Jeep Sahara exhaust manifold

[Chuck52]

The continuing saga of my son's '97 Sahara.....

There has been some kind of class action suit filed about the exhaust manifolds on the 4 liter Jeep staight six engines. My son's is now on at least it's third....he bought it used in 2000, so he doesn't know if it had the original one then. There are at least three after market designs available. One has some kind of "expansion" pieces on the first and sixth tube, which are supposed to relieve the stress on the tubes and help prevent cracking. Another looks the same, but without the corrugated expansion pieces. The third has an "improved" design that is supposed to better align the tubes with the exhaust ports. This latter one is stainless steel, as are some of the second kind, and maybe some of the first kind. The prices on the web range from about $120 to over $400, more or less in the order given. I think the first type is either the original design or perhaps like the OEM replacement part, with the bellows things supposed to fix the original cracking problem. The third kind is probably the best design....at least it's the most expensive. Does anyone know if it is so vastly superior to the other two that we should pay twice the price? The last manifold, now cracked, looks like number two, but may not be stainless. It lasted about two years, and part of that it was parked while Mark played in the Persian Gulf. The expansion bellows on the first type require four additional welds, and that may be a drawback, but maybe they give enough play to actually relieve the stress which presumably leads to cracking. Experience anyone?

Chuck

[Pat]

My Jeep was a bit older (1943) but aren't any of the manifolds repairable? SS usually welds pretty nicely.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[Autotech]

I don't have any direct experience with the Jeep manifold problem, although I am aware of it and have dealt with similar issues on other vehicles, so you can take my advice for what its worth...

Generally this manifold cracking issue started to show up as manufacturers moved from cast iron maniflods to tubular steel. This was done for two reasons - weight savings, and more flexibility in manifold design for better flow. There may have also been a cost issue, but considering design and retooling costs I doubt it. These tubular manifolds are generally made of stainless due to the high exhaust temps at the exhaust port, and with modern engine controls using lean mixtures these temps have contiinued to rise.

The drawbacks are twofold. First, on long engines like a straight six the total expansion amount can be fairly large. This presents little problem whil expanding since the manifolds are strong under compression, but as the manifold cools it is forced to stretch - this causes the cracking. this issue is aggravated by stainless being relatively brittle, accelerating the cracking.

As far as your situation goes my first question is have you had the manifold on the vehicle rewelded? I have done many stainless manifolds/headpipes and had excellent success. Because the weld generally fills the void created by the crack it actually lengthens the stressed dimension relieving some of the cause of the original crack. On a Jeep the manifold shold probably be "tacked" in the vehicle to set the relative positions, then removed in one piece and fully welded on the bench.

As far as replacement manifolds, the "flex tube" type are used as oe on many vehicles and seem to work well. I would use that manifold before laying out all the extra for an aftermarket manifold - unless it has features or materials shown to be substantial improvements. I'd also want a warranty to help justify the high price.

Gregg

apologies for the poor spelling and punctuation - on a short break and rushing...

[jimbrown]

I do not have my 97 any more but I sure they came with the ones that had the expansion joint in the middle. I would just weld it. Any half decent welder can handle it. If not go with the stainless with the expansion joint. Also tell him to stop washing it when the engine is hot.

[robertn]

My B-in-law put a header on his '85 CJ7 years ago, and ran it until he swapped the 6cyl for a TBI 250 Chevy a couple years ago. He never had cracking issues. I'll ask him what he put on...

[robertn]

My B-in-law ran a Borla header. It had a million mile warranty. Ran it for at least 10+ years before he swapped to a v8.