Cylinder liner from older ,lower powered engine had a uniform walk thickness and the cooling was achieved by circulating cooling water through a space formed between liner and jacket.
The cooling water space was sealed from the scavenge space using o – rings and a tell tale of passage between o rings led to the outside of the cylinder block to show a leakage.

To increase the power of the engine for a given number if cylinder.

Increase efficiency of engine
Or more fuel must be burnt per cycle.

If burn more,the volume of combustion since must be increased and finally fir combustion of this greater mass of fuel ,large diameter liner having thickness at top accommodate higher stress and prevent cracking of material.
But if thickness of liner is increased,cooling water is further away from working surface of liners.Increased surface temperature means that material strength is reduced, and the oil film burnt away,resulting in excess wear and increased thermal stressing.

–The alternative is to take cooling water close to the liner wall, and using tangential bore cooling is one way to do this without compromising the liner’s strength.

Holes are bored from the underside of the flange formed by the increase in liner diameter.The holes are bored upward and at angle so that they approach the internal surface of the liner at. Holes are then bored radial around the top of the liner so that they join with the tangentially bored holes.

It was found on some large bore, long-stroke engines,that the undercooling took place further down the liner.Why is this a problem?

The hydrogen in the fuel combines to form water with the oxygen and burns. This is normally in the form of steam, but it will condense on the liner surface if it is cooled and wash away the film of lube oil. Fuels contain sulfur as well. This burns in the oxygen and combines the products with the water to form sulfuric acid.
If this condenses on the liner surface, then corrosion can take place. Once the oil film is destroyed, wear will occur at an alarming rate.One solution is to insulate the outside of the liner so that there was a reduction in the cooling effect. On the latest engines, the liner is only cooled by water at the very top, relying on the air in the scavenge space to cool the lower part of the liner.

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