Riviera Exhaust Manifold Question

[36 Dodge]

So I have an exhaust leak on the passenger side and I found a nipple on the manifold that is open, can someone please tell me what it's used for and is there a way to cap it? Thanks in advance!!

[Dales90]

The hot gas bypass valve is controlled by the thermostat coil in your picture. The nipple is for the tube which guides heat to your carb thermostat.

[RivNut]

No need to cap it.  It's a the bottom of a tube that runs through the exhaust manifold.  Outside air goes through it to provide heated fresh air to the choke.  It should have a steel tube on the other end, sheathed in an insulating material, that runs to the choke housing. A rubber tube goes from the air horn on the carb to the end of the tube you're questioning.  That is the supply for filtered fresh air to be heated.  

 

Doubtful that is the source of your leak.

Edited August 18, 2019 by RivNut (see edit history)

[36 Dodge]

1 hour ago, RivNut said:

No need to cap it.  It's a the botyom of a tube that runs through the exhaust manifold.  Outside air goes through it to provide heated fresh air to the choke.  It should have a steel tube on the other end, sheathed in an insulating material, that runs to the choke housing. A rubber tube goes from the air horn on the carb to the end of the tube you're questioning.  That is the supply for filtered fresh air to be heated.  

 

Doubtful that is the source of your leak.

Thanks for the lesson, the shop manual doesn't show much. Again thank you!!!

 

[RivNut]

Here's a picture of a 63 Riviera engine.  I don't have the software to label or circle parts of the picture.

 

The carb pictured is the Rochester 4GC but it's plumbed the same as a Carter AFB. I'm calling the back of the carb 12:00. At 10:00, a rubber tube comes from the neck of the carb an ties into a metal tube.  That metal tube goes around the exhaust manifold and inserts into the 'nipple' you questioned in the picture that you posted. Coming off of the top of the manifold is the other end of the tube.  Inserted into that tube (the other end of the 'nipple' tube) is a steel tube that runs to the choke where it is bolted to the choke housing. (On this engine, the sheath around the tube does not extend all the way to the exhaust manifold. ???) Cool filtered air enters the rubber/steel tube and travels through that tube, the tube inside the exhaust manifold, and the sheathed tube to the choke.  The heated fresh air is what causes the coiled bi-metal spring inside the bakelite choke housing to contract and open the choke.

 

The piece of the exhaust manifold that has a spring and counter weight has nothing to do with the choke operation.  When that flapper is closed, it forces exhaust gasses up through the intake manifold to warm the bottom of the carburetor during cold weather operation.  Once the coiled bi-metal spring on the counter weight heats up, it will open the flapper and the exhaust gasses pass through the pipes.  Your paricular flapper is a separate piece that bolts between the manifold and the exhaust pipe.  In some applications, this flapper is built into the exhaust manifold.

[psychostang]

The only issue with these tubes, is that eventually they crack and let exhaust gases into the carb.  This fills the choke housing, including the little shutoff piston with carbon.  That's usually why the choke gets stuck.  Put your hand there, while the engine is running and see if any gases come out.

[RivNut]

24 minutes ago, psychostang said:

The only issue with these tubes, is that eventually they crack and let exhaust gases into the carb.  This fills the choke housing, including the little shutoff piston with carbon.  That's usually why the choke gets stuck.  Put your hand there, while the engine is running and see if any gases come out.

I've never seen that happen.  

[telriv]

That happens when the metal plate is NOT USED under the carb.  above the base gasket.  The way we use our cars today the heat under the carb. is NOT nec. any longer. I just block the holes in the manifold UNDER the carb.  I even block/gut the heat riser valve. DON'T block the 4 holes in the heads with Hi Perf. gaskets. The manifold needs some heat in it to flash the cat pee we have today they call gasoline.  IF you do the carb./car will BOG/hesitate.

[1965rivgs]

9 hours ago, RivNut said:

I've never seen that happen.  

I have seen this occur MANY times...

Tom

[RivNut]

2 hours ago, 1965rivgs said:

I have seen this occur MANY times...

