Teaching my son to be a man of his word

My old man always said a man is only as good as his word. Been trying to pass that down to my boys but it's harder than it sounds with everything being casual now. Yesterday my 14 year old said he'd help me work on the truck then flaked to hang with friends. We had a long talk about commitment and following through. I'm not trying to be harsh but he needs to understand that your reputation depends on being reliable. Any of you have good ways to drill this home without sounding preachy?