Chevrolet Repair: harmonic balancer, chevy astro van, chevy astro

Question
how do i know if the harmonic balancer is out on a 1990 chevy astro van 4.3?  v6  have been told the rattling noise is coming from there, also been told that it is a piston. please help.the fuel pump was recently replaced then rattling started .also oil change and spark plugs.

Answer
Hello Tina,
If you remove the drive belts from the water pump, alternator, etc, and grab the pulley on the crankshaft, it shouldn't be loose on the shaft, or have any looseness in it.
It is possible to have a bad spot in a belt, or a bent idler pulley, that causes the belt to rattle around.
If you think the rattle is in that area, while the belts are off, you can start the engine and run it for ten seconds or so to see if the rattle is gone.
A fan clutch on the water pump is a common cause of rattle up there also.
Loose mounting bolts and brackets on power steering pump,transmission cooler lines, a/c compressor, and belt tensioners are also posibilities.
Also, check for cracked fan blades.
Van