ChinaRiders Forums - View Single Post - RX3: Engine Top End Rebuild at 22,450 Miles

SpudRider · 04-27-2017, 04:43 AM

Note: In addition to the information below, refer to the following thread.

http://www.chinariders.net/showthread.php?t=15546

Assembling the NC250 Engine

Preparing the Piston

Place a wristpin circlip into the left side of the piston.
Install new piston rings in the piston
Lubricate the piston rings and the piston skirts with oil
Invert the piston over the cylinder, and orient the piston with the mark facing the exhaust header.
While compressing the piston rings, press the piston into the bottom of the cylinder.

Installing the Cylinder

Install the cylinder guide pins (A). Install a new cylinder base gasket.

Pull the zip tie on the cam chain up through the timing hole in the cylinder, and also place the cam tension lever through the timing hole.

With the engine leaning to the left, lower the cylinder and piston near the connecting rod

Lubricate the piston pin with motor oil, and push the piston pin through the piston and the connecting rod.
Stuff a rag into the hole surrounding the piston to prevent dropping a wristpin circlip into the engine.

Install the remaining wristpin circlip.
Remove the rag from the cylinder block
Push the piston into the cylinder

Lower the cylinder onto the engine block

Installing the Cylinder Head

Replace the two dowel pins (A).
Install a new cylinder head gasket.
Install the cam chain guide (B).

Pull the timing chain completely through the cylinder and cylinder head

Install the cylinder head.

Tighten the 4 nuts (B), incrementally, in a crisscross pattern. Final torque for each nut is 28 foot-pounds (50 Nm).

Install the bolt (A), which retains the clip supporting the hose leading from the contaminant separator to the air box. This bolt should be tightened to a torque of 9 foot-pounds (12 Nm).

Check, and make sure the crankshaft is positioned at the TDC mark on the flywheel.
If necessary, hold the cam chain and rotate the crankshaft to the proper position.

Installing the Camshaft

Rotate the engine so it leans on the right side
Remove the large zip tie from the cam chain.

Place the camshaft into the cylinder head, and attach the cam chain. Keep tension on the left (forward) side of the cam chain, and align the two timing marks on the cam sprocket so they face upward.

Install the large washer (A) with the proper orientation.

Install the bearing. Install the bolt and washer (B), and the retaining clip [C]. Install the rubber plug (A).

Place the rocker cover on top of the cylinder head, and verify the two timing marks on the cam sprocket are properly aligned in the check holes.

Double check to verify the flywheel is still at TDC. If necessary, remove the rocker cover, rotate the flywheel, and/or move the timing chain on the sprocket to get the proper alignment.

Repeat the previous steps until the flywheel and cam sprocket are properly aligned.
After proper alignment is verified, remove the rocker cover.

Installing the Rocker Cover

Evenly apply a small amount of oil-resistant silicone to the mating surfaces of the rocker cover. I recommend Permatex Ultra Black RTV Silicone.

Install the rocker cover onto the cylinder head.

Install the 8 bolts in the cylinder head. Don't forget to install the 4 copper washers.
Tighten the bolts incrementally, in numbered sequence. The final torque of all the bolts is 9 foot-pounds (12 Nm).

Replace the Automatic Cam Chain Tensioner (ACCT)

Install the ACCT with the two screws at the base.
Install the spring and O-ring.
Install the center bolt to set the spring pressure.

Adjust Valve Lash

Adjust the valve lash, and replace the valve covers.

You are now ready to re-install the engine into the frame of the motorcycle.

04-27-2017, 04:43 AM	#12
SpudRider Join Date: Jul 2008 Location: Idaho Posts: 25,054	Note: In addition to the information below, refer to the following thread. http://www.chinariders.net/showthread.php?t=15546 Assembling the NC250 Engine Preparing the Piston Place a wristpin circlip into the left side of the piston. Install new piston rings in the piston Lubricate the piston rings and the piston skirts with oil Invert the piston over the cylinder, and orient the piston with the mark facing the exhaust header. While compressing the piston rings, press the piston into the bottom of the cylinder. Installing the Cylinder Install the cylinder guide pins (A). Install a new cylinder base gasket. Pull the zip tie on the cam chain up through the timing hole in the cylinder, and also place the cam tension lever through the timing hole. With the engine leaning to the left, lower the cylinder and piston near the connecting rod Lubricate the piston pin with motor oil, and push the piston pin through the piston and the connecting rod. Stuff a rag into the hole surrounding the piston to prevent dropping a wristpin circlip into the engine. Install the remaining wristpin circlip. Remove the rag from the cylinder block Push the piston into the cylinder Lower the cylinder onto the engine block Installing the Cylinder Head Replace the two dowel pins (A). Install a new cylinder head gasket. Install the cam chain guide (B). Pull the timing chain completely through the cylinder and cylinder head Install the cylinder head. Tighten the 4 nuts (B), incrementally, in a crisscross pattern. Final torque for each nut is 28 foot-pounds (50 Nm). Install the bolt (A), which retains the clip supporting the hose leading from the contaminant separator to the air box. This bolt should be tightened to a torque of 9 foot-pounds (12 Nm). Check, and make sure the crankshaft is positioned at the TDC mark on the flywheel. If necessary, hold the cam chain and rotate the crankshaft to the proper position. Installing the Camshaft Rotate the engine so it leans on the right side Remove the large zip tie from the cam chain. Place the camshaft into the cylinder head, and attach the cam chain. Keep tension on the left (forward) side of the cam chain, and align the two timing marks on the cam sprocket so they face upward. Install the large washer (A) with the proper orientation. Install the bearing. Install the bolt and washer (B), and the retaining clip [C]. Install the rubber plug (A). Place the rocker cover on top of the cylinder head, and verify the two timing marks on the cam sprocket are properly aligned in the check holes. Double check to verify the flywheel is still at TDC. If necessary, remove the rocker cover, rotate the flywheel, and/or move the timing chain on the sprocket to get the proper alignment. Repeat the previous steps until the flywheel and cam sprocket are properly aligned. After proper alignment is verified, remove the rocker cover. Installing the Rocker Cover Evenly apply a small amount of oil-resistant silicone to the mating surfaces of the rocker cover. I recommend Permatex Ultra Black RTV Silicone. Install the rocker cover onto the cylinder head. Install the 8 bolts in the cylinder head. Don't forget to install the 4 copper washers. Tighten the bolts incrementally, in numbered sequence. The final torque of all the bolts is 9 foot-pounds (12 Nm). Replace the Automatic Cam Chain Tensioner (ACCT) Install the ACCT with the two screws at the base. Install the spring and O-ring. Install the center bolt to set the spring pressure. Adjust Valve Lash Adjust the valve lash, and replace the valve covers. You are now ready to re-install the engine into the frame of the motorcycle. __________________ Spud "Never argue with an idiot. He will drag you down to his level, and beat you with experience." Mark Twain 2015 Zongshen ZS250GY-3 (RX3) 2006 Zongshen ZS200GY-2 (Sierra 200) 2005 Honda XR650L 2004 Honda CRF250X 1998 Kawasaki KDX220 Mods made to my Zongshen ZS200GY-2: http://www.chinariders.net/showthread.php?t=6894 Last edited by SpudRider; 04-27-2017 at 06:17 AM.
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