What's the meaning of "run in"

Question

From movie Titanic(1997), you can find a transcript here

Ismay: So you've not yet lit the last four boilers?

Smith: No, I don't see the need. We are making excellent time.

Ismay: The press knows the size of Titanic. Now I want them to marvel at her speed. We must give them something new to print! This maiden voyage of Titanic must make headlines!

Smith: Mr. Ismay, I would prefer not to push the engines until they've been properly run in.

Ismay: Of course, I'm just a passenger. I leave it to your good offices to decide what's best. But what a glorious end to your final crossing if we were to get to New York on Tuesday night and surprise them all! Make the morning papers. Retire with a bang, eh E.J.?

Ismay: [Smith nods reluctantly] Good man.

What's the meaning of run in here? From thefreedictionary, run in can be translated into two meanings:

1. A quarrel or an argument.
2. Printing Matter added to a text.

Of course, neither is suitable for the context. So how to explain "run in" here?

Answer 1

The break-in or mechanical run-in is a standard procedure for a brand new engine, like those on the Titanic.

I think (and someone more familiar could confirm) that "run in" is the British term. It means the same thing as the Americanism "break in". To break something in is to take something brand new and use it in such a way that it reaches a higher capacity for performance. You might break in a new pair of leather boots so they fit you better and don't cause blisters when you walk, or the engines on a brand new ship.

I found "run in" in the Oxford dictionaries, confirming my theory that it's a Britishism used almost exactly the same way as the Americanism "break in" with respect to engines and mechanical things. The Brits also use "break in" the way Americans do for other (non-mechanical) things.

Answer 2

As they are talking about engines, the logical meaning would be that the engines would have to operate (run) for some time before they become fully capable of working at their hardest.

This was a new ship, with brand new engines. Logically, the machinist would be hesitant to push the engines to the max without any good reason. After they would have been used for some time, all flaws would be know and removed, they would be "run in", and they would be more trustworthy under full steam.

An alternative expression is "break in":

http://en.wikipedia.org/wiki/Break-in_(mechanical_run-in)

Answer 3

Running in an engine was a factory requirement. A defined mileage should be reached before the vehicle was condidered safe to run at top speed. Cars had a sticker in the rear window when new..'Running in, please pass'. Equalizing engine wear - 'bedding in" the components - was necessary because of the varied tolerances of the metals used. Modern forging techniques have precluded the need for this inconvenience.