Heat Riser Block off plate...

[Millardo]

I posted about this earlier, but now I'm in assembly phase.

The heat riser in my 1F 1972 exhaust manifold essentially does not exist. The butterfly flapper is long gone and the rest of the mechanism corroded beyond use. I understand why it was there originally.

Has anyone had a problem cracking the intake manifold without the use of this heat riser valve/flapper?

I see a block off plate was used after 1975.

Is it worth fabbing a plate? If I did, it would need a gasket top and bottom of the plate, and then I don't believe the manifold ears will line up.

I know with a plate it would be harder to warm up, but I don't live in a cold climate. And this 40 is a sunny Sunday cruiser...

I'm trying to find comfort in not going to the trouble to fab a plate.

Anyone? Thanks in advance!

 

[Millardo]

Anybody?

 

[Pighead]

It seems to me that it was the later model intake manifolds that needed the block-off plate to protect them from the higher heat from the later exhaust manifolds...
I have not of too many early intake manifolds cracking from loss of the butterfly flapper. Good luck, YMMV.

 

[Millardo]

It seems to me that it was the later model intake manifolds that needed the block-off plate to protect them from the higher heat from the later exhaust manifolds...
I have not of too many early intake manifolds cracking from loss of the butterfly flapper. Good luck, YMMV.

Thanks Pighead. That's what I was hoping to hear. The machinist suggested tack welding a butter-fly-like piece in the neck of the exhaust manifold. So as to be a permanent redirection of the exhaust off the bottom of the intake manifold.
He's not a LandCruiser guy, but a very experienced 6 cylinder machinist.

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[Millardo]

Thanks Pighead. That's what I was hoping to hear. The machinist suggested tack welding a butter-fly-like piece in the neck of the exhaust manifold. So as to be a permanent redirection of the exhaust off the bottom of the intake manifold.
He's not a LandCruiser guy, but a very experienced 6 cylinder machinist.

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Has anyone done this?

 

[Fast Eddy]

I wouldn't put anything in there. There's plenty of heat flowing around inside there, IMO.

 

[SteveH]

I would follow your machinists direction on this. I have had a '78 intake manifold crack. I'm not sure a more effective heat plate would have stopped it, but who knows. To me, anything that can direct heat away from the carburetor (in any way possible) is a good thing.

 

[Millardo]

I would follow your machinists direction on this. I have had a '78 intake manifold crack. I'm not sure a more effective heat plate would have stopped it, but who knows. To me, anything that can direct heat away from the carburetor (in any way possible) is a good thing.

Thanks SteveH. I went round and round with this. But finally told the machinist to go ahead. It will simply be a 3/16 steel piece meant to deflect heat exhaust away from the bottom of the intake manifold. Guess I will be the ginny pig on this idea...
I will post a follow up, so as to be a complete thread for future interest to others.

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[antFJ]

Just a thought.. Could you machine a little off the mating surface where it meets the bottom of the intake and replace the now missing material with your own custom block off plate?

 

[Millardo]

Just a thought.. Could you machine a little off the mating surface where it meets the bottom of the intake and replace the now missing material with your own custom block off plate?

You could certainly do that, and we spoke of it. But we decided the plate would be so close to the bottom of the intake, that you probably wouldn't get a great benefit. And we know that the original flapper set up works when intact. So we'll just duplicate the flapper shape, and make it permanent.
It will take longer to warm up, but shes a summer driver in SoCal.

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[Spike Strip]

On mine I just locked the heat riser in the open position (warm) against the block-off plate, per the recommendation of my machinist, who is a cruiser guy. Been working fine. Warm ups? I'm in the SFV so don't worry about it.

Frankly, I'd be more worried about no roll bar... Even though it's a Sunday-go-to-breakfast cruiser.

 

[Millardo]

On mine I just locked the heat riser in the open position (warm) against the block-off plate, per the recommendation of my machinist, who is a cruiser guy. Been working fine. Warm ups? I'm in the SFV so don't worry about it.

Frankly, I'd be more worried about no roll bar... Even though it's a Sunday-go-to-breakfast cruiser.

I know what you're saying about the roll bar. I have a perfect, pads intact, factory '74 roll bar and short jump seats for that year. But in the end I decided it was more valuable to stay completely original. The wheels will be grey soon and front bumper replaced. Then the only non-original will be the suspension and tires. And if I can't get the ride to smooth out, the springs will be going back to stock as well.

Thanks for your comments.

