I feel like every time there’s a train in a movie, they show an engineer walking along the cars hitting each car’s undercarriage with a rod or hammer. I have also seen this in documentaries, so it’s not just Hollywood. What is the reason for this?
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I work in power plants and can attest to the trailing method. There are very large bolts (3″ diameter and larger) and the most simple and quick way to check if they are torqued properly is to tap em with a hammer. A nice ring is a torqued bolt. A flat sounds means it’s not tight enough.
Edit: the hammer should also bounce off. Kinda a feel thing to I guess.
They’re [wheel tapping ](https://en.m.wikipedia.org/wiki/Wheeltapper). Basically hitting the wheels then listening to the sound it makes. It’s to check the wheels to make sure they aren’t damaged.
As the other poster says, it’s ‘wheel tapping’. If there’s a crack, it breaks up the sound waves travelling around the wheel when it’s hit so it doesn’t ring with pure tone.
If you ever have a cracked plate or mug, the difference in sound can be quite noticeable when compared to another one in the set.
[Whisked away to Bulgaria](https://www.youtube.com/watch?v=ycPEBwDm0GI) via the innerwebs, for a call and respond demonstration.
Great question OP.
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