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56 choke thermostat tube issue


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Now the carb is running and the choke set. I am hooking up the thermostat tube that runs from the exhaust manifold to the thermostat housing. The housing is pulling vacuum from the tube but from what I can see the hole where the tube inserts is blocked off - meaning the vacuum cannot pull hot exhaust from the manifold through the tube and into the housing to move the thermostat coil. Attached is a photo of the tube going to the manifold ... is this the correct location? If so then why would it be blocked?

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It should not be blocked unless someone did it on purpose, who just wanted to eliminate the choke heat tube after it rusted off and didn't want an exhaust leak.  I pulled one that I have on my shelf now that somebody did that with.

 

Yank or drill it out and replace the tube that runs through the manifold.  It's most likely rusted out inside the manifold.

Edited by lancemb (see edit history)
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Just to be clear, the choke does not draw exhaust, that would destroy it. It draws clean air heated by the exhaust. If exhaust is getting in the tube, you will need to take care of that.

 

The pictures don't show enough for me to tell, but on some engine designs the tube runs clear through manifold and exits the other side. That way, there is exhaust heating the outside of the tube, and hot fresh air inside the tube for the choke. On some other engine designs, there is just a cast iron fresh air chamber in the manifold that gets hot from exhaust on the other side of the cast iron.

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Another photo showing the hole the existing tube sits in. Feeling around with a dental pick, it definitely feels like a blind hole. And there is no hole directly on the other side of the manifold. There is a hole at 90° to this blind hole. It directly faces the dipstick and engine block and is difficult to access but using a piece of wire I can tell it goes in  fair way. It is certainly likely these holes could meet up but again the hole that the existing tube is sitting in, is blocked.

 

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I am very familair with 57-58 design, and am guessing 56 was same way.  As bloo stated, the tube is meant to go all the way across the manifold, not letting exhaust gas in.  As one can imagine, they rust out easily.  When this happens it's better to block it off then leave it be.  Even better, replace the tube.

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3 hours ago, 56 Buick said:

Hi John, when you say 'back side' do you mean where the arrow is on the attached photo?  The arrow shows the location of a port or hole where the hole opening faces the engine. Thanks

 

location - Copy.jpg

 

Went through this on both a 55 and a 56. The arrow above is the correct side where the heat chamber is.  If you stand at the passenger fender facing the passenger bank of the engine, the port that the carbs heat pipe plugs into is almost directly behind the leftmost (nearest the firewall) bolt that attaches the exhaust manifold to the cylinder head.  Now - assuming all the passenger side 56 manifold designs are the same for this feature, just feel around the back left side of the manifold and you should feel a small pipe about 1/8-1/4 inch sticking out.  I believe the heat passage is fully cast into the 56 manifold.  The chamber does not allow exhaust gas to enter, rather pulls air across some risers cast inside the manifold that act as a heat exchanger.  On the 55 manifold (mine at least - early 55), there was a metal plate riveted over the top of the chamber which disintegrated over time.  WIth that plate gone you could see the inside the chamber = the cast "risers" that the outside air was pulled across to warm the outside air to the choke. 

 

Where the pipe is in your photograph looks more like something that was drilled pr a casting hole to accommodate the pipe.  On my 55 manifold, since the heat exchanger was useless without a cover and the nipple to attach the heat tube to also gone,  a heat stove "kit" was installed into the manifold - basically a bolt that has about 1/4 - 1/2 inch hollowed out in it that threads and seals into a hold drilled into and through one wall of the manifold.  The carb heat tube sits inside that hollowed out bolt section.  Not original but worked great and the choke opened up quick.  No running issues.  So the way the heat tube is sitting in your original picture reminded me of that. 

 

The heat tube routes from the carburetor alongside the inside back of the valve cover, follows the block down near the oil pressure line and connects unseen behind the exhaust manifold.  When I switched to the 56 motor I made it a point to remove my earlier fix and return it to proper configuration.  Looks better too.

