The crankshaft’s job is to work with the connecting rod to convert the piston’s gas pressure into torque and send it to the driven working machine. The crankshaft is subjected to the action of gas pressure as well as the inertial force and moment generated by reciprocating and rotating motion during engine operation. The crankshaft generates complex alternate stresses such as bending, torsion, shearing, tension, and compression as a result of these cyclically changing loads. Bending, twisting, and breaking the crankshaft are common difficulties. The crankshaft journal rotates at a fast relative speed due to high gas pressure and inertial force, making liquid lubrication impossible during alternate working circumstances. As a result, journal wear is unavoidable. The failure of the crankshaft installation to satisfy the standard criteria, inappropriate selection of bearing bushes, and improper use and maintenance will all exacerbate the crankshaft damage during use and maintenance. The crankshaft 4tnv94l is a good choice.
Common Crankshaft Damage
Wear of Journals
The crankshaft journal wears unevenly and is generally machined into an elliptical shape in the radial direction; the wear is also uneven and tapered in the axial direction. The wear of the journal causes an uneven load distribution on the journal, making it impossible to develop an oil film on the surface, which speeds up journal wear and diminishes strength.
The rounded corners of the transition between the crankshaft and the journal, as well as the oil holes, are the most common locations for crankshaft cracks. The former is a dangerous radial fracture; the latter is an axial crack that develops in the axial direction following the oil hole.
Crankshaft Bending and Twisting Deformation
After a long period of usage, the crankshaft will bend and twist owing to incorrect use or maintenance, resulting in increased vibration during diesel engine operation, rapid wear of parts, and in severe cases, crankshaft fracture incidents.
Inspection of Crankshaft
Wear on journal surfaces is checked. Measure the dimensions of each portion of the journal with an outside micrometer. For each journal, two measurement places and two measurement axes should be chosen: vertical and parallel to the crank arm. The taper, ovality, and wear are then calculated. It is necessary to fix the taper or ovality if it exceeds the limit.
Crankshaft bending inspection To set up the crankshaft, use the center of a grinder or lathe to align the center holes at both ends. Check the center hole for accuracy, then use a micrometer to measure the difference in neck swing between the flywheel connecting plate and the installation timing gear.
Mechanical injury to each joint is examined. Use the inner diameter indicator to check whether the matching clearance between the inner diameter and the outer diameter of the bearing exceeds the limit for bearing hole wear at the rear end of the shaft. Check the axial clearance and shoulder width to see whether they are beyond the limit.
Cracks in the crankshaft are examined. Cracks on the journal’s surface will be clearly visible when the diary has been wiped clean and examined with a magnifying glass.
Repair of Crankshaft
The surface of the crankshaft journal is worn and distorted, and it can be ground using a crankshaft grinder to the repaired size after other problems are repaired.
Repair of mechanical damage: ① A ring can be inserted into the bearing hole at the back end of the shaft to fix it once it has been worn. ②Electric welding is used to fix shoulder wear, which is subsequently followed by turning and grinding. ③ If the keyway is slightly worn, it can be corrected and a larger key pin configured; if the keyway is significantly worn, it can be cut to the repair size on a milling machine and a key pin for repair given. ④If the hole in the flywheel fastening screw is worn out, it can be reamed to the correct size and the screw reinstalled. ⑤ If the oil-resistant thread becomes worn, it can be deepened on the lathe to the typical tooth form and polished with gold steel sandpaper. ⑥Grinding can be used to fix scratches and scuffs on the journal surface. ⑦ Make the crankshaft straight. When the amount of bending exceeds the limit, straighten it with a hydraulic press.
Technical Prerequisites for Scrapping
When a journal’s surface crack surrounds it or has multiple longitudinal cracks along the centerline, and the journal is worn to the final repair size, it can be fixed with metal spraying and electroplating equipment; otherwise, it will be discarded.