cylinder head (head) - The finned aluminumpart on top of the engine that is responsiblefor dissipating most of the engine’s heat. Thecombustion chamber is machined into thebottom of the head.

Dyno - Abbreviation for dynamometer. Aprecise piece of testing equipment thataccurately measures engine power andtorque output over the engine’s entire RPM range.

EZ-Start - Traxxas on-board electric startingsystem. The system consists of a hand heldstarter control unit and an on-board gearboxwith an electric motor to spin the engine.

Filter foam - The oiled foam element inside theair filter housing. The filter foam in the TRX2.5R must be thoroughly cleaned and re-oiledafter every hour of run time.

Fit - Usually refers to the fit of the piston andsleeve. If the fit is tight, the piston will feel verytight at top of the sleeve, and the engine willhave good sealing and compression. If the fit

is loose, compression will be low and both thepiston and sleeve should be replaced.

Flame-out - Occurs when the engine stopsrunning 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 andgallons from hobby dealers. The 10% and20% labeling refers to the percentageamount of nitromethane contained in the fuel (see “nitro percentage” definition).

Fuel mixture - The ratio of fuel to air asdetermined by the needle settings of the carburetor.

Fuel tubing (fuel line) - The thick siliconetubing that carries fuel from the fuel tank to the carburetor.

Glow plug - The glow plug is located in thecylinder head at the top of the combustionchamber. It contains a platinum element thatglows red hot when voltage is applied. Whenthe engine is being started, the heat from theglow plug ignites the fuel mixture and startsthe combustion process.

Glow plug driver - This tool clips onto the glowplug and supplies the required voltage tolight the glow plug element. It is also called

TRX 2.5R • 9

TERMS TO KNOW

an igniter. EZ-Start equipped engines do notrequire this separate tool.

Header - The aluminum tube that connectsthe exhaust system to the engine exhaustport. The length and diameter of the headermust be carefully selected to extract themost power from the engine.

High-speed needle (HSN) - Adjusts thecarburetors fuel/air mixture at high RPM.

Idle speed - The speed (RPM) the engine runs at when the transmitter’s throttletrigger is at neutral.

Idle speed screw (ISS) - Located on thecarburetor body. This screw adjusts the idleRPM of the engine.

Lean - A running condition where the engine is not getting enough fuel (for theavailable air). Symptoms include engineoverheating, or the engine runs for a shorttime and then stalls, particularly at highspeed. This is a dangerous condition thatshould be corrected immediately or it canruin 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 thatcontrols the low-speed fuel mixture.

Needle valve - Valve consisting of a taperedneedle that closes against a correspondingseat to regulate fuel flow.

Nitro - Abbreviation for nitromethane, a component of model engine fuel thatimproves fuel combustion and poweroutput. Nitro also refers to a class ofR/C powered by model engines instead of electric.

Nitro content - The amount of nitromethaneused in the fuel. Usually measured as apercentage of the total fuel volume. Traxxasengines are optimized to use 10-20% nitro.30% nitro may be used for racing.

Nitromethane - Nitromethane is a componentin the fuel that increases power from thecombustion process up to a point. Enginesare generally optimized to use a range ofnitro content for the best power.

O-ring - Rubber “O”-shaped ring used as asealing gasket.

Pipe - Abbreviation for the tuned exhaust pipeon a nitro engine. See “Tuned Pipe”.

Piston - The piston is the internal engine partthat is attached to the upper end of theconnecting rod and moves up and down inthe cylinder sleeve. The precise fit betweenthe piston and the sleeve creates a seal thatallows engine to have the requiredcompression for combustion.

TRX 2.5R • 10

TERMS TO KNOW

Port - Ports are openings in the sleeve thatallow atomized fuel to enter the combustionchamber and burned exhaust gasses to exit.The shape and location of the ports are alarge factor in controlling the engine timingand power output.

Priming - Manually causing fuel to move fromthe fuel tank up to the carburetor. This issometimes necessary after the engine hasbeen sitting for a long period of time and allof the fuel has drained back to the tank. On aTraxxas model this is done by holding yourfinger over the exhaust tip for one or twoseconds while the engine is starting.

Punch - A term that refers to how quickly themodel responds to throttle input or howquickly it accelerates.

Rich - A running condition where the engine isgetting too much fuel for the available air. Itis better to run an engine slightly rich toincrease engine life. Excessively rich mixturescause the engine to have sluggishperformance with exaggerated blue smokeand unburned fuel coming from the exhaust.

RPM - Abbreviation for revolutions per minute(how many times the engine crankshaftspins 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 requiredcompression for combustion. The sleeve in a TRX engine is made of brass and is then hard-chrome plated.

Slide carburetor - The throttle on a slidecarburetor closes and opens by sliding abarrel in and out of the carburetor body. This type of carburetor is preferred forperformance use because it provides a less restrictive “straight-through” air paththan the barrel carburetor design.

Stall - When the engine stops running, usuallydue to an incorrect fuel mixture setting orrunning out of fuel.

Tuned pipe - The tuned exhaust pipe usuallyconsists of a specially-shaped metal orcomposite chamber with baffles that isdesigned to enhance the power output ofthe engine.

Wear-in - Fitment process that occurs duringengine break-in where internal engine partsdevelop an even more precise matched fitthrough actual use under controlledcircumstances.

WOT - Abbreviation for wide-open throttle.

TRX 2.5R • 11

THE FUEL

The FuelUse the Right FuelIt’s imperative that you use the correct fuel in your TRX 2.5R for maximum performance andengine 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 to meet all requirements for usein Traxxas engines.

• Traxxas Top Fuel is made with just the right balance of the highest grade natural andsynthetic 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 switchback and forth between 10% and 20% fuel. If you break-in your engine on 20% fuel, thenalways use 20% fuel.

