last time when i started my car, it made one "clack" sound and then started just fine. just one clack. it sounded like metal hitting metal. it was about 55 degrees out. car doesn't burn much oil or leak oil. smokes a little but not real noticeable.

cold starting- i have a MB cold starting guide that talks about holding your pedal all the way down and crank the engine that way. even though 55 is not cold, i thought i try it. i think this sound usually happens when i try this method. tried it 2 or 3 times only.
normally, the initial start, the car cranks about 4 seconds, one or two cylinders fire up, keep cranking, and then the rest. i think that is normal.

what could it be ? valves hitting something ? something to worry about ? i've owned the car 2400 miles and so far its starts and runs great.

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1982 240D 4spd 232k (deceased)