Automotive industry metallurgists have developed superior crankshafts that eliminate most problems of the past. However, if it is necessary to repair an older, badly worn crankshaft journal, it can be built up with either SMAW, GTAW, or GMAW. Before welding, it is usually good practice to turn the worn surface and shoulder down evenly, so that when the weld metal is
added it will be of uniform thickness and structure. The shoulder should be turned down to solid base metal and rebuilt with weld metal.
Because of its low heat input, GMAW is probably the fastest and least expensive method of rebuilding crankshaft journals. The short-arc method of GMAW deposits a steel bond on the crankshaft which is equal to the shaft in density. The alloy of the shaft mixes with the welding wire to form a homogeneous deposit which blends with the original metal.
The shaft can be built up with GMAW and an automatic welding head. The shaft is centered in a lathe and turned. The welding head is attached in a fixed position, then indexed over the weld zone. The welding wire is fed automatically to the arc.
The weld deposit is made while the crankshaft rotates in the lathe at 2 rpm. Welding is done uphill, using a high-tensile steel electrode, 0.8 rnm (.030 in.) diameter, with a 75% argon-25% carbon dioxide shielding gas mixture. Distortion is held to 0.13 mm (0.005 in.), and the average weld time for rebuilding a journal is three to five minutes. Shielded metal arc welding can also be used with either bare or coated electrodes.