What About Other Fuels?Can other brands of fuel be used besides Top Fuel? There are other fuels that can providesatisfactory performance, however, there could be long-term costs in the form of decreasedengine 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 spentover two years developing the TRX 2.5R Racing Engine. No one knows more about the specificfuel requirements of Traxxas engines than Traxxas engineers. We strongly urge you not to takechances with your engine investment and use the Traxxas fuel made for the TRX 2.5R.

You may use higher nitropercentages than 20% incertain circumstances. Call 1-888-TRAXXAS for more information.

TRX 2.5R • 12

THE FUEL

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 reclaim fuel from your vehicle’s tank.• 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 4 in this manual.

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

The TRX 2.5R air filter assembly consists of 3 pieces:1. A rubber filter base 2. A plastic housing consisting of a permanently assembled mesh cap and body3. An oiled foam element

You must clean the filter after every hour of runtime, even if the filter looks clean. Dust (whichis often too fine to see) and dirt constantly move through the filter anytime the engine isrunning. Even if you can’t see dirt on the filter, it is present inside the foam after any amount ofruntime. 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 ofpremature engine failure.

TRX 2.5R • 13

THE AIR FILTER

Air Filter Cleaning Instructions1. Remove the air filter from the carburetor bore by pulling the

entire filter assembly firmly to the side to release it. Do notpull straight up.

2. Disassemble the filter. Pull the rubber air filter neck out ofthe filter body. With the base removed, the foam element isvisible in the bottom of the filter body. Pull out the foamelement.

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

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

5. Oil the foam element with foam filter oil. Use the supplied Traxxas filter oil (part# 5263) or ahigh-quality, special-purpose foam filter oil like what is used for off-road motorcycle andATV engines.This type of filter oil is available at motorcycle pro shops. Apply 30 drops of theTraxxas filter oil evenly to the top, bottom and sides of the filter element (30 total dropsdivided among the 3 surfaces). Squeeze the filter element repeatedly to help spread the oilthroughout. The filter element should be evenly colored by the oil. Even color indicates thatthe oil is distributed evenly. Do not squeeze out excess oil.

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 filter neck fitssecurely on the carburetor with no gaps or air leaks.

Clean your air filter after everyhour of runtime to avoidengine damage, even if thefilter looks clean.

If you use compressed air todry your air filter assembly,wear safety glasses and avoiddirecting compressed airtoward your skin.

If foam filter oil is notavailable, clean 30 or 40weight motor oil can besubstituted, but is notpreferred. Never run theengine without a properlyoiled filter!

TRX 2.5R • 14

THE CARBURETOR

The CarburetorUnderstanding the carburetor adjustmentsThe carburetor performs several functions. Itcontrols the engine’s speed by restricting theintake of air and fuel into the engine. It atomizesthe fuel (suspends the fuel droplets in the air) andalso controls the air/fuel ratio of the mixtureentering the engine (how much air for a givenamount of fuel). To help provide a betterunderstanding of engine tuning and why it’s necessary, thefollowing is a brief explanation of the air/fuel combustion processthat takes place inside the engine.

In order to create the cylinder pressure that results in power, the engine burns the air/fuelmixture. Both air and fuel, in correct amounts, are needed for proper combustion. It is thecarburetor’s job to mix the air and fuel together (atomize the fuel), in the correct proportion forthe best possible combustion. This is the ideal air/fuel ratio required for the engine. The idealair/fuel ratio 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-changingconditions. For example, colder air is moredense (more air molecules) for a givenvolume of air and therefore requires morefuel (more fuel molecules) to maintain thecorrect air/fuel ratio. Warmer air is lessdense (fewer air molecules) and thereforeneeds less fuel to maintain the correctair/fuel ratio. The tuning needles are thereto adjust how much fuel is made availablefor the carburetor to mix with the availableair (atomization).

Air

Fuel

Dense Air Less Dense Air

Factory Needle SettingsIf 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

TRX 2.5R • 15

THE CARBURETOR

The Fuel Mixture NeedlesThe amount of fuel metered and atomized bythe carburetor is controlled by the two mixtureneedles; the high-speed needle and the low-speed needle. The low-speed needle is used tometer the fuel used by the engine at idle andlow RPM (part-throttle) engine speed. The high-speed needle is used to meter the fuel when thethrottle is open from part throttle to wide-openthrottle (WOT). Two needles on the TRX 2.5Rprovide 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 themain water valve on a garden hose. Turn it clockwise to close the valve, counter-clockwise toopen it. When the throttle is at idle or partially open, the low-speed needle again meters thefuel flow at the outlet (needle seat) where the fuel enters the carburetor venturi. This secondvalve acts like the spray nozzle at the end of the garden hose in our example. When youaccelerate from idle, the throttle opens and the low-speed needle is pulled away from theneedle seat. This allows more fuel to flow with the increased air flow. As the throttle isincreased, the low-speed needle is pulled completely away from the needle seat leaving it fullyopen. At that point, fuel metering is entirely controlled by the high-speed needle. Again, usingour 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 mixtureincreases the amount of fuel in the air/fuel mixture ratio and leaning the fuel mixturedecreases the amount of fuel in the air/fuel mixture ratio.

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

Water Valve (Controls Overall Flow)

High Speed Needle

Water Nozzle (Controls Fine Flow)

Low Speed Needle

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

See Tuning the TRX 2.5R forBest Performance on page22 for complete informationon adjusting the air/fuelmixture and idle speed.

TRX 2.5R • 16

THE CARBURETOR

Tuning the engine means finding theperfect balance between the two;excellent power to meet your needswhile maintaining good lubrication for long engine life. The optimal fuelmixture setting is rich to provide asafety margin against having a leancondition if some variable changes (such as the temperature from one day to the next). General fuel mixturesettings are measured by the number of turns the needles are turned out from fully closed. Thefuel mixture settings have been pre-set from the factory to typical break-in settings. Do notreadjust 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 maybe required to compensate for fuel, temperature, and altitude. Adjustments are usually made in1/8 or 1/16-turn increments.

