Common damages and maintenance of crankshafts

The crankshaft is the core transmission component of the engine, which is subjected to periodic impact loads and rotational centrifugal forces for a long time, and is prone to various types of damage. If not repaired in a timely manner, it can cause engine shaking, power decline, and even complete machine scrapping. Mastering the common types of crankshaft damage and maintenance methods is the key to ensuring stable engine operation.

1、 Common damage types of crankshafts

The damage to the crankshaft is mostly concentrated in the core stress bearing area, and journal wear is the most common problem. The main journal and connecting rod journal are prone to roundness and cylindricity deviations due to long-term friction with the bearing shell, and surface scratches are often caused by insufficient lubricating oil and impurities. Fatigue cracks often occur at the transition fillet between the journal and the crank arm, where stress is concentrated. Long term alternating loads can easily cause microcracks, and in severe cases, can lead to crankshaft fracture. In addition, crankshaft bending deformation may occur, often caused by sudden impacts such as engine detonation and piston sticking, manifested as crankshaft axis deviation and keyway wear. Due to repeated impacts of the transmission gear, metal peeling and increased clearance at the keyway may occur.

2、 Conventional maintenance methods for crankshafts

The maintenance of crankshafts should follow the principle of "inspection first, repair later". The first step is visual inspection. After cleaning the surface oil stains, use the naked eye or magnifying glass to check whether there are cracks, pull marks, and deformation of the keyway at the journal and fillet; The second step is the detection of form and position errors, using a dial gauge and a deflectometer to check the curvature of the crankshaft and the roundness and cylindricity of the journal. If the curvature exceeds 0.15mm, straightening is required, and if the journal wear exceeds the tolerance, grinding and repair are required.

For crack detection, in addition to visual inspection, magnetic particle inspection should also be used to accurately detect hidden fatigue cracks by utilizing the magnetic marks formed by magnetic particle adsorption on the crack. If cracks are found, the crankshaft needs to be replaced directly and repair use is prohibited. The journal grinding and repair should be carried out on a dedicated grinding machine. After grinding and repair, the surface roughness of the journal should meet the standard, and suitable bearing shells should be selected according to the new size; When the keyway wear is minor, it can be welded and re milled. If it is severe, the crankshaft also needs to be replaced.

3、 Precautions for use after maintenance

Before installing the repaired crankshaft, it is necessary to ensure that the fit clearance between the journal and the bearing shell meets the original factory standards, to avoid excessive clearance causing poor lubrication and insufficient clearance causing shaft holding. After installation, high-quality lubricating oil should be added. After cold start, idle preheating should be carried out to fully lubricate the friction surfaces with lubricating oil and avoid immediate high-speed operation. In daily use, it is necessary to regularly replace the engine oil and oil filter to prevent impurities from entering the lubrication system, and to avoid long-term overload and detonation operation of the engine, reducing the impact load on the crankshaft and extending its service life.