TRX Pro.15 Engine Rebuild

Article #50385

TRX Engine Rebuild

STEP 1: Removing the carburetor is not necessary to rebuild the engine, unless you intend to replace the internal bearings of the engine. Remove the carburetor by loosening the 3mm locknut and pulling the carburetor straight up.

STEP 2: Changing the piston and sleeve assembly
Use a 5/16 inch nut driver to remove the glow plug and copper gasket.

STEP 3: Use a 2.5mm Allen wrench to remove the four 3x12mm cap-head screws that fasten the cylinder head. Rock the cylinder head gently from side to side to release it from the sleeve. Note the thin aluminum head gaskets. We recommend that you replace these gaskets with new gaskets upon reassembly.

STEP 4: Remove the backplate and the starter shaft. Replace the backplate gasket with a new one during assembly.

STEP 5: The piston and sleeve are a matched set. When the piston and sleeve are disassembled, they must be reassembled in the same orientation. Use a hobby knife to scratch a mark to indicate the location of the piston in relation to the pinning of the sleeve.

STEP 6: Pull the sleeve straight up and out of the crankcase. If the sleeve will not move, rotate the crankshaft until the sleeve pushes up.

STEP 7: Rotate the crankshaft to bottom dead center. Lightly grab the connecting rod with a pair of needlenose pliers and gently pull it off of the crankshaft journal.

STEP 8: Remove the connecting rod and piston through the top of the crankcase.

STEP 9: To remove the connecting rod from the piston, use a sharp-pointed tool to remove the small metal G-clip in the side of the piston. Do not re-use the old G-clip. When installing a new connecting rod, use the supplied new G-clip.

STEP 10: Removing the clutch and flywheel
It is not necessary to remove the clutch assembly unless you are servicing the clutch, crankshaft, or engine bearings. Use the tip of a small screwdriver to remove the E-clip which holds the clutch bell gear.

STEP 11: Remove the clutch bell gear and the clutch shoes. Note that there are two 5x8mm PTFE washers, one on each side of the clutch bell gear. Check the clutch shoes for excessive wear or cracking around the pin holes. If the clutch shoes are worn to the point that the clutch spring contacts the clutch bell, then the shoes must be replaced.

STEP 12: Grip the flywheel with a pair of pliers (locking pliers work best). Remove the clutch adapter nut with a 10mm deep socket. Hold the engine just above your workbench and tap the flywheel from behind with a non-marring hammer (plastic or wood). Several easy blows may be necessary to release the flywheel and split beveled cone.

STEP 13: The flywheel and the split-beveled cone should pull smoothly off of the crankshaft.

STEP 14: Remove the crankshaft by pulling it straight out of the crankcase.

STEP 15: The bearings are press-fit into the crankcase. To remove them, the crankcase must be heated with a heat gun. The crankcase will expand with heat and release the bearings. To avoid the possibility of burns or other damage, do not attempt remove the beaigs. Clean the bearings by flushing them with denatured alcohol and then place one or two drops of after-run oil on the races.

STEP 16: Before installing a new connecting rod, you can increase connecting rod life by polishing the crankshaft journal. Use 1200 grit sandpaper to remove the surface scratches followed by liquid metal polish to buff the crankshaft journal to a bright, smooth shine. Rinse thoroughly with Traxxas Nitro Wash or denatured alcohol. Lube with after-run oil.

STEP 17: Use the 1200-grit sandpaper and the liquid metal polish on the wrist pin also.
Rinse thoroughly with denatured alcohol and lube with after-run oil.

STEP 18: To assemble the connecting rod and piston, place a drop of caster oil in the top end of the connecting rod. Insert the wrist pin through the piston and the top of the connecting rod. Secure the wrist pin with the G-clip. Make sure the G-clip fits securely into the groove machined in the piston. Be careful not to scratch the sides of the piston.

STEP 19: Reinstall the crankshaft into the engine and make sure that it spins freely. Insert the connecting rod and piston assembly through the top of the crankcase. The G-clip should face the carburetor. Put a drop of castor or after-run oil in the bottom end of the connecting rod. Use your fingers to gently push the end of the connecting rod over the crankshaft journal.

STEP 20: Place another drop of oil on the connecting rod bushing. Rotate the crankshaft several times to distribute the oil.

STEP 21: Insert the sleeve into the top of the crankcase. Rotate the sleeve so that the notch in the sleeve will line up with the pin in the crankcase. Holding the engine upside down will make it easier for the sleeve to go over the piston.

STEP 22: Install new head gaskets on the head. Use one thick and one thin gasket. Reinstall the head using the 3x12mm cap-head machine screws. Tighten the screws in small increments, in a criss-cross pattern, until all the screws are tight.

STEP 23: Reinstall the starter shaft. Align the notch in the starter shaft with the crankshaft journal pin (arrow).

STEP 24: Reinstall the backplate and a new backplate gasket with the 3x8mm cap-head machine screws. Tighten the screws in small increments, in a criss-cross pattern until all the screws are tight.

STEP 25: Install the appropriate size ball bearing into one side of the clutch bell gear. The Nitro Stampede? comes stock with an 18-tooth clutch bell gear which requires 5x11mm ball bearings.

STEP 26: Turn the gear over and install the other ball bearing.

STEP 27: Install the split-beveled cone onto the crankshaft. Next, install the flywheel. Install the clutch adapter nut with a 10mm deep socket. Grip the flywheel with pliers while tightening the adapter nut.


STEP 28: Install the clutch shoes exactly as shown in the drawing (trailing edge engagement). Next, install a 5x8mm PTFE washer followed by the clutch bell gear (with bearings installed). Install the remaining 5x8mm PTFE washer followed by the E-clip (see step 14).

STEP 29: Reinstall the carburetor with a new O-ring, header, a NEW glow plug, and engine mount. Use a new header gasket when re-installing the header on the engine. Reinstall the engine in the truck in the reverse order of removal. Don't forget to reconnect the yellow grounding wire to the engine mount. The rebuilt engine must now be broken in.


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