It is a shabby straddle riding motorcycle, the owner of self-report has traveled tens of thousands of kilometers, ran to me here to repair, asked him what the situation, he said he this car is good, is a high speed when there is a "scratching" sound, feeling very strange, a bit empty today, came to ask me to help him see what the reason.
Intrigued by his description, I picked up the car and inspected it. This car is a bit old, start the engine in place, step on the gas, the engine sound is quite good, it seems to maintain the line, carefully listen to the engine, cylinder and other parts, and no abnormal noise. Ask the owner is which voice, the owner listened carefully, said the abnormal sound did not appear, initially ruled out the possibility of engine abnormal sound.
Is it the abnormal sound caused by the external harmonic earthquake? Then check the brake linkage, handle and other activities and easy to loose parts, there is no abnormal phenomenon.
It seems to have to try the road, ran to the shop outside the straight road, using the highest gear, high speed driving, ran for a while, as the owner of the car described the "scratching" sound.
Listen carefully, the sound is similar to the air vibration produced by the air squeezing when a motorcycle is speeding through a bridge rail or pier. Sound has a sense of air vibration, therefore, the focus of the inspection should be placed on the exhaust pipe and other parts.
Check the periphery of the exhaust pipe and find that the rocker arm screw at the lifting lug is loose. It is suspected that the rocker arm screw is made to vibrate when the exhaust pipe is running at high speed, so tighten the rocker arm screw. After tightening, habitually shake the exhaust pipe to check if it is firm.
But at this time, it was accidentally found that the welding place between the lifting lug and the exhaust pipe, because of long-term running vibration, there was a crack, and there was oil discharge, it was difficult to find this crack without shaking the exhaust pipe. Think of the abnormal sound you hear, and instantly understand that this is the source of the abnormal sound, not the vibration caused by insufficient fastening.
Remove the exhaust pipe, repair the tear with oxygen welding, cool it, and then load the car to ride. No matter how hard you work, there is no abnormal sound, which proves that the fault has been eliminated.