Muscletang engine shows a smooshed spark plug!

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I started a tear down of the engine top to make sure the valvetrain is good, heads and to check for manifold possibly sucking oil from the valley. I was planning on removing the heads to check on the gasket since I have been noticing some black sooth coming from the heads at the front of the engine. In any case, I found a surprise with the plug of cylinder 7. The plug looks smooshed but shows no signs of significant impact. The other plugs look good. Strange is that the engine was running well. I did check the plugs a few times after I rebuilt the engine so this probably happened within the last two years. Maybe that explains the power drop off I showed in the dyno earlier this summer. Maybe I have been running on 7.5 cylinders for a while. Right now it is anyone's guess, but I am suspicious that some debris got there and hopefully did not cause more damage. One possibility is that I noticed that the epoxy and reinforcement I placed on the intake manifold to block the exhaust passage was gone. I don't know how this is all connected, but could some of that stuff made its way into the cylinder. Tonight I will be checking compression in all cylinders just as I had planned for checks and then remove the heads to check what awaits me there.

20211117_232337 (pug 7).jpg

20211117_224931.jpg

20211117_224943.jpg

 

timachone

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Uh, that's a strange damage...  :classic_blink:  Looks like something of harder material went sideways against the plug. Maybe some of your block off plate. Hopefully it found its way out immediately through the exhaust valve in the right moment and you don't have more damage. 

I'll keep my fingers crossed!

 

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Tony-muscle,

Hoping you dodged a bullet there, I would put more faith in a leakdown test than a compression test, even an airhold test on that cylinder compared to the others.

Either ditch the partial turkey pan or go with a full one, as the way you have it now is not the risk of future gasket failure.

You still have the option of having the heat passages welded closed.

Perhaps the dyno was right.

Boilermasteer 

 
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Tony-muscle,

Hoping you dodged a bullet there, I would put more faith in a leakdown test than a compression test, even an airhold test on that cylinder compared to the others.
The compression test is not really intended to troubleshoot the plug issue. I had planned this test just to check the health of the engine before I remove the heads. Once I remove the heads I should be able to see firsthand what happened.

 
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Do you think the spark plug was even able to ignite the mixture the way it is? Was the engine running so well with 7 cylinders or maybe this one was partially operating?

 

timachone

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I think it was operating but spark was weak especially on higher revs. Spark ring is very carbonated so no good burn there...

 

Don C

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If you look closely at the porcelain under the ground strap it appears to be clean around the edges. It also looks like the edge of the porcelain is broken off under the ground strap, so some spark may have been happening down in the housing.

It does appear that it could be possible for that piece of epoxy to bounce back and forth in the exhaust passage until it made it past the exhaust valve. It's also possible the chunk of gunk held the exhaust valve open and it contacted the piston. If that happened or if a piece of debris is keeping the exhaust valve from fully closing compression or leak down tests will show a bad cylinder.

 
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If you look closely at the porcelain under the ground strap it appears to be clean around the edges. It also looks like the edge of the porcelain is broken off under the ground strap, so some spark may have been happening down in the housing.

It does appear that it could be possible for that piece of epoxy to bounce back and forth in the exhaust passage until it made it past the exhaust valve. It's also possible the chunk of gunk held the exhaust valve open and it contacted the piston. If that happened or if a piece of debris is keeping the exhaust valve from fully closing compression or leak down tests will show a bad cylinder.
That's the only plausible explanation I can find right now so I am keeping my fingers crossed.

Two questions I have:

- Where does the heat passage intersects the exhaust port, does it intersects only the exhaust of the middle cylinders, how big is that intersection? Is there a schematic somewhere showing the passages?

- Is it safer/better to weld the passage shut? If so, at the manifold or at the heads?

 

Don C

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There's a passage from the crossover opening to the #2 or #7 exhaust port (depending on which side the head is on) that's about the same size as the crossover opening.

I've used the 5836 Mr. Gasket and 1228 FelPro intake gaskets that have the exhaust crossover blocked. If you don't trust the gasket material to hold up you can place a piece of stainless steel between the gasket and head. I personally wouldn't weld the passage closed, that could lead to cracks forming. If you do decide to weld a plug in the passage I would do it on the intake side, much easier to get to.

Due to problems others have experienced with FelPro lately I wouldn't recommend using them, though.

 
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There's a passage from the crossover opening to the #2 or #7 exhaust port (depending on which side the head is on) that's about the same size as the crossover opening.

I've used the 5836 Mr. Gasket and 1228 FelPro intake gaskets that have the exhaust crossover blocked. If you don't trust the gasket material to hold up you can place a piece of stainless steel between the gasket and head. I personally wouldn't weld the passage closed, that could lead to cracks forming. If you do decide to weld a plug in the passage I would do it on the intake side, much easier to get to.

Due to problems others have experienced with FelPro lately I wouldn't recommend using them, though.
Thanks. Since the culprit is #7, that makes the explanation of debris from the crossover very plausible. I don't trust the gasket material since both times that I have left it they end up burning up and disappearing. I think a SS thin plate may work or a piece of aluminum can as I have read around.

 

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Besides the compression I would also recommend a leak down test.   I would do it now so you know what  might or might not be going on with the valves and rings in that cylinder before you pull the heads.   A  visual inspection might not give you a "real" answer if there is any other damage. 

I would do the leak down and focus on seeing if you can hear any air hissing out the exhaust/intake or out of the block oil filler, dipstick tube, or PCV valve indicating valve or ring issues.   

Hopefully the spark plug is the worst of it.  I would agree with you on that is probably why you had the drop in your dyno run. 

 
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Don C

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Here's what the crossover passage looks like from the exhaust port

Exhaust Port-r.jpg

 
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Last night I tested compression and removed the valve covers. The compression was 180psi in all cylinders including #7. I tried to inspect with the camera but a long story short, I had issues with it and it ended up getting stuck inside. The valve train looks like new. I don't have a leak tester and due to time constraints I won't be able to do it. I think I will learn a lot more once I remove the heads which I am hoping to accomplish next week. I have been going to the gym for a while so I can lift 50+ pounds while bending over the engine bay :biggrin:

 
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Wow, that's a real mystery.

Just for the heck of, here's a pic of what I did to block off the crossover on the manifold. You've seen it before I'm sure. I used some 1/16" SS, hand cut a ledge for it to sit on, the staked it in place along with some exhaust cement. I've had no issue since with excessive heat under the carb and that was the reason I did it.

IMG_0639_LI (3).jpg

 
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