Question for those who have replaced their timing chains

[anthrax323]

I had always been under the impression that a timing chain was a lifetime component of the engine, barring premature failure... Recently, I learned that this is not the case - it seems as though it should be replaced every 60,000 or 70,000 miles (much like a timing belt).

Though it is recommended to periodically replace it, many, many people report 300,000+ miles on their 4.0's on the original timing chain, so it sounds as though the recommended interval is a very conservative recommendation in the real world.

The ignition and fuel delivery system in my 2001 is spot-on and healthy, but the engine is ever-so-slightly less than smooth at idle. It feels almost as though it stumbles every few seconds, but definitely not enough to be cause for alarm - the idle speed is stable, and this is something I've felt with virtually every higher-mileage engine I've come into contact with (particularly inline 6's). Again, it's very subtle, and pretty much expected at this point given that my engine is pushing 165,000 miles.

My question is this: would slack/slop in the timing chain result in a less-than-perfectly smooth idle assuming that *every* other aspect of the engine is perfect? This is a broad assumption, but I guess I'm wanting to know how much of an impact a fatigued/worn timing chain can have on the smoothness of the engine.

 

[Talyn]

A lose timing chain would most likely not cause a stumble. Its possible, but unlikely. What it will do it retard the cam timing. A side effect of a lose timing chain can be an out of synch cam sensor.

http://motorage.search-autoparts.co...estandard//motorage/292005/169830/article.pdf

The short of it:
Bring piston #1 up to TDC on compression stroke. Insert some sort of locking pin through hole on bottom of sensor body and hole in window wheel, locking the wheel in place. put sensor in place with socket pointing toward the rear. You may have to move the oil pump to get it to line up with the cam and pump. Once in, bolt down and remove pin.

I would also check the basic stuff, spark plugs (Use NGK), air filter, tps, etc.

 

[anthrax323]

Wow, fascinating read - it really hits home with the BS I occasionally subject myself to in the Unix world ("No way it could be that simple..."). My engine has had no running problems outside of the heat soak issue, but I'll give this a shot.

Given how involved the replacement of the timing chain is (relatively speaking), I'll save that for when I get back from TX and have fully recovered from surgery... I'd like to go ahead and pick up new evaporator and heater cores and just take the whole damned car apart for a few days.

On the plugs note, I was surprised to hear that NGK's were now recommended over the Champions... I do have Champions in there now, but will likely go ahead and replace them this evening. I hit the road on a 1,400 mile trip to TX on Friday evening, so all these things should be done anyway.

 

[Talyn]

00+ (maybe earlier?) prefer the NGKs. Back when I was dealing with the heat soak issue I put some Champions in. It some how made the heat soak worse, or at least the missing part of it. Overall I think NGK makes a better plug than Champion anyhow.