timing chain question

Hi,
I'm getting ready to replace the rear seal on a '92 4.0 L. The question is whether to do the timing chain too. I can hear a light scraping type of sound when I run the engine a little above idle speed. The harmonic balancer looks OK and all the accessories are smooth and quiet when I spin them by hand individually. The car has 175K miles, but I don't know its history. I've read some posts that say the timing chain outlasts the rest of the engine while others say replace it.
Is there any way to check it for excessive slack by turning the crankshaft back and forth, while watching the rocker arms or distributor?

Thanks

The FSM says 1/2" or less of deviation in the chain. I don't think you can realistically check it without pulling the cover.

I replaced mine (both chain and sprockets) at 197,000 miles. Closer to 1" deviation, and it had just started to scuff the cover.

I also replaced mine (88) at around 175K, It had started to rub the cover and the seal was leaking anyways, Autozone complete chain and gears cost (I think) 39.00.
I sleeved the balancer while I was at it. well, there was also the mounts, the pump, tstat etc etc..its amazing what you can replace when the front of teh engine is exposed :0

I replaced mine at somewhere around 200,000 miles and the old one was as tight as the new one. I guess a lot has to do with maintenance schedules -- I bought mine new and changed the oil religiously every 2500 miles up to 175,000, then switched to full synthetic and a 5000 mile interval.

I have a dim recollection of someone on the old XJ forum coming up with a test of chain slack that involved turning the engine backwards and seeing how much engine rotation it took before the distributor rotor started to move, but I don't remember the details of how much was too much, etc. Does anyone?

12 degrees is a number I recall for GM 350 engines.

I'd change it-

Hey, do it while you got it off the road and up on jackstands!! Probably could use it, and you would be able to catch the front seal too. Is a fair indicator of slack by rotating the crank back and forth noting the slack. Exactly how much, that 12 degrees sounds reasonable. Maybe it's been done before on that engine? I would not use AZ timing chain components. Have found serious problems in the quality of those kits in the past. I'd go OEM, or maybe NAPA if were me and you care about your vehicle.

Thanks for the input gentlemen.
I decided not to do the timing chain now because I ran out of time to work on it. While I had the pan off, I found that I could get my finger and a ruler into the timing chain area reasonably well. This is not as accurate as having the cover off, but it looked to me like the chain would move about 7/16 of an inch, so I felt a little better about letting it go for another year or so.
Just for reference, I tried a measurement of the rotation of the crackshaft needed to take up the slack. I made a little wire pointer that came near the edge of the harmonic balancer. I turned the crank clockwise to take up the slack, and scribed a mark on the pulley edge. Then I held the distrutor rotor in a clockwise direction to take up any backlash between it and the camshaft, and started slowly turning the crackshaft backwards until I just felt movement in the rotor. About 6 trials gave results of about 4 or 4.5 mm of movement at the edge of the h.b.