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When the diesel generator is working, the surface of the crankshaft journal bears a considerable unit pressure, and the sliding friction speed is relatively high. The heat dissipation effect of the journal is poor, and the surface of each journal is highly susceptible to abrasive wear.
Therefore, the diesel generator must check the crankshaft during maintenance, find out the situation, and choose the correct repair method to ensure the fatigue strength and wear resistance required for the diesel generator crankshaft.
Reasons for diesel generator crankshaft failure
Taper Wear of the Connecting Rod Journal
The reason for the taper wear of the connecting rod journal of the diesel generator is that the oil passage leading to the connecting rod journal of the diesel generator is inclined. As the crankshaft rotates, the smooth diesel generator slips under centrifugal force. The mechanical impurities in the oil accumulate on one side of the connecting rod journal of the diesel generator set, which accelerates the wear of the side journal and makes the diesel generator set wear into a tapered shape.
Bending of the Connecting Rod and Wear of the Leading Journal
The bending of the connecting rod and the non-perpendicularity between the centerline of the cylinder and the crankshaft’s centerline will cause the journal to be subjected to uneven force in the axial direction and cause wear. The wear of the leading journal of the diesel generator is mainly due to the influence of the centrifugal force of the connecting rod, the connecting rod journal, and the crank arm, which causes relatively large wear on the side close to the connecting rod journal of the diesel generator and the bearing. The stress is concentrated on the rounded part of the journal of the diesel generator and around the oil hole, which is prone to cracks. The presence of cracks will cause the crankshaft of the diesel generator to break.
Presence of Cracks and the Need for Flaw Detection
Therefore, a flaw detector is required to detect the presence of cracks. If there is a circular or longitudinal crack with a crack length greater than 20mm, it should be blown off with a chisel or a gas-cutting gun, and corresponding measures should be taken after arc welding.
Scratches and Burns on the Journal Surface
Scratches and burns may also appear on the journal surface. Scratches are mainly caused by a dirty diesel generator set oil, and burnt tiles of diesel generator cause burns sets due to insufficient lubrication, too thin oil, or blockage of oil passages for the connecting rod journal of silent diesel generators, eccentric grinding, and concentric grinding methods can be used. The concentric grinding method keeps the axial position of the connecting rod journal unchanged after grinding; meaning, the crank radius and distribution angle remain unchanged. The eccentric grinding method is based on the positional grinding of the worn connecting rod journal surface. At this time, the position of the centerline of the journal of the diesel generator and the radius of the crank have changed. Generally, the crank radius after grinding is larger than the original, so the compression ratio increases.
Uneven Variance in Cylinder and Importance of Crankshaft Repair
The cylinder of the diesel generator varies unevenly. At the same time, the center of mass of the entire crankshaft of the silent diesel generator is not on the centerline of the leading journal of the crankshaft, which causes the crankshaft to be unbalanced and generate additional power when the quiet diesel generator rotates. Because the crankshaft of the diesel generator set is often damaged during use, and the price is relatively high. Therefore, it is significant to repair the crankshaft.
Preparations for extending crankshaft life
- Correctly repair pre-existing damage on the main bearing centerline and connecting rod.
- Insert the crankcase bearing shell and bearing cap. Always remember the continuity and cleanliness of the oil holes and the diameter of the main bearings and connecting rod journals.
- Thoroughly clean the oil passages in the crankcase with compressed air.
- Thoroughly lubricate the sliding surfaces of the bearing shells with an approved oil.
- Install the main bearing caps. Be sure to note the number of the main bearing cap. Apply lubricating oil to the main bearing screws and tighten to the specified tightening torque.
- Check that the crankshaft turns freely. Check the axial play of the crankshaft and adjust if necessary.
Tips to increase the service life of the crankshaft
- Have sufficient oil volume in the engine (according to the generator manufacturer specifications).
- Proper oil specification, do not use contaminated or stale oil.
- Avoid contaminating engine oil with coolant or fuel.
- Prevent faults in the oil circuit that could cause oil pressure problems (such as failure of the oil pump, failure of the oil pressure relief valve, loss of the injector nozzle or oil filter housing, clogged lines and pipes, etc.).
- Prevent the engine oil from getting too hot, which may cause the lubricating oil film to rupture.
Signs of a bad diesel generator crankshaft
Because the crankshaft is an integral part of the engine in the diesel generator, a damaged crankshaft is usually immediately noticed. Some root causes of a bad crankshaft are:
- Forging or casting defects
- insufficient lubrication
- bearing wear
- Loose main bearing cover
- Bearing hole deformation
- Improper bearing clearance
- bearing failure
The result of these conditions can be cracked or even broken crankshafts. You may hear the engine rattle or notice low engine oil pressure. In severe cases, the engine will stop running.
If you notice any of these signs, shut off the engine. Don’t try to run it in this condition.
Causes of crankshaft misalignment
When a diesel generator’s crankshaft is fully assembled into the engine, it is a massive component. Initially, align the entire crankshaft in a straight line (the connection from the center of the crankshaft forms a straight line) and set it on top of the main bearings.
But over time, the straight line may be deviated and misaligned due to various factors. Some misalignment is acceptable within limits, but if it exceeds the manufacturer’s ratings, failure to do so could result in crankshaft damage or even breakage.
The causes of crankshaft misalignment are as follows:
- Damaged or worn main bearings
- Loose engine foundation bolts cause vibration
- The main bearing bolts are loose, and the main bearing is damaged
- The bending moment on the crankshaft is very high due to the excessive force of the piston assembly
- Crankcase explosion or fire
- Defective or worn intermediate shaft bearings
- Deformation of the platen – damage to the beam
- Tie bolts are loose or broken
- Structural weakening due to corrosion
BISON is one of China’s earliest generators and diesel generator manufacturers. The main products are diesel engines, generators, and diesel generators, providing users with one-stop design, supply, commissioning, and maintenance services at any time. BISON always insists on employing first-class talents, building first-class enterprises, manufacturing first-class products, creating first-class service, and striving to build a first-class domestic enterprise. If you have any questions, please visit our website or email [email protected].
Diesel generator crankshaft
You may hear the engine rattle or notice low engine oil pressure (via gauges or warning lights). In severe cases, the engine will stop running. If you see these signs, pull over immediately and shut off the engine. Don’t try to drive it any farther.
Unfortunately, crankshaft repair is a complicated process that professionals should only do. The bearing journal grinding must be carried out on special equipment.
The crankshaft is the backbone of the internal combustion engine. The crankshaft is responsible for the regular operation of the engine and converts linear motion into rotary motion.
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