In your motor, timing is everything. That's why your timing chain and/or timing belt are so vital to the operation of your entire vehicle. You see, without a properly installed and adjusted timing chain or timing belt, the valves on your engine don't open and close at the appropriate times. A sloppy timing chain can result in poor running, valve clatter, and loss of power, while a broken timing belt can cause your engine to stop running or, on an interference application, cause your valves to crash into your pistons. If that sounds expensive to you, you're right. If a broken timing belt can cause so much damage, why doesn't everyone use a timing chain? For all its advantages, a timing chain is noisier, less efficient, and more expensive than a timing belt. These timing belt / timing chain comparisons are particularly relevant on the overhead cam engines that are so common these days. Since an OHC timing chain would be so long, a timing belt actually has less lash and stretch resulting in better camshaft timing and improved efficiency. So don't think that, just because your manufacturer specified a timing belt for your favorite ride, they're looking forward to the day they can supply you with a remanufactured engine. In many cases, a timing belt makes more sense than a timing chain. While a timing chain may last the life of an engine, a timing belt has specific requirements for replacement intervals. Check your owner's manual for timing belt replacement mileage and follow those requirements to the T. If you have a timing chain instead of a timing belt, signs that your timing chain may need replacement include loss of power and noise from the timing cover at the front of your engine. Unlike the timing belt crowd, you probably won't destroy your engine by running with a worn out timing chain. You might get run over by a semi on the interstate, however, trying to accelerate with that clapped out engine and its stretched timing chain!