 

Pictures below courtesy of eBay. Look to far left of the manifold you can see the pipe sticking out. The hole in the middle near that square feature below looks like where your inlet pipe is setting. 

 

image.thumb.png.fa7db8e92bc0bf84f4c19ab745a7b0c2.png

image.png.1bcf4f9ce091b56137b5cbccf7bf7c00.png

 

The car was just running today so its uncovered and accessible - could probably snap a pic if you really need it.  Hope this helps.

 

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Check out the thread "Vacuum Line routing to choke" from two weeks ago in this same forum category, bought the kit from CARs, flared one end, bent the other end around so it slipped into that inside manifold nipple then simply bent it toward the choke, slid on provided insulation, screwed the brass nut on the choke threads, easy! had what appeared to be plumbers putty plugging up the hole, it dug out easily when I did the carb rebuild. 
couldn't figure out how to gather the frayed insulation ends, thus the tape for now 

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CAC407EF-BC29-430B-A1EF-5AAB475EB88E.jpeg

Edited by jw1955buick (see edit history)
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FYI after some investigation I have found that the other side, of the tube sitting out at the rear of the exhaust manifold, is actually the hole in the centre of the manifold that faces the engine block (see arrow in photo within previous post above). I have now bent my existing tubing to run from this hole up to the choke thermostat housing. Appears to operate the choke thermostat but the tube certainly gets hot. Is there a danger of overheating the carburettor with these thermostat tubes?

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To clarify, here is a pic showing the tube path on a 57 manifold.  The 56 manifold uses the exact same tube, through at least 59 (and I think 60).  The pencil shows the path of the tube and you can see it sticking out on the bottom.  The other pic is of the tube itself when not installed (an NOS example).

20200105_141153.thumb.jpg.026f0da307bf1491400f98047a03d5c2.jpg

 

20200104_213317.thumb.jpg.b79dbfb22608f8d2a1ab125963ab54cd.jpg

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19 minutes ago, 56 Buick said:

Just for info, how hard are those tubes to pull if they were to be replaced?

Easy.  You can just drill out both ends and it will then be loose.  You can then fish it out pretty easily.  It's easy to make your own, too.

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54 minutes ago, lancemb said:

Easy.  You can just drill out both ends and it will then be loose.  You can then fish it out pretty easily.  It's easy to make your own, too.

 

I just looked at my spare '56 manifold and saw that tube, just like you said.  However, the end of the tube is plugged just like @56 Buick said.  That hole on the engine side does appear to be the air inlet, but the tube appears to be solid.  So I am wondering if the tube is perforated in the area underneath the label.  If not then how does the air get drawn into the tube to be heated?

 

 

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39 minutes ago, JohnD1956 said:

 

I just looked at my spare '56 manifold and saw that tube, just like you said.  However, the end of the tube is plugged just like @56 Buick said.  That hole on the engine side does appear to be the air inlet, but the tube appears to be solid.  So I am wondering if the tube is perforated in the area underneath the label.  If not then how does the air get drawn into the tube to be heated?

 

 

 

The air does not need to get drawn up the tube to the choke. The  tube itself slowly gets warm allowing the choke coil to slowly warm until it kick down the high idle cam.   If direct smoldering hot exhaust was pushing up that tube the plastic choke cover and probably the housing would melt 

Edited by avgwarhawk (see edit history)
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42 minutes ago, JohnD1956 said:

 

I just looked at my spare '56 manifold and saw that tube, just like you said.  However, the end of the tube is plugged just like @56 Buick said.  That hole on the engine side does appear to be the air inlet, but the tube appears to be solid.  So I am wondering if the tube is perforated in the area underneath the label.  If not then how does the air get drawn into the tube to be heated?

 

 

The tube is not perforated (that would be bad, to draw in exaust) and goes all the way through like a straw.  If yours is plugged, it shouldn't be.  It should draw in fresh air through the bottom.

