Any way of knowing if/ when an original stock dampner is toast?
could try another one but figure they are all as old.

As long as it's not all rusted/pitted the only things that could go bad on one is the rubber ring between the hub and outer ring and the seal surface.

I tried a good looking stock piece on my 470. it lasted like 6 months and then it spun. I don't think that the old passenger car pieces were designed to be on a higher output engine. My car is just a nice street car not a racecar. I would not reuse a stock balancer again. There is usually something for sale here in the swap section.

Stupid question but how could you tell that.
Rubber ring show evidence of tearing?
Sounds like I need to look at timing mark and keyway closer.
Thanks all.

Yup.
The damper’s rubber ring will naturally decay with age, mileage, exposure to hot chemicals, vibration, ozone, and ultra-violet light, and become unsuitable for even a stock engine, let alone high performance or racing use.
Visible signs of damage and potential failure include:
» rubber is missing
» rubber is discolored gray or “chalky”
» rubber has surface cracking
» rubber has been partially extruded
» damper rim is dented or bent
» damper is loose on its hub or on the crankshaft nose
» damper rim has excessive runout (“wobble”)
» “squeaking” noise that defies detection
If you have any doubts about the integrity of a factory damper, remove it (and rebuild it, if you wish).
Even a high-mileage (but apparently undamaged) damper has lost some effectiveness due to hardening of the rubber parts, which also changes its frequency range. Even if not damaged, it’s not doing the job if it doesn’t “float” the inertia ring as it was designed to do, which is at specific RPM points (not continuously).
The bad ones I’ve seen that we know slipped (the engine won’t run with the ignition timing marks aligned, but seems OK if you tune it “by ear” and check for pinging) all look damaged, but this obviously only catches them when they’re toast. If you can rotate it with a big strap wrench or a seat belt, or wiggle it front to back, it’s gone. It’s important that this be fixed, because the harmonics occur in narrow RPM ranges, and cruising in exactly that speed for an hour might throw the outer ring right off (into the belt, fan, radiator, &c.). Do not make this your last purchase. Do not “just to run it for a while like this”. It may not last a while.

put a line of paint on the dampner from the outside to the inside piece, across the rubber section. If the line shifts at all, the dampner is bad.

The timing is right where its been the last ten years. just cant figure the vibes.
Doesnt look defective but dont know what else could be.
balanced assy, billet wheel, aftermarket pressure plate all neutral.
cant hurt to put one on, just wish could pinpoint unless something else.
If I dont have 15 dampners here, I dont have one.
may swap one out for giggles, see if anything vibes different, then I have clue.
No dougbt a new one be nice regardless.
Thanks all. keep you posted.