Rust & Restoration: Preparing a Cast Iron Exhaust Manifold
Part 3c: Parts (Cleaning up one of the parts purchased)
If you are paying attention, we are up to "Part 3c" in the series on acquiring parts for your project. You may recall a few blog posts ago that I had a few good deals on Y Block engine parts during one full day of travel here in Ohio and Indiana. I came away with quite a bit. One of my wonderful finds was a passenger side, cast iron exhaust manifold (B9AE-9436 A) that had no cracks or repairs. Its surface condition was extremely rusty and one of the studs had been broken. Both the original down pipe and the heat riser were still attached. The B9AE version of the Y Block exhaust manifolds flows much better than what was offered in 1954-56. The ports and passageways are some of the largest from the factory. And, since a 4 cycle engine is basically an air pump, decreasing restrictions and optimizing flow are very helpful for horsepower gains. As you look at the photos and watch the video you can see that the B9AE manifold has the provision for a hot air tube that feeds the thermostatic choke on the carburetor. Ford went this route because of the 56/57 intakes that had the sheet metal heat tube in the center. It would often rot out and open the thermostatic choke to dirty exhaust air.
What follows is the entire process from beginning to end. If you would rather watch the video than read the post and look at the pictures then scroll to the bottom and click the link.
The next issue to face was the removal of the broken studs from the manifold flange. From the "after" picture below you can see how much corrosion and "rust-welding" there was on the flange. This was a chore in and of itself to drill out both studs and to retap the threads. But, as you can see this all worked out well in the end. Restoration work on original exhaust manifolds is quite the labor of love, but it feels great, I say to see a part like this rescued from wreck and ruin!
The main issues with original cast iron exhaust manifolds are their fragility and the corrosion. By the time you get the part in your hands, most probably it has been through thousands of heat cycles or maybe even open to the weather. A lot of times these manifolds have been secured to the heads and the exhaust system since new (hence the problem with studs for the flange). There are a multitude of ways to deal with the rust and corrosion. With most parts I begin with the blast cabinet and a session with glass beads - usually this is the best answer. Since a cast iron manifold can be quite delicate, I chose to use electrolysis. (That is why the title picture above shows the manifold sitting in a tub of water.) I'm sure you remember science class and the flow of electrically charged particles from negative to positive. In the modern day there are many historians and archaeologists who will use electrolysis to remove corrosion from ancient artifacts made of ferrous metals. Probably the most notable of which would be cannons that are taken from sunken ships.
What do you need to get electrolysis going?
Your part made of ferrous metal
A water-tight container
A large piece of sacrificial metal (or a few smaller pieces evenly spaced)
Lengths of wire - usually the coat hanger thickness works well
Continuous low voltage charge (I use a 12 volt battery charger)
Borax or similar cleaning powder (for your water solution)
Wire brush (to remove some of the loose corrosion and debris)
You can tell from the video that it did not take long for the miracle of science to do its work on the manifold. Even the pivot shaft on the heat riser loosened up considerably. After a few sessions the manifold was removed and dried. Next, it was time to attack the one remaining nut that secured the down pipe and the heat riser to the manifold. I used penetrant, heat, etc to try to get that nut to budge. No go. You can see from the picture below that I just sheered off the stud itself. Even while the spacer was sitting on the manifold studs it still did not come free. I had to take a cut-off wheel and carefully place it between the manifold and the spacer to cut the studs. Even after that I had to drive the remnants of both studs out of the spacer with a punch. They finally came free!
The next issue to face was the removal of the broken studs from the manifold flange. From the "after" picture below you can see how much corrosion and "rust-welding" there was on the flange. This was a chore in and of itself to drill out both studs and to retap the threads. But, as you can see this all worked out well in the end. Restoration work on original exhaust manifolds is quite the labor of love, but it feels great, I say, to see a part like this rescued from wreck and ruin!
I cleaned up the surface of the flange with a flap disc on my grinder.
Knowing that I would need new studs, I ordered a set of 4 on eBay with the correct thread and diameter size. Why 4 you may be wondering? Welp, whoever uses this manifold in its extended lease on life will now have what is needed to choose between keeping the original heat riser/spacer or just simply eliminating it altogether.
I have already listed this item for sale - just go to this page on my website to take a look. I have quite a bit listed on eBay, but I do pay a fee for having the store show up here on the site. If you want to make an offer on the item lower than what is listed, please feel free to do so. Since I pay for the advertising I have no qualms about working a deal with you through another means. A few words of advice on installation... since these cast iron manifolds are fragile, do not overtorque your bolts! From the factory, the exhaust manifolds did not have gaskets for the mating surfaces of the head. These days, every engine kit comes with a set and it is common to see exhaust gasket sets for sale from almost anyone that sells Y Block parts. Keep in mind that with a perfectly straight mating surface you would need no gasket for exhaust. However, once a manifold, even the heavy cast iron version, is removed from the engine, there may be a little warpage. This is often not recognizable to the naked eye. The exhaust gaskets will compress a little, but it is advisable to be very gentle with the manifold and only snug up to the head with decreased torque - this way you will not crack a flange! Of course, many mechanics will use a hi-temp silicone to aid the seal.
Cast Iron Exhaust Manifold Restoration Video
As we finish up another blog post, let me invite all of our subscribers (and anyone else to whom you send this link) to join us for the Fast Fords at Dragway 42 on Father's Day weekend. The information is on the flyer below.
The Hot Rod Reverend
aka Daniel Jessup