The Idle Speed AdjustmentThe idle speed screw controls the closed position of the throttle slide. When the throttle servois 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 trimon the transmitter to adjust idle speed. The idle speed should be set as low as possible and stillmaintain reliable running.

LeanRich

TRX 2.5R • 17

BREAKING-IN THE TRX 2.5R

Breaking in Your TRX 2.5R Racing EngineThe TRX 2.5R Racing Engine uses a ringless, aluminum-brass-chrome (ABC) piston/sleeveconstruction. This type of engine design relies on a very precise running fit between the pistonand sleeve for cylinder sealing. Engine break-in is necessary to allow the piston and sleeve todevelop an extremely precise fit and optimum cylinder sealing. Therefore, proper enginebreak-in is critical to achieving the fastest, most reliable engine performance.

Allow yourself about 1 to 11/2 hours to complete the break-in procedure. The engine break-inperiod will take 5 tanks of fuel. The break-in time is not the time to impress your friends withyour new engine. You must wait until the engine is fully broken in before attemptingsustained high speed running. Patience and careful attention during break-in will reward youwith the best-performing TRX 2.5R Racing Engine 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. Manyowners report not experiencing any of these symptoms with the TRX 2.5R Racing Engine. Werecommend replacing the glow plug with a new one after the engine break in procedure.

Engine Break-in ProcedureThe focus during break-in is to vary and limit the engine speed. This will be accomplished byaccelerating and stopping at different rates for the first 5 tanks of fuel. As the engine begins tobreak-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 alarge, flat, paved surface. Apply all throttle and braking actions gently. Abrupt accelerationor braking could cause the engine to stall unnecessarily.

Never run your modelindoors. Since the TRX 2.5RRacing Engine exhaustfumes are harmful, alwaysrun your model outdoors,in a well-ventilated area.

Your TRX 2.5R RacingEngine doesn’t usuallyrequire priming. If you doneed to prime yourengine, watch the fuel linecarefully to avoid floodingyour engine. See page 29for information on clearinga flooded engine.

Your carburetor is pre-setat the factory to give thecorrect air-to-fuel ratio and idle speed for enginebreak-in. Do not adjust the carburetor unless you observe a poorrunning condition thatrequires correction.

TRX 2.5R • 18


Important points to remember during break-in:• 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 glowplug or extremely high engine temperatures.

• Do not attempt to break in the TRX 2.5R Racing Engine by idling it on a stand. This will producepoor results.

• Keep extra Traxxas glow plugs (part #3231 or 3232) handy. The break-in process can causedeposits to form on the plug leading to plug failure.

• Change or clean your air filter after break-in.• Follow the instructions exactly for each of the first 5 tanks of fuel.

Starting Your TRX 2.5R Racing Engine for the First TimeBefore you start your TRX 2.5R Racing Engine for the first time, make sure you have read allinstructions and precautions in this manual. Pay close attention to the tank-by-tank break-ininstructions in the next section, and make sure you have read and understood them beforeyou 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 TRX 2.5R Racing

Engine indoors until you’re ready to start it, then take it outside.1. Turn on the radio system .2. Make sure the throttle is in the idle position.3. Pull the starter handle with quick, short, continuous pulls, 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 within5 seconds, prime the engine by briefly (one or two seconds) covering theexhaust 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.

See Important Points toRemember on page 4 forother precautions.

TRX 2.5R • 19


5. Once fuel reaches the carburetor, the engine should quickly start and idle.6. Proceed with the engine break-in.

If your engine doesn’t start, refer to the TRX 2.5R Racing Engine troubleshooting section at www.Traxxas.com. If you still have problems, contact Traxxas Customer Support at 1-888-TRAXXAS.

Tank 1

1. Drive the model with the body off.2. Driving procedure: Gently pull the throttle trigger to about 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 (use the installed clamp).

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-speedneedle 1/4 turn by turning the needle counterclockwise.

Tank 2

1. From tank 2 forward, model should be driven with the body on.2. Driving procedure: Gently pull the throttle trigger to about 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 stoppingprocedure 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.

As you gain experience inthe hobby, you maydiscover that many peoplehave differing opinions onwhat is the properprocedure to break-in amodel engine. Only use theTraxxas break-in procedure.Other break-in procedurescould result in a weak,damaged, or otherwise poorperforming engine. Theprocedure outlined herewas extensively tested andproven to yield betterperforming engines thanother “common” break-inmethods. Even if you haveyears of experience usingmodel engines, please donot ignore this caution!

TRX 2.5R • 20


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: onethousand one, one thousand two, one thousand three, and then stop. Repeat this starting andstopping 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 creepforward when stopped. Reduce the idle speed by turning the idle adjustment (see page 19) on the carburetor counterclockwise.

3. When the fuel tank is nearly empty, shut off the engine and refuel. From here on, you do notneed 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. Thengently apply the brake to stop. Count the three seconds out while accelerating: one thousandone, one thousand two, one thousand three, and then stop. Repeat this starting and stoppingprocedure 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 thethree-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, holdfor 2 more seconds, and then gently apply the brake to stop. Count the five seconds outwhile accelerating. Repeat this starting and stopping procedure until the fifth tank of fuel isnearly empty.

2. The model should now be shifting into second gear. If it is not, try turning the high-speedneedle clockwise 1/8 turn to lean the fuel mixture slightly and test for shifting.

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

Tank 6

STOP! Clean your air filter before you proceed. Refer to the instructions on page 13. During thesixth tank of fuel, the engine can be tuned for general performance use. Proceed to the nextsection in this manual for instruction on tuning the engine.

Winter Break-in TipsDuring the break-in process, the piston and sleeve wear into each other to form a precise fit. Theengine needs to heat up to a temperature of at least 200 to 215 degrees to allow the piston andsleeve to achieve this fit properly. A precise fit between these two components is critical forproper compression and optimum performance. If the engine runs too cold during break-in, thepiston and sleeve will not expand to their appropriate sizes for break-in. This can lead topremature wear of these components. This wear may not become apparent until winter has passed and the engine is operated under warmer running conditions.