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16 minutes ago, avgwarhawk said:

 

The air does not need to get drawn up the tube to the choke. The  tube itself slowly gets warm allowing the choke coil to slowly warm until it kick down the high idle cam.   If direct smoldering hot exhaust was pushing up that tube the plastic choke cover and probably the housing would melt 

Hmmmm if I disconnect the tube on my engine then the choke thermostat housing is definitely pulling a vacuum through the tube attachment, so it appears that when the tube is attached then it will be pulling hot air. My choke thermostat housing cover is metal.

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56 minutes ago, 56 Buick said:

Hmmmm if I disconnect the tube on my engine then the choke thermostat housing is definitely pulling a vacuum through the tube attachment, so it appears that when the tube is attached then it will be pulling hot air. My choke thermostat housing cover is metal.

 

If I'm not mistaken the vacuum is present in the choke housing to open the butterfly valve. There is a passage with piston type set up that opens the butterfly valve. 

Note the cylinder shape inside the choke housing with a arm attached. This operates the butterfly valve via vacuum as I understand it. 

 

Q1222-w600-2l.jpg

Edited by avgwarhawk (see edit history)
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21 minutes ago, avgwarhawk said:

 

If I'm not mistaken the vacuum is present in the choke housing to open the butterfly valve. There is a passage with piston type set up that opens the butterfly valve. 

Note the cylinder shape inside the choke housing with a arm attached. This operates the butterfly valve via vacuum as I understand it. 

 

Q1222-w600-2l.jpg

I believe you are correct but I am sure I can feel suction at the point where tube attaches to the choke thermostat housing cover plate.

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48 minutes ago, 56 Buick said:

I believe you are correct but I am sure I can feel suction at the point where tube attaches to the choke thermostat housing cover plate.

 

I'm sure you do as this port is now open and free to pull vacuum. When the tube is attached to choke housing and the other end is plugged into the manifold dead end a open vacuum source is now eliminated. 

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in section 3A, page 3-5 there is a description of the right side exhaust manifold.  It says, in part,  the carburetor choke heat stove consists of an  alloy steel heating tube mounted in a drilled hole in the manifold and a heating chamber "located on the outside of the manifold".  So it would appear that the hole in the center of the manifold (on the engine side) is an opening into the heating chamber.   

section -3-16 sub section a: describes the choke system for the Carter 2 bbl.  It says, in part,  that there are two slots in the choke piston cylinder that allow vacuum to draw heated air up from the choke heat stove, and around the thermostatic spring, past the piston , and into the intake manifold. 

In section 3-20 sub section g: the manual says that except for some minor details of construction, the choke on the Carter 4 bbl is identical to the choke on the Carter 2 bbl.

For the Stromberg carb, in section 3/23, subsection h: it says there is no vacuum employed in that carb's choke system. The choke is controlled manually. 

Then in section 3-28 sections a and 😄 it talks of the Rochester 4 bbl choke using vacuum for the piston and "restrictions"  'in the choke housing  are the source of the vacuum to draw air through the choke heat stove. 

 

What is not in the book ( that I can find) is talk of the plug in the end of the alloy metal heat tube.  But on my spare manifold it looks for certain that this was a factory plug.  Maybe a stainless steel ball.  I will try to get some good pictures of that tomorrow but I wonder if that ball is there to slow the air flow in the heat tube in the choke stove system.  Perhaps to prevent the choke from opening fully too soon?  At any rate, the one I can look at does not appear to be merely a plug from a rotted tube.  

 

@56 Buick If you hooked your choke heat riser to that hole in the center of the manifold, then I think that is incorrect. But it may work okay.  I can't imagine either port would result in a hotter air temp in the choke stove system.   However, on my car, the heat riser pipe runs from the choke housing down to the manifold, then turns to run parallel with the inside edge of the valve cover to the rear of the engine.  Then loops around the back of the head and comes forward to connect to the alloy metal heat tube at the rear of the exhaust manifold. 

