Signs

• If a timing belt breaks while the engine operates, the driver should ask the repair techs to check for bent valves while they replace the belt. Symptoms of bent valves include a lack of engine compression and telltale scoring on the pistons, according to 2 Car Pros.
  
  

Diagnostic Setup

• Auto repair shops commonly perform a compression check to diagnose bent or otherwise impaired valves. This procedure involves first removing the spark plugs and disabling the ignition coils, then attaching a compression gauge to a spark plug hole while cranking the engine, according to AA1Car.
  
  

Considerations

• The compression gauge should indicate 140 to 160 lbs of pressure across multiple readings. Low or inconsistent compression readings indicate a problem with a piston ring or cylinder rather than a bent valve. An engine with consistently low or nonexistent compression readings suffers from bent valves.