• Warm the engine to approximately room temperature by removing all fuel and storing thevehicle inside at room temperature until just before starting the engine. An extremely coldengine can become difficult to start.

• After the engine is running, it is important to keep the temperature of the engine to at least 200 to215 degrees during break-in. In weather below 45 degrees, the TRX 2.5R Racing Engine will tend torun at lower temperatures between 160 to 180 degrees (when tuned at proper break-in mixturesettings). This is too cool for break-in. Do not lean the engine to increase engine temperature!This will also decrease lubrication and cause your piston/sleeve to wear prematurely. TRX 2.5R • 21


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.

Gradually accelerate over 3 second count.

Accelerate over 3 second count,hold for 2 seconds.

TRX 2.5R • 22

TUNING THE TRX 2.5R

• Wrap the cooling head with a paper towel, clean rag or sock to help keep the engine running atthe recommended 200 to 215 break-in temp. If too much heat is contained, the engine may runtoo hot. Make sure that you monitor the engine's temp closely for the first couple of tanks untilyou get the right amount of cover for the cooling head. This will, of course, depend on yourcurrent weather conditions. Adjusting the cover up and down, exposing more or fewer coolingfins, is a convenient way to regulate engine temps.

• For owners that do not have access to a temperature probe, a drop of water on the cooling head(around the glow plug area) should slowly sizzle for approximately 6 to 8 seconds when theengine temp is 200 to 210 degrees. If the water sizzles for only a few seconds, then it is likely thatthe engine temp is over 220 degrees and needs to cool down. If the water takes a long time ordoes not evaporate at all, then the engine is too cool.

• We do not recommend that you operate your engine below 35 degrees Fahrenheit. If you insiston running your vehicle below 35 degrees, be aware that nitro engines may be very difficult tostart and tune at those extremely cold temperatures. Also, at temperatures below freezing, nitrofuel can actually begin to gel up, and this can be harmful to the engine.

• Follow the remaining break-in procedures as outlined in this owner's manual. This, along with thesteps listed above, will ensure a good break-in for your new nitro engine and provide many hoursof enjoyment.

Tuning Your TRX 2.5R Racing EngineThe engine’s performance depends on the fuel mixture. Turn the mixture needles clockwise tolean the fuel mixture and counterclockwise to richen it. Leaning the fuel mixture will increaseengine power up to the engine’s mechanical limits. Never run the engine too lean (notenough fuel flow). Never lean the engine until it begins to cut-out or stall. Leaning theengine beyond the safe allowable limits will result in poor performance and almost certainengine 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.

TRX 2.5R • 23

TUNING THE TRX 2.5R

If any of these conditions are present, stopimmediately and richen the high speed mixture 1/4 turn. The engine will probably be slightlyrich at that setting and you can then retune forperformance. Always tune for performance bystarting rich and moving leaner toward the idealsetting. Never try to tune from the lean side.There should always be a light stream of bluesmoke coming from the exhaust. Before youbegin tuning, the engine should be warmed upto its normal operating temperature andrunning slightly rich. All final tuning adjustmentsmust be made to the engine at its normal operatingtemperature. You can tell the engine is running rich bynoting 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 AdjustmentWith the engine warm and running at a rich setting, gradually lean the high-speed fuel mixturein 1/16 turn increments. Make several high-speed passes after each adjustment to clear out theengine and note any change in performance. The TRX 2.5R is extremely powerful. Remember toapply the throttle gradually to prevent wheelies or loss of control. Continue this procedure untilthere 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 improvement2. The engine begins to cut out at high speed (Danger!)

When tuning forperformance, watch closelyto notice when there is nolonger any increase in speedor power when the high-speed mixture is lean. If you lean the high-speedmixture to the point that theengine cuts-out, hesitates, orstalls, you are well into thedanger zone and enginedamage is likely. Richen thehigh-speed needle 1/4 turnand retune.

TRX 2.5R • 24

3. There is a sudden loss of power during acceleration (Danger!)4. The engine begins to overheat. Symptoms of overheating include:

If any of the above conditions occcur, richen the fuel mixture to the optimum setting byrichening the high-speed needle at least 1/8 turn counterclockwise and retest. This settingwill extend engine component life.

Low-Speed Fuel Mixture AdjustmentThe low-speed mixture is always set after the high-speed needle is correctly adjusted. Set the low-speed mixture using the following pinch test.

1. Once the engine is warm, do several high-speed runs to confirm that the high-speed needleis set correctly.

2. Bring the vehicle in and pinch closed the fuel line going into the carburetor. The engineshould 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 high-speed runs, and retest.

4. If the engine dies immediately without speeding up, then richen the low-speed needle 1/8turn, 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.

Idle Speed AdjustmentOnce the high and low-speed mixtures have been set, reduce the idle speed to the minimumreliable idle speed. Remember, this adjustment should be made while the engine is running atnormal operating temperature.

1. Turn the throttle trim on the transmitter so that the brakes are applied. This ensures thatthe throttle slide is resting against the idle adjustment screw.

TUNING THE TRX 2.5R

For your convenience, thelow-speed needle has apositive stop that preventsit from being over tightenedand damaging the needleand seat. This also providesan easy way to gauge howmany turns out from closedthe low-speed needleadjustment is set to.

• Fluctuating idle speed• Hesitation or stalling during acceleration• Steam or smoke coming from the engine

(not exhaust)

• Popping or clattering sound whendecelerating (detonation)

• Temperature measurement above 270° F at the glow plug

When adjusting the low-speed fuel mixture, it isvery important to makeseveral high-speed runswith your model betweenadjustments to clear outany excess fuel. Performthe pinch test immediatelyafter. If the engine isallowed to idle for a longperiod of time, it could“load up” with fuel andgive you an inaccuratemeasurement from yourpinch test.

TRX 2.5R • 25

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 to its original position.

