Timing Chain Rattle

[rxm6]

I have this timing chain rattle every time the engine warms up to operating temp and idles down to 700. It's not consistent and it's almost random when it occurs. Thinking it was the chain guide, I pulled off the valve cover to find the chain guide already removed. I did however notice small scratches on the roof of the valve cover. However, they are very few and look old so I don't believe its hitting there. I then put the car in gear and pushed it (good workout) and watched the chain and tested it every few feet to see that it was tight and no visible wear or damage. Chain was tighter on some revolutions than others, but it wasn't anything that would cause a chain rattle. So, I replaced the valve cover and started the engine again and paid careful attention to the sound. When warming up with idle around 1000, the sound is never present, however after the car warms up and the idle sits down to 700 the rattling will begin. I listened from the top of the engine and I could hear the rattle, but then I listened below the engine and it seemed to me that the rattle was louder from below. My car is lowered, so it could be acoustics, but I shoved my ear as far as I could in there and it still seems the rattle is louder from the bottom. So my first question is: is there a chain guide on the bottom as well? My second question is: why would the rattle only occur at lower rpm's? My final question is: if the chain is tight with no real play, what could be causing that rattle (broken sprocket tooth?? I would think if it were this, I'd be hearing that rattle at all rpm's.)

[addisonblck]

hmmm... interesting....mine does the same thing...i havent notice if its coming from the top or the bottom yet. id say it rattles at low rpms because there less tension on it but when yoiu rev it, the chain has tension on it. but that would contridict ur how statment then.... hmm....ill be tryin to findout as well so if i get anything ill let you know..,.

[spank044]

Remember the lower tensioner is hydraulic, so when the car idles down and the oil warms up and thins, there will be less pressure on the chain so it will vibrate ever so slightly. Your easiest fix will be a step thicker oil and a bump of 100 rpms.

[rxm6]

Ok, let me be a nOOb for a second.

If I didn't want a quick fix, would this involve changing the tensioner or other things as well?
Modified by rxm6 at 12:20 PM 3/28/2008

[JP240SX]

I had the same problem with my engine and after a lot of diagnostics I found that the chain and sprokets needed to be replaced and the oil pump.. I had low oil pressure... thats why the lower tensioner makes the noise because is hydraulic... I replace both and problem solved..

[jinxmotoring]

replace the chain its stretched from wear