exhaust manifold leak on 84 258 J10

[marc]

Friends, I am doing the preliminary research for installing the Howell EFI (st. legal version) in my J10. The truck is very stock, including the annoying old and beateb up BBD2 carb. The odometer reads ~91000 miles but the vehicle the signs of someone working it over. It has what sounds like a smallish exhaust leak that closes as the engine heats. I suspect the manifold. It is my understanding that these manifolds are put on the head without a gasket, do people retrofit a gasket or maintain the no gasket fit? The motor has had some weird work done on it, notably all the smaller bolts holding the original plastic valve cover( replaced the useless thing) were poorly helicoiled? Numerous bolts appear to have been either over torqued or inadequately torqued so I am thinking a first step might be seeing if I can work the manifold bolts loose and retorque them? I know the bolts require care to move. I gather that even a small exhaust leak can confuse the EFI. Appreciate any thoughts or suggestions from you all.
Marc

[tgreese]

This is a common problem for inline sixes. The length of the manifold makes them prone to warping, and hard to seal.

First I would localize the leak. There are mechanic's stethoscopes that are used for this purpose.

Leaking exhaust gas will erode the iron surfaces. Look for leaks at the manifold-to-pipe connection too.

If you keep the iron-on-iron seal, the manifold and the cylinder head surfaces need to be smooth and flat. Your local machine shop can surface the manifold easily, and bring it back to factory-fresh condition. The cylinder head would need to be removed from the engine, if surfacing were needed.

A gasket will fill in some minor warpage or erosion. However, the composition and metal gaskets sold by FelPro and others will not seal indefinitely. At some point they will blow out and you will have a leak again. Leaks where composition gaskets have failed are large and noisy, in my experience.

There are also expensive header gaskets like Remflex, or copper gaskets, which are said to seal well and be much more durable than the conventional gaskets.

[Srdayflyer]

i have had several jeeps with the I-6 323 , 258 all had exhaust and intake gaskets i never had much problems with the exhaust gasket leaking as much as i had with intake gasket leaks, i usually planned on changing them every 400 thousand miles or so , the issue i call gasket creep due to the fact the exhaust is cast iron and the intake is in most cases aluminum and the difference in thermo expansion and contraction between the 2 the intake just causes the creep and loosening of the retainer nuts and washers also effected by this matter, i just had to retorque the E/I nuts on my cj this is the 3 time with only 27,000 mile since rebuild, thats been my experience with the I-6 engines