 

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25 minutes ago, JohnD1956 said:

in section 3A, page 3-5 there is a description of the right side exhaust manifold.  It says, in part,  the carburetor choke heat stove consists of an  alloy steel heating tube mounted in a drilled hole in the manifold and a heating chamber "located on the outside of the manifold".  So it would appear that the hole in the center of the manifold (on the engine side) is an opening into the heating chamber.   

section -3-16 sub section a: describes the choke system for the Carter 2 bbl.  It says, in part,  that there are two slots in the choke piston cylinder that allow vacuum to draw heated air up from the choke heat stove, and around the thermostatic spring, past the piston , and into the intake manifold. 

In section 3-20 sub section g: the manual says that except for some minor details of construction, the choke on the Carter 4 bbl is identical to the choke on the Carter 2 bbl.

For the Stromberg carb, in section 3/23, subsection h: it says there is no vacuum employed in that carb's choke system. The choke is controlled manually. 

Then in section 3-28 sections a and 😄 it talks of the Rochester 4 bbl choke using vacuum for the piston and "restrictions"  'in the choke housing  are the source of the vacuum to draw air through the choke heat stove. 

 

What is not in the book ( that I can find) is talk of the plug in the end of the alloy metal heat tube.  But on my spare manifold it looks for certain that this was a factory plug.  Maybe a stainless steel ball.  I will try to get some good pictures of that tomorrow but I wonder if that ball is there to slow the air flow in the heat tube in the choke stove system.  Perhaps to prevent the choke from opening fully too soon?  At any rate, the one I can look at does not appear to be merely a plug from a rotted tube.  

 

@56 Buick If you hooked your choke heat riser to that hole in the center of the manifold, then I think that is incorrect. But it may work okay.  I can't imagine either port would result in a hotter air temp in the choke stove system.   However, on my car, the heat riser pipe runs from the choke housing down to the manifold, then turns to run parallel with the inside edge of the valve cover to the rear of the engine.  Then loops around the back of the head and comes forward to connect to the alloy metal heat tube at the rear of the exhaust manifold. 

 

My car definitely does not have any restriction or ball sitting in the end of the alloy tube. I know that if I blow compressed air into the alloy tube then it comes out of what now appears to be the heat chamber. Which is where I have the stove pipe inserted. 

 

In comparison to your setup, I guess that with my setup it is possible the stove pipe could be hotter (at the choke thermostat) given it has less distance to travel to the choke thermostat.

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Sounds like the issue is whether the alloy tube end (where the choke stove pipe is usually attached) should be blocked. So that the stove pipe is not necesaarily drawing heated air but rather just heat?

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13 hours ago, 56 Buick said:

Sounds like the issue is whether the alloy tube end (where the choke stove pipe is usually attached) should be blocked. So that the stove pipe is not necesaarily drawing heated air but rather just heat?

 

Does  draw heated   air as the end does not access the inside of the exhaust manifold from my understanding.  The air inside the enclosed tube gets hot as well as the tube itself.  It takes time for the heating to occur so the engine will stay at high idle thus warming faster.  If direct flaming hot exhaust were to travel that tube the choke coil would unload the fast idle cam  much to quickly.   

Edited by avgwarhawk (see edit history)
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On 1/5/2020 at 4:19 PM, lancemb said:

To clarify, here is a pic showing the tube path on a 57 manifold.  The 56 manifold uses the exact same tube, through at least 59 (and I think 60).  The pencil shows the path of the tube and you can see it sticking out on the bottom.  The other pic is of the tube itself when not installed (an NOS example).

20200105_141153.thumb.jpg.026f0da307bf1491400f98047a03d5c2.jpg

 

20200104_213317.thumb.jpg.b79dbfb22608f8d2a1ab125963ab54cd.jpg

 

 

Best description here.  The long pipe in the second picture. runs directly through the manifold at the angle shows with the red pencil pictured.  Hot exhaust flows around this tube heating the air the fresh cool air that is being drawn in from one end, out the other and up the tube to the choke housing. 

