Timing chain noise, advice please!

Hi all,
I have a 94 Altima with 173,000 km. Lately I've noticed some noise from the timing chain area at idle. It's always had some noise there, but it
seems like it might be more pronounced now. Basically it's a sort of threshing mechanical sound, but it's got a sort of "beat" to it that happens at a rate of about 4 or 5 times per second at idle. When it's cold in the morning, I also get an occasional "crunch" type sound from this area, but I'm not sure it's coming from under the valve cover or not. I had it checked by the dealer a couple of times, the first time I had it in for service and they checked, but didn't hear anything. They did note that the upper guides had been removed already.
In the last couple of weeks, it's been -18C and below a few days, and I've noticed another sound that's more pronounced than usual (maybe I'm just paranoid!). It's a rotational sound that I can hear only when accelerating lightly or keeping constant speed with little load on the engine.. it almost sounds like a dull metal-on-metal knock... but it's not really abrasive sounding.. I had a water pump go bad on an old Civic, and it almost sounds like that did. I don't know if this is at all related to the timing chain sound or not, but it almost sounds like it could be. I had it down to the dealer last week for a road test with their shop foreman, and he was able to hear the rotation sound once he got behind the wheel, but didn't think it was anything serious. His only real suggestion was that it might be something in the transmission. While I had him trapped away from the dealership, I had him listen under the hood, for the timing chain noise, and he thought there might be some slack in the chain, but again it didn't seem like he thought it was anything critical. I'm fine with that, but it's my engine and I hear it all the time, so it's not as easy for me to dismiss, although maybe I should since he's the expert. I just would hate to have been right all along and have the timing chain snap on me.
Anyone have any suggestions as to what I should do? I guess there aren't many options, but I'm wondering how often anyone's seen these engines blow a chain, and if there's usually any warning sign or not. According to the dealer, they can't really inspect the chain without getting into a lot of work, so if I was going to get them to do that, it sounds like I might as well get the chain replaced anyway.
Would you folks recommend replacing the chain at this age? If so then maybe I'll just do that and put my mind at ease. The car runs great otherwise and still has lots of spirit, so I don't think there's anything really fundamentally wrong with it. If there's anything I could do to maybe help better identify what I'm hearing, I'll do it!
Thanks as usual for the help.
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JM, It's common for the 94' Altima to have timing chain noise. Do you know if the lower guide was replaced with the updated part when the upper guides where removed. AT 170k I say it's time for new timing chains, guides, and tensioner, before it does any more damage. It won't be cheap thou.

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brystok wrote:

Yep sounds like it's chain time to me too.
--

Steve

http://www.atlantaracing.com
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Ok. I think I'll go to the other dealer in town and see what they think. I don't mind getting it done, it might sting a bit but it's the only way to be sure it's taken care of.
I was under the hood again tonight, trying to nail down where the various sounds are coming from, and I think the rotation sound I mentioned second in my original post is actually coming from something outside of the engine. It sounds like it might be the alternator or something in that area. It's hard to hear it at idle, but if I rev it up, for a moment I can hear the sound before the revs come up to where I have the throttle. I can't hear the sound at all when I'm listening directly over the valve cover. I wonder if a hose or screwdriver held up against a few of the things on the serpentine belt would be able to identify the source. One thing I forgot to mention was that although the sound is worse when cold, it seems more related to the air temperature than the engine temperature. During the cold days last week, even after the engine was fully warmed up, the sound was much more noticeable than it is this week, in warmer weather. So that to me would indicate it may be something external to the engine.
I'll post my findings as they come in. :)

know
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As for using a screwdriver or hose to locate the source - about 30 years ago I bought a mechanics stethoscope - like doctors use - except it has about a ten inch metal rod on the end for listening to engine noises. I can put it on an alternator, water pump, etc., and get a pretty good idea of where a noise is coming from. However, it is VERY loud if you bump it against anything when you have the ear pieces in your ears. I don't know if they still make them or not, but it was cheap and has lasted a long time.

cheap
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I just saw one of these today, beleive it or not! I think I'll pick one up tomorrow, they were only $20 or so. Unfortunately the area I'm listening in is right around the belts so I'll have to be careful to not get the tube snagged anywhere!

you
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JM wrote:

A screwdriver works great, never heard of using a hose..
Something else you can try, remove the belts and crank it up. If the noise is still there, it's inside the engine.
--

Stacey

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I thought of that, but unfortunately I don't have a garage, and I'm pretty sure I'd have to get under the car to do that... which wouldn't be fun at -23C. :)

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