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

SpudRider · 04-27-2017, 04:17 AM

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

http://www.chinariders.net/showthread.php?t=15545

Removing and Disassembling the NC250 Engine from the RX3 Motorcycle

Perform the following, preliminary steps.

Place the motorcycle on the Center Stand

Remove the clutch cable and all electrical connections from the engine
Remove the MAP/T sensor from the intake manifold
Remove the bolts holding the intake manifold to the engine

Drain the coolant.
Remove the radiator hoses from the cylinder head and water pump.
Remove both radiators from the frame.
Remove the exhaust header.
Remove the perimeter engine bracket.

Remove the Swingarm and Shock Absorber

Remove the rear Wheel
Remove the lower shock linkage
Remove the swingarm
Remove the shock absorber

Remove the Engine from the Frame

Remove the two bolts at the rear of the engine, near the swingarm bolt
Support the weight of the engine on a jack
Remove the two bolts holding the cylinder head to the frame
Balancing the engine on the jack, remove the swingarm bolt
Lower the engine from the frame

Set the crankshaft to TDC on the compression stroke, which will release pressure on the rockers and all four valves. Remove the two plug bolts from the cylinder head to verify the camshaft is in the proper position.

Remove the automatic, cam chain tensioner (ACCT)

First remove the center bolt to release the spring pressure.
Remove the spring and O-ring.
Remove the two screws at the base of the ACCT.

Caution:
After removing the ACCT, return the plunger to its initial position by pressing on the locking cam, and pushing the plunger to the base of the tensioner.

Removing and Inspecting the Rocker Cover

Before removing the rocker cover, remove the valve covers.

Remove the bolts from the rocker cover. Take care to remove the numbered bolts crosswise, from the outside in, to properly release the tension on the cylinder head.

Note: Remove only the numbered bolts. Loosen the bolts in the numbered sequence from 1 to 8. Take note of the four copper washers.

Note: The two large, 10 mm bolts are not removed. They are holding the rocker pins inside the rocker cover.

Remove the rocker cover from the cylinder head. It is not necessary to remove the two screws that lock the rocker pins, unless you need to replace either the rockers, or the rocker pins.

Note: If you remove the rocker pins, always verify their correct orientation, or the oil lubrication passages will be in the wrong position. Improper orientation of the rocker pins will starve the cylinder head of oil, and damage the engine.

While the rocker cover is removed, check the axial and radial movement of the cam rollers on the rockers. If a cam roller is damaged, replace the rocker.

Also check the surface of the cap at the end of the tappet. If the cap is deformed, replace the tappet. This will allow the tappet to make better contact with the valve head, prolonging the life of the valve.

Removing the Camshaft

Remove the rubber stopper (A).
Remove the bolt and washer (B).
Remove the retaining clip (C).

Remove the bearing adjacent to the cam sprocket.

Note: Check the bearings for axial and radial movement. If either bearing is loose in either radial, or axial movement, replace the bearing.

Carefully note the correct orientation of the washer (A). The washer must be properly installed to support the weight of the decompression mechanism, and provide enough space for its proper operation.

Note: If the washer (A) is not properly installed, it might also cause noise in the engine.

Remove the washer. Finally, remove the cam chain, and put a large zip tie around it, so you can retrieve the cam chain from the engine. Lower the cam chain into the timing hole, and remove the camshaft.

Removing the Cylinder Head

Remove the bolt (A), which retains the clip supporting the hose leading from the oil contaminant separator (OCS) to the air box. This bolt should always be removed first, before releasing the torque of the four cylinder nuts.

Next, remove the four cylinder nuts (B).

Note: Loosen the nuts incrementally, in a crisscross pattern, to properly release the tension from the engine.

Remove the cylinder head.

Remove the cylinder head gasket. Remove the two dowel pins (A). Remove the cam chain guide (B).

Note: Always replace the cylinder head gasket.

After the cylinder head is removed you can replace the valves, lap the valves, and replace the valve stem seals

Removing the Cylinder

Remove the cylinder.

Remove the two guide pins (A). Remove the cylinder gasket.

Note: The cylinder has a Nikasil coating, and does not contain a sleeve. If the nikasil coating is in good condition, you can reuse the cylinder.

Removing the Piston

The piston has a coating of molybdenum and graphite on the skirt, which lubricates contact with the cylinder. If the piston skirt is in good condition, you can reuse the piston.

Note the orientation of the piston. The arrow on the piston must face the exhaust header.

Stuff a rag into the hole surrounding the piston to prevent dropping a wristpin circlip into the engine. Using needle nose pliers, remove one of the wristpin circlips. From the opposite side of the piston, push the piston pin out of the piston, and remove the piston from the connecting rod of the crankshaft.

