market dynamics
Motorcycle stubborn abnormal noise, camshaft journal abnormal wear real culprit here
Release date:2022.07.21

A CL125-5 cross-riding motorcycle ran nearly 60,000km. Due to the user's misuse of inferior oil, abnormal wear of camshaft and carbon accumulation in combustion chamber were caused. Related parts were replaced and reassembled. But less than three months, the user reported that the left cylinder valve gap noise is too large, re-adjust the test run, abnormal sound is still not eliminated.

I received the information and came to the maintenance site. I checked the relevant parts and lubricating oil road, but failed to find the fault point. Open cylinder head, remove valve rocker arm camshaft, inspect right end journal, wear normal

Pinch the camshaft left bushing by hand, feel the gap is large. Using calipers to hold the camshaft, take off a ф 20mm clamping spring at the left end of the camshaft and compare it with the normal camshaft. It is found that the spiral groove on the journal at the left end of the camshaft is obviously different, as shown below.


Originally, CL125-5 motorcycle is imitation of Japanese CB125T motorcycle, the camshaft left and right ends of the journal surface spiral groove processing for left-right rotation, engine operation, lubrication system through the special lubricating oil channel into the camshaft left and right ends of the bushing oil hole, the oil into the cylinder cover oil pool, lubrication camshaft parts. The brief structure is shown below.

Due to the abnormal starting point of R1.5×1.5 guide oil groove processed at the left end of the camshaft of the broken car, it is separated from the 4×6mm positioning keyway at the left end of the camshaft. Most of the lubricating oil cannot enter the cylinder head oil pool along the R1.5×1.5 guide oil groove, but can only flow from the 4×6mm positioning keyway to the outside of the bushing, so that the left end of the CAM shaft journal lacks normal lubrication. Produce abnormal wear and tear, and emit abnormal sound.

The fault has a certain concealment, because the left end of the camshaft is provided with bushing and the shaft is blocked by a retaining ring, if the left end of the spring is not removed and the bushing is removed, it can not be found from the appearance.

The fault point has been found, replace the genuine camshaft components brought from the factory, apply a small amount of molybdenum oil mixture on the left and right journal surface and the inner hole of the bushing, hold the shaft and install 20mm shaft clamp spring to the outer side of the journal bushing at the left end of the camshaft with spring pliers.

Then cover the timing chain in turn according to the specified procedures, and properly adjust the timing of gas distribution. Install the rocker arm components of the left and right cylinders, and adjust the inlet and exhaust valve clearance of the left and right cylinders with the plug ruler and special tools, as shown in the following figure. Finally tighten the cylinder head cover.

Start the motorcycle, warm it up a little, listen carefully to the engine sound, basically normal. Thousands of meters on the road, the vehicle acceleration is sensitive and smooth. After several months of use, the motorcycle and engine were found to be running normally, and the fault of large left cylinder valve sound of the original vehicle was completely eliminated.

Because of the different structure of each engine, the way of lubricating camshaft and journal must be different. Maintenance should not let go of a doubt, not to be confused by its illusion, do serious, meticulous, only in this way, in order to take detdetments, fast troubleshooting.