I also have a timing chain question. I have a 94 Altima (see post below...) with 175,000 km and have been wondering about the timing chain for a while. There is a sewing-machine-like sound from underneath the valve cover at the timing chain that I guess is probably normal, but every so often sometimes there's an occasional crunch or clacking sound that makes me a bit nervous. Anyway I know it's really impossible to diagnose from a description of the sound what might be wrong, if anything, but my question is this:
How much slack is normal in the upper chain?
I had the valve cover off a few weeks ago, and the upper chain at least looks fine, not mangled or anything, and the teeth on the camshaft sprockets all appear to be intact and free from damage, which is good. And although between the two cam sprockets there was no slack, I did notice about 1/2 inch of slack (forward and back) on the front section of chain between the idler sprocket and the exhaust camshaft. Is that excessive? I'm a little puzzled as to why there'd be slack at that span and yet none along the top section as well.
Anyway, just thought I'd throw that out out there, I'm trying to get around to getting a quote on getting the whole thing looked at and/or replaced to be safe, but any extra knowledge I have beforehand is always good.
Thanks in advance.