My 4 year old does not like to play with much. Limited interests?

My 4 year old son has very limited interests. He only likes things with motors like sweepers, weedwackers, lawnmowers, electric sanders and things of that nature. I give him a variety of toys, but he turns them all into one of these things with a hand-made cord and everything! He will make the noises almost as perfectly as a person can to mimic their sounds while playing and is very good at constructing these motorized/electrical units from almost anything. He makes them from tinkertoys, blocks, toy vehicles, baskets...everything! I want him to broaden his interests but he won't take to it. He'll say no to a game or other activity, and that he wants to play sweepers. Occasionally I can get him to draw something briefly or listen to a story, but it's right back to his obsession almost instantly. No he does not have any of the childhood disabilities such as autism or anything...he is just obsessed literally! He does like to play cooking and to play with his cars (only he pretends they are alive-like pets). He has a very creative imagination but I wish he would use it with more variety. He learned to use his fine motor skills with his hands early and does much with his hands, a lot like his dad. But life is not just about motorized objects. Any advice?