TIANJIN, Feb. 2 (Xinhua) -- With engines roaring and the smell of diesel fuel in the air, Gao Lu, clad in blue, crammed his body into the narrow gap in the locomotive with a hammer in hand, prepared to examine the bulky machine.

He reached the hammer to the lid of the cylinder, then put the bottom of the handle close to his ears, held his breath and listened to the sounds transmitted by his tool.

Gao, 41, has been working on examining locomotives in north China's Tianjin Municipality for over 20 years. He comes from a long line of railway workers - his grandfather was a train driver and his father a railroad mender.

During the Chinese New Year each year, they come under the greatest pressure, as tens of millions travel by trains during the Spring Festival travel rush to reunite with their families.

"There were obvious swishing sounds," Gao said after examining the engine. "That is caused by the changes in the gaps between the air valves, and it needs to be adjusted."

The changes may result in uneven amounts of air being sucked into the machine, thus causing suboptimal fuel consumption. That might affect the machine's operation and increase black smoke that pollutes the environment, Gao added.

Last year, Gao and his team went through 500 locomotives and found faults in over 20 of them. Other colleagues at the railway station call them "locomotive tuners."

A diesel engine contains tens of thousands of parts, many, like air valves and gears, are hidden inside. Troubleshooting the problems can only be done by listening to its sounds.

The engine creates tremendous noise when running and it takes practice to identify the abnormal sounds.

"The roaring machine is very distracting, and I couldn't hear any abnormal sounds when I first started the job," Gao said.

Gao used to spend hours practicing diagnosing the sounds with help from more senior workers. He also memorized a map of the internals of the engine with meticulous detail.

In a typical round of examination, Gao has to go up and down the locomotive tens of times. "During the summer, the locomotive is like a hot pot, our clothes are soaked with sweat even before we start working," he said.

Years of practice and experience have enabled him to distinguish even the slightest sound differences and quickly diagnose the fault.

After becoming a senior worker himself, Gao compiled a guide with 33 kinds of abnormal sounds of locomotives, the structural maps of the engines and the repairing methods, for his younger colleagues.

"Our job is to make the diesel engines 'sing' better," Gao said.