8n intake/exhaust manifold burn out question

When i rebuilt my 12v, side distro 8n 80 eng hours ago, I used some hi temp liquid steel putty to reform a flat surface for the manifold to really seal against the gasket. It seems it has burned out in not only the usual area to the "left" of the manifold but also at the front or "right" as well.

Besides re-inspecting the manifold for issues, is there anything engine related that could be causing this to fail again? I know i need to adjust the valves as I have not done that since the valvetrain refresh, but I can't come up with any ideas about what would be causing the gasket to burn up.

Thanks,
Cam

Sorry: To my knowledge there is no material, epoxy or otherwise that will make up the gap. The temperature is too great. You will need to replace or machine the exhaust manifold.

(quoted from post at 05:28:57 01/03/17) When i rebuilt my 12v, side distro 8n 80 eng hours ago, I used some hi temp liquid steel putty to reform a flat surface for the manifold to really seal against the gasket. It seems it has burned out in not only the usual area to the "left" of the manifold but also at the front or "right" as well.

Besides re-inspecting the manifold for issues, is there anything engine related that could be causing this to fail again? I know i need to adjust the valves as I have not done that since the valvetrain refresh, but I can't come up with any ideas about what would be causing the gasket to burn up.

Thanks,
Cam

Click to expand...

You don't say whether it is the manifold that is burned or the block face where the manifold connects.

I had a manifold start leaking on my 8N. It made a clicking type noise and I could actually feel the air coming out with my finger around number 4. When I removed the manifold, it was burned around the number 4 cylinder. With a straight edge placed on it you could see how much of the material was gone.

I didn't bother trying to fill it in since a new manifold was not that expensive. The faces on my block looked good so I just installed the new manifold and new gaskets.

Sometimes if you run it too long with a leaking manifold, it will actually start eroding the block face as well as the manifold. I've heard stories of guys here that have successfully used some product to reface the block, so it is possible if it's not too bad.

One of those guys will probably be along shortly and tell you what they used for the repair.

Build up the low areas with brazing rod and machine it flat

You may be right, BUT, there have been MANY posts on how and what to use to solve the problem. I suspect those that have had success may pipe in. Hey Bruce !!

The brazing rod will work used it before on ither
projects

(quoted from post at 03:02:15 01/04/17) The brazing rod will work used it before on ither
projects

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would love to try this, but i spent a ridiculous amount of money getting this thing running and tearing this down to the block is a deal breaker for me.

(quoted from post at 23:20:55 01/03/17) You may be right, BUT, there have been MANY posts on how and what to use to solve the problem. I suspect those that have had success may pipe in. Hey Bruce !!

Click to expand...

Bob, I know how to solve the problem in terms of new gasket, quiksteel, new manifold etc.

I want to know what motor conditions cause this to happen. You are all trying to tell me how to fix something, and I want to know why it happens, not how to fix it. I want to cure the disease, not the symptom.

When i initially rebuilt the engine, i noticed the exhaust manifold needed some help with making the gasket seal. but I now see this burning around the #4 and new burning around the #1. Something is wrong that is causing more cylinders to be burnt rather than just time.

(quoted from post at 07:31:19 01/04/17) When i initially rebuilt the engine, i noticed the exhaust manifold needed some help with making the gasket seal. but I now see this burning around the #4 and new burning around the #1. Something is wrong that is causing more cylinders to be burnt rather than just time.

Click to expand...

My bet is exhaust leaks cause the erosion.

TOH

[/quote]

Sure, but why does a (assuming) perfectly normal engine generate an exhaust leak in the beginning. I realize my issues could be from an unsupported gasket, but there has to be something that changed from factory steady state conditions to cause a gasket to fail. IE too lean caused exhaust temp over heat, valves slightly open during compression blew out gasket, something like that.

[b:58a7c90061]"there has to be something that changed from factory steady state conditions to cause a gasket to fail."[/b:58a7c90061]

the consensus of opinion about this issue seems to be that manifold design is flawed. the problem u are experiencing is very common (i dealt with it myself, and it was apparent it was an ongoing issue for the previous owner), and i have no reason to think from what i've read that there is any magic wand to prevent it from happening again.

the only thing i can think of in your particular case, since u say it's happening in front of number 1 as well, is that maybe your timing is off and the engine is running hotter than normal?

in lieu of that, i don't know what else to do besides deal with it as needed.

(quoted from post at 08:19:22 01/04/17)
Sure, but why does a (assuming) perfectly normal engine generate an exhaust leak in the beginning. I realize my issues could be from an unsupported gasket, but there has to be something that changed from factory steady state conditions to cause a gasket to fail. IE too lean caused exhaust temp over heat, valves slightly open during compression blew out gasket, something like that.

Click to expand...

Chicken and egg question. But your block is 50+ years old and lots has changed since it left the factory. Blocks distort over time and you have erosion/pitting from a previous burn out. Liquid steel and the like are bandaids. Once the erosion starts the only way you are going to reliably stop it from recurring is to deck the manifold sealing surface on the block. That will get you back to "factory" condition. Then use a good manifold, preferably new or reconditioned that you know is flat and free of imperfections and seals with just the gasket. John Smith once posted a picture of how he machines the sealing surface on the flathead block with nothing more than a Bridgeport but I have not been able to find it again. John - you out there?

TOH

Did you re torque the manifold mounting nuts after running a bit?

TOH,

yea i totally understand this block is not "factory fresh". just curious why, assuming you had a fresh block from the factory, this condition would develop. seems it's not anything in particular, just a design that develops the issue.

Probably did not re-torque the nuts on the manifold. It was 2 years ago and i was deployed one of those years so i can't remember, but for the sake of discussion id say no.

Thanks all for your comments.