Fine-Tuning the CarburetorAfter fine-tuning your TRX 2.5R Racing Engine at the end of the break-in procedure, no majoradjustments 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 weatherconditions 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 yourcarburetor needles to compensate for changes in temperature and barometric pressure (airdensity) from day to day. Generally, you’ll need to richen the fuel mixture when the weather iscolder than your baseline temperature and the air density is higher. Lean the fuel mixture whenweather is warmer than your baseline temperature and the air density is lower. The chart belowprovides general guidelines on how weather conditions affect air density when they movehigher or lower than your baseline setting (see page 14 for detailed info on how air densityaffects mixture settings).

If the...Humidity

Pressure (barometer)

Temperature

Altitude

Nitro %

is..LowerHigherLowerHigherLowerHigherLowerHigherLowerHigher

then the air density is...

Slightly more denseSlightly less dense

Less denseMore denseMore denseLess denseMore denseLess dense

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

Slightly richerSlightly leaner

LeanerRicherRicherLeanerRicherLeanerLeanerRicher

TUNING THE TRX 2.5R

TRX 2.5R • 26

TUNING THE TRX 2.5R

Tuning the Engine by TemperatureThe following procedures require an optional infrared temperature probe or on-board temperaturegauge (Traxxas on-board digital temperature gauge, part #4091). Engine temperature can be usedas an effective tuning aid when you understand the relationship between engine temperature andambient temperature. The engine operating temperature, when tuned for maximum performance,will vary according to atmospheric conditions. The atmospheric condition that has the mostinfluence on engine temperature is air temperature. Expect the engine temperature to vary almostin direct proportion to air temperature. Assuming you tuned the engine for the same maximumperformance each day, the engine will run about twenty degrees hotter when it’s ninety degreesoutside than it would in seventy-degree weather. For this reason, we cannot give you a definitivetemperature range that indicates the best possible engine tuning. The temperature gauge can aid you in tuning by giving you a relative indication of how youradjustments are affecting the engine and by preventing you from exceeding maximum enginetemperature. For example, as you lean the fuel mixture, the engine performance will increase alongwith the temperature. If you continue to lean the fuel mixture and the temperature increases butthe engine performance does not change, then you have exceeded the maximum safe leansetting. Even if it’s 100°F outside, you should be able to tune for maximum performance. Try tokeep your engine from exceeding 270°F when measured at the glow plug. If tuning for maximumperformance results in engine temperature exceeding 270°F, try to increase airflow to the engineby cutting out the rear of the body, windshield, and front valance. If the engine temperature stillcannot be kept below 270°F, richen the high-speed needle slightly.

TRX 2.5R • 27

TROUBLESHOOTING THE TRX 2.5R

Troubleshooting Your TRX 2.5R Racing EngineThe following section addresses some very basic engine and radio questions you may have aboutyour TRX 2.5R Racing Engine. Most questions arise from simple user errors or minor adjustments thatare easy to correct. If you can’t find a solution for your TRX 2.5R Racing Engine here, visit our web siteat Traxxas.com and click on the Customer Support menu. There you will find a much more extensiveand detailed online troubleshooting area. In addition, you may call Traxxas Customer Service at 1-888-TRAXXAS (outside the US call 972-265-8000).

Engine spins but will not start:• If you’re using a glow plug igniter, make sure it’s fully charged and connecting properly to the glow

plug. If the igniter is fully charged, then replace the glow plug. It is normal for glow plugs to requireperiodic replacement. Only use Traxxas heavy-duty long glow plugs (part #3231 or #3232).

• Check to make sure the fuel is getting to the carburetor. Remove the fuel line where it connects tothe carburetor to see if there is fuel in it. If not, you may need to prime the engine. Reconnect thefuel line and then refer to page 18 for instructions on priming the engine.

• Check your fuel mixture settings. It may be necessary to adjust the fuel mixture if the outsidetemperature or barometric pressure has changed significantly since the last time the engine was run (see Fine Tuning the Carburetor on page 25). 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 22).

• The engine could be worn. If the fit between the piston and sleeve is loose, compression is reducedand the engine will be difficult to start when it is warm, and may tend to stall when running andwhen the throttle is closed suddenly to idle. Engine life depends on many factors including fueltype, air filter maintenance, needle settings, and how the engine was used. For example, if theengine was allowed to ingest dirt from lack of air filter maintenance or running through water, thenthe internal engine components could wear out extremely fast.

TRX 2.5R • 28


Engine will not spin (pull start or electric starter will not turn the engine):• 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 29 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 enginedamage. See page 29 for info on clearing a flooded engine and releasing a stuck piston. (Note: It isnormal for the engine to be extremely tight and hard to turn when the piston reaches the top of thecompression 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 needlesetting. The symptoms described above can occur when the air density is very low, such as in highmountainous elevations and extremely cold temperatures. Under these conditions, lean the fuelmixture slightly, 1/8 turn, and see if there is any improvement in starting and idling. Lean the fuelmixture only 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 extremeatmospheric conditions can also make the factory preset break-in settings too rich and cause thesymptoms described above. Again, try leaning the fuel mixture slightly, 1/8 turn, to see if there isany improvement in starting and idling.

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 22).

• Try a new Traxxas glow plug. Sometimes a glow plug will work well enough to start the engine butnot be able to deliver the engine’s full performance potential.

TRX 2.5R • 29


• If the fuel mixture seems to be set correctly, make sure the fuel is fresh. If the fuel is old, or was leftuncapped for a long period, then some of the important fuel components could have evaporated.Try new, fresh, Traxxas Top Fuel.

• 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, it can become flooded with fuel. When the engineis flooded it will no longer turn due to excess fuel in the combustion chamber, preventing upwardmovement of the piston. Use the following procedure to clear a flooded engine:

1. Remove the glow plug and gasket with the glow plug wrench supplied with your model. A 5/16" (8mm) nut driver will also work.

2. Turn the model upside down.3. Pull the starter handle several times to clear the engine of excess fuel.4. Turn the model over and reinstall the glow plug and gasket. 5. Do not prime the engine. Apply 1/2 throttle and pull the starter. The engine should

start immediately.

