Subaru's unique engine layout has driven it to incredible success over the years.

People who love Subarus really, really love their Subarus. But this Subaru engine is designed in such a way that big problems are commonplace.

If an engine has four cylinders, chances are they’re arranged in-line—unless that engine was made by Subaru, of course. A boxer-four is second only to all-wheel drive as a Subaru calling card. But the ...