The valve train is a critical set of components on an engine. Every cylinder has a minimum of two valves: an intake valve and and exhaust valve. Each valve has springs, lifters and rocker arms that control the opening and closing of the valve when the engine is running. A malfunctioning valve train affects the drivability of a vehicle. A bad valve is noisy at best and results in a disabled vehicle at the worst.
Listen to the engine when idling. Use the automotive stethoscope to listen to the engine while it idles. A tapping, clicking or rattling noise indicates the valves need adjustment. Remove the valve cover with a socket wrench and use the feeler gauge to measure the distance from the tip of the rocker arm to the valve stem. Every manufacturer publishes the proper specifications for this distance. If the measurement exceeds this specification, adjust the valve according to the vehicle's service manual.
Check if the engine backfires. Damaged valve springs or sticking valves are one cause of this symptom. If the backfire is through the carburetor the intake valve is sticking. If the backfire is through the exhaust, the exhaust valve is sticking.
Check for excessive oil consumption. Worn valve stems or damaged valve guides allow oil to leak past the valve stem and into the cylinder. Smoky exhaust also results from this problem.
Check if the engine diesels or continues to run after being turned off. Check for sticking or damaged valves. Insufficient oil levels to reach and lubricate the valve train can cause this issue.
