Reasons for Cylinder Liner Wear and Ways to Measure it

All types of machines and parts get worn out due to continuous usage and working. Proper maintenance and routine checks are necessary to ensure that the machines work for a longer time. In this article we will have a look at various reasons that leads to cylinder liner wear and how it can be minimized. 

Reasons for Cylinder Liner Wear

The wear in the cylinder liner is mainly because of following reasons:-

1) Due to friction.
2) Due to corrosion.
3) Abrasion
4) Scuffing or Adhesion

Frictional Wear

Whenever two surfaces slide over each other, friction is produced which leads to wearing down of both the surfaces. In liner wear the surfaces are piston rings sliding over the cylinder liner. The frictional wear depends upon various factors like speed of movement between the surfaces, material involved, temperature, load on engine, pressure, maintenance, lubrication, and combustion efficiency.

Corrosion

The wear due to corrosion is cause due to the burning of heavy fuel oil in the combustion space. This happens because heavy fuel oil contains high sulphur content. During combustion, acids are formed inside the space which should be neutralized by cylinder oil which is alkaline in nature. The production of acids will be more if sulfur content is more, leading to the formation of sulphuric acid. Sulphuric acid is formed due to absorption of the condensate or moisture present inside the combustion space.

Sulphuric acid corrosion is found more in the lower part of the liner as the temperature of jacket water is very low. Corrosion due to sulphur will be high due to the presence of water in fuel and condensate in the air. This wear is generally seen between the quills. The wear near the quills enlarge and gives a characteristic of the clover leaf shape to the wear pattern. This phenomenon is called clover leafing.

Abrasion

This type of wear is due to the hard particles present and formed during combustion. Catalytic fines in the fuel and the ash formed during the combustion causes abrasive wear.

Adhesion or Scuffing

This is a form of local welding between the particles of piston rings and the liner surface. As the piston is moving inside the liner, the welding which has occurred breaks and leads to the formation of abrasive material. The abrasive material will increase the rate of wear of the liner. This is generally caused by insufficient lubrication due to which large amount of heat is produced and microscopic welding of rings and liner surface takes place. Due to this type of wear the liner loses its properties to adhere cylinder oil to the surface. One more reason or this phenomenon is polishing of the surface caused by scuffing, giving liners a mirror finish.

How Cylinder Wear Can be Minimized?

Cylinder wear can be minimized by carrying out the following steps:

1) By avoiding any ingress of water inside the liner by properly treating the fuel oil.
2) By maintaining the correct feed rate and grade of cylinder oil.
3) By avoiding ingress of moisture from the charge air.
4) By maintaining proper jacket water temperature.

How Cylinder Liner Wear is Measured or Gauged?

Cylinder liner has to be gauged at regular intervals as specified in the maintenance manual. The records of gauging are kept for each cylinder and wear rate is calculated.

The liner has to be cleaned and inspected before the gauging. Generally while taking the measurement the temperature of the liner and micrometer should be kept at the same temperature. If the temperature exceeds than that of the liner or vice versa then the readings has to be corrected by multiplying the value with the correction factor and deducting the value obtained from the reading taken. The reading obtained at the end will be the correct reading.

The cylinder liner wear is measured by a standard template, which consists of  strategically positioned holes, wherein the micrometer is placed and the readings are taken.

The readings are taken for both port starboard and forward aft positions. This is done because the wear is not same in both direction and the ovality is checked.

The wear rate will be different in the liner. The wear will be more in the top one third part as combustion takes place there and temperatures and pressure is also very high at the top.

An approximate normal wear rate of the liner is about 0.1 mm per 1000 running hours.
The wear rate increases if the engine is overloaded. Generally the liner has to be replaced when the wear is about 0.6-0.8% of the bore diameter or as per the manufacturer’s recommendation.