BB exhaust manifold leak

[Kenneth T.]

I replaced the donuts on my exhaust manifolds, LS5, 454. I had gaskets on the manifold to head and put them back without them, as original. I have a putt, putt leak on one cylinder. Vas is los?

I tightend them up to no avail. Has anyone else had this problem?

I checked the archives with no answer to this specific problem.

Ken

[Dick W.]

Re: BB exhaust manifold leak

You probably have a slight warpage of the manifold. If it is minor, you might get by using Permatex hi temp silicone as a sealer. It is the copper colored. If it any more than minor you will have to take the manifold to a machinist and have him slightly mill the mating surface

[Rich P.]

Re: BB exhaust manifold leak

Ken,

They never had gaskets from the factory. So to make sure you dont have a leak when assembling like the factory did is to put a thin coat of High temp gasket sealent between the head and manifold. Then when you tighten them you wipe the excess off. And if you put the right amount in there is almost none to clean. I have always used permtex copper. I have had cars together like this for 20 years with no problems.

Rich

[Kenneth T.]

Re: BB exhaust manifold leak

Dick, Rich,

I have it but put them up dry. I will have to get them loose and put some of the copper on them. It has been so long and I need a couple of the "circle" bolts anyway, so it will not be a waste of time.

Thanks, Ken

[Joe L.]

Re: BB exhaust manifold leak

I replaced the donuts on my exhaust manifolds, LS5, 454. I had gaskets on the manifold to head and put them back without them, as original. I have a putt, putt leak on one cylinder. Vas is los?

I tightend them up to no avail. Has anyone else had this problem?

I checked the archives with no answer to this specific problem.

Ken

Ken----


First, make sure the leak is not coming from the packing (i.e. "donut" gasket). Usually, this is the source of exhaust leaks at the manifold. If you had no leaks from the manifold-to-cylinder head interface prior to replacing the packing, I doubt that any were created during the packing replacement UNLESS you cracked the manifold during the process. It happens.

[Kenneth T.]

Re: BB exhaust manifold leak

Ken----


First, make sure the leak is not coming from the packing (i.e. "donut" gasket). Usually, this is the source of exhaust leaks at the manifold. If you had no leaks from the manifold-to-cylinder head interface prior to replacing the packing, I doubt that any were created during the packing replacement UNLESS you cracked the manifold during the process. It happens.

Hey Joe, thanks for the quick reply. I always hold your judgment in high regard. The leak was originaly from the donut. However, the NEW leak came from the number two front cyl, up top. I can feel the leak, despite tightening it to a scary degree. I put back the gasket and all is silent now. I don't need unnecessay deductions if I can solve them first. Smells like machine shop?

Ken

[Joe L.]

Re: BB exhaust manifold leak

Hey Joe, thanks for the quick reply. I always hold your judgment in high regard. The leak was originaly from the donut. However, the NEW leak came from the number two front cyl, up top. I can feel the leak, despite tightening it to a scary degree. I put back the gasket and all is silent now. I don't need unnecessay deductions if I can solve them first. Smells like machine shop?

Ken

Ken------


In that case, you may well have established that you need to have the manifold surfaced as others have mentioned. Still, it seems very strange to me that you apparently didn't have the leak at the #2 position manifold runner before you replaced the packing, but you have it afterwards. Manifold warpage occurs over time, not suddenly.

In any event, I would check the manifold very carefully for cracks after you have it off and especially in the area of the #2 runner. Then, if you wish, use a precision straight-edge to make clear any warpage. You should be able to readily see it, especially if the problem is in the #2 position.

[Tom L.]

Re: BB exhaust manifold leak

Ken, just a note. Back in my stock car racing days we used corvette 2 1/2" centerdump manifolds because that's the best the rules allowed. We never put anything on the mating surfaces as you have done. The put-put leaks always went away after carbon built up in the gap. Maybee take it for a run, when weather allows, and see what happens. I know how tight that engine compartment is. Have fun!!