Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Chinese diesel engine manufacturer China Yuchai International (NYSE: CYD) sank 14% on Friday, after the departure of a key executive prompted a Wall Street analyst to downgrade the stock.

So what: Citing the retirement of China Yuchai's President Boo Guan Saw, Piper Jaffray downgraded the shares to neutral from overweight, and slashed its target on the stock to $24 from $43. Saw said he's making the move to spend more time with his family, and his move doesn't appear related to any sort of corporate mischief, so it's tough to wrap my head around such a drastic target price slash.

Now what: Today's double-digit plunge has "overreaction" written all over it. While Saw is certainly a well-respected industry veteran, it's hard to imagine that any head honcho not named Jobs or Buffett is worth a whole 14%-plus in market cap value. With the shares now trading at an even wider P/E discount to main rival Cummins (NYSE: CMI), China Yuchai might be worth checking out.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.