B01.40-0032-81
Cavitation without corrosion
During engine operation,the cylinder liners are submitted to pulsation coming from the internalcombustion. Therefore, when a combustion occurs,also occurs an expansion of the cylinder linerwall of fractions of a millimeter due to theforce of the gas in expansion against theinternal wall. After the gas expansion,the cylinder wall returns to its normal dimension. This return occursin a short elapsed time with no possibility of the coolant filling immediately the space created,originating tiny bubbles of vacuum which,when imploding at the cylinder liner wall,detach small metal particles,making a hole in it.
Preventive measures to inhibit cavitation:
Utilize the coolant with the specifications and proportions recommended by the manufacturer (50% additive by volume).
Periodically control the level and the concentration of the coolant.
Replace the coolant with the specifications and proportions recommended by the manufacturer (50% additive by volume).
Replace the coolant at recommended intervals.
Maintain the engine temperature within the recommended operating range.
Maintain the cooling system components in perfect operating conditions (reservoir cap, radiator, hoses, thermostat, coolant pump etc.).
Reuse of cylinder liners affected by cavitation
Cylinder liners with erosion caused by cavitation can be reutilized, provided the erosion depth is less than 0,5 mm, i.e., does not compromise the safety thickness of the cylinder liner wall.
Should its reutilization be possible, when installing, turn the cylinder liners by 90° from its original position, so the corrosion area remains in an area of less expansion, i.e., greater contact with the engine block, avoiding further erosion in this area.
The erosion must not reach the area of the cylinder liner's sealing rings. In this last case, the cylinder liner must be replaced.
Before installing, the cylinder liner must be thoroughly clean in its entire outside wall.
B01.40-0033-81
Cavitation with corrosion
Electrolytic or electrolysis corrosion
Resultsfrom chemical disintegration of metal due to theaction of small electric currents thatarise when two different metals, such asiron and copper, get in contact withwater. This electric current, although weak,with time it ends up attacking the externalwalls of the cylinder liner.
In modern engines,a brass ring is utilized below theliner's collar, so this electricitypasses to the block and from this to the chassis,through a grounding strap.
B01.40-0034-81
Chemical corrosion
Results, chiefly,from oxygen attack present inwater to iron, of which cylinder linersare made, giving origin to iron oxide orrust. This phenomena is accelerated whenthere is a greater presence of oxygen inthe water, due to failures in the sealingof the cooling system, with the possibilityof air penetration through the hoses,connections, faulty caps, low coolantlevel, between others.
Chemical corrosion is also acceleratedby making use of untreated water,with corrosive substances present,as acid or alkaline water, or still by lack ofthe corrosion inhibitors recommendedby the assembler/engine manufacturer.
Corrosion can occur under the following circumstances:
Lack of the recommended additives in the preparation of the coolant.
Incorrect proportion n the mix utilized at replenishing or periodic replacement.
Lack of periodic replacement of the coolant leading to the loss of its properties becoming corrosive.
Use of salty or too acid water in the preparation of the mix.
The engine remained inoperative for too long (over 1 year) or without due preparation for prolonged immobilization.
Reuse of cylinder liners affected by corrosion
Thoroughly clean the cylinder liner removing all oxidation. If the corrosion depth does not compromise the safety thickness of the liner's wall, it can be reutilized.
If the oxidation reached the sealing rings area, the liner must be replaced.