A timing chain failure is your vehicle's equivalent of a massive heart attack. It can easily destroy the engine and turn your car into a smoking wreck. The timing chain turns one or more camshafts that open and close the intake and exhaust valves so it has everything to do with how well your engine runs. Timing chains last longer than belts, but they do wear out and loosen over time. Knowing what to look for can keep your vehicle off life support.
Start Up Rattle
Timing chains are made to specifications that match their operating tension to a given application. As a chain loosens, it falls out of spec, and the symptoms begin. The first thing you will notice is a rattling sound that lasts for a few seconds when you cold-start the engine. This happens because most of the oil is still in the pan and the oil pressure is low. As the oil pressure rises and the tensioner engages, the chain tension and lubrication improve, and the rattle goes away. Even though it stops, you shouldn't ignore it as the chain will continue to wear until its guides break. This will loosen the chain some more and make the rattle louder. It might even continue when the engine warms up.
Rough Idle and Power Loss
Since the opening and closing of the intake and exhaust valves are directly affected by the timing chain, any tension loss can cause the valves to move at the wrong time. If the intake valves open late, the pistons won't pull enough fuel and air into the chamber for good combustion. If they open early, the pistons might interfere with the engine's breathing by pushing exhaust gases out the intake manifold. Likewise, if the exhaust valves open late, the pistons won't push all the exhaust gases from the cylinders. If they open early, some of the fuel-air mixture will escape from the cylinders, and combustion will suffer. Since the timing chain also affects the distributor, ignition timing and fuel delivery, you'll notice the difference whenever you press on the gas or warm up your car.
Misfiring and Backfiring
When the valve and ignition timing is off because of a loose timing chain, the fuel-air mixture in the cylinders ignites at the wrong time, and the engine misfires. Misfires cause incomplete combustion and higher emissions, and they leave carbon deposits on the plugs and valves. When a carbon build-up gets hot enough, it ignites the fuel-air mixture before the plugs fire and makes the engine backfire. This incomplete combustion from misfires can also leave unburned fuel in the tailpipe. Backfires that come from the exhaust are caused by this unburned fuel.
Coolant in the Oil
When a timing chain gets so loose that it's ready to break, it rubs against its protective timing cover and wears a hole in it. You'll know this is happening because of the loud clattering noise it makes. You'll also know that you waited too long to fix it if you see coolant in your oil. Don't wait until this happens or your timing chain breaks. If you have an interference engine, where the valves can touch the pistons, and your chain snaps, you'll be replacing your engine or the car.