Information On Assessing Wear Of Main Bearings And Main Bearing Journals - AH03.20-P-1000-02MM
Engine All (4xWD, CAR, smart)
Engine All (Light transporter)
Due to statutory change regarding the use of heavy metals, in agreement with vehicle manufacturers, the policy with regard to the use of lead, cadmium, chrome? and mercury for vehicles and their replacement parts has changed.
This also affects bearing materials in engine construction.
As a result, since March 30, 2011, there has been the globally valid specification that, after a repair, vehicles must be equipped with bearing materials free of heavy metals.
The bearing materials free of heavy metals then have an effect on the emergency running characteristics of the engine when there is a lack of lubricant.
All further information regarding bearing materials and their characteristics can be found in commercially available literature.
Always replace main bearings (1) as a set.
The following notes should help with the assessment of the main bearings (1) and should also support with making a professional decision on their condition and further use.
The following illustrated damage profiles are only a selection of the possible ways in which the main bearings (1) might be damaged. Not all of the possible damage profiles are shown here. When assessing the forms of damage, always incorporate the surface condition of the main bearing journal (3) into the damage diagnosis.
Wear or damage to the main bearings (1) frequently occur as a result of the following points:
- Lacking engine oil
- Poor engine oil quality (oil viscosity) or engine oil thinning/engine oil contamination, e.g. caused by fuel ingress
- Soiled or damaged oil filter
- Fault in oil circuit, e.g. oil pressure too low
- Too little or too much clearance between main bearings (1) and main bearing journals (3)
- Inadequate cleaning during engine repair
- Excessive sealant following an engine repair
After an engine repair and before engine start, the oil circuit must be filled with approved engine oil. Then crank the engine several times with the starter until oil pressure is established.
Main bearings (1) without damage
The main bearings (1) are uniformly smooth across the entire main bearing surface (arrows A) with no visible score marks and no wear to the antifriction coating.
Continue to use main bearings (1).
Main bearings (1) with normal running marks
The main bearings (1) are uniformly smooth across most of the main bearing surface (arrows A) without visible score marks and without wear to the sliding layer.
Continue to use main bearings (1).
Two black dashes on the bearing race spine of the main bearing (1), approx. 30° to 45° below the end of the main bearing (1)
Inconsequential imprints on the bearing shell spine of the main bearing (1) from the coating process during production. They do not exert any influence on bearing usage.
Continue to use main bearings (1).
Main bearing (1) has seized due to a foreign object
The main bearing surface (arrows A) exhibits complete destruction. The main bearing (1) has seized up to the supporting shell and has rotated in the main bearing seat.
Do not continue using main bearings (1).
Main bearing (1) has seized due to inadequate lubrication
The main bearing surface (arrows A) exhibits mixed friction as a result of oil starvation damage. This is consequential damage due to insufficient oil pressure or plugged oil supply bores.
Do not continue using main bearings (1).
Main bearing (1) with extensive wear to antifriction coating
The wear-in surface is worn away and the bearing material underneath is exposed. The worn area (arrow B) is clearly visible by the shiny spot. This is normal wear due to a long operating period.
Do not continue using main bearings (1). A major assembly replacement is not required.
Score marks (arrow C) on main bearing (1)
Score marks (arrow C) are clearly visible and clearly perceptible. These are caused by dirt and foreign objects in the oil circuit, e.g.:
- By faulty oil filter
- By use of grinding materials during engine repair
- By insufficient cleaning during engine repair
Do not continue using main bearings (1).
Bearing surface of thrust plate (2) without damage
The bearing surface of the thrust plate (2) is uniformly smooth across the entire surface and without visible score marks. The lubricating oil pockets (arrows D) are clearly visible on both sides of the thrust plate (2).
Continue to use thrust plates (2).
Bearing surface of thrust plate (2) with light score marks and scratches (arrows E)
Light score marks and scratches (arrows E) caused by fine dirt particles in the oil circuit.
Continue to use thrust plates (2), if all thrust plates (2) do not show further damage.
Thrust plates (2) in engine 254, 256, 651, 654 and 656
In engines 254, 256, 651, 654 and 656, the thrust plates (2) are secured on the main bearing (1) at the factory. These serve as assembly aid in engine works. If the fastening points of the thrust plates (2) become loose during engine mode, they are held in position by lugs (arrows F) at the main bearing (1). This is not a defect and does not result in engine damage.
As of engine number 651 XXXX XX 194 505, the main bearings (1) with thrust plates (2) are installed at the 4th main bearing block instead of at the 3rd main bearing block.
Continue to use thrust plates (2) and main bearings (1).
Bearing surface of thrust plate (2) with very visible and perceptible score marks (arrows G)
The score marks (arrows G) are caused by dirt and foreign objects in the oil circuit, e.g.:
- By faulty oil filter
- By use of grinding materials during engine repair
- By insufficient cleaning during engine repair
- By low oil pressure (insufficient lubrication)
Do not continue using thrust plates (2).
Treads (arrow H) on the main bearing journals (3) without damage and with normal running tracks
The treads (arrow H) of the main bearing journals (3) are uniformly smooth on the entire surface and without visible or noticeable score marks.
Continue to use crankshaft (4).
Treads on the main bearing journals (3) with score marks (arrows I)
The score marks (arrow I) on the treads are visible and clearly perceptible. These are caused by dirt and foreign objects in the oil circuit, e.g.:
- By faulty oil filter
- By use of grinding materials during engine repair
- By insufficient cleaning during engine repair
- By low oil pressure (insufficient lubrication)
Do not continue using crankshaft (4).