Determine the Cause of Piston Failure

Determine the Cause of Piston Failure based on Inspection and Engine Use

Finding the reason for engine problems is essential in order to prevent future breakdowns. According to Bill Mirth, North American heavy-duty sales manager with the FP Diesel brand of Federal-Mogul Corp., if a piston is found to be at fault, it is critical to find out what caused the piston to fail.

“It’s important to understand that very few pistons actually fail,” says Mirth. “In truth, they are damaged by a faulty operating environment. These conditions commonly include lack of lubrication, abnormal combustion, the presence of debris within the engine, clearance issues that lead to physical contact between the piston and another part and operational issues such as over-reving (sic) or overloading the engine or improper shutdown.”

The life of a piston is directly related to its environment. “As a result, virtually all situations resulting in damage to a piston can be traced to an issue unrelated to the construction and quality of the piston itself,” says Mirth. “In other words, the worst thing a technician can do is simply assume the piston was at fault and ignore the actual cause of the damage. In that case, he’s just throwing parts at the problem, which invariably leads to additional issues.”

Jay Wagner, heavy-duty brand manager with Clevite Engine Parts, cites fueling problems as another cause of piston failure. “If the engine injection system is delivering the wrong amount of fuel, at the wrong time or for the wrong duration and with a poor spray pattern, this can result in excessive heat, erosion or a washing of the cylinder walls with fuel,” explains Wagner.

In order to prevent heat build-up that can lead to piston damage, it is important the correct level of lubrication reaches the piston at the skirt and piston pin. Wagner advises technicians to examine piston oilers. “Many of these are very delicate in relationship to other parts of the engine and are bumped easily, resulting in either a broken or improperly directed oiler,” he says.

Contamination wreaks havoc on pistons, too. Water contamination causes erosion and fuel and lubricant dilution. “Contamination can be water, fuel, particulates from the air intake or foreign objects,” says Wagner. “Particulates can wear the ring lands, resulting in increased oil consumption. Foreign matter can be anything including nuts, bolts, valve train or turbocharger parts, and much of the time foreign matter in the combustion chamber is the result of another component failing.”

Scuffing and scoring are the results of contaminants entering the air intake or lubrication system, eventually leading to piston seizure. If a technician suspects an abnormal level of scuffing is taking place, he should begin inspecting the following: engine coolant temperature; engine oil temperature, level and grade; oil pump; cylinder liner surface finish; piston ring pack design; cylinder pressures and temperatures; piston and ring clearance in the cylinder; incorrect combustion; injector overspray and fuel sulfur content. According to Wagner, a malfunctioning cooling system can sometimes be blamed for piston failure as well.

It is helpful to know the conditions under which the affected vehicle has been operated. “It’s important to know the specific conditions under which the parts were damaged,” says Mirth. “The technician can ask his customer some questions that will help in the overall process of diagnosing the failure and then repairing it.”

“The driver has to be aware of changes in the operation of the engine,” says Wagner. “This can include fluctuations in oil pressure, higher than normal operating temperatures, unusual noises and any change in fuel and oil consumption. After speaking with his customer about the problems the vehicle was experiencing, the technician then needs to ensure that proper repair procedures are addressed.”

Pistons should be inspected for cracks in the bowl due to heat stress, cracks on the surface area of the wrist pin bore and wear in the piston ring grooves.

“A detonation-related issue will be fairly obvious because of the damage to the head of the piston,” says Mirth. “For example, the results of lubricant starvation will be evident on the walls of the cylinder or liner as well as on the piston skirt.

“A shattered piston crown may be an indication of a clearance issue, meaning the piston may have made contact with a valve. A fracture around the piston pin bore might indicate that the pin was installed improperly, which then caused it to seize.”

Piston failure usually leaves a vehicle unable to be driven. If the failure is caught and addressed early, repair can often be limited to simply replacing the piston and sleeve. However, catching the problem early is difficult.

“There always is a great deal of debris deposited in the engine so a complete flushing is required in any case,” says Wagner. “There are many things on an engine that can operate marginally, but pistons are not one of them. From the time the driver or technician realizes there is a problem until the vehicle no longer can be driven can be measured in seconds.”

According to Mirth, repeated engine failure can often be attributed to improper installation of parts or use of the wrong replacement parts. If visual differences can be seen between the old part and the new part, the supplier should be consulted to be sure it’s correct.

The installation requirements in the engine manufacturer’s service manual should be followed closely to ensure maximum component performance and durability.

AMSOIL synthetic motor oils provide superior wear protection for pistons and other wear-sensitive engine components, keeping engines running at top performance for extended drain intervals.