Hello Alvin,
What filler metal and process your job shop weldor should use will largely depend on where the crack is on that head. If it's in the combustion area and they tried to arc weld it, the head is already ruined. An arc welded deposit will not seal in that area. A crack in the combustion area can only be successfully repaired using the oxy-fuel process and ni-si-b powder or pure cast iron rod as a filler metal.If the crack is not in the combustion area, an arc process using a ni based filler metal should work fine with proper procedure and prep. The arc process would be my last choice, personally. The first step in the procedure, in any case, would be to clean the head in a sodium hydroxide cleaning system. Next, prep the weld area by completely removing the crack. Small cracks that cannot be seen with your eye most likey emanate from both sides of the big crack. To totally remove these you must grind completely through the head where possible. Ideally, the part should be placed in an oven and brought to 700°F soaked. This could take 2 or 3 hours. Even for a small head like the one from your garden tractor. Once the heat has soaked through, remove the part from the heat, clean it with a stainless steel brush, weld it completely, place it back in the heat. Take the temp up to 800°F soaked and slowly ramp down below 200°F before removing it. The flame spray torch with a powder like our #3326 is what most professionals use. Others use a pure cast iron material like our #925 and braze the part in a forge. The #925 works well with the GTAW process for other cast iron applications and is especially useful where color match is important. To learn more about these processes you are welcome to visit our site or call with your questions. There is a posting down below with a phone number and site link.
HTH,
Steve
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