This isn't anything new to my 2.8L V6, but the tach likes to sort of "shiver" up and down at idle. There's really no rhythm or regularity to it. And it's not just the needle: I can remember my dad putting the timing light on it a few months back, and for every flash of the timing light, the mark on the harmonic balancer jumped to a different place (completely at random). There's probably about 100RPM of "play" up or down from about a 750-800RPM idle at any given time (just a guess). The intake is clean, and the plugs, wires, rotor, cap, and coil are all new (acted the same before and after changing all of that). The engine has been driven moderately "nicely" (no racing or anything, never taken to the track), with ~120K miles. I wouldn't say that the car runs rough or anything--no smoke out of the tailpipes ever, it always starts, never dies (although it doesn't seem to have any pulling power until I hit ~2500RPM).

It's really not a "problem", per se, but I'm just wonedering why... My dad and I were setting the timing on the rebuilt engine in my IROC last night, and I was surprised to see that the timing mark on the balancer can actually stay dead still, and that made me think about how unsteady it was on my V6...

Thanks

 

Over the course of 120K miles your timing chain has stretched. Replace the chain and the mark will stop dancing around

 

Yes, that'd do it.

Can that be done with the engine still in the car? Where could I get a timing chain for this engine?

The thing that sort of concerns me is that, if this engine is anything at all like the 350 I just rebuilt, the bottom of the timing cover butts right up against the front of the oil pan. If that's the case on this engine as well, would I need to replace the oil pan gasket as well (seems to me that it would be a great place for oil to get out)?

 

The timing chain can be change with the engine in the car and a stock replacement chain can be had for about $30 at any auto parts store. The oil pan's fron does overlap on thes motors but a generous layer of sealant usually works...