The good thing about the TR3 engine is the valves are not interference, so even if the chain tensioner is bad you will not damage the engine from a slipped chain. Usually the chain will wear a hole through the front cover, resulting in a bad oil leak before it quits running.
If it's rod knock or piston slap, that will go a long time before fixing too. It will slowly get worse until it does not quit after warm-up. You can try thicker oil to help for a while.