Anhui Lu 'an, a domestic single cylinder 125 motorcycle driving more than 40,000 kilometers, the user specializes in long-distance transportation, the vehicle is more bitter and lazy maintenance. Forget to replace the oil once, resulting in serious wear of the cylinder piston, but under the helpless, find a small stall near the road to repair, replace the damaged parts, after reinstall, the engine power returned to normal, but the cylinder head is still abnormal sound. The maintenance worker checks and adjusts the valve clearance and timing chain tensioning adjustment mechanism, and its sound cannot be excluded.

This car is very strange, the cylinder piston is newly replaced, the cylinder head part of the parts have also been carefully inspected, the preliminary judgment is that the exhaust valve rocker arm R face is seriously worn, replace the valve rocker arm, the cylinder head abnormal sound still exists, no matter how to adjust the valve clearance, that is, there is abnormal sound.

In fact, there are many reasons for the abnormal sound of the cylinder head. In order to find the root cause of the fault, first confirm that the valve timing is installed correctly, the intake and exhaust valve clearance is normal, remove the valve rocker arm seat assembly, and carefully check the wear condition of the valve rocker arm, camshaft lift part, camshaft journal and bushing.

Inspection results: the camshaft journal and bushing wear evenly, the newly replaced valve rocker arm R30 arc also does not have a zigzag wear mark, and then check the rocker arm spring is not broken, as if everything is normal.

Where does the sound of the cylinder head come from? With doubts, I installed the valve rocker arm seat assembly in accordance with the normal assembly method, adjusted the valve clearance, and carefully observed the contact between the valve clearance screw and the top of the intake and exhaust valve rods while turning the crankshaft with a socket wrench.

At this time, it is found that the contact between the valve clearance adjustment screw on the exhaust valve rocker arm and the valve rod tip is not normal, and the front R7 ball head of the valve clearance adjustment screw on the intake valve rocker arm is basically in contact with the middle of the valve rod tip, while the R7 ball head of the front of the exhaust valve clearance adjustment screw is deviated from the center of the valve rod tip and contacts near the edge.

Then disassemble the decomposing valve rocker arm seat for inspection, and take care of it with a concentrating flashlight. It is found that the top of the exhaust valve has been knocked into a collapsing shape by the valve clearance adjustment screws, and the top of the exhaust valve rod has been knocked into a pit by the valve clearance adjustment screws. Obviously, there is no surfacing of Stari alloy powder at the top of the exhaust valve rod.

Due to the impact and sliding friction of the valve rocker head, the top surface of the valve rod is easily worn. In order to improve its wear resistance, according to the relevant technical requirements, the top of the genuine exhaust valve rod should be surfacing with the appropriate thickness of Stalli alloy powder as shown in the figure above.

Obviously, the valve replaced by the user last time in the roadside stall is a fake and shoddy part, because its head hardness is low, it can not withstand the long-term knock of the valve gap adjustment screw and is concave, so that the valve gap increases and causes the clicking sound.

Replace the exhaust valve clearance adjusting screw as shown in the figure above and the exhaust valve, check the R7 ball head at the front end of the valve clearance adjusting screw in the middle of the valve rod tip, adjust the valve clearance, and reinstall the removed parts.

Start the engine, whether it is cold or hot engine state, the sound in the cylinder head is basically normal, the abnormal sound in the cylinder head disappears, and the original fault confirmation is completely eliminated.

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