Can we make a exhaust/intake manifold sticky?

Spike Strip

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The block off plate was intended as a seal for a cracked intake, to prevent vacuum leak, or as a guard against the possibility of the intake crackling.

Mine was done with the flap locked in the hot position, but you still have to cut off the top of the flap for the plate to seat properly. I thought it seemed kind of restrictive at the time, but MAFs machinist was doing the work and it was a first for him too. We thought that was the best way to do it, then.

**Edit: just remembered since it was over 10 years ago. Had to keep the appearance of the thermoflap to be able to pass California visual smog inspection. That still applies.****

Doing it today, I would absolutely remove the flap entirely and have the holes sealed and no plate, provided your intake has never cracked. Much more free flowing and still heat the intake.
 
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reddog90

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@OSS @Spike Strip What is the downside of using the block off plate? It seems like the intake would still heat up, although slower, and the block off plate would either prevent a crack from happening in the future or create a dead end for a crack that appears? And if the original design intent of the heat control valve was to direct heat away from the heat riser once it reached a certain temperature, why would we want to remove the heat control valve and also not use a heat riser block off plate? That seems like it would be more prone to causing a cracked intake at some point?

@Spike Strip, it doesn't look like I would have to trim my flapper plate to reassemble it in the hot position with a heat riser block off plate? It also looks like I could just grind down the spot welds on the heads of the small bolts holding the flapper plate to its shaft and just remove the plate. That seems easier than removing the entire heat assembly and then plugging holes left behind.

PuuwahE.jpg
 

roadstr6

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@OSS @Spike Strip What is the downside of using the block off plate? It seems like the intake would still heat up, although slower, and the block off plate would either prevent a crack from happening in the future or create a dead end for a crack that appears? And if the original design intent of the heat control valve was to direct heat away from the heat riser once it reached a certain temperature, why would we want to remove the heat control valve and also not use a heat riser block off plate? That seems like it would be more prone to causing a cracked intake at some point?

@Spike Strip, it doesn't look like I would have to trim my flapper plate to reassemble it in the hot position with a heat riser block off plate? It also looks like I could just grind down the spot welds on the heads of the small bolts holding the flapper plate to its shaft and just remove the plate. That seems easier than removing the entire heat assembly and then plugging holes left behind.

PuuwahE.jpg
You can do it that way, sure. But be aware that the bushings on either side of the shaft can (and sometimes do) leak. I believe the shaft rides on bronze inserts that, over time, waggle out and create a leak. The one on my 55 leaked from the rear bushing. The only way to be 100 percent sure you 'll never have a leak is to remove the shaft, tap the holes on either side and install set screws or bolts to block them off.
 
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When I did my manifold overhaul I removed my broken flapper plate and then welded the pivot holes closed. Abs I have a block off plate in there.
 
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LazarusTaxa

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Just my opinion, but I would definitely remove the flapper, bolt or weld the holes shut, and put in a block off plate. It's not an important thing to have, with very little to gain and quite a bit to lose (leaky exhaust and cracked intake).
 

OSS

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The way I understood it is the Heat Control flapper valve’s primary purpose is to quickly heat up the intake manifold when engine is cold by directing exhaust up into the intake manifold.
Then when the flapper’s bimetal valve heats up and twists the flapper’s shaft, the flapper for the most part is rotated into an orientation that stops directing the exhaust up into the manifold.

If you look at the drawing in the manual, you can see that there’s still a fairly large air passageway up to the intake manifold when the flapper is in the Hot position.
The flapper doesn’t completely redirect the hot air down into the exhaust pipe, only encourages it to do so.
If a block off plate completely separates the two manifolds, the intake manifold likely will always be cooler than ideal for optimal performance.

That’s not to say that the block off plate is bad, since the engine clearly will run with one, but it’s not ideal in cooler climates.

The belief is: the intake can crack because sometimes the Heat Control valve stays stuck in the cold position

F91C4AEB-7BED-4337-AE25-F44E18B8D187.jpeg
 

reddog90

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Anyone know how to remove the bushings that the flapper shaft rides on? I think I'm going to remove the bushings and drive in expansion plugs to block off those holes.
 

g-man

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@OSS @Spike Strip What is the downside of using the block off plate? It seems like the intake would still heat up, although slower, and the block off plate would either prevent a crack from happening in the future or create a dead end for a crack that appears? And if the original design intent of the heat control valve was to direct heat away from the heat riser once it reached a certain temperature, why would we want to remove the heat control valve and also not use a heat riser block off plate? That seems like it would be more prone to causing a cracked intake at some point?

@Spike Strip, it doesn't look like I would have to trim my flapper plate to reassemble it in the hot position with a heat riser block off plate? It also looks like I could just grind down the spot welds on the heads of the small bolts holding the flapper plate to its shaft and just remove the plate. That seems easier than removing the entire heat assembly and then plugging holes left behind.

PuuwahE.jpg

I opted to rotate my flapper valve to the "hot" position and pin it there with the block off plate and gaskets on either side. In the "hot" position it diverts exhaust air downward and out. That is what you want. Once you pin it there by sandwiching the intake to the exhaust and bolting it. It can't flip back to the cold position because it is bumping the block off plate. You could trim the flapper so it will still rotate but do you really need the intake to warm up quickly? And if you trim it then less plate there to divert hot air downward.

BTW...peening with a ball peen hammer while heating with a torch is an excellent way to remove the rest of that metal gasket material on your manifold.
 

reddog90

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Generally those are drilled, tapped and closed with an appropriate threaded plug.

Edit: I would worry about an expansion plug coming out due to heat cycling.
How do I turn a tap in those bushings? Only thing I can think of is to use a socket that fits over the end of the tap and a long extension to clear the end of the manifold and turn it with a ratchet.
 

FishTacos

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How do I turn a tap in those bushings? Only thing I can think of is to use a socket that fits over the end of the tap and a long extension to clear the end of the manifold and turn it with a ratchet.
Carefully, after drilling the hole and (ideally) using a sized ream to make the hole the proper size. Or just the right drill bit. And oil. And being extra careful. Or maybe with a vice grip. But, again, carefully.
 

Spike Strip

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If you have to buy a large drill bit and tap (the way I would do it) it might be more cost effective to just take to a machine shop and ask them to do it and provide the proper tapered plug they thread the hole for. Should be inexpensive and quick for a shop.
 

FishTacos

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If you have to buy a large drill bit and tap (the way I would do it) it might be more cost effective to just take to a machine shop and ask them to do it and provide the proper tapered plug they thread the hole for. Should be inexpensive and quick for a shop.
That's a really good point.

If you don't have those tools it will probably save you money to farm that out.
 

reddog90

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Generally those are drilled, tapped and closed with an appropriate threaded plug.

Edit: I would worry about an expansion plug coming out due to heat cycling.
Don't expansion plugs perform well through heat cycling?

I called about a dozen machine shops this morning, only one would look at it. They just called back and said they don't have a way to hold the manifold correctly to tap it and they're concerned about breaking off taps in the cast iron. There's another one half an hour away I can try tomorrow, just have to find the time to get down there for them to see it.
 

reddog90

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Two more machinist said no after seeing it in person yesterday. Found an old school guy that does a little of everything today and he’s going to machine tapered plugs to fit the holes and weld them in place. Hopefully it doesn’t crack.
 

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