Exhaust Manifold Help

[CCCC]

Talking 1972 402 BB passenger side exhaust manifold.

First, thanks to those who replied earlier with ideas on how to deal with exhaust manifold bolts that have been unmoved for almost 40 years and 100k miles, and might have been "frozen". Good news is that they were not frozen.

Bothersome news is that, as I finally got after the exhaust leak today, found that the front and rear manifold bolts were not snugged up tight - not loose, but easily could get some turn on them. And, these are the two locations of the leaks I could hear with tubing to ear. All other bolts were tight.

Am ready to go back together with the new gasket, but want available experience and knowledge beforehand. Questions:

1. Is it more likely that the bolt at each end of the manifold slowly worked out a bit and enabled the gasket to deform and leak, or that the gasket degraded and blew out a bit, and left the bolts not snug?

2. Is it at all common for a cast manifold for this truck to "bow" out a little bit at its ends. (Have not put the manifold face on a straight edge and do not want to further disconnect and remove unless really important to do it).

3. Other than thoroughly cleaning the bolts, particularly the threads, is there anything additionl that should be done - or anything applied to the threads - before re-assembly? I am an old timer - not up on all of the current chemicals and techniques for these jobs - don't want to miss any improvements.

Thanks for any help.
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[oldgold70c10]

Never-seize is the best for exhaust bolts. Lets you tighten the up good, and get em loose if you ever have to.

[Sillyoldman]

You'll need to remove it to replace the gasket anyway. May as well inspect it for a warp or cracks. It would be a good time to have it planed.

[vectorit]

You may want to think about getting new bolts, since age and heat can cause them to stretch. But, probably not necessary. If you do decide to do that, make sure you get proper bolts designed for exhaust manifolds.

I always brush on anti seize lubricant on those bolts, and even on a lot of other stuff especially head bolts and spark plugs.

It may just be me and my old habits from owning Corvairs, and dealing with motorcycle engines that I tend to use this stuff more so than most. But, all it takes is one seized spark plug or head bolt to get into the habit to use anti seize.

[CCCC]

Thanks oldgold70c10, I did not know of that product and will get it.

Sillyoldman, thanks for the advice and I am sure it is sensible. In this case, looks like I have sufficient space easily to slip the new gasket down between the head and the manifold, set the bolts and torque it up. I do not dodge work but, if I do not have to, would rather not open up that flange/gasket to get the manifold free. Some of those donut gasket/fittings have given me fits in the past and would rather leave well-enough alone if I can get away with it.

Because it took more than 100K miles for this original gasket to go, and in that I've driven hundreds of thousands in these old Chevs/GMCs and never had a problem with manifold warping (that I know of !), I am tempted to snug it up and give it a run. If I do that and it soon leaks, I will have it off there quick and shaved just as you advise. Then again, maybe I will remove and get it planed anyway.

Thanks again - any other replies out there?

[mr48chev]

I used to work in a shop that specialized in rebuilding cylinder heads and they resurfaced the face of every exhaust manifold that came through the shop on a big belt sander. It made for zero exhaust manifold to head leaks on the engines I installed there.

[CCCC]

Thanks vectorit and mr48chev. Good advice. All of you guys make this forum a great place. Went ahead and removed the manifold and cleaned it up. Looks quite plane on the straightedge but wire brush does not get it fully smooth, so will run it on a friend's long belt sander to see what's up - may have some pitting. If it does, will get it planed as Sillyoldman suggested. . Living so remote is an issue when this happens - never have needed any machining done and people near here have to send all machine jobs to Albuquerque - 300 miles - not good. So today I went on a search and found a retired journeyman machinist about 35 miles away who has a fully equipped shop for his enjoyment. Said he would plane it if needed and said he can do heads if i ever need such. So, a new and very helpful find.