Depends. If it's just the serpentine belt pulley bolted to the harmonic balancer then, when you stumble
across one in better condition for the right price then you should consider making a low cost smoothness
upgrade.
On the other hand, if the serpentine belt pulley is in good condition but it's jumping around like that
because the harmonic balancer it's bolted to is jumping around, then that should be replaced as soon
as practical. Here's an exploded diagram of what you've got:
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By the way, your water pump pulley in the background is showing you what's possible
in the serpentine belt subsystem. Almost dead smooth.
For what it's worth I scoured the FSM for a runout spec for the harmonic balancer, and
found nothing. But I did manage to find a discussion in a Corvette forum where they
were discussing a TSB having to do with excessive harmonic balancer runout leading to
a chirping serpentine belt?
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Note: The spec the TSB gave for total allowable runout is 0.40mm. (0.0157" for us yanks.)
Kinda hard to visualize that way, but knowing that 0.0156 = 1/64" means that it doesn't
take much shake, rattle, or roll on the front of the crank to cross the threshold for the
LS TSB above.
Disclaimer: If you look at the attached picture of the LS harmonic balancer you can see
that for improved packaging the serpentine belt pulley is now part of the outer harmonic
balancer ring, so this helps to explain why serpentine belt chirping could be caused by
excess runout stemming from a bonding issue between inner hub and outer ring.
To reiterate, you have a serpentine belt pulley on the front of your crank's harmonic balancer
that's bolted to the hub. If you could take another look, and try to see if your balancer is
running smooth, but at the same time the pulley still has the runout observed in your
prior video, than replacing the pulley with one with less runout will be a good thing.
One last thing. If the front main bearing journal has more than ~.002-.003" total
wear, then you will hear a deep thudding for the first second or two of engine operation
until the oil pressure comes up and takes up the extra clearance. In other words,
if your engine is quiet down there as most small blocks are, then the front of the
crank is running dead smooth. The TSB I found on balancer runout are considered
wobbly when the travel is in excess of ~.015".
If I had to guess, I'm thinking that if you put a dial indicator to your harmonic balancer
that you will get a reading well within that spec. But if you then put the same dial indicator
on your serpentine belt pulley that you will find enough runout to explain what we all
saw in your video.
Hope this helps to explain what you observed.
Cheers --
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