Remove the piston rings from the piston.

04-27-2017, 04:17 AM	#11
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=15545 Removing and Disassembling the NC250 Engine from the RX3 Motorcycle Perform the following, preliminary steps. Place the motorcycle on the Center Stand Remove the clutch cable and all electrical connections from the engine Remove the MAP/T sensor from the intake manifold Remove the bolts holding the intake manifold to the engine Drain the coolant. Remove the radiator hoses from the cylinder head and water pump. Remove both radiators from the frame. Remove the exhaust header. Remove the perimeter engine bracket. Remove the Swingarm and Shock Absorber Remove the rear Wheel Remove the lower shock linkage Remove the swingarm Remove the shock absorber Remove the Engine from the Frame Remove the two bolts at the rear of the engine, near the swingarm bolt Support the weight of the engine on a jack Remove the two bolts holding the cylinder head to the frame Balancing the engine on the jack, remove the swingarm bolt Lower the engine from the frame Set the crankshaft to TDC on the compression stroke, which will release pressure on the rockers and all four valves. Remove the two plug bolts from the cylinder head to verify the camshaft is in the proper position. Remove the automatic, cam chain tensioner (ACCT) First remove the center bolt to release the spring pressure. Remove the spring and O-ring. Remove the two screws at the base of the ACCT. Caution: After removing the ACCT, return the plunger to its initial position by pressing on the locking cam, and pushing the plunger to the base of the tensioner. Removing and Inspecting the Rocker Cover Before removing the rocker cover, remove the valve covers. Remove the bolts from the rocker cover. Take care to remove the numbered bolts crosswise, from the outside in, to properly release the tension on the cylinder head. Note: Remove only the numbered bolts. Loosen the bolts in the numbered sequence from 1 to 8. Take note of the four copper washers. Note: The two large, 10 mm bolts are not removed. They are holding the rocker pins inside the rocker cover. Remove the rocker cover from the cylinder head. It is not necessary to remove the two screws that lock the rocker pins, unless you need to replace either the rockers, or the rocker pins. Note: If you remove the rocker pins, always verify their correct orientation, or the oil lubrication passages will be in the wrong position. Improper orientation of the rocker pins will starve the cylinder head of oil, and damage the engine. While the rocker cover is removed, check the axial and radial movement of the cam rollers on the rockers. If a cam roller is damaged, replace the rocker. Also check the surface of the cap at the end of the tappet. If the cap is deformed, replace the tappet. This will allow the tappet to make better contact with the valve head, prolonging the life of the valve. Removing the Camshaft Remove the rubber stopper (A). Remove the bolt and washer (B). Remove the retaining clip (C). Remove the bearing adjacent to the cam sprocket. Note: Check the bearings for axial and radial movement. If either bearing is loose in either radial, or axial movement, replace the bearing. Carefully note the correct orientation of the washer (A). The washer must be properly installed to support the weight of the decompression mechanism, and provide enough space for its proper operation. Note: If the washer (A) is not properly installed, it might also cause noise in the engine. Remove the washer. Finally, remove the cam chain, and put a large zip tie around it, so you can retrieve the cam chain from the engine. Lower the cam chain into the timing hole, and remove the camshaft. Removing the Cylinder Head Remove the bolt (A), which retains the clip supporting the hose leading from the oil contaminant separator (OCS) to the air box. This bolt should always be removed first, before releasing the torque of the four cylinder nuts. Next, remove the four cylinder nuts (B). Note: Loosen the nuts incrementally, in a crisscross pattern, to properly release the tension from the engine. Remove the cylinder head. Remove the cylinder head gasket. Remove the two dowel pins (A). Remove the cam chain guide (B). Note: Always replace the cylinder head gasket. After the cylinder head is removed you can replace the valves, lap the valves, and replace the valve stem seals Removing the Cylinder Remove the cylinder. Remove the two guide pins (A). Remove the cylinder gasket. Note: The cylinder has a Nikasil coating, and does not contain a sleeve. If the nikasil coating is in good condition, you can reuse the cylinder. Removing the Piston The piston has a coating of molybdenum and graphite on the skirt, which lubricates contact with the cylinder. If the piston skirt is in good condition, you can reuse the piston. Note the orientation of the piston. The arrow on the piston must face the exhaust header. Stuff a rag into the hole surrounding the piston to prevent dropping a wristpin circlip into the engine. Using needle nose pliers, remove one of the wristpin circlips. From the opposite side of the piston, push the piston pin out of the piston, and remove the piston from the connecting rod of the crankshaft. Remove the piston rings from the piston. __________________ 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 05:31 AM.
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