Piston Stuck at Top Dead Center (TDC): A new engine will typically have a tight fit between the piston and the top of the sleeve. This is atapered fit. The fit should not be too tight to start the engine. If the engine is stuck at TDC, then use a pair of needle nose pliers to grasp the flywheel from the bottom of the engine. Rotate the flywheelcounter-clockwise (when viewed from the air intake side [front] of the engine). You should see theflywheel turn and feel the piston become unstuck from the sleeve.

TRX 2.5R • 30

MAINTAINING THE TRX 2.5R

Maintaining and Storing Your TRX 2.5R Racing EngineTRX 2.5R Racing Engine 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. Follow proper maintenance and storage proceduresto avoid damage to your engine. 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 13. We cannot stress

enough the value of cleaning your air filter at the scheduled intervals. Do not neglect your airfilter maintenance!

• Clean the outside of the engine of accumulated dirt, oil, and grime. Accumulated grime willdecrease 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 31 forafter-run maintenance procedures.

• Inspect the vehicle for obvious damage or wear. Look for:1. Loose or missing screws2. Cracked, bent, or damaged parts 3. Cut or loose wiring 4. Cut or kinked fuel lines5. Signs of fuel leakage

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

After-run ProcedureYou must perform after-run maintenance on your Traxxas engine whenever the model will bestored for longer than a few hours. Taking the time to prepare your engine for storage will rewardyou with longer engine life, easier starting, and better performance.

If the engine is worn ordamaged enough torequire replacing thepiston, sleeve, orconnecting rod, considerexchanging your oldengine for a brand newengine under the terms ofthe Traxxas Lifetime EngineReplacement Plan (ERP). Itcould save you time andeffort. Details are in yourdocumentation package or on Traxxas.com.

Don’t put the fuel fromyour tank back into yourfuel jug. Dispose of itproperly, following city orcounty regulations.

Always wear eye protectionwhen using compressed airor spray cleaners andlubricants.

TRX 2.5R • 31


When a nitro engine is shut off, some excess unburned fuel remains in the engine. The methanol inmodel engine fuel is hygroscopic, which means it easily attracts and absorbs moisture. This moisturecan cause rust and corrosion on the steel engine parts (crankshaft, bearings, wrist pin and startershaft) if the fuel is not removed from the engine. There are after-run oil products available from yourhobby dealer or you can use WD-40™, a common household lubricant. To ensure your TRX 2.5RRacing 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 theexcess fuel to be consumed by the engine. Be sure the throttle is in the idle position. You mayhave 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 model 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 andinto 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. Pull the starter handle continuously for about 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 13 for air filter

maintenance instructions.10. Replace the glow plug and reinstall the air filter.

The TRX 2.5R is designed to be easily rebuilt. Critical engine components suchas the crankcase, crankshaft,

and engine bearings are made to extremely highquality standards and shouldunder normal circumstancesoutlast multiple sets of pistons,sleeves, connecting rods, and wrist pins (reciprocatingassemblies). It could be moreeconomical for you to continueto use your good bearings and crankshafts, and simplyreplace the reciprocatingassembly as needed. Engineassembly is not difficult andreplacing the reciprocatingassembly does not requireany special tools or skills.

Denatured alcohol (availablefrom home centers and paintsupply stores) in a spray bottle is an extremely effective cleaner. Be sure to wear safety glasses andgloves when working with denatured alcohol.

TRX 2.5R • 32


Other periodic maintenance:• 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 sealeffectively (loss of compression). Symptoms include the engine being difficult to start whenwarm, stalling when warm, and stalling when throttle is suddenly closed to idle. Replace thewrist pin and G-clip whenever the piston and sleeve are replaced. Follow the instructions forthe proper break-in procedure of a new TRX 2.5R Racing Engine whenever the piston andsleeve are replaced.

• Connecting rod: The connecting rod should be replaced when the piston and sleeve arereplaced or after three gallons of fuel, whichever comes first. Also replace the piston wristpin and G-clip whenever the connecting rod is replaced. As with other internal enginecomponents, the connecting rod’s life depends on the engine’s usage and the quality andfrequency of the engine’s maintenance.

TRX 2.5R • 33

These instructions are for the rebuildingof the Traxxas TRX 2.5R engine once theengine has been removed from thechassis. These instructions wereperformed on an engine equipped withthe EZ-Start electric starting system.Engines equipped with pull starters orbackplates (without starter) are similar. It is very important to clean the exteriorof the engine and EZ-Start systemthoroughly before disassembly. Theseinstructions show you how to replace theentire internal reciprocating assembly.

Rebuilding the TRX 2.5R Racing Engine

The following instructions are for enginesequipped with IPS crankshafts using Traxxasclutch components. For multi-shaft™

crankshafts in non-Traxxas applications,follow the manufacturer’s directions forclutch installation removal.

2. Remove the 5.0mm E-clip from thecrankshaft (Nitro 4-Tec owners will need toremove the 3x10CS screw) and slide the5x8x0.5TW with the clutch bell off of the crankshaft (Nitro 4-Tec owners willneed to slide two 5x8x0.5TW off the pilotshaft.) Caution: It’s important to use eyeprotection when removing the E-clipfrom the shaft to prevent the clip fromcausing an injury. Pull the clutch shoesoff of the flywheel pins.

Remove the flywheel nut from thecrankshaft using an 8mm socket (202)and disconnect the flywheel from thecrankshaft by lightly tapping the back of the flywheel with a rubber or plastic mallet.

Place a small flat blade screwdriver intothe slot of the split cone washer and twistslightly to loosen the split cone from thecrankshaft (203). Slide the split conewasher off of the crankshaft. The engine is now ready to be rebuilt (204).

1. Start by removing the exhaust pipeand header from the engine by removingthe two 3x15CS screws (102 & 103).

Remove the three 3x12BCS screwsthat secure the EZ-Start (or pull start)assembly to the engine and separatethe drive unit from the engine (104). If your engine is equipped with abackplate, proceed to step 2.

