Don't do it by halves

While browsing through my collection of old motor cycle magazines I came across: "the valves snapped in halves". This gave me pause for thought. Surely the phrase should be "the valves snapped in half"? But then I thought again. No-one would write "the valves snapped in quarter"; you'd write "quarters" or "thirds" or any other fraction you'd care to name.

Clearly you can't break something into a single half (unless possibly you're a zen buddhist). I was left wondering when this illogical use of the singular "half" appeared, and why. Hardly earth shaking, I know. I've been using "half" all my writing life and now I want to use "halves" but can't because no-one else does.

Subs! Copy editors! You have the power. Bring back halves!