Tom

Tom,

You probably see more parts in a year than I'll see in a lifetime.  I've never seen one crack, but I've only seen a few compared to what you've seen.   Any suggestions on how to avoid or repair damage to that tube.

 

 

[36 Dodge]

18 hours ago, RivNut said:

Here's a picture of a 63 Riviera engine.  I don't have the software to label or circle parts of the picture.

 

The carb pictured is the Rochester 4GC but it's plumbed the same as a Carter AFB. I'm calling the back of the carb 12:00. At 10:00, a rubber tube comes from the neck of the carb an ties into a metal tube.  That metal tube goes around the exhaust manifold and inserts into the 'nipple' you questioned in the picture that you posted. Coming off of the top of the manifold is the other end of the tube.  Inserted into that tube (the other end of the 'nipple' tube) is a steel tube that runs to the choke where it is bolted to the choke housing. (On this engine, the sheath around the tube does not extend all the way to the exhaust manifold. ???) Cool filtered air enters the rubber/steel tube and travels through that tube, the tube inside the exhaust manifold, and the sheathed tube to the choke.  The heated fresh air is what causes the coiled bi-metal spring inside the bakelite choke housing to contract and open the choke.

 

The piece of the exhaust manifold that has a spring and counter weight has nothing to do with the choke operation.  When that flapper is closed, it forces exhaust gasses up through the intake manifold to warm the bottom of the carburetor during cold weather operation.  Once the coiled bi-metal spring on the counter weight heats up, it will open the flapper and the exhaust gasses pass through the pipes.  Your paricular flapper is a separate piece that bolts between the manifold and the exhaust pipe.  In some applications, this flapper is built into the exhaust manifold.

Thanks for the information. When I purchased the car the previous owner had replaced the original carb with a Eldelbrock, I don't like it I am already searching for a Rochester.

 

[36 Dodge]

13 hours ago, psychostang said:

The only issue with these tubes, is that eventually they crack and let exhaust gases into the carb.  This fills the choke housing, including the little shutoff piston with carbon.  That's usually why the choke gets stuck.  Put your hand there, while the engine is running and see if any gases come out.

I think you are correct because before I disassemble it I could feel air leaking and that is why I asked if there was a way to cap it. I will put it under pressure and see if it's leaking. Thanks! 

 

[RivNut]

If it's exhaust gases you'll know it.  It will be as hot as touching the exhaust manifold.  Because of the laws of thermodynamics, hot air rises.  You could just be feeling a natural draft of heated fresh air coming through the tube.  It it's an exhaust leak you'll hear it before you feel it.

[telriv]

One way to pinpoint a leak is with a piece of steel line or whatever you have around.  Something like a 3/16ths. or 1/4" steel or copper or aluminum tubing/line.   You'll be using it like a stethoscope, sort of like using a screwdriver to your ear & touching parts until you find where the noise is coming from.  Well with the tube you do the same thing by putting one end to your ear & fishing around until you hear where the exhaust is coming from.

You'll be able to hear the exhaust leak WITHOUT touching the hot exhaust manifold & prevent yourself from possibly getting burned.  In the case of the tube projecting from the bottom of the manifold you will have to bend the tube in a U shape to reach under there.

 

Tom T.

[1965rivgs]

9 hours ago, RivNut said:

Tom,

You probably see more parts in a year than I'll see in a lifetime.  I've never seen one crack, but I've only seen a few compared to what you've seen.   Any suggestions on how to avoid or repair damage to that tube.

 

 

Ed,

  Not sure if they crack or just corrode through but I have experienced them leaking exhaust and fouling the choke. As Tom T points out, leaving out the stainless plate under the carb will also direct exhaust into the choke stove because the vacuum passage which feeds the choke stove originates in the area of the exhaust crossover betwen the primary barrels in the base of the carb. I attempted to repair one once by inserting another tube into the original but found there is a flat metal ribbon, like a twisted dipstick, in the tube that is difficult to remove. The ribbon must encourage the air traveling through the tube to pick up more heat compared to just traveling straight through by swirling the air.

  I have seen replacement NOS manifold tubes on Ebay but didnt check to see if they were for Nailhead applications. I always just replaced the manifold,

Tom

[carbking]

Not exactly sure the format used by Buick on this application.