101

102

103

104

201

203

204

202

TRX 2.5R • 34

REBUILDING THE TRX 2.5R

3. Remove the glow plug from thecooling head and discard the plug.The glow plug should be replacedwith a new one anytime the engine is rebuilt.

Remove the four 3x6CS (3x6BCS onengines equipped with non-starterbackplate) screws from the backplate ofthe engine and pull the backplate fromthe crankcase (301).

Remove the cooling head from the engine case by removing the five3x12CS head bolts (302). Be carefulnot to lose or damage the copperhead gasket. If the head gasket isdamaged, replace it with a new one.

4. Locate the bottom of the sleevethrough the rear opening of thecrankcase. Press the bottom of thesleeve upward with a plastic orwooden stick (401), this is to preventinternal damage to the crankcase. The sleeve should slide up and out of the crankcase (402). (Note: If thesleeve does not slide out of thecrankcase with reasonable effort,slightly warm the crankcase with ahair dryer or heat gun to about 130° F.The sleeve should slide out easily at

this temperature. Use gloves toprotect against burns. ) Rotate thecrank to where the rod and piston arelocated at TDC (top dead center)(topof the piston’s stroke)(403).

Gently pull on the bottom of theconnecting rod with needle nosepliers, sliding the rod off of the crankpin (403). Be careful not to damagethe connecting rod if the rod is being reused.

The rod and piston assembly willexit the top of the crankcase (404).

5. Push the end of the pilot shaft through the crankcase. Thecrankshaft should exit the rear of the crankcase (501). Loosen the 3.0NLjust below the base of the carburetor(502). Slide the carburetor up and outof the crankcase (503). Now thecrankcase is ready to be flushed clean and inspected.

301

302

401

402

403

404

501

502 503

6. Flush the crankcase and bearings out with out with denatured alcohol orelectric motor spray. Dry the crankcasewith compressed air (601). Caution: Do not let the compressed airspin the bearings and always use eyeprotection when using compressed air.

Inspect the crankcase and bearingsfor damage or missing parts. Make surethat the bearing cages are not brokenand check for corrosion inside of thecrankcase. The bearings should feelsmooth and have little play. Make surethe bearings spin freely and that thereare no particles or grit in them. Replacethe bearings if there are any signs ofdamage. Inspect the exhaust O-ringgasket and the backplate O-ring gasketfor tears (602). Replace these O-rings if needed.

7. Apply a few drops of machine oil orafter-run oil to the bearings. Inspect thecrankshaft for corrosion and also checkfor scratches or score marks around theintake port of the crankshaft (see arrow).Check the crank pin for wear (701). Theconnecting rod should fit and rotatesmoothly on the crank with no playbetween the rod and the crank pin. Ifthere is play between a NEW connectingrod and the crank pin then the crank pinis worn and the crankshaft will need tobe replaced.

Important: Do not reuse a damaged or worn crankshaft. This will dramaticallyshorten the life of your rebuilt engine. If there are damaged or worn parts beyondthe piston, sleeve and connecting rod it maybe best to take advantage of the TraxxasEngine Replacement Program. 8. Slide the crankshaft back through thecrank bearings until it stops. Inspect thecarburetor O-rings for damage and therubber throttle arm boot for tears (801 & 802).

Unscrew the hi-speed needle all the wayout of the needle housing (803) and flush outthe hi-speed needle housing and thecarburetor body with denatured alcohol orelectric motor spray. Use compressed air todry the components. Remember: Alwayswear safety glasses when using compressedair to prevent injury. Reinstall the hi-speedneedle into the needle housing and returnthe mixture setting back to the factoryrecommended break-in setting (four turnsout from fully closed).

Carefully insert the carburetor into the crankcase until fully seated. Whilepressing the carburetor firmly into thecrankcase, tighten the pinch bolt (804). This process ensures that the upper O-ring forms a good seal between thecarburetor and the crankcase.

601

602

701

801

803

804

802

TRX 2.5R • 35


10. Lube the outside of the piston with after-run oil and make sure thecrank is at BDC (bottom dead center),then slowly lower the sleeve until It isjust above the piston. Rotate the crankslowly to bring the piston into thesleeve. If there is any resistance, stop!Repeat until the piston movessmoothly into the sleeve. Bring thepiston close to TDC, then push thesleeve in fully. Important: The slot (inthe lip) at the back of the sleeve mustkey into the pin at the back of thecrankcase opening (1001). Do notinstall the cooling head until these twoitems are keyed into each other.

Place the copper head gasket onto thesleeve and fit the cooling head into the sleeve (1002). Note that there aretwo slots notched through the cooling fins on each side of the cylinderhead. These slots are for access to the engine mounting screws. The fivehead bolts should line up with the five holes on top of the engine caseand the access slots on the cooling head should line up with the slotsmanufactured into the crankcase. Be careful not to damage the copperhead gasket (see picture 1002 for orientation).

While pressing the head squarely onto the sleeve, thread the head boltsinto the engine case just until they stop. Do not tighten down these boltsindividually. It is very important to attain even pressure around the coolinghead. Slowly tighten each screw, just a little at a time, in a crossing pattern(see picture 1003) until each bolt becomes snug. Finish each bolt in thesame pattern with 9-11in•lbs. of torque.

9. Apply a drop of after-run oil in thepiston’s wrist pin bore, before installingthe wrist pin. Locate the oil hole (refer topic 901) in the connecting rod and theskirt relief side of the new piston.

Insert the connecting rod into the pistonwith the piston skirt relief and the oilhole on the same side (901). Line up thewrist pin bore in the rod with the wristpin bore in the piston and slide the wristpin through the larger opening in thepiston. Note that the closed end of thewrist pin should be inserted first into theopening. The orientation of the wrist pinhelps keep the wrist pin cool.

