Blocking off manifold's exhaust crossover

[tony-muscle]

As I am putting my engine's top end back together I need to figure out how to best block the exhaust crossover. Last time I tried high-temp epoxy with wedged nickel coins as reinforcement, but the epoxy broke away and as many of you read a few months ago, a chunk of epoxy ended up in the cylinder damaging a plug. That said, I don't want to try the epoxy option again. I have a 0.018 sheet of stainless steel that I am planning on cutting to place between the intake and heads, which brings up the question of either placing the SS sheet between the intake manifold and gasket or between the gasket and heads. I read "somewhere" to use the latter but that doesn't make much sense to me. My thought is to place it between the manifold and gasket because in that way I should create a good seal of the exhaust. If I place the SS sheet between the gasket and head then I could have exhaust leaking through it. Any opinions?

 

[jpaz]

Pretty sure Stanglover did this mod.

 

[tony-muscle]

Pretty sure Stanglover did this mod.

You are right. He responded to my original plug post:
https://7173mustangs.com/threads/muscletang-engine-shows-a-smooshed-spark-plug.39677/#post-398286
@Stanglover, can you clarify if the SS sheet is between the intake manifold and gasket? It seems that you blocked the crossover first and then placed the SS sheet over it. I wonder if just placing the SS sheet would work without any backing. I am a bit shy of putting anything in there given my bad experience. However, the SS sheet should be able to protect the exhaust cement or whatever is behind it.

 

[Don C]

I would place it between the gasket and head, to keep the exhaust gases away from the gasket, as much as possible. The trick is to cut the stainless plug big enough, but not so big that the gasket can't seal around the perimeter of the plug, and keep it in place during installation. With the plug that thin the gasket will compress enough to seal around it.

 

[tony-muscle]

I would place it between the gasket and head, to keep the exhaust gases away from the gasket, as much as possible. The trick is to cut the stainless plug big enough, but not so big that the gasket can't seal around the perimeter of the plug, and keep it in place during installation. With the plug that thin the gasket will compress enough to seal around it.

Good point. Maybe can use a thin layer of high temp copper gasket maker between head and SS sheet to keep it in place and help with sealing.

 

[Don C]

Good point. Maybe can use a thin layer of high temp copper gasket maker between head and SS sheet to keep it in place and help with sealing.

Yes, that's what I would do. Glue it on at the same time the gasket is glued to the head.

 

[Stanglover]

Well, you took the words off my keyboard!!
As most know, I have posted on this subject before. What I came up with was to insert a piece of SS into each port of the cross over. If I recall, it was .062" thick. I can go over that again if needed, but here I believe the question is an extra piece of 'insurance' placed over the head's heat port. What I used was .020" SS cut big enough to insure the port was completely covered, but not so big it would cause a leak at the intake port. I trimmed the paper gasket opening so the insert fitted within it. This was held in place with Permatex 2, but other suitable gasket sealer will work.
As Don says, glue it in place with the gasket. It's just to make sure it doesn't move and cause an issue with head/intake sealing.
I didn't take any pictures of that I'm afraid, but I can repost pics of the intake if required.
EDIT: I think I also mentioned before that I gently, repeat, gently flattened the embossing around the valley pan cross-over ports to make sure there was no interference due to the slightly thicker .020" SS compared with the paper gasket used.
If one is NOT using the valley pan but with thicker intake to head gaskets, size the SS plugs thickness accordingly. Hope that makes sense.

 

[Q1SVT]

FYI, .018 thick anything is going to get you in trouble... no need to use SS, Al melts @ over 1200*, it will never see that temperature .

Old days we used a thin piece of a beer can... last time I just used heavy duty Aluminum foil [kitchen use] sprayed a little permatex on the Al and stuck it to the gasket. Or use very thin shim stock.

You are planing to use a gasket [not the turkey pan] and most if not all block the crossover. As stated place the material between the head and gasket

jm2c

 

[Stanglover]

FYI, .018 thick anything is going to get you in trouble... no need to use SS, Al melts @ over 1200*, it will never see that temperature .

Old days we used a thin piece of a beer can... last time I just used heavy duty Aluminum foil [kitchen use] sprayed a little permatex on the Al and stuck it to the gasket. Or use very thin shim stock.

You are planing to use a gasket [not the turkey pan] and most if not all block the crossover. As stated place the material between the head and gasket

jm2c

FYI, I used .020" SS because that is what I had on hand and besides, I usually ere on the side of caution. With the block off plates installed in the manifold, this was just a bit of extra precaution. The intent here was to post what I personally did on my engine to cut the excessive heat under the carb and it works fine, but I understand your point too. Actually, and I'm not 100% sure, but isn't there a gasket made for this purpose with a metal insert? I thought I read that somewhere.

