TRX Engine Rebuild Instructions
TRX Racing Engine Rebuild Instructions
instructions below are for the rebuilding of the Traxxas TRX 2.5, 2.5R,
and 3.3 Racing Engine once the engine and EZ-Start® system have been
removed from the chassis. Before you remove your engine for a rebuild,
consider trading it in for a new engine using the Power-Up Program.
Rebuilding engines from parts can be costly and time consuming, and can
be outside the mechanical skills of many enthusiasts. With the Power-Up
Program, a worn out or damaged engine can be traded in for a brand-new,
factory-fresh TRX® Racing Engine right away by simply exchanging your
worn engine at your local hobby store. The cost is 1/2 of the retail
price of the new replacement engine. It’s less expensive than rebuilding
the engine yourself and you get the peace of mind knowing your engine
is brand new (not refurbished), and ready to deliver the power and
reliability you expect. In many cases, installing the new engine only
takes minutes and you're back in action.
- Start by removing exhaust pipe and header from the engine by removing the two 3x15CS screws.
- Remove the three 3x12BCS screws that secure the EZ-Start assembly to the engine and separate the gear housing from the engine.
the 5.0 E-clip from the crankshaft and slide the 5x8x0.5TW with the
clutch bell off the crankshaft. Caution: it's important to use eye
protection when removing the E-clip from the shaft to prevent the clip
from causing an injury. Pull the clutch shoes off the flywheel pins.
the flywheel nut from the crankshaft using an 8mm socket and disconnect
the flywheel from the crankshaft by lightly tapping the back of the
flywheel with a rubber or plastic mallet. Place a small flat blade
screwdriver into the slot of the split cone washer and twist slightly to
loosen the split cone from the crankshaft. Slide the split cone washer
off of the crankshaft.
- The engine is now ready to be rebuilt.
the glow plug from the cooling head and discard the plug. The glow plug
should be replaced with a new one any time the engine is rebuilt.
Remove the four 3x6CS screws from the back plate of the engine and pull
the back plate from the crankcase.
- Remove the cooling head from
the engine case by removing the five 3x12CS head bolts. Be careful not
to lose or damage the copper head gasket. If the head gasket is damaged,
replace with a new one.
- Locate the bottom of the sleeve
through the rear opening of the crankcase. Press the bottom of the
sleeve upward with a plastic or wooden stick. This is to prevent
internal damage to the crankcase. The sleeve should slide up and out of
the crankcase. Note: If the sleeve does not slide out of the crankcase
with reasonable effort, slightly warm the crankcase with a hair dryer to
about 130 F. Do Not use an open flame to warm the engine! The sleeve
should slide easily at this temperature.
- Use gloves to protect
against burns. Rotate the crank to where the rod and piston is located
at TDC (top dead center). Gently pull on the bottom of the connecting
rod with needle nose pliers, sliding the rod off of the crank pin. Be
careful not to damage the connecting rod if the rod is being reused. The
rod and piston assembly will exit the top of the crankcase.
the end of the pilot shaft through the crankcase. The crankshaft should
exit the rear of the crankcase. Loosen the 3.0NL just below the base of
the carburetor. Slide the carburetor up and out of the crankcase. Now
the crankcase is ready to be flushed clean and inspected.
the crankcase and bearings out with denatured alcohol or electric motor
spray. Dry the crankcase out with compressed air. Caution: Always use
eye protection when using compressed air. Inspect the crankcase and
bearings for damage or missing parts.
- Make sure that the
bearing cages are not broken and check for corrosion inside of the
crankcase. The bearings should feel smooth and have little play. Inspect
the exhaust O-ring gasket and the back plate O-ring gasket for tears.
Replace these O-rings if needed. Note: Never use engine sealant or RTV
on a TRX engine. They are precisely engineered to use special O'rings
for a proper seal.
- Apply a few drops of 'Mobil 1' synthetic
motor oil to the bearings. Inspect the crankshaft for corrosion and also
check for scratches or score marks around the intake port of the
crankshaft. Check the crank pin for wear. The connecting rod should fit
and rotate smoothly on the crank with no play between the rod and the
crank pin. If there is play between a new connecting rod and the crank
pin the crank pin is worn and the crankshaft will need to be replaced.
IMPORTANT: Do not reuse a damaged or worn crankshaft. This will only
cause more problems inside the engine. If there are damaged or worn
parts beyond the piston, sleeve and connecting rod it may be best to
take advantage of the ERP program.
- Slide the crankshaft back
through the crank bearings until it stops. Inspect the carburetor
O-rings for damage and the rubber throttle arm boot for tears. Note that
on carburetors that have a lower O-ring, it is necessary to replace it
when the carb is removed.
