What can cause a bent exhaust valve? My Honda '98 CRV with auto transmission (85,000 km) bent an exhaust valve on its own. We determined there had not been any piston to valve contact, timing belt had not jumped a tooth, valve and spark timing were right on the money, and the engine had never been overheated. Valve lash was regularly and correctly adjusted every 25,000 km. After removing the cylinder head, the metal around the guide of the bad valve was ok and so the valve hadn't been off center on its seat before it failed. We're stumped.