1. Cold press calibration: This method is usually performed on a press machine. Firstly, place the crankshaft on the V-shaped block of the press working plate, and place a copper or lead sheet between the press rod and the crankshaft to prevent damage to the contact surface between the crankshaft and the press rod. The direction of pressure should be opposite to the direction of crankshaft bending, and the pressure should gradually increase in sections. After calibration, the crankshaft may undergo "elastic deformation" and "aftereffects", so the reverse bending amount is generally greater than the bending amount. For crankshafts with large curvature, they should be calibrated multiple times to prevent excessive compression curvature from causing the crankshaft to break, especially ductile iron crankshafts that are more prone to breakage. After calibration, it should be heated to 180-220 ℃ and kept for 5-6 hours to prevent elastic deformation and aftereffects.
2. Surface tapping correction: For crankshafts with small curvature, the "surface tapping" method can be used for correction. According to the direction and degree of crankshaft bending, use a spherical hammer or air hammer to strike along the left and right sides of the crankshaft arm, causing deformation of the crankshaft arm and displacement of the crankshaft axis, thus achieving the purpose of correcting the crankshaft.
3. On site calibration: Place the cylinder block upside down on the work platform to make it flat, install old bearings (tiles) on the front and rear bearing seats, add a small amount of lubricating oil to the bearings, and then place the crankshaft on top. Gently rotate the crankshaft by hand, measure the maximum bending position of the intermediate shaft neck, and mark it. Use soft aluminum or other soft materials to cushion the bearing cover, slowly tighten the crankshaft bearing cover bolt, wait for about 1 hour, then loosen the bolt, and test whether it is calibrated with a dial gauge. If the allowable standards are not met, continue to adjust until the requirements are met.
Testing method: When checking the bending of the crankshaft, the main journals at both ends of the crankshaft are usually supported on a platform with V-shaped brackets and checked with a dial gauge. Place the dial gauge pin vertically on the third main journal and slowly rotate the crankshaft. If the difference between the maximum and minimum readings of the dial gauge exceeds 0.1mm, it should be calibrated.
Preventive measures: To avoid crankshaft bending, it is recommended to conduct strict inspection of the crankshaft before engine assembly. If the curvature of the crankshaft exceeds the technical standard, it should not be forcibly assembled. After installing the main bearing on a crankshaft with excessive curvature, the crankshaft may become half tight and half loose during rotation, resulting in additional pressure on the bearing shell, accelerating wear and even burning.
