When to replace timing chain on 78 Regal?

I have a '78 Buick Regal with a 3.8l 231cc Buick V6. The Chilton's says to replace the timing chain at 120-150k. The car has 133k. I've been told not to worry, but I understand that if the thing breaks it
can trash the engine. What would you folks advise? Does it give much in the way of warning signs before it goes? Also, would getting a new chain improve performance?
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There really is no interval on timing chains, but you can get some idea of the play by getting a socket on the crank pulley bolt and rotating the crank back and forth just enough to feel the free play before the cam moves, this is a judgement call here, but there should be maybe 1" of free movement, some will argue more or less is acceptable. This will let you know if it is really badly worn.

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snipped-for-privacy@yahoo.com wrote:

Does it give much

>> One test is to put socket / breaker bar on crank pulley, remove distributor cap, gently " budge " engine, see if rotor spins. If you can move breaker bar [ turn crank ] more in one direction than the other before the rotor turns, than you have chain wear. The trick is to notice when the rotor just starts to turn. This test will show if chain has slack, will not reveal severely worn gears. In the " good old days " cars had stiff valve springs, and high lifting cams, this combo put a lot of stress on chain sprocket. The nylon coated cam sprocket would often shed teeth.
Some " Muscle cars " would break chain at 50,000 miles or sooner A broken chain may / may not damage valves Check all valves after a failure. The V6 has fewer valves, less lift, so I could understand the rational in not bothering. If the engine runs good, doesn't gulp oil, new chain, sprockets, water and fuel pumps, all easy to get at, gotta come off anyway parts.
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