Hi Marianna,
I find this question anything but daft. In fact, it leads directly to the wide field (or swamp?) of idioms. To me little lorry doesn't sound quite right. Is it just the lilting alliteration which fits badly with the massive machine? On the other hand, there is a considerable difference between saying "we have a small problem" or "a little problem". In the first case, we are sure to solve it, while this looks less sure in the second case, which reverberates with irony.