Help with exhaust manifold flange gasket. Please

[discostew]

Minor thread resurrection. Last week I replaced the passenger side exhaust manifold to cylinder head gaskets and the cat-back exhaust. So far, so good, although reinstallation of the exhaust manifold bolts took lots of patience and delicacy to avoid stripping threads. I don't want to repeat that process.

The final piece in my exhaust puzzle is the Y-pipe to exhaust manifold gasket. I have new gaskets, studs, and nuts. From reading this (and other threads here) it sounds like the best approach will be to leave the exhaust manifold tight in place against the cylinder head instead of loosening those bolts to get more wiggle room at the Y-pipe junction. The only other material it sounds like I should have on hand is hi-temp sealant.

Any other strategy tips? The challenges I anticipate include:

1. Accessing the nuts on the flange studs - any special tools or techniques to get at these? Advance soaking is a given.
2. Having enough play in the y-pipe to separate the flange to remove the old gasket and insert the new one.
3. Replacing the studs: should I bother? New nuts are a given.
4. Keeping the Y-pipe flange mating surface even with the exhaust manifold surface when re-tightening. I don't want to go through all this only to find a gap (and leak) when I turn the engine on at the end of the project. Tighten opposing nuts incrementally, alternating nuts to keep surfaces even?

Any suggestions or lessons from prior experience appreciated. I'd like to do this with the minimum of rearranging other components if possible.

Everybody drink!

 

[fishEH]

I'd say pull the manifold for either approach. I've been able to successfully drill a few downpipe studs in place, but it was a pain.

 

[simondewing]

Near impossible to drill manifold studs out with it in place.
When they snap its better to remove the manifold and use heat to free up the broken stud.
If there is a stub either a stud extractor or vice grips can be used.
If its snapped flush use heat and a left handed drill to extract the remains.
If you have to drill oversize and heli-coil it needs to be done in a drill press with the manifold securely clamped to keep the alignment.
Using a scrap exhaust flange as an alignment jig also helps.
Problem is the iron manifold is softer than the steel stud so the drill tends to run off if you drill freehand

 

[Tugela]

Torch worked. Everything is back together and my Disco now sounds civilized. Next question at the risk of thread drift: my ScanGauge is showing some large fuel trim numbers. I thought this was caused by the exhaust leak and a new Y-pipe would resolve them, but they're still beyond what you'd want.

One bank has short term trims at zero and long term trims at 0.8. Great. The other bank is showing readings either in the positive low 20s or negative low 20s, I forget which. I understand that long term fuel trim takes a while to average out, but my short term numbers are still far from zero with the shiny new Y-pipe. Could this be fouled oxygen sensors (thanks to the exhaust leak) or might the culprit be something else? I can move the sensors around and see if the funky readings follow them.

 

[Gordo]

Better luck than I had. Took my y pipe off a D1 project and broke 3 studs. (By hand, soaked for days and heated). I figured I’d weld nuts on and pull them out and replace. No dice two welds broke and one stud broke. I ordered two used manifolds with the studs out and a new stud kit. Not worth the hassle of drilling and taping when I got two manifolds with studs removed, new studs and bolts for less than 80$ shipped. Royal PiTA haha