How to Diagnose a Jumped Timing Chainby Chris Stevenson
The timing chain has the important job of synchronizing the crankshaft rotation with the camshaft. This direct link provides the timing of the valves during their opening and closing sequences. Without precise timing, which a good timing chain in good working order provides, the ignition and camshaft timing will not perform in the precise sequence to complete a four-cycle combustion stroke. A timing chain will send out a number of warning signs before it fails completely. An observant owner can detect these warning signs by paying attention to a few peculiarities that will effect engine starting and performance.
Checking for a Jumped Timing Chain
Open the hood. Place the vehicle in park with the emergency brake set. Start the engine but be sure the battery has a full charge and is operating at peak performance. Note the speed at which the engine tries to start, comparing it with a normal start condition. An engine with a jumped timing chain will show signs of very sluggish and slow starting. This happens because the firing sequence is retarded due to a chain that has jumped a tooth. A chain that has jumped two or more teeth may not start at all.
Listen for any abnormal engine noises, with the engine idling, in the vicinity of the timing chain cover. Chains that have slipped time have slackened and can sometimes rattle during cold start or idle, or produce a swishing or scraping noise. Loose chains typically hit the inside of the timing chain cover. A rough running engine may accompany such noises.
Test-drive the vehicle and while slowly accelerating listen for any backfiring (popping) noises. Try a rapid acceleration and look for engine stumbling and backfiring. Any such symptom means that the timing sequence has changed. Sometimes a rattling sound, stumbling and backfire will all combine--a sure sign that the timing chain has skipped position.
Park the car. Place it in park with the emergency brake set. Locate the timing marks on your vehicle. They will appear on the crankshaft pulley and on a small metal tang connected to the engine block right above it. Use a rag to clean any dirt and oil from the mark. Look up your timing specifications in your owner's manual. Use chalk to mark the pulley and the block scale. Hook up the timing light to the number one cylinder and start the engine. Aim the timing light at the marks. If the timing marks do not come close to alignment or you do not see any alignment at all, it means the chain has jumped position.
Locate the top of the timing chain cover. Some vehicles have small inspection plates that allow you to remove them to check the condition of the timing chain and tensioner. Remove the plate bolts with the appropriate socket and wrench. Hold a strong shop light over the opening. Examine the chain and see if it hangs loose, or if the pads on the tensioner have worn away. Sometimes tensioners will freeze up and not provide the correct pressure against the chain. A loose chain will tell you that the tensioner has failed.