The question you need to ask yourself is whether the cause of your engine failure was Trent's actions (or inactions) or whether it was the poor condition of your engine. It appears fairly clear that it was the latter, and that it would therefore not be reasonable to expect him to have responsibility for your loss. Your engine was going to fail regardless.
While he probably made a mistake in terms of communication and allowing himself to get into this situation (and no doubt regrets it), that doesn't make him responsible for the damage. People make mistakes, that's life. As others have pointed out I think you need to take responsibility for your engine yourself and accept that you need to foot the repair bill. On the other side of the coin Trent will no doubt take away a lesson in risk management.
Hopefully the experience won't detract from your interest in cars, or from Trent's willingness to help out others.