Notes On Assessing Wear On Connecting Rod Bearings And Connecting Rod Journals - AH03.10-P-0001-03MM
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 vehicles must be equipped with bearing materials free of heavy metals after a repair.
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 connecting rod bearings (1) as a set.
The following notes should help with the assessment of the connecting rod 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 connecting rod 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 connecting rod journals (2) into the damage diagnosis.
Wear or damage to the connecting rod bearings (1) frequently occur as a result of the following points:
- Lacking engine oil
- Poor engine oil quality (oil viscosity) or engine oil thinning/contamination, e.g. by fuel entry
- Soiled or damaged oil filter
- Fault in oil circuit; e.g. oil pressure is too low
- Too little or too much clearance between connecting rod bearings (1) and connecting rod journals (2)
- 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.
Connecting rod bearing (1) without damage
The connecting rod bearing (1) is uniformly smooth across the entire connecting rod bearing surface, with no visible score marks and no wear to the antifriction coating (arrow A). Depending on the connecting rod bearing technology used, the overlay may vary from high-gloss to matt or dark.
Continue to use connecting rod bearings (1).
Connecting rod bearing (1) with normal running tracks
The connecting rod bearing (1) is uniformly smooth on the largest section of the connecting rod bearing surface, with no visible score marks and no wear to the antifriction coating (arrow A).
Isolated embedded particles are to be classified as non-critical. Continue to use connecting rod bearings (1).
Connecting rod bearing (1) with extensive wear to antifriction coating (arrow B) on engine OM607/622/626
The antifriction coating of the connecting rod-side bearing shells (yellow and gray) exhibits wear to the antifriction coating (arrow B). The bearing material underneath (copper colored) is exposed and displays a typical, safe running profile.
Continue to use connecting rod bearings (1). A major assembly replacement is not required.
Two black dashes on the bearing race spine of the connecting rod bearing (1), approx. 30° to 45° below the end of the connecting rod bearing (1)
Inconsequential imprints on the bearing shell spine of the connecting rod bearing (1) from the coating process during production. They do not exert any influence on bearing usage.
Continue to use connecting rod bearings (1).
Running surface on connecting rod bearing (1) with score marks (arrow C) Score marks (arrow C) are clearly visible and clearly perceptible on the
connecting rod bearing surface. These are due to dirt and foreign objects in the oil circuit caused, e.g.:
- By faulty oil filter
- By use of grinding materials during engine repair
- By insufficient cleaning during engine repair
Do not continue using connecting rod bearings (1).
Connecting rod bearing (1) with wear in the edge area (arrow D)
Connecting rod bearing (1) has wear on one side in the edge area (arrow D). This can be traced back to a bent or broken connecting rod as a result of a fluid lock. Possible causes of a fluid lock are:
- Aspirated water
- Leaky fuel injectors or injection valves
- Aspirated engine oil, e.g. by defective exhaust gas turbochargers
Do not continue using connecting rod bearings (1).
Connecting rod bearing (1) has seized due to inadequate lubrication
The connecting rod bearing surface exhibits mixed friction as a result of oil starvation damage (arrow E). This is consequential damage due to insufficient oil pressure or plugged oil supply bores.
Do not continue using connecting rod bearings (1).
Connecting rod bearing (1) has seized due to foreign objects
The connecting rod bearing surface exhibits complete destruction (arrow F). The connecting rod bearing (1) has seized up to the supporting shell and has rotated in the connecting rod small end.
Do not continue using connecting rod bearings (1).
Treads (arrow H) on the connecting rod journals (2) without damage and with normal running tracks
The treads (arrow H) of the connecting rod journals (2) are uniformly smooth on the entire surface and without visible or noticeable score marks.
Continue to use crankshaft (3).
Treads on connecting rod journals (2) with score marks (arrow G)
The score marks (arrow G) on the treads of the connecting rod journals (2) are visible and clearly perceptible. These are due to dirt and foreign objects in the oil circuit caused, 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 (3).