Rattling Sound at Cold Cold Start.
Some things it is NOT. 1)Piston slap--goes away much too fast, 2) loose wrist pin same as 1) ,3)loose connecting rod bearing is much too high a pitch.
Potential causes 1) internal leak in hydraulic timing chain tensioner, allowing chain slap on start--low probability because sound is one surface hitting another, not a multi-parts rattling; 2) collapsed hydraulic valve lifter--moderate-high probability ; 3) defective cam timing adjuster--highest probability a known issue try to locate it to one side, one cam by careful listening on cold start.
IF the noise does NOT quiet in 5 to 10 sec, do not drive!!! A broken cam chain or non-turning cam adjuster will wreck the engine immediately.It if does this every cold start, cam adjuster most likely. A valve lifter not likely to always be under load holding valve open and leaking down the same.




In the end of that theme... camshaft journals in the back go dry for a short while... new heads or 1800car4kids.
All these troubles courtesy of these special tensioners
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