Sometimes that perfect vintage part isn't so perfect. This is especially true when it comes to early model cast iron engine parts. There might be some obvious problems, but are those the only issues? Are you sure? Before you swap in that new old part, spend the time to repair any problems and make sure it's in tip top shape. Part Examination: Quite often, hairline cracks in cast iron heads or engine blocks are difficult to spot, and may go unnoticed. This is especially true for cylinder head cracks. Failure to notice and repair cracks can be disastrous, often resulting in total part malfunction. To ensure that all potential flaws are uncovered, a process called magnafluxing can be used on the part(s) in question. Simply stated, magnafluxing involves the use of an electromagnet that is attached to a ferrous part to be examined, causing the part to become temporarily magnetic. A fine ferrous dust is then lightly sprinkled on the part. Any flaws or cracks present will disturb the magnetic field around the flaw, causing the ferrous dust to adhere erratically (see Figures 1-2 below). Most machine shops will have the capability to magnaflux parts. Some quality mechanics will also have this capability. If you wish to magnaflux parts yourself, inexpensive electromagnets and ferrous dust, often sold as a magnaflux kit, can be purchased at some welding/gas equipment providers, and can also be found online. Figure 1: Magnaflux process applied to a cast iron head with a suspected crack. Notice how the head appears to be in good shape. (click on thumbnails for larger image) Figure 2: Cylinder head crack fully revealed by ferrous dust Part Preparation: Once all the cracks and flaws have been detected, the next step is to prepare the part for repair. Lets use a single crack in an engine block as an example for this process. Grinding: Unfortunately, things are going to get worse before they get better. Use a silver pencil or equivalent non-permanent marking tool, and fully outline the crack to be repaired. Take a 4.5 angle grinder, and grind a 45-degree bevel on each side of the crack, for the full length of the crack. Grind the bevel to half the depth of the crack. This amount of grinding will enlarge the width of the crack, which is to be expected (e.g. a crack that is 1/16 wide may end up being 1/4 wide after being properly beveled). Drilling: One of the problems with welding cast iron is how it reacts to heat. Quite often, the heat of the welding process will cause an existing cast iron crack to expand, thus causing it to elongate. To combat this, drill a 3/16 hole just beyond each end of the crack, to ¼ the depth of the crack. Be sure to use a small amount of drill chill or equivalent cutting fluid to keep the friction heat created by the drill bit low. Once drilled, these holes will serve as expansion joints, and will be filled later during the welding process. Cleaning: Use a file, sand paper, or steel wool to remove any scaling or oxidation around the surface of the crack. Use a steel brush to clean the beveled area of the crack. Compressed air can then be used to blow the minute debris from within and around the crack. Use a low heat torch (e.g. butane torch) to heat the crack, evaporating any liquid and thus ensuring it is completely devoid of any moisture. If you are stick welding, select a spot close to the crack where the welders grounding cable may be attached. Use a file, sand paper, or steel wool to remove any scaling or oxidation in this area to ensure the best ground connection possible. Pre-Heating: For the best results when welding cast iron, pre-heating the work piece is essential. A conventional oven can be used to heat soak a piece to get it to a desired working temperature (~ 500+ F). The time and temperature required to heat soak a particular part depends on the size of the part. Nevertheless, this is often impractical due to the size of the part in question, such as an engine block. In instances such as this, an Oxyacetylene torch with a rosebud tip can be used to heat larger areas. When using this method, apply the heat as slowly and evenly as possible over a large area. Do not concentrate the heat near the crack. Please note that this method is difficult to master, and can often result in further damage to the cast iron. That being said, welding cast iron can be done cold, but is not recommended. If welding cast iron without pre-heating is unavoidable, selecting the appropriate filler rod or electrode is critical. Welding Cast Iron: There are really only three welding process that can be effectively used to repair cast iron: Stick welding, Gas welding, and Spray welding. The machinery necessary to Spray weld is very expensive, and is not commonly available to the layman. For these reasons, spray welding will not be addressed in this article. As for stick and gas welding, the single most important item to successfully repairing cast iron is the electrode or filler rod. Cast iron is a difficult material to weld because it is full of minute imperfections due to the casting process. This results in a porous surface that is ultimately brittle. When stick welding cast iron, a Nickel (Ni) electrode is typically used. However, the Nickel is much harder than the surrounding cast iron. This difference in hardness often results in future cracking, and can be an absolute nightmare. Electrode / Filler Rod: If you are going to gas weld, be sure to select a filler rod that has a high presence of silver. Such an alloy offers the best strength and flexibility characteristics. I personally only use the stick process when welding cast iron. When selecting an electrode, look closely at the metallurgic makeup of the electrode. Desired characteristics are a relatively soft metal that has the ability to elongate and be machined. High content