Technically, timing chains are designed and built to last the entire life of the engine. So in theory, you should replace it only when it's broken. However, if the chain breaks while your engine is running, it could wreak considerable havoc, so waiting for a break isn't the best practical strategy. Before a timing chain breaks there are signs of wear, and it isn't hard to check for them. If your Jeep Cherokee is showing some of the signs, it is time to replace the timing chain.
The timing chain connects the camshaft to the crankshaft via a gear system so that the top and bottom ends of the engine rotate together. If the timing chain has stretched and is skipping teeth, the timing will be thrown off badly, causing the Cherokee to run inefficiently, if at all. If the timing chain breaks altogether, the Jeep's engine will simply shut off, and many valve train components can be damaged in the process.
Remove the distributor cap on the Cherokee's engine so that you can see the rotor. Then rotate the engine by hand with a wrench on the crank pulley very slowly. The rotor should begin to rotate with the engine almost immediately. If there is any delay, it is likely that the timing chain is stretched and needs to be replaced. Another way is to put a timing light on the Cherokee while the engine is idling, and watch the timing mark. If it wanders a few degrees in either direction, then the chain is probably stretched. Sometimes, a loose chain will cause a loud clicking, especially when the engine is cold and under power. The noise tends to go away once the engine warms up.
If you need to replace your timing chain, be forewarned that it is a pretty in-depth operation. Most of the components on the Jeep's engine, including the alternator, power steering, and water pump, all have to be removed to access the timing chain cover. Removing the grille of the Cherokee and the radiator is also recommended for ease of access. Unless you have a lot of experience working on engines, it is a job best left to the professionals. However, if you decide to tackle it, the only crucial thing to remember is to line the camshaft and crank gears up using the dots on them, as per the instructions they come with. Those dot placements are there for a reason, and the timing of the Cherokee will be based on how those gears are installed with the chain.
