I replaced the heads earlier this year, but it didn't occur to me to resurface the exhaust manifolds so I found it not sealing correctly. I realized I happened to have a set of exhaust manifold gaskets I got just in case, so to get the car back on the road quicker I just used those. It worked great until just a short time ago when I noticed header noise. It was pointed out to me that there was a manifold leak, and looking at it I saw a chunk of the gasket missing, and we're talking about thick metal gaskets. I wouldn't believe it if I didn't see it for myself. Does anyone have suggestions on how this could have happened?

 

Here's a picture I took. I understand gaskets weren't used in the factory but it seemed like the best chance of making sure everything sealed together correctly.

 

What brand exhaust manifold gasket did you use?

 

This was the fix we used years ago in shop, I apprenticed in. Anytime an Olds V8 came in with leaking exhaust manifolds, we installed a gasket and away they went. It may be a warped manifold or a shitty gasket. We never had one come back that I recall.

 

SCE, specifically it was this one which seems to no longer be available and is superseded by a new model which looks the same. It looked really good on the outside, metal, nice and thick.

The manifold is definitely warped, both of them are. The new heads were fully rebuilt stock (the old ones were shot) and the initial reinstallation produced significant exhaust leaks and unmuffled engine noise coming from the manifolds. The gaskets fixed the problem. I'm just not sure how a piece of what appears to be solid metal just comes out.

 

I think you'll find the exhaust manifold face on the heads is mot flat either. The exhaust manifold face could have been lightly machined to make it flat.

 

I've never seen the FelPro exhaust manifold gaskets fail that way. You'd have to remove the head to measure the exhaust manifold surface to determine if it was warpped. MAW just replace the exhaust manifold gaskets.

 

There really is no need to remove the head. Clamp or wedge a straight edge or flat, thick metal to the exhaust surface and shine a light from below. Check the areas with light shining through with feeler gauges. .

 

If that is the center bolt, you may have over torqued it. I would just use a set of Fel-Pro gaskets and be done with it. They are very forgiving.

 

The chunk was near the back between the two rear most bolts. All the bolts are on tight, except the one farthest back which was kind of loose. Please help me to understand how overtorqued bolts leads to the gasket partially disintegrating. What am I missing?

 

By over-torquing, you warp the manifold flange, causing a leak on the inside of the manifold. The hot exhaust gasses will start to burn the gasket from the inside(regardless of gasket material), until it burns thru to the outside.

 

 

Ok, now im understanding. So it seems undertorqing can cause the same problem. Thanks.

 

Once you replace the exhaust manifold gaskets make sure you show us a pic of the one that failed.

 

Isn't the use of Hi Temp Silicon Gasket think 800° usually successful solving this problem?

 

Definitely helps. Optimum Grey, a very heavy body RTV plus almost invisible compared Copper and Red RTV good to 700 degrees intermittently. Copper coated gaskets in Optimum Grey might be the cheapest and quickest alternative.

 

The new gasket finally came today and I got them changed out. Sadly I won't be able to post pictures of it because it broke apart when removing it. It was very well stuck on the head even though I used no bonding agent at all. It was super brittle too, in fact it was so brittle I could take the bigger chunks and break them into smaller chunks with my hand, which given that it was very solid when installed was quite surprising.

Based on what I saw I have a theory about what happened. There has been an issue i only recently was able to get fixed of the tip of the tail pipe being too low and striking the road when going up an incline (like entering a slanted driveway from the road). This happened a few times, which I think caused the rear most bolt to walk out somewhat, and with how brittle the gasket was the chunk just broke on its own. Then the exhaust gas just pushed it out.

 

I guess that shows that SCE exhaust manifold gaskets are junk. You should have taken a picture of the bits of exhaust manifold gasket and posted it on Summit too.

 

Get REMFLEX 11-001 gaskets. Torque to 20 foot pounds and you're done.
Felpro's etc don't work.

 

Why didn't you develop an exhaust leak at the exhaust manifold to down pipe ? Why didn't all the exhaust manifold bolts "walk out" ? Why didn't you re-torque things after running the engine a few minutes and cooling down ?
I have a theory. It appears to be a series of installation errors.

 

^^^^^^^^^^^^^^^^^^^^X2, I agree, very well made.

 

A.) The downpipe connection to the manifold did develop a leak the last time it struck the ground because it didn't reseat itself right, but you're forgetting that it has springs that allow it to move without breaking and it was able to return to its position before. The manifold on the other hand is rigid, so it absorbs the stress fully unlike the tailpipe which is also mounted on movable hangers. If the tailpipe couldn't move then it would break whenever the engine shook or moved in any way.

B.) That one bolt walked because that was where the stress point was, the distribution of force isn't equal. There is a reason this happened on the passenger side and not the driver side which is still working fine.