 

[Millardo]

 

[Fast Eddy]

finally told the machinist to go ahead. It will simply be a 3/16 steel piece meant to deflect heat exhaust away from the bottom of the intake manifold.

You'll need to diagram this so it can be understood.

But we decided the plate would be so close to the bottom of the intake, that you probably wouldn't get a great benefit.

The air gap is plenty. Dual pane windows in your house work ok? If you're trying to increase the life of the intake, this is the way to go. My '78 has this plate and it does take a bit longer to warm up. I've been running the restored setup with the SOR plate and the original CA Thermal Reactor (TR) manifold for about six years so far.

we know that the original flapper set up works when intact. So we'll just duplicate the flapper shape, and make it permanent.

The original flapper, as you're implying, makes it warm up faster by increasing the hot gas pressure until the manifolds are warm, controlled by the bi-metal spring holding the flapper shut.

The flapper does nothing to protect the intake once it's warm. Putting it in there permanently is just adding to your back pressure a little and will actually cause the intake to remain a bit hotter all the time.

 

[Millardo]

You'll need to diagram this so it can be understood.



The air gap is plenty. Dual pane windows in your house work ok? If you're trying to increase the life of the intake, this is the way to go. My '78 has this plate and it does take a bit longer to warm up. I've been running the restored setup with the SOR plate and the original CA Thermal Reactor (TR) manifold for about six years so far.



The original flapper, as you're implying, makes it warm up faster by increasing the hot gas pressure until the manifolds are warm, controlled by the bi-metal spring holding the flapper shut.

The flapper does nothing to protect the intake once it's warm. Putting it in there permanently is just adding to your back pressure a little and will actually cause the intake to remain a bit hotter all the time.

Son of a ****!

NOW I think I get it. So you're implying on start up, the "flapper" is closed causing increased hot gas pressure, thus heating the intake manifold. When hot, the bi-metal spring opens the "flapper" reducing hot gas pressure. And that this is the position meant for normal operation.

I have been thinking just the opposite.

Tell me I have it correct please. I will not make a permanent flapper if that's the case. I need to make a phone call to the machinist!

 

[Pighead]

Relax. I think Eddy has it backwards. On these F engines anyway, without the thermo-nucular exhaust manifold, the flapper is open when cold, allowing hot exhaust gasses to hit the ceiling of the exhaust manifold, which is also the floor of the intake manifold...when everything is warm, the flapper, theoretically, would close to prevent the intake from getting too hot.
I've cracked a couple '74 exhaust manifolds in the 25 years I've had this Pig, but I've never seen a F intake manifold crack under the carb. I've seen plenty of 2F intake manifolds crack there.

 

[Pighead]

WTF have you been smoking Eddy?

The original flapper, as you're implying, makes it warm up faster by increasing the hot gas pressure until the manifolds are warm, controlled by the bi-metal spring holding the flapper shut.

The flapper does nothing to protect the intake once it's warm. Putting it in there permanently is just adding to your back pressure a little and will actually cause the intake to remain a bit hotter all the time.

 

[Millardo]

Relax. I think Eddy has it backwards. On these F engines anyway, without the thermo-nucular exhaust manifold, the flapper is open when cold, allowing hot exhaust gasses to hit the ceiling of the exhaust manifold, which is also the floor of the intake manifold...when everything is warm, the flapper, theoretically, would close to prevent the intake from getting too hot.
I've cracked a couple '74 exhaust manifolds in the 25 years I've had this Pig, but I've never seen a F intake manifold crack under the carb. I've seen plenty of 2F intake manifolds crack there.

Okay, this is from the repair manual. It seems strange that it reads, "As the engine warms up, the heat control valve coil closes the valve and directs the exhaust gases away from the intake manifold." Okay, got it...

BUT then says, "If the valve is stuck in closed position, the intake will be subject to excessive heat..."
Anyway, given that it's a 1F, I'm going to leave it with no flapper. Because I need to move on.

Pighead, doesn't the manual read strange to you.?

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[Millardo]

Pighead, are you out there?

 

[Fast Eddy]

Pighead, are you out there?

I sent him some of what I've been smoking, so he won't be around for a day or so.

He is, indeed, correct. I was talking about a 2f manifold where the flapper is down in the pipe, not up in the top by the "entrance" to the intake. It's closed when cold and open when hot. The diagram and instructions from the 1f version makes it very clear.

Now I remember seeing a 1f manifold at a swap meet before with the big flapper up there. I think if I was going to have the flapper in there, I'd get it all right with the working spring, etc.