When I say this series has been haunting me for a couple of decades, it's an understatement. I remember loving this series, but I also remember it being a bit weird, and maybe even a bit science heavy for kids.
There were a number of books in it (I believe), and all I can remember is this young kid would go over to his neighbor's house, and the neighbor was an eccentric, old, scientist. I -feel- like they'd go to alternate dimensions and that sort of thing.
But the books themselves seemed old in 1986, so they might've been from the 70s?