The disassembly and assembly of the valve rocker arm is closely related to the valve train. Due to the different structures of the engine and the cylinder head, the disassembly and assembly methods also vary. Here is a brief introduction to several typical vehicles.

For the CG125 and XF125 model motorcycles (tappet type), first ensure that the timing mark "· ·" on the camshaft timing gear is aligned with the "·" on the crankshaft timing gear. In this state, place the piston at the top dead center position and install the piston assembly, cylinder head, tappet and other valve train parts respectively. Then install the dedicated valve rocker arm assembly for the tappet model onto the cylinder head. Pay attention to checking that the axial clearance of the valve rocker arm on its assembly shall not exceed 0.10mm. The axial clearance here is too large, which will cause abnormal sounds.

For models such as GS125 and GN125, first rotate the crankshaft to move the piston to the top dead center of the compression stroke, remove the CAM chain tensioner and the driven gear of the tachometer, and then remove the cylinder head cover. Unscrew the fixing bolts of the rocker shaft and pull out the rocker shaft with a pair of pliers. Then the rocker shaft can be taken out. The installation and disassembly sequence is opposite. It should be noted that before installing the rocker arm, molybdenum disulfide grease must be applied to the rocker arm shaft to enhance the lubrication effect.

For the GY6 and CB125T models, first remove the cylinder head cover, then rotate the crankshaft to make the piston move to the top dead center position (for the GY6 model, the chain tensioning device needs to be loosened). Remove the rocker arm seat assembly, screw the M5 bolt into the M5 threaded hole at the top of the rocker arm shaft, apply force to pull out the rocker arm shaft and take out the rocker arm (for the GY6 model, the one-way stop plate also needs to be removed). When assembling, make sure the end with the M5 thread faces outward to facilitate the next disassembly and maintenance.

For the WY125 and JH125 models, first remove the camshaft sprocket, then take off the cylinder head cover, unscrew the rocker arm shaft positioning plate, screw the M6 bolt into the end of the rocker arm shaft and pull it out, and the rocker arm can be taken out. The installation and disassembly sequence is opposite. Before installation, a small amount of engine oil must be applied to the outer circle of the rocker arm shaft to enhance lubrication.

After the valve rocker arms of the above-mentioned models are replaced and installed, the valve clearance must be adjusted to the specified values for each model. After the adjustment is completed, it is necessary to rotate the crankshaft for more than two turns and check again whether the clearance of the intake and exhaust valves has changed. If the change is significant, it may be caused by excessive radial runout of the base circle of the camshaft or excessive clearance between the journal at both ends of the camshaft and the bearing (sleeve). The cause must be identified to prevent the engine from making abnormal noises and other related malfunctions.

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