 

[Q1SVT]

Sorry Stanglover... was not referring to your comment...

Was to OP

I have a 0.018 sheet of stainless steel that I am planning on cutting to place between the intake and heads, which brings up the question of either placing the SS sheet between the intake manifold and gasket or between the gasket and heads

 

[Big Red Mach 1]

I did it and used .125 SS on my Blue Thunder intake which was way too thick, and a pain in the butt to cut. Should have used .062

 

[tony-muscle]

I did it and used .125 SS on my Blue Thunder intake which was way too thick, and a pain in the butt to cut. Should have used .062

Did you have any issues with leakage?

 

[71ProjectJunk]

FYI, I used .020" SS because that is what I had on hand and besides, I usually ere on the side of caution. With the block off plates installed in the manifold, this was just a bit of extra precaution. The intent here was to post what I personally did on my engine to cut the excessive heat under the carb and it works fine, but I understand your point too. Actually, and I'm not 100% sure, but isn't there a gasket made for this purpose with a metal insert? I thought I read that somewhere.

Have you taken the intake off after you did this to see if the block off plates survived? I remember trying this on a Chrysler 440, that uses a valley pan tray on the intake. I took an old valley pan tray and cut two pieces of it and used them to block off the heat crossover passages. When at a later date, I took the intake off they had melted away, LOL. They did not survive the heat. I was wondering if the Stainless Steel pieces you used have survived.

 

[Stanglover]

Have you taken the intake off after you did this to see if the block off plates survived? I remember trying this on a Chrysler 440, that uses a valley pan tray on the intake. I took an old valley pan tray and cut two pieces of it and used them to block off the heat crossover passages. When at a later date, I took the intake off they had melted away, LOL. They did not survive the heat. I was wondering if the Stainless Steel pieces you used have survived.

No, I haven't needed to remove the intake since it was reinstalled (after the rubber end seals leaked) back in 2016. My best guess is at least the 1/16" thick block-off plates are still good and the .020" SS are probably still there. I'm not about to remove the intake to see either!!
Being that the reason I did this was to lower the heat under and around the carb, I have not had a recurring issue with that, so I can only deduce all is still good.
My first attempt and thought was just to block off the two holes under the carb, which was achieved with a couple of 5/16" set screws, screwed in. That helped, but the block off plates worked better.

 

[c9zx]

SCE gaskets and Mr. Gasket both sell intake gaskets with blocked heat crossover. I confirmed several years ago that the gasket will not burn through at the heat crossover. Chuck

 

[tony-muscle]

I think part of the problem is to only focus on the melting point of the metal. We need to look at the strength of the material over temperature. While aluminum (beer can or turkey pan) will melt near 1200F, it had lost most of its strength at about 500F (depending on which alloy). Therefore a thin sheet of aluminum may bent very easily over time, and loose seal, as the exhaust temperatures are reached. On the other hand SS will hold much better at those high temperatures.


https://burnsstainless.com/blogs/articles-1/yield-strength

 

[basstrix]

I've done this several times. I used to have several of the block-offs around...one set is on my 460 and I have one spare.... They came with new intakes I had bought a long time ago. The ones I've used are plain steel and measure .015 thick. I've always placed them between the head and the gasket with a small dab of permatex on a couple of corners just to hold it in place.

I recommend installing the intake without any gaskets and checking the gap at top and bottom with a feeler gauge. Ideally, you want line to line between both heads and intake but you probably won't get that. I don't know what the limit is for out of square, but I'd guess no more than .010.

 

[tony-muscle]

I recommend installing the intake without any gaskets and checking the gap at top and bottom with a feeler gauge. Ideally, you want line to line between both heads and intake but you probably won't get that. I don't know what the limit is for out of square, but I'd guess no more than .010.

Good idea, but how do you access the bottom of the intake to measure the gap? Should I use some type of clay?

 

[Stanglover]

SCE gaskets and Mr. Gasket both sell intake gaskets with blocked heat crossover. I confirmed several years ago that the gasket will not burn through at the heat crossover. Chuck

Good to know Chuck, thanks for that info.

 

[Stanglover]

I think part of the problem is to only focus on the melting point of the metal. We need to look at the strength of the material over temperature. While aluminum (beer can or turkey pan) will melt near 1200F, it had lost most of its strength at about 500F (depending on which alloy). Therefore a thin sheet of aluminum may bent very easily over time, and loose seal, as the exhaust temperatures are reached. On the other hand SS will hold much better at those high temperatures.


https://burnsstainless.com/blogs/articles-1/yield-strengthView attachment 62042

Thank you Tony.