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15 hours ago, 56 Buick said:

Sounds like the issue is whether the alloy tube end (where the choke stove pipe is usually attached) should be blocked. So that the stove pipe is not necesaarily drawing heated air but rather just heat?

 

Not to belabor this, but just to clarify:   I am not saying there is, or should be,  a restriction at the end where the upper tube attaches to the exhaust manifold, which appears to be this end:

DSC00309.JPG.7b8ca80e38d277a274efaf81e6460602.JPG

 

Instead, the opposite end of this lower tube as shown here:  DSC00307.JPG.519d4ec89a129de4879328daf76e50f1.JPG

 

This end of the tube is capped off.  I scraped it to make sure it was a plug and not just some debris.  At first I thought maybe this was a ball bearing intended to block part of the opening to cause a restriction.  I now see it is a solid end and it appears impossible that air could be drawn into the lower tube at this location.   

 

A probe in the hole in the center of the manifold ( the hole just below the letter M in the word Workmate) showed that this is a chamber of sorts, not just a piece of tubing itself:

 

DSC00308.JPG.fbad5648a33c4e4a863247186d92bad9.JPG

 

And one can see the subject tube inside the manifold running from the last port to the area where the plug is.  

 

So my original comment was, if this lower tube is plugged, and it seems to be plugged from the factory, then how does the vacuum draw air into the lower tube?  That's why I thought the tube Lance showed may have had perforations under the label.  That labeled area appears to fall inside the chamber behind the center hole. And that would be consistent with the description in the manual saying that the choke stove chamber is outside the exhaust port area.  And if 56 Buick blew compressed air into the exposed part of the lower tube and the air exited from the center hole than obviously there has to be a perforation in the lower tube to allow that (or he just blew a hole in it by trying).  

 

At any rate, I would definitely agree that one does not want exhaust gases inside the choke housing.  

DSC00303.JPG

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16 hours ago, JohnD1956 said:

Not to belabor this, but just to clarify:   I am not saying there is, or should be,  a restriction at the end where the upper tube attaches to the exhaust manifold, which appears to be this end:

DSC00309.JPG.7b8ca80e38d277a274efaf81e6460602.JPG

Okay, this is the same as mine where this end of the tube is clear and outside air can be drawn into the alloy tube .

 

16 hours ago, JohnD1956 said:

Instead, the opposite end of this lower tube as shown here:  DSC00307.JPG.519d4ec89a129de4879328daf76e50f1.JPG

 

This end of the tube is capped off.  I scraped it to make sure it was a plug and not just some debris.  At first I thought maybe this was a ball bearing intended to block part of the opening to cause a restriction.  I now see it is a solid end and it appears impossible that air could be drawn into the lower tube at this location.

This is the same as my manifold where this hole is blind with no effective opening.

 

16 hours ago, JohnD1956 said:

A probe in the hole in the center of the manifold ( the hole just below the letter M in the word Workmate) showed that this is a chamber of sorts, not just a piece of tubing itself:

 

DSC00308.JPG.fbad5648a33c4e4a863247186d92bad9.JPG

 

And this 'opening' '(the hole just below the letter M in the word Workmate)' is where compressed air vents from when I blow compressed air into the alloy tube at the other end of the manifold.  This 'opening' is where I have inserted my choke stove tube with the other end attaching to the choke thermostat housing cover.  So the system operates by the choke thermostat housing having a slight vacuum that will draw air up the choke stove tube.  Outside or external air is drawn in the other end of the alloy tube with that air being heated by the heat of the exhaust passing over/around the alloy tube.  The heated air (not exhaust gas) then enters the choke stove pipe.  The heated air travels up the choke stove pipe to the choke thermostat housing where the heat causes the bi-metal coil spring to move the choke plate.

 

Thanks all.

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