03-0050 Recognizing dust damage to pistons and cylinder walls or liners
Note
If excessive oil consumption exists or in the event of engine failure, it is often unclear whether dust damage or normal wear and tear exists.
Possibility of recognizing problem
Severe dust deposits in the elbows of the intake passages at the clean air end (between air cleaner and engine) are a reliable indication of dust damage. A very fine film is permissible on engines with an oil bath air filter.
The shank wear pattern of a piston and the honing pattern of the cylinder also provide indications of damage caused by excessive dust levels.
Piston without dust damage
The shank wear pattern of the piston is characterized by its large area and the machining grooves are still clearly visible within this area.
Note
The machining grooves around the circumference are intentional recesses which are filled with oil and contribute to improved lubrication.
Piston with dust damage
The wear pattern on the shank has a mat appearance (as if rubbed with pumice stone) and the machining grooves are completely worn away within the contact area. In this advance stage, there are already slight fretting streaks on the shank and the piston rings are sharp-edged.
Cylinder walls and liners without dust damage
The honing is visible over the entire contact surface - more or less clearly depending on the type of engine. The honing may be partially worn away at the reversal point of the first piston ring.
Cylinder walls and liners with dust damage
The signs of machining from honing are either no longer visible at all or only very weakly.
In this advanced stage, a wear shoulder can be felt at the reversal point of the first piston ring. Poor sealing of the intake passages at the clean and unfiltered air ends (upstream and downstream of the air cleaner ), grooves or chafing points at the intake hose, sharply increased dust deposits, entraining of dirty oil from the oil bath air filter (if excessive quantity of oil), installation of non-approved start pilot systems and such like may cause dust damage.
When performing maintenance work, therefore, carefully inspect all the intake passages and connections so that concealed leak points or cracks are also detected.