 

Years ago, we replaced hundreds of these things on Pontiac, Cadillac, and Oldsmobile tripower manifolds.

 

In general, there was a steel tube which was pressed into the heat crossover in the intake manifold. Inside the steel tube was a piece of twisted steel ribbon (think very early barb wire fencing) that was used as a delay to slow the passage of the air, assuring that the air would be properly heated. The tubes simply rusted/corroded until they developed holes. Used to take 30~35 years. We purchased stainless steel tubing to replace the steel (we are out of this tubing, and there were several different non-standard diameters).

 

The procedure, with the manifold off of the engine, was to drive out the remains of the old tube, fabricate a new twisted steel ribbon, cut the correct diameter stainless tube to the correct length, and drive it into the manifold. Once the tube was driven into place, we added the twisted ribbon.

 

For an insertion tool, we chucked a bolt with a greater diameter than the tube into our lathe; turned about a 1/4 inch of the end slightly less than the INNER diameter of the tube (it could be inserted into the end of the tube).

 

This procedure worked well.

 

One other issue with the Cadillacs only. Every Cadillac manifold was cracked on the driver's side where the tube had been inserted; which meant a trip to the welding shop to eliminate the exhaust leak before inserting the new tube.

 

Later Pontiac manifolds had a plate with an attached tube loop that bolted into the exhaust crossover from the top of the manifold. These have been reproduced, and are readily available.

 

Jon.

Edited August 20, 2019 by carbking (see edit history)

[psychostang]

Jon:  Buick used the same design as the Cadillac you stated.  A tube is inserted from the top/back towards down/forward.  Then you have a metal tube attached to the air horn with rubber, which takes inlet air to the exhaust.  Then a second tube comes around and up past the manifold to the Choke thermostat housing.

[RivNut]

There are two separate topics being discussed as one here. 

 

The original thread asked about the tube that runs through the exhaust manifold and supplies heated fresh for the choke.  

 

The other discussion has to do with exhaust gas that is piped through the intake manifold to heat the base of thr carb.  

 

I think that all contibutors know of each separate system, but are intertwining their comments which makes it confusing.  The original post asked about the 'nipple' on the exhaust manifold.  Let's help 36Dodge with his original question.

[36 Dodge]

With my bad luck it figures that the tube is bad! Besides welding the ends shut does anyone have any other suggestions? And like I mentioned before it does not have the stock carburator, the previous owner replaced it with a Eldelbrock carb.

[RivNut]

The tube is for heated fresh air to open the choke gradually as the engine warms up to operating temperature.   IF you don't drive the car in cold weather and IF the Edelbrock carb 1) has no choke, 2) has a maual choke, 3) or has an electric choke, you can probably cut the tubes off close to the manifolds and plug the outer ends.   I have no idea what it would take to put a new tube, with the spiraled wire down the center of it, into a manifold.  I'm sure others will jump in as well.

[Ted "Wildcat65" Nagel]

On my 401 with an Edelbrock (no Choke) i drilled out the tube and tapped the holes and plugged them.  

Your picture looks like my Riviera manifold when I pulled it off.  I replaced the manifold on that.

Ted

Edited August 29, 2019 by Ted "Wildcat65" Nagel (see edit history)

[carbking]

This is probably going to be a less than popular opinion, but I would highly suggest pulling the manifold, driving out the old tube, and inserting a new one (see my earlier post).

 

At some time, you are going to want that engine to perform as it is capable of performing; and it will NEVER do that with the clone. If you weld, tap, whatever, to the manifold now as a band-aid; then you will have to undo the band-aid when you decide to fix it right.

 

Even if you temporarily decide to leave the clone on the engine; once you have the manifold tube sealing the exhaust, the issue will be solved, without the need of capping either end. Hot air moves through the tube because of vacuum being supplied to one end of the tube from the choke portion of the carburetor. If the clone has an electric choke, manual choke, or no choke; then there would be no connection to the tube. Even if the new tube is left open at both ends, there will be no exhaust leak if the outer circumferance of the tube is sealed in the heat passage.

 

Jon.

Edited August 29, 2019 by carbking (see edit history)