TIANJIN－With engines roaring and the smell of diesel in the air, Gao Lu, clad in blue and hammer in hand, crammed his body into the narrow gap in the locomotive to check for any trouble.

He placed his hammer on top of one cylinder, then put the bottom of the handle close to his ear, held his breath, and listened to the vibrations.

Gao, 41, has been fixing locomotives in Tianjin for over 20 years. He comes from a long line of railway workers－h(huán)is grandfather was a train driver and his father a railroad repairer.

During the past Chinese New Year, the engineers came under the greatest pressure, as tens of millions of people traveled by train during the holiday 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 and increase fuel consumption. That would in turn affect the machine's operation and produce black smoke that pollutes the environment, Gao added.

Last year, Gao and his team tested 500 locomotives and found faults in more than 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 inside, hidden from view. Troubleshooting the problems can only be done by listening to the sounds an engine makes.

An engine creates tremendous noise when it is 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.

He used to spend hours practicing diagnosing the sounds with help from more senior workers. He also memorized a detailed diagram of the internal workings of the engine.

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

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

After becoming a senior worker, Gao compiled a guide with 33 kinds of abnormal sounds of locomotives, diagrams of the engines and repair methods, for his younger colleagues to follow.

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