Using core mobile engine models, crack major theory (3,4)

I believe the answer is:

big idea

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'using core mobile engine models crack' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'major theory' is the wordplay.
'major' becomes 'big' (I've seen this in other clues).
'theory' becomes 'idea' (idea can mean a theory).
'big'+'idea'='BIG IDEA'

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I've seen this clue in The Irish Times.

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