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A substantial clunking has started when the engine is idling but goes away when the engine speeds up. And when the engine is turned off, there is generally one last clunk.

It is on a 1990 Buick Lesabre and the noise is in the area of the power steering pump and the serpentine belt tensioner pulley. Both of these parts have been replaced with no effect. Using a rod to the ear, I feel that the noise is loudest at the end of the valve cover near the power steering pump. I am thinking that the noise is from the valve train in that area. I don't know what is under the valve cover specifically. I suspect something like a timing chain tensioner, timing chain, valve rocker arm, if they are used, loose sprocket. I have never had to tear down one of the 3800 engines and would be interested to have feedback form one that has or one that has had a similar problem.
Does anyone have a picture of the valve train of the 3800 engine?
Is this a two hour job or a two day job?

I would appreciate a quick response; my wife is demanding a new car.
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Sounds like the classic harmonic balancer failure. If yours is real bad, you would be able to turn the balancer by hand back and forth 25-30 degrees or so. This is where the outer ring bonding rubber breaks loose from center portion. As the engine runs the balancer rattles pretty good. When you shut it off, the ring bounces back a time or two which can be heard after engine is shut down. You may need a puller to get it off. Good luck.... Jake
 
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