CG paragraph straddle motorcycle is Honda design earlier cheap transport business, it has stable performance, reliable operation, compact structure, the price is cheap, maintenance is convenient wait for a characteristic, the market popular more widely, over the years has been favored by the vast number of motorcycle users favor. The car installed with single cylinder four stroke 157 fmi natural air cooling engine, utilizing down-setting CAM distribution way and CAM tappet drive mechanism. Because of its structural reason, CAM tappet drive agencies use after period of time, will be issued abnormal sound, give a motorcycle users and maintenance personnel debugging to bring a lot of inconvenience.
CG) distribution device work process is: engine crankshaft timing gear and CAM shaft gear meshing, through the rocker arm and tappet drive, and the radial seat components on the valve rocker arm for upper and lower action, to realize the intake and exhaust door switch, in order to meet the requirements of the engine valve timing, make the engine run continuously.
To analysis and discussion of valve-train abnormal sound, must understand the CAM tappet drive mechanism characteristics, we first to discuss CG of engine crankshaft institutions of axial positioning and axial clearance control problem: due to the CG of the engine crankshaft left when the correct gear with camshaft gears are adopt bevel gear structure, engine in action, will produce axial force. Moreover, CG paragraph on both ends of the crankshaft bearing with the crankcase bearing hole for clearance fit (that is, people often say that bearing outside running round structure), the left, right face must leave a gap, so that more heavy crankshaft axial channeling dynamic tendency, will be issued abnormal sound. Again, the engine work, piston do reciprocating motion, the connecting rod plane motion transfer to crankshaft, into the rotary motion, and at the same time will piston are under linear direction of force, into a moment to the output. The principle of internal combustion engine that reciprocating inertia force by the piston group and connecting rod capitulum period of generation, rotary inertia force by the big end and crank generation, when the engine is running, reciprocating inertia force and the rotating inertia force of the alternating stress, then all focus on crankshaft assembly, crankshaft rotating motion produced inevitably vibration. According to the calculation, crankshaft axial clearance more than 0.40 mm, will produce the channeling dynamic and a different voice, to the crankshaft operation and the normal work of the engine bring huge hidden trouble.
For maximum control crankshaft axial channeling dynamic and two of oblique gear (namely crankshaft timing gear and CAM shaft gear) brought about by the axial thrust, especially in the left crankshaft box bearing hole peripheral was installed on axial thruster. Axial thruster top pin, spring and pressure pin body composition, when crankshaft produce axial movement, axial thruster within the spring can play the slow crankshaft axial thrust role. So, crankshaft axial clearance is controlled in a certain range of less than, at the same time also to cushion the crankshaft timing bevel gear and CAM shaft helical gear brought about by the axial thrust and impact on abnormal noise. So, in the maintenance of the engine crankshaft mechanism, must pay attention to the axial clearance, and control crankshaft axial clearance of axial thruster is installed in place. If the axial thruster spring failure, crankshaft in operation process will produce abnormal noise, and should change in time axial thruster components. Normally, each motorcycle driving 15000 ~ 20000 km, need to check a (open left cover, remove magneto rotor can inspect), and apparent feeling to replace.
Because of the set of valve-train CAM particularity, to eliminate the abnormal sound of valve-train, we can refer to the following procedures and deal with:
1. The next set CAM distribution device, because of push rod reciprocating motion without coplanar impact, it will give the rocker arm a axial additional moment, increase the rocker arm to HuiCuan dynamic tendency. Therefore, in the cylinder cover on the radial component, the valve rocker arm and radial bearing between the axial clearance is strictly controlled in 0.05 mm or so, most of not more than 0.10 mm. Open machine inspection, can use 0.05 ~ 0.10 mm feeler tablet measurement, if the gap is too big, can cause running noise, should inspect feeling to replace.
2. Check the intake and exhaust door clearance. Rotary key levels crankcase cover on the surface of the two screw, the use of impact wrench cranking, make the flywheel “T” mark alignment left box cover timing inspection port scribed line, at the same time to observe the two tappet available fingers rotation, explain cylinder in compression stroke end position. At this time, with 0.02 mm thickness of the clearance gauge sheet into valve clearance adjustment screw and valve stem end between, such as feel gap is too big, can through the valve clearance adjustment screw and adjusting nut properly adjusted, until it reaches standard value so far.
3. Such as through the above adjustment, distribution agencies still have running different sound, can check the rocker mechanism. The rocker arm there are two, respectively control air intake and exhaust rocker arm, inspection, should look round the rocker arm and push rod contact Φ 6 mm, deep 2.5 mm concave groove, if with an irregular shape, indicating the eccentric wear phenomenon. The root causes of it, may be the rocker arm shaft hole and CAM shaft axis not parallel, cause cylinder jacket rocker arm shaft under 12 mm hole be ground into the oval. From the pin shaft cylindrical surface look, if there are obvious indentation and window, explains namely cylinder body rocker arm shaft hole processing wrong, should be replaced cylinder TiZong into. If the valve tappet have bending deformation, can cause push rod brush touch part and a different sound. Inspection will be push rod flat on glass surface, in rolling process a feeler tablet plug in the void place, such as more than 0.10 mm, then replace it.
4. In replace cylinder body that should be paid attention to in two of the rocker arm under the right end equipped with corrugated play mat, its role is to offset the rocker work under the channeling dynamic different sound, therefore, in the decomposition down rocker reassemble, when the first can’t leaks installs, the second its direction cannot be put back. If the cylinder body under the rocker arm shaft hole plane (namely loading waveform play mat depth size) processed deep, the waveform play mat elastic effect, will disappear, rocker arm in bobs, will produce axial impact and cause abnormal sound. To this, can put two waveform play mat compensation.
5. In CG section type of valve mechanism, camshaft arrangement in the upper left of the crankshaft, because design reasons, this CAM shaft gear and crankshaft timing gear two tooth surface were not heat treatment, belong to the soft tooth surface state. In the disassembly process, should check two gear tooth surface, do not