What is the best way to tell if the Chain tensioner is going on the fritz? A friend of mine has a '87 420SEL and had the top end rebuilt and new chain rails installed. The car was running great for months but when it was started last nite the "marbles rattling in a tin can" sound came from the motor. Removing the oil filler cap you can hear it louder. Shut off the engine and he called his mechanic. He said to bring it back in tomorrow. Well, started it up today and it is quiet as a kitten! No noise at all, even revved up to 3500 RPM's!. Let it heat up, shut it off, waited 3 hours then started it up again and it's still quiet. Could this be the tensioner clogging and sticking? The mechanic said he did not replace this when the top end was rebuilt.