- Unscrew the high-speed needle all the
way out of the needle housing and flush out the high-speed needle
housing and the carburetor body with denatured alcohol or electric motor
- Use compressed air to dry the components. Reinstll the
high-speed needle into the needle housing and return the mixture setting
back to the factory recommended break-in setting (four turns out from
fully closed). Carefully insert the carburetor into the crankcase until
fully seated. While pressing the carburetor firmly into the crankcase,
tighten the pinch bolt. This process ensures that the upper O-ring forms
a good seal between the carburetor and the crankcase.
- Apply a
drop of oil in the piston's wrist pin bore before installing the wrist
pin. Locate the oiler hole in the connecting rod and the skirt relief
side of the new piston. Insert the connecting rod into the piston with
the piston skirt relief and the oiler hole on the same side as shown.
Line up the wrist pin bore in the rod with the wrist pin bore in the
piston and slide the wrist pin through the larger opening of the piston.
Note that the closed end of the wrist pin should be inserted first. The
orientation of the wrist pin is to help keep wrist pin cooler.
the wrist pin clip (G clip) into the groove of the wrist pin bore of
the piston. This will retain the wrist pin inside of the piston. Be sure
to fully seat the G clip in the groove in the piston!
the piston and connecting rod assembly into the top of the engine case
with the oiler hole of the connecting rod facing toward the crankshaft.
Apply a drop of oil onto the crank pin before installing the connecting
rod onto the crank pin. Slide the connecting rod over the crank pin and
rotate the crank pin to the bottom center of the crankcase.
the outside of the piston and slide the new sleeve into the engine
case. Make sure the piston fits into the sleeve without binding. Press
the sleeve all the way down into the engine case. Important: The slot
(in the lip) at the back of the sleeve must key into the pin at the back
of the engine case opening. Do not install the cooling head until these
two items are keyed into each other.
- Place the copper head
gasket onto the sleeve and set the cooling head into the sleeve. Note
that there are two slots notched through the cooling fins on each side
of the cylinder head. These slots are for access to the engine mounting
- The five head bolts should line up with the five holes
on top of the engine case and the access slots on the cooling head
should line up with the slots manufactured into the engine case.
careful not to damage the copper head gasket (see picture for
orientation). While pressing the head squarely onto the sleeve, thread
the head bolts into the engine case just until they stop. Do not tighten
down these bolts individually. It is very important to attain even
pressure around the cooling head. Slowly tighten each screw just a
little at a time in a crossing pattern, (see picture) until each bolt
becomes snug. Finish each bolt in the same pattern with 9.7in/lbs of
- Connect the back plate with the starter shaft to the
engine case. Important: The reliefs that are manufactured into the back
plate must face up to match the ports inside of the engine case (see
picture for orientation).
- Key the starter shaft to the crank pin by slowly rotating the starter shaft as pressure is applied towards the crankshaft.
the starter shaft is keyed into the crank pin, join the back plate to
the engine case and secure the assembly with the four 3x6CS screws.
Install a new glow plug (#3231 is recommended for the TRX 2.5 Racing
Engine, and 3232X for the 3.3) into the cooling head. The engine is now
rebuilt and ready for the installation of the clutch assembly and the
- Slide the split cone washer over the pilot shaft with the larger opening toward the engine case.
the flywheel over the pilot shaft and join it up with 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 up to the flywheel and
tighten the flywheel with 62.0 in-lbs. of torque against the flywheel.
the clutch shoes onto the flywheel. Key the flywheel pins into the
holes of the clutch shoes (See picture for orientation of the clutch
shoes). Racer Tip: By reversing the direction of the clutch shoes, the
clutch shoes will provide a little firmer bite against the interior wall
of the clutch bell. This is useful on higher bite surfaces that offer a
higher level of traction.
- Clean and lube both clutch bell
bearings and install a ball bearing into each side the clutch bell and
slide the clutch bell over the pilot shaft followed by the 5x8x0.5TW.
Fasten the 5.0 E-clip (wearing safety glasses) around the pilot shaft to
retain the clutch assembly.
- Clean the roller clutch with
denatured alcohol and lube the roller clutch with Mobil 1 synthetic
motor oil. Slide the EZ-Start® system (with the roller clutch) onto the
starter shaft that exits the back plate of the engine. Note that the
roller clutch is to be installed onto the starter shaft so that the
clutch engages the starter shaft clockwise and rotates freely
- Note that the engraved text on roller clutch
faces the engine backplate for correct rotation. Fasten the EZ-Start®
gear case to the back plate with the three 3x12BCS screws.
the exhaust header and pipe assembly back onto the rear of the engine
case. With the two 3x15CS screws. The engine, clutch, exhaust system
and EZ-Start® assembly is now ready for installation into the chassis.
- NOTE: Newly rebuilt engines require Break In!