Nickel (Ni) rods are typically used when welding cast iron. However, when cooled, Nickel is very hard and can lead to future cracking because it is harder than the surrounding cast iron. There are several electrodes available that are Nickel based, but alloyed with other materials to increase elongation characteristics. Refer to the link below for a list of alternative electrodes. http://www.mwa-international.com/products.asp?id=7 The Process Of Welding: Since I do not gas weld cast iron, this article will only detail the stick welding process. For the first weld run, use the push, rather than the drag process. Place the electrode at approximately a 50-degree angle at one end of the crack, just prior to the 3/16 expansion hole. You should be facing the work piece in a manner where you can push the electrode to the other end of the crack. Make the first weld run in a slow steady motion, welding to the other end of the crack, and stopping just prior to the other 3/16 expansion hole. This push process will ensure maximum penetration, and will help push the weld puddle into the bottom of the crack. Use a slag hammer to peen the initial weld of any slag and scaling. Let the weld cool for a minute. For the second weld run, start at the opposite end of the crack, and use the drag process to pull the electrode back towards you, welding in a slow steady motion. Be sure to peen the weld. Let the weld cool for a minute. Continue to repeat this process, thus building up the weld in the crack. For wide cracks, weld beads may have to be run side by side in order to fill the gap. This is typically not the case for automotive cracks (if you do find it necessary to do this, use a grinder to bevel the welds into one another, and fill the bevel with a third weld bead). Once the weld bead reaches the top of the crack, use the push technique to make one last run. This run should be slightly taller than the surrounding casting, and should completely fill the gap between the walls of the crack. Move the electrode in a half-moon shape while pushing the weld puddle forward. This will result in maximum penetration (see Figure 3). Figure 3: Properly stick welded cast iron crack If the part is small enough, place it back in heat soak to slowly cool over several hours. If the part is large, wrap a heat blanket around it and allow it to cool for several hours. Finishing Let the repaired cast iron part completely cool over 24 hours. If the repaired area is not in a readily visible area, it is best not grind the weld, as grinding reduces the welds integrity. Otherwise, once the repaired part has completely cooled, repaired crack can be ground flush or machined. Metal S***ching Cast Iron: There is an alternative repair method to welding cast iron, which is Metal S***ching. This is a relatively new process, and one I dont have any particular experience with. However, I have heard of it being used to make repairs in some of the most demanding conditions with good success. Please refer to the link below for information on Metal S***ching. http://www.lockns***ch.com There it is- A concise guide to repairing cast iron. Cheers.
Thought I might add a quick explanation on how to repair a hole in cast iron. The process of repairing a hole in cast iron is essentially the same as repairing a crack. All the same steps up to the welding process apply (see Figure 1 for a properly prepared hole) . As for the welding process itself, there are some slight variations. Place a piece of graphite across the bottom of the hole (see Figure 2). The graphite will act as a backing, and allow you to weld across the spans of the hole. Graphite wedges can be obtained from a welding/gas supply vendor. The first weld should be run across one small edge of the hole's perimeter. Peen the weld, then grind a bevel on the side of the weld bead with a die grinder. Weld a second bead into the first where the bevel was ground. Peen and grind a bevel. Repeat this process until you have spanned the hole with weld bead. When done correctly, the weld will be as strong, or stronger, than the host material. Figure 1: A thrown rod results in a huge hole in a cast iron engine block. The perimeter of this hole has been ground. Notice how the edges of the hole have been beveled and cleaned. The quarter is present for size reference only Figure 2: Graphite backing used to support the weld bead across the hole. The first weld was laid on a small portion of the hole's perimeter. Each weld run should be ground with a die grinder prior to making the next weld run into it Figure 3: Welding process completed. Enough subsequent beads have been laid into one another to span the hole Figure 4: Welds have been ground flush <!-- / message --><!-- controls -->
This is my favorite! "Metal S***ching Cast Iron: There is an alternative repair method to welding cast iron, which is Metal S***ching. This is a relatively new process, and one I don’t have any particular experience with. However, I have heard of it being used to make repairs in some of the most demanding conditions with good success. Please refer to the link below for information on Metal S***ching. http://www.lockns***ch.com "
Excellent write-up on the process. I've always been instructed to Arc only on cast iron and we have 3phase / Spray arc process' also. Carl Hagan
As long as you're giving advice......how would you deal with a crack that is open on both ends? This one on my 250 Chevy 6 goes from the left front headbolt hole to the water pump surface. These are prone to cracking here .
I have always had stuff done at the machine shop but that was their thing and I would just take apart and put it all back together . WOW that was a great write up explaining the process of Magnafluxing and reparing the cracks in blocks and heads . Now I know how it is all done !
