What does a worn timing chain sound like?

I know it's a stupid question to ask on the net where I can't actually hear it, but I have a 92 Caprice 305 with 308k on it, original timing chain and
tranny as well.
The engine purrs like a kitten and doesn't burn any oil but I am getting this "rattling" sound after the engine warms up and the car is idling in PARK. If I step on the gas a little or shift to drive/reverse the rattling goes away. Actually it kind of sounds like it is coming from the tranny but it's difficult to isolate.
I am going to change the timing chain, water pump this week but I was curious if anyone had any ideas?
Like I said car runs fine except for that.
I was wondering if the screen in the tranny might be semi clogged and at idle there is not enough pressure to pump the fluid? I have NEVER changed the fluid and it is still bright pink and doesn't smell at all.
Any ideas?
psycho
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Hi
Sounds like a timing chain to me. I have a 1988 Olds with a 3800 engine that had the timing chain and tensioner replaced at 150,000 while I was doing the heads. At about 190,000 I started getting a rattle that sounds like what you are describing. It's almost erie, how close the symptms are. I kept on ruling out the timing chain because I had replaced it. After chasing the damm thing for about a year, timming chain was the only thing left and I descided to tear it down again. I found that the after market chain and tensioner after 40,000 had more wear that the original GM parts after 150,000. After replacing these the thing purrs like a kitten.
Ted M
PS Now the air conditioning compressor is begining the rattle, damm, damm
psycho snipped-for-privacy@yahoo.com wrote:

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I had one going bad once - it sounded like marbles in a coffee can.
doug

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One other thought, the flex plate [ flywheel ] can fail, and make noises. My 76 Chevelle had all four webs broken, yet car drove fine, except for occasional grinding noise. Noise present on shallow bumps and corners, quiet otherwize.
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451ctds wrote:

A worn timing chain would be pretty loud at all times. With the engine idling, you can use a mechanic's stethoscope to listen in on the timing chain under its cover. It should sound smooth. Watch out for the cooling fan.
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Good advice. I'm checking it out this weekend. Whatever is causing it is getting worse :( I suspect maybe the transmission.
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psycho snipped-for-privacy@yahoo.com wrote:

Are you sure it isn't the suspension that is making the noise? What leads you to believe it is the engine or transmission?
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It does it while the car is standing still :)
Here is what happens:
Start car and all is fine. Drive say 20 miles and then stop, put car in park and you will hear a clattering coming from the drivers side of the car underneath, not on the top half of the engine. Sounds like the pistons are going to fly out of the engine. Rev engine up a little and clatter stops. Rev engine high and let foot off throttle, it will clatter until engine settles down and then will be ok for a bit until it settles down again and then it might clatter and might not. Also, and I am ashamed to say this, but I have NEVER changed fluid/filter/screen on this tranny in the 300k+ miles I have owned it. Fluid is still bright pink and it shifts fine. In my defense, i learned a LONG time ago that trannys are sensitive beasts and that putting new fluid in an older tranny dislodges gunk that makes things worse. An old timer at an independent shop once told me if you go past 30k without a change of fluid, leave it alone. I have followed his advice and every single one of my trannys has gone well past 200k miles. However, I change the fluid/filter in my 2000 Dodge Caravan every 20k because that is a known shit tranny.
Reason I suspect tranny is I think raising idle, raises pressure in pump and allows fluid to circulate better.
Reason I think it is timing chain is because it seems to be timing related. Upper half of engine sounds smooth as silk.
It's the weirdest thing I have ever heard.
Psycho.
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psycho snipped-for-privacy@yahoo.com wrote:

hm, yeah, this might be over my head.
i know what you mean about the tranny fluid thing - when i first got my '69, we changed all of the fluids - next thing we knew, we were in the middle of a major 6-lanes-in-all-directions intersection with a dead tranny, lol. not a lot of fun.but it was all good - it gave me a good excuse to dump the powerglide and drop in a real purpose-built th350.
however, don't forget that this could be the first of your trannies to go awry after never changing the fluid. i'm pretty sure my old powerglide was on its way out anyways since it already had a little slip with a side of rough and tumble.
have you gotten any other suggestions from others?
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Wow!!
Same exact thing happened to me with a 1974 Buick with about 70k on it. I was a youngster and inherited the beast and of course I changed all the fluids. Car died right in the middle of a very busy intersection in NYC due to transmission failure. !

I'm toying with the idea, but this would be #2 (see above!!).

Most people are saying timing chain which at 300k+ miles should have been changed 200k ago.
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