Summershandy

Broken Manifold tubing

Recommended Posts

Well, last night the line off the exhaust manifold finally fell off. Guess it got bent one too many times. I'm blaming the machine shop haha. Here's an old picture of what I'm talking about. I drilled out the broken part fitted in the manifold and rebent the line to reach the choke spring again. My question, what would hold or seal it back in the manifold. I'm not sure the temps there and reading on JB weld and Permatex Copper sealant they seem to be rated around 500 - 700 fahrenheit. The tubing is a pretty snug fit and sits in about a 1/4" which is about the thickness of the manifold, so there's some meat there. 

 

 

 

 

IMG_6593 - Copy.JPG

  • Like 1

Share this post


Link to post
Share on other sites

Normally the end of the tube is swaged and slip fits into the manifold hole.  Rust causes it to stick. There should be an internal tube (or a drilled passageway in the casting) that serves as the hot air stove to prevent sucking exhaust into the carb. Be sure drilling the broken stub out did not breach this tube.

  • Like 1

Share this post


Link to post
Share on other sites

It probably doesn't need sealer if it fits tight.There tubes just pull hot air (not exhaust). If I felt I had to seal it, I might use Walker Acousti-Seal. It is good enough for exhaust, but is brittle when cured. The tube would still need to be mechanically solid on it's own.

 

I have made several similar tubes for 60s-70s Fords over the years, and those typically had a shoulder crimped into the pipe that serves as a stop when you drive it in. It should fit fairly tight in the hole. I made a ring out of steel wire and brazed it on to duplicate the shape of the shoulder.

 

That Pontiac tube looks so short it couldn't possibly fall out, As long as it is not so loose it rattles, I don't think it would matter at all if the joint at the hot end leaked.

 

 

Share this post


Link to post
Share on other sites
11 minutes ago, joe_padavano said:

There should be an internal tube (or a drilled passageway in the casting) that serves as the hot air stove to prevent sucking exhaust into the carb. Be sure drilling the broken stub out did not breach this tube.

 

Good advice. Make sure there is no way it can suck exhaust! On my 36, there is no such problem because the heat stove is just a big open air cavity cast into the manifold, and there is a plate (3.602) bolted over it. I think Pontiac flatheads had the same setup clear to the end but I am not sure. It would pay to check.

 

wpff4e0f08.jpg

Share this post


Link to post
Share on other sites
37 minutes ago, Bloo said:

On my 36, there is no such problem because the heat stove is just a big open air cavity cast into the manifold, and there is a plate (3.602) bolted over it.

 

Well I'll be darned guys. I had thought this was drawing exhaust not just hot air! That's why I was concerned about an exhaust leak. I think my set up is like Bloo's. Looking down the hole it seems to have a cast looking floor about an inch down. I sketched what I feel with my finger inside the port. Without breaking off the bolts to get the cover off, I think I have an air cavity. You'd think when I drilled I would have felt an air tube. I always drill by feel. You guys agree? 

 

 

IMG_6806.JPG

IMG_6807 - Copy.JPG

Share this post


Link to post
Share on other sites

I forgot to add...I took a piece of wire and was able to scratch the cover from the inside, made that tinny sound. The hole appears to be at one end of the cavity and not in the middle like I thought.

Share this post


Link to post
Share on other sites

Yeah, thats like mine more or less. I can't really see because It is so close to the engine. These setups should NEVER suck exhaust, but as Joe pointed out, some cars have more thin tubing inside separating exhaust from clean hot air.

 

Your drawing sums up what is in there. It is the standard Pontiac flathead setup. An open cavity. Cold air comes in the holes in the cover.

 

One thing you should also look at closely is your intake. Most DO have tubing (more like exhaust tubing) about the diameter of the carb flange and directly under it. The thin wall of the tubing separates the intake manifold from exhaust being sent up from the heat riser. Look down through the carb hole, and up from the heat riser hole, you'll see. They are notorious for rusting out and letting exhaust into the intake manifold.

 

I am fairly sure all the one barrel cars have this setup. I am not sure how Pontiac approached it when they went to two-barrel.

Edited by Bloo (see edit history)

Share this post


Link to post
Share on other sites

Not exactly certain how this manifold is set-up, but appears to have a "cavity" (heat stove). The carburetor has a small passage-way connected to manifold vacuum that runs into the choke housing under the internal choke pull-off, which pulls the choke open AFTER the bi-metallic spring relaxes from heat. The vacuum then bleed from behind the piston to cause a vacuum on the entire choke housing, which obviously is connected to the hot air tube, so the vacuum pulls the hot air into the choke housing.

 

Since the entire choke housing is under vacuum, for best results any warpage of the choke housing should be eliminated, making certain the gasket from the housing to the choke cover actually seals.

 

Many later (V-8) manifolds had a steel tube pressed completely through the exhaust cross-over, and this tube was connected to the visible hot-air tube. These pressed-in tubes burned through after roughly 30 years. If one sees the result of raw exhaust in the carburetor choke housing, one should replace this tube prior to rebuilding the carburetor.

 

Jon.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now