Install the wrist pin clip into the grooveof the piston’s wrist pin bore (902). Thiswill retain the wrist pin inside of thepiston . Caution: Do not allow the pliersto scratch the piston, and make surethat the clip expands into the groovebefore moving on.

Lower the piston and connecting rodassembly into the top of the engine casewith the oil hole of the connecting rodfacing toward the crankshaft. Apply adrop of oil onto the crank pin beforeinstalling the connecting rod onto thecrank pin. Slide the connecting rod overthe crank pin and rotate the crank pin tothe bottom center of the crankcase (903).

901

902

903

1001

1002

1003

SkirtRelief

OilHole

TRX 2.5R • 36


OilHole

Skirt Relief

11. Inspect the backplate bushingand starter shaft for wear and cleanthem with denatured alcohol. Fastenthe backplate with the starter shaft tothe crankcase. Important: The reliefsthat are manufactured into thebackplate must line up to match theports inside of the engine case (seepicture 1101 for orientation).

Key the starter shaft to the crank pinby slowly rotating the starter shaft as pressure is applied towards thecrankshaft. Once the starter shaft iskeyed into the crank pin, join thebackplate to the engine case andsecure the assembly with the four3x6CS screws (1102). (On non-startermodels simply fasten the backplate tothe crankcase with (4) 3x6BCS screws).

Install a new glow plug (Traxxas #3232is recommended for the TRX 2.5R) intothe cooling head. The engine is nowrebuilt and ready for the installation of the clutch assembly and the EZ-Start system (if so equipped).

12. Slide the split cone washer over thepilot shaft with the larger end of thetaper toward the engine case (1201).Slide the flywheel over the pilot shaftand onto the split cone washer.

The split cone washer should fit inside of the tapered hole in the flywheel. Thread the flywheel nut all the way upto the flywheel and tighten the flywheelwith 55-65 in•lbs. of torque against theflywheel (1202).

13. Slide the clutch shoes onto theflywheel. Key the flywheel pins into theholes of the clutch shoes (See picture1301 for orientation of the clutch shoes).

Tip: By reversing the direction of theclutch shoes, the clutch shoes willprovide a little firmer bite against theinterior wall of the clutch bell. This isuseful on higher bite surfaces that offera higher level of traction.

14. Clean and lube both clutch bellbearings and install a ball bearing intoeach side the clutch bell and slide theclutch bell over the pilot shaft followedby the 5x8x0.5TW (1401).

Fasten the 5.0 E-clip (wearing safetyglasses) around the pilot shaft to retainthe clutch assembly.

Note: The Nitro 4-Tec will need two5x8x0.5TW placed onto the pilot shaftbefore the installation of the clutch bell, then secure the assembly with the 3x10CS screw.

1201

1202

1203

1301

1401

1102

1101

TRX 2.5R • 37


15. Clean the roller clutch with denaturedalcohol or electric motor spray, and lubethe roller clutch with after-run oil. Slidethe roller clutch onto the starter shaft asshown (1501).

Note: The roller clutch is to be installedonto the starter shaft so that the clutchengages the starter shaft clockwise androtates freely counter-clockwise. Theengraved text on the roller clutch facesthe engine backplate for correct rotation.

Slide the EZ-Start system or pull start ontothe starter shaft that exits the backplate ofthe engine. Line up the drive with theroller clutch. Fasten the EZ-Start gear caseto the backplate with the three 3x12BCSscrews (1502). Fasten the pull starter with(4) 3x12BCS.

16. Inspect the exhaust O-ring andreplace it if it is damaged or torn. Fastenthe exhaust header and pipe assemblyback onto the rear of the engine case withthe two 3x15CS screws (1601).

The engine, clutch, exhaust system and starter assembly is now readyfor installation into the chassis (1602).

Follow the instructions for the properbreak-in procedure of a new TRX 2.5RRacing Engine.

1501

1502

1602

1601

TRX 2.5R • 38


TRX 2.5R • 39

INDEX

.15; 7ABC; 7, 17After-run Procedure; 30, 31Air Filter; 5, 6, 7, 8, 12, 13

aftermarket filter; 12cleaning; 13filter foam; 8oil; 13

Air Intake; 6Backplate; 6Big Block .15; 7Break-in; 7, 17, 18, 19, 20, 21

Tank 1; 19Tank 2; 19Tank 3; 20Tank 4; 20Tank 5; 20Tank 6; 21winter break-in; 25

Carburetor; 6, 7, 14, 15, 16carb; 7factory settings; 15slide; 10understanding; 14

Clean-out; 7Clutch Bell; 6Combustion chamber; 7Connecting rod; 7Cooling fins; 8

Crankcase; 6, 7Crankshaft; 6, 7Cylinder head; 8

head protector; 6PowerTune™ head; 6

Dyno; 8EZ-Start; 8Fit; 8Flame-out; 8Flywheel; 6Fuel; 4, 8, 11

handling; 12intake; 6nitro content; 11other fuels; 11Traxxas Top Fuel; 11tubing; 8

Fuel Mixture; 8, 15atomization; 14high-speed mixture; see “High-Speed Adjustment”lean; 9, 15, 16leaning; 9low-speed mixture; see “Low-Speed Adjustment”ratio; 14rich; 10, 15, 16

Glow plug; 8driver; 9

Header; 9High-Speed Adjustment; 22

high-speed needle; 6, 9Idle Speed; 9, 16, 23

idle speed screw; 6, 9Low-Speed Adjustment; 23

low-speed needle; 6, 9Maintaining and Storing; 30Needle valve; 9Nitro; 9O-ring; 9Piston; 9Port; 10Priming; 10Pull Starter; 6Safety; 4Sleeve; 10Stall; 10Starting; 18Throttle Arm; 6Troubleshooting; 27

clearing a flood; 29Tuned pipe; 10Tuning; 21

by temperature; 26fine-tuning; 24

Wear-in; 10WOT; 10

1100 Klein Road, Plano, Texas 750741-888-TRAXXAS

®

051007

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