03-0050 Recognizing dust damage to pistons and cylinder liners
Note
If oil consumption is high or if the engine fails, it is often not clear whether the damage results from dust or from normal wear and tear.
Possibilities of recognizing dust damage
Severe deposits of dust in the elbows of the intake passages at the clean air end (between air filter and engine) are a clear indication of dust damage. A very fine coating is permissible on engines with an oil bath air filter.
The stem contact pattern of a piston and the honing pattern of a cylinder also provide indications regarding damage resulting from heavy concentrations of dust.
Piston without dust damage
The stem contact pattern of the piston is large in appearance and the machining marks are still clearly recognizable withing this area.
Note
The machining marks around the circumference are intentional recesses which are filled with oil and contribute to improve the lubrication.
Piston with dust damage
The contact pattern at the stem is matt in appearance and the machining marks are completely worn off within the contact surface. In an advanced state, slight seizure marks already exist on the stem and the piston rings are sharp-edged.
Cylinder liners without dust damage
The honing is recognizable over the entire contact surface - more or less clearly depending on the type of engine. The honing may be partially eroded at the reversal point of the first piston ring.
Cylinder liners with dust damage
The machining marks from honing are visible only very weakly or not at all.
In an advanced state, a wear shoulder can be felt at the reversal point of the first piston ring. Poor sealing of the intake passages at the unfiltered and clean air ends (upstream and downstream of the air filter), grooves or chafing points at the intake hose, increased dust deposits, entraining of dirty oil from the oil bath air filter (if excessive quantity of oil used), installation of non-approved start pilot versions and such like can cause dust damage.
When performing servicing, it is therefore necessary to carefully check all the intake pipes and connections so as also to determine any concealed leak points or cracks.