Can a trained mechanic can tell difference between a rod knock or a timing chain rattling?

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Depending on the vehicle, a mechanic should easily be able to differentiate a rod knock from a timing chain rattle. The main reason is, the two noises are completely different. Also, timing chains don't make much noise even when going/gone bad. If there is any noise coming from a timing chain, it would be more of a ticking noise. While a rod knock is a lower pitched noise. Also, the location of the noise is going to help diagnose as well.

If there is a rod knock, more than likely there's going to be a lot of metal in the oil. A rod knock is caused from too much clearance between the crank journal and the rod bearing. Quite often, this happens because the bearing has spun and 1/2 of the bearing now overlaps its mate. Because of this, there's usually a lot of bearing material which is floating around in the engine oil. If the mechanic believes there is rod knock, they can drain the oil and inspect it for shiny metal particles, as well as pull the oil filter apart and look for metal particles in the filter pleats.

There's just about no way to tell if the chain is going/gone bad, other than if it skips timing or pulling the front of the engine apart to inspect the chain. Most timing chains don't go bad over the life of the engine. They are said to be good for the life of the vehicle (there are exceptions). Most engines today don't have timing chains, but rather timing belts. Timing belts need to be changed every so often as preventive maintenance. I've never heard a timing belt make noise. When they go bad, it is usually catastrophic for the engine.

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