If your 500 cubic inch Caddy motor is just not running right despite a full tune up and carb rebuild, there's a good chance the Cadillac timing chain is stretched or just plain worn out. This information goes for other underhead-cam Cadillac motors too: A high-mileage engine that refuses to be tuned via normal methods may have a Cadillac timing chain that has jumped a tooth or that just isn't providing the accurate timing necessary for your engine to run well. The same could be said about the Cadillac timing belt too, but a Cadillac timing belt really doesn't stretch: It breaks. A broken Cadillac timing belt can mean that you're simply stuck, or it can mean that you're going to get stuck with the bill for a new engine. It depends upon the relationship between your valves, your pistons, and your Cadillac timing belt. The Cadillac timing chain isn't quite as dramatic about its business. Used on nearly every V8 Cadillac pre-Northstar, the Cadillac timing chain runs a short distance between the crankshaft and camshaft in order to turn the cam and operate the valves. If your valves aren't opening and closing at the right time, nothing else in your engine is going to work right-that's why a stretched Cadillac timing chain causes poor engine operation. And if your Cadillac timing chain is in bad shape, there's a good chance that the rest of your engine could use an overhaul too. Think of the Cadillac timing chain as an 'engine wear indicator.' The same can't be said about the Cadillac timing belt. It needs to be changed on a regular basis to ensure reliable engine operation. If you skip on a new Cadillac timing belt, you might be spending next year's vacation money on a new engine instead.