Inspection
1. Even if you decide to replace the main and connecting rod bearing shells, it is necessary to subject the old bearing shells to the most thorough inspection, since such an inspection can provide valuable information about the condition of the engine (pic. 20.1).
2. Defective bearings may be caused by lack of lubrication, dirt and other foreign particles, motor overload or corrosion. Regardless of the cause of the defect, its cause must be found and eliminated before the engine is assembled, otherwise the defect will reappear.
3. To inspect the liners, remove them from the bearings and caps. Lay them on a clean surface in the order they are installed in the engine. This will allow you to compare the condition of the liners with the condition of the respective crankshaft journals.
4. Dirt and other foreign particles enter the engine in different ways. They can remain there after disassembly - assembly, they can penetrate through the filter or through the crankcase ventilation system. Then they can get into the oil, and with it - into the bearings. Often, metal particles that have entered the crankcase during machining are found, as well as products of natural wear of engine parts. Sometimes you can find particles of abrasive left in the engine after surface treatment, such as honing. Regardless of origin, small hard particles are embedded in the soft surfaces of the liners and are well distinguished. Large particles do not penetrate into the material of the liner, but scratch the liner and neck. The best way to prevent bearing damage from this cause is to thoroughly clean all parts and reassemble the motor in a sterile environment. It is also recommended to change the oil and filter more often during engine operation.
5. Insufficient lubrication (or stop the oil supply) has many interrelated reasons. Engine overheating (can make the oil film too thin), motor overload (can contribute to the extrusion of the oil film and from the bearing), oil leak (increased bearing clearance, oil pump wear) - all this can lead to a violation of the normal regime of lubrication of bearings. Blocking the lubrication hole of the bushing if it is installed incorrectly will also leave the bearing without lubrication and cause destruction of the bearing. An external sign of bearing failure due to lack of lubrication is the anti-friction layer of the liner worn down to the base. Sometimes the steel base of the liner may turn blue due to overheating.
6. Bearing life can sometimes be caused by driving style. Running the engine at low speeds at wide open throttle creates high pressure on the bearings and can cause grease to be squeezed out. Such loads create high stresses on the surface layer of the liner material and cause fatigue spalling of the material. In the end, the anti-friction material can simply crumble and wear off the steel base. Frequent driving for short distances can lead to corrosion of the bearings. This is due to the fact that condensate and gases that cause corrosion are not removed from an insufficiently warmed-up engine. These products get into the oil and form acids and sludge there. Together with the oil, they enter the bearings and cause corrosion.
7. Improper bearing assembly can also cause bearing failure. Overtightening the mounting bolts can reduce the operating clearance in the bearing and thus deprive it of sufficient oil. Dirt that got between the liner and its bed during assembly, when the bearing is tightened, can cause its local deformation and further rapid failure.
Insert selection
8. If the liners are damaged or excessively worn, and also if the clearance in the bearings does not match Technical Data (see paragraphs 24 or 26). it is necessary to replace the liners by selecting them as described below. However, if the cash has been resharpened, oversize inserts must be installed and in this case the procedure described below must not be used!
9. In the workshop where the shaft was reground, they will help you choose the right size liners or advise you on how to do it. The repair size of the liners depends on how much metal has been removed from the necks. The groove is usually done in increments of 0.25 mm. Sometimes it is necessary to remove different parts of Meiariria from the main and connecting rod journals. especially in cases of damaged connecting rods. As a rule, a machined crankshaft has a marking that indicates which layer of metal has been removed. For example, marking "25-25" means that both the main and crankpins have been machined 0.25mm. Such a crankshaft requires the installation of liners with repair dimensions 0.25 mm less than the nominal (1st repair size).
10. Regardless of how the liners were selected, the main criterion for checking the correctness of the choice is the clearance in the bearings, which must correspond to Technical Data. Use a 'plastic feeler gauge' to check the clearance.