Q Some engine makers have changed
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over from wet-type cylinder liners to the dry type despite the known advantage of wet liners that they provide better heat dissipation. What are the advantages of dry liners?
ADry liners have two advantages, namely structural rigidity and freedom from cavitation erosion. in a dry-liner engine the liner sleeves are in effect inner cylinder bores of outer bores that farm part of the block structure which is thereby given additional strength compared with a structure having wet liners that are not an integral part of the block.
A wet liner has better heat dissipation properties than a dry liner tlecause the heat has a relatively short path to the cooling water and its flow is not interrupted by the -gap" between the surfaces of the liner and the block. This disadvantage can, however, be minimized by giving the two surfaces a fine finish that provides intimate contact between the surfaces.
Cavitation erosion is produced by cyclic high-frequency distortions of a wet liner resulting from variations of cylinder pressure and of thrust pressures produced by the pistons. These may be Likened to repeated hammer blows on the inside of the bore and they result in the liquid on the outside being momentarily displaced to form small vacuum pockets on the surface. These pockets immediately collapse and the liquid impacts on the metal with considerable force. When the veh,cle is operating at higher outputs, these impacts are continuous and eventually cause erosion of the surface. And this may necessitate relatively early replacement of the sleeves.
It is pertinent to add that dry liners can readily be rebored. When wet liners are excessively worn they are replaced by new liners. While easy replacement has obvious advantages an operator may well prefer to rebore if the necessary facilities are availabie.