Great tech 1959, Im gonna be needing this pretty soon as I have an intake I want to play with. Thanx a bunch.....!! Rat
Good thread. This brings back memories of a time when I was 16-17 (Dec'73) and working for an old family friend here in Sth Aust. His name was Harold Wendt. He was a mechanic/engineer who did a lot of this type of work on cylinder heads, cylinder blocks trans housings etc. He knew that pre-heating was essential. What he did, firstly, was to dig a hole next to the shed where the welding table was placed. The hole was about 18" deep and filled with saw dust. The table looked more like giant barbeque grille. This consisted of a series of bars like a rack or grill with a solid sheet to enclose the base. Living in a wine growing region old vine stumps were plentiful.On top of this table were placed a good number of the vine stumps. The Cylinder head was placed in a****st the stumps on the table. The Cyl head had been previously prepared in much the same manner as described in the original post. Next step was to "light the Barbeque" and let the flames die down to coals. The head was now preheated. The welding operation was done by gas welding method. Harold knew all too well that he needed to use appropriate welding rods for the task. Harold , no fool, knew he was welding cast iron so needed cast iron rods. Solution , straighten out some cast iron piston rings which he had plenty of lying around from years of rebuilding engines. Instant welding rods. The welding up job was then conducted with the head on the "BBQ" . On completion the head was then placed in the sawdust pit and allowed to cool down for about 2 days . The sawdust would burn down a bit and retain the heat but would otherwise well insulate the head and allow slow cooling to prevent cracking. After everything had cooled down the head was retrieved and then all welds dressed and valve seats cut etc to prepare the head for final ***embly and refit. All of the cast iron welding was done this way and worked well.
Welding cast isn't as bad as some think, as the one said, preheat is the main thing. 1. V the crack out if you can. 2. Clean it good. 3. If the crack ends on the casting, drill a hole so it won't run on you when you start preheating and welding. 4. preheat at about 450 to 500 degrees at least 30 minutes, with fire brick around the casting, and the furtherest areas fron the heat covered with some asbestos cloth or a welding blanket. 5. Weld up the crack, taking exreme care not to let any cold or cool air hit the casting. 6. After welding, cover it up with the blanket, let the fire bricks stay around the edge until you can spit on the edge and it not sizzle, usually 2 to 3 hours. This is called preheat welding, and is usually done with long gas torches, in a enclosed space, but will work for arc welding. For cracks that run to the edge, tack weld the edge first, then drill your hole at the start of the crack. Grind it out to a V, make sure to get a good enough tack to where it won't pop loose when preheating. Preheat it with all the bricks and blankets around, start at the edge and go toward the start of the crack, after welding, let it cool down slowly. On Holes in the sides of blocks, grind in out good and smooth so to have no stress risers and cracks, jagged edges showing, cut a piece of plate about the same thickness as the surrounding area, preheat it and lay in some br***. You have to get the cast hot enough to burn the oil out of the pores of the cast or it won't stick or it'll pop loose later down the road after your engine is in the car an d running. I've seen this happen. Well, the sewing method works, and worked better than I thought when they first used it at a shop I was working at. You can get a kit from Sealace for sewing up cracks in heads on deisel engines. Only pros should do this though. Hope this helps............Keeping the sparks flyin! Screamin' Metal
Oh, before I forget, the bigger the casting, the longer the preheat time. I use a general rule of thumb, 2 hours on heads, so the head expands all the way through equally, on blocks, About 1 1/2 hours.
Quick HAMB Metallurgist technical lesson time: The reason cast iron is so difficult to weld is because it has 3-4 % carbon (C). Normal mild steel is about 0.2% C. What happens when welding is the excess carbon forms iron carbides right at the fusion line. So when the weld shrinks as it solidifies, it pulls. The carbides are very strong but brittle. The preheating helps because it gives less thermal expansion difference between the base metal and the weld. Slow cooling also helps as it minimizes the stresses. Peening is very good as it helps put compressive stresses in the weld to counteract the shrinkage tensile stresses. A ductile filler helps also. All the recommendations are good. I just wanted to add what is the reason behind the recommendations. Cast iron welding is difficult to do to prevent fusion line cracking.
Um, metal s***ching is not a relatively new process really. I had an item s***ched back in the 60s, so it's at least 40 years old. I forgot the trade name for it.... something like Metalock I think.Good tech BTW.
1959...Thanks for the info, I have used nickel rod in the past but I am going to try the rod that you suggest.....I have a ford tractor block to work on....
Oh, and let me add if any welding or brazing is done to the block or head....be sure to check your critical surfaces, the mains can get out of line, and need to be align bored, and on the surface of a head, might need to be surfaced if it gets out...... Only experienced welders should tackle welding in the combustion chamber, in the intake runner where you can hit the water jacket, and close to the mains in the block. Always check your mains by turning the crank when torq-ing your caps down. Any binding.....stop immediately!!!!!!! I've only had about 25% of the blocks be OK'ed after welding, during preheat and the welding process, the block actually moves around very slightly due to the stresses of heat. I usually feel better with a visit to the align bore machine after heating a block for any length of time. On heads, if you have hardened valve seat inserts, you need to check them, they can come loose and fall out after welding, not to mention at least, a valve job and surfacing is usually needed. I've seen people do a quick repair and didn't think they hardly put heat on a head, only to have the seat insert trying to go up and down with the valve.
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