- Piston pins should not be hammered into pin hole
- Piston rings should not be mounted by hand, always use a good quality ring installing tool/expander
- While finally installing the piston & ring assembly in the cylinder, care should be taken that the ring gaps are not aligned and are at equal angles with respect to each other
- Make sure to sufficiently lubricate the piston/ring while inserting in bore, this is required for initial lubrication
- Use a good quality ring compressor while fitting the piston/ring in the cylinder
- The ‘top’ marking on the ring indicates that it should be installed with ‘top’ mark towards top of the piston
- In oil rings with springs, the spring joint should be exactly opposite to the end gap of the end gap
- A good quality circlip plier should be used for installation, also ensure proper fitment of the circlip in one groove and keep the open end downwards in position
- Do not check the tension of the rings by repeatedly pressing it by hand, it can easily disturb the alignment of the end gaps
PISTON RING ASSEMBLY ERRORS
Assembly errors can and will contribute to high base pressure and can cause oil to bypass the rings. This can create a build-up of abrasive carbon, which can lead to ring scuffing, a loss of ring control, and possible piston seizure.
PROBABLE CAUSES
- Piston ring end gap misalignment
- Expander end gap is same as oil ring end gap
When piston failure has occurred, it is extremely important to thoroughly inspect all of the engine components during the disassembly procedure. This thorough inspection will lead you to the possible cause or causes of the piston failure and will ensure that the same piston failure doesn’t occur once the engine is repaired and placed back into service by your customer.
Ring scuffing leads to ring face wear, which results in ring face damage and a loss of ring control. This causes high base pressure, oil consumption and possible piston scoring, due to the abrasive materials created by the ring scuffing condition. This can cause piston seizure if not addressed.
PROBABLE CAUSES
- Fuel wash-down
- Debris ingestion
- Severe overloading during running period
- Lack of lubrication
- Overheating due to pre ignition
- Lean mixture
- Cooling defect
PISTON SEIZURE ON MAJOR & MINOR THRUST SIDE
The skirt area of the Piston exhibits heavy frictional wear with seizure marks on both major and minor thrust sides. It may be concluded that piston clearance was too small. This damage occurs after short operation (new condition), since thermal expansion is impeded by the insufficient clearance.
DAMAGE CAUSED BY JAMMED RINGS
Rings have jammed because of oblique running of the piston losing their sealing effect. Hot combustion gases can blow pass the rings, destroying the oil film. This defect can also be caused by an oil carbon, dirt, metal chips in the case of incorrect assembly.
CAVITATIONS OF LINERS
Cavitations of liner is caused by vibration generated by piston bouncing against cylinder wall , particularly in the region of piston dead center. This causes the water jacket to vibrate too. When the cylinder wall gives in during the vibration phase, a vacuum a generated in cylinder for short time, and vapor bubblers will form consequently.
When the column swings back, these bubbles collapse. The water forced against the surface and erodes the metal.
Source : Article provided by Goetze http://www.goetzeparts.in/learning-centre/tech-tips.html
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Nthoiwa (Thursday, 14 June 2018 14:17)
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