The Analysis Of Motorcycle Gear Fatigue

We have discussed about the tooth face wear of motorcycle gear in last article. Here is the analysis on gear fatigue.

• Tooth fatigue

There are two kinds, mechanical pitting or peeling.Pitting is spots and pit on the tooth face while the pit expand and become slice and then peel from tooth face.The specific reasons are:

1. Material is defect. There are too much nonmetaland brittle impurities inside the steel, or the fiber flow of steel and direction of working face is inconsistent and fatigue life is the lowest when it is 90°.
2. Tooth face decarburization. Carbon content is 0.3% ~ 0.6% or decarburized layer of the tooth face is 0.2 mm will cause fatiguecrack Carbon content is commonly 0.7% ~ 1.0% while 0.8% ~ 0.9% is ideal.
3. Processing method of tooth face. Due to the different processing method, like gear hobbing, shaping and shaving, there will be a different angle betweenmeshing line and cutting mark, then the contact fatigue life of tooth face is also different. It is proved by practiced  that the fatigue life is longer if the cheap brakes are shaved
4. The tooth face is too rough or the error of tooth shape is too large.
5. Defect lubricant oil.

• Resolution:

1. Ensure the quality of steeland use the purified melting
2. Ensure the quality of heat treatment, especially the depth of hardening layer, the surface hardness and the surface carbon content, so when choosing those motorcycle sprocket, you need to choose high quality products to ensure the above indicators.
3. Use motorcycle gear withgear shaving processing tooth surface.
4. Ensure the machining quality, reduce the tooth face roughnessand improve the tooth accuracy.
5. Improve the lubrication conditions and adopt lubricating oilwith a proper viscosity.

• Example:

1. Fault. Riding a motorcycle after 8000 km, speeding at 5 gear, there is abnormal sound. Open motorcycle gear box, found that there is serious tooth pitting erosion, especially the driving gear.
2. Detection.  Check the appearance, there is serious pitting erosion on the driving and drivengear, near pitch line. Look from the working face, it is hobbing gear. The lubricating oil is fine. Test size of the fault parts, common normal line slightly gets smaller. So it should bethe problem during heat treatment, the surface carbon content is not enough, the standard is between 7% and 1.0%.
3. Analysis. From the above test, the main cause of personal watercraft parts pitting should be heat treatment, surface hardness and surface  carbon content didn’t reach the standard. Hobbing machining is also a disadvantage.

We will continue the analysis of the last fault of motorcycle gear in next article.