I was able to find a loft of references to "destorcedores" in fishing and boating, but none in the gas and deisel context.

In the Wiley Civil Engineering & Construction Dictionary, I found the following that may be of use:

Straightening Machine: Máqina enderezadora

Straightening rolls: Cilindros de enderezar (which sounds like it fints into your text)

Straightening Tool: enderezador (which is sufficiently nebulous, that you might be able to use it in a pinch).

Good luck.

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Note added at 2002-01-07 02:04:23 (GMT)
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See Cecilia\'s answer below, which I think is the correct one! Good job.

or 'untwisters' - lacking more context it's hard to say but that's the literal translation