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22nd November 1963
Page 37
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IMPROVED lubricants, design and more accessible layouts had done a great deal to meet the requirements for longer engine life and easier, quicker reconditioning methods which had been demanded in recent years. Mr. G. W. Yarwood, of Hepworth and Grandage Ltd., in his award-winning paper "A brief survey of cylinder liner, piston and ring technique" (presented to the Institute of Road Transport Engineers in London yesterday) said that this demand was the result of rising workshop and operating costs.

Many interesting points were made in the paper, which was a review of cylinder liner, piston and ring techniques covering both design and overhaul. Dealing with wet liners, Mr. Yarwood said that blocks must be carefully designed and in reconditioning one Should look for topface distortion. A breaking stress could easily be raised at this point if the seating was not true, flat and free from dirt and rust. To avoid heavy cross stresses, the gasket should not exert pressure across the full top-face of the flange.

Liner Cavitation One trouble affecting wet liners, which was dealt with fully, was cavitation erosion attacking the outer surface of the liner in contact with the cooling water. This occurred usually in the form of pits in the surface of the iron. Many preventive experiments had been tried on designs where the trouble occurred. Varying success had been obtained with metal sprayings and coatings of copper, resin and aluminium oxide, but none seemed 100 per cent successful although chromium plating appeared to be the best remedy to date, with nickel plating and ceramic coating being effective to some degree.

Most methods, said Mr. Yarwood, have one thing in common-,-they are expensive. There was uncertainty in some places as to the most. suitable bore finish, but of importance was that a burnished finish must be avoided if the rings are to bed in rapidly. In fitting new rings into a worn bore, the glaze should be removed for the same reason.

Considerations in the design of pistons were dealt with, and this was followed by a general review of research, design and development practice of components.

Re-ringing with special ring equipment, or fitting new pistons with special rings, was becoming increasingly prominent at the intermediate dock stage of overhaul. Practically every piston ring maker had invented an "infallible " oil control ring. Types offered were described and the life expectancy of overhauls using this type of equipment were said to depend on the

use of good lubricating oil. No oil control ring could contend with the buildup of oil sludge and a good-quality detergent oil was an economy.

Well Established The chrome-plated top ring was well established throughout the world and the only problem—that of bedding-in—had been overcome in several ways—by tapering the periphery, by giving it a fineturn phonographic" finish, and by coating it with a very mild abrasive.

In closing, Mr. Yarwood said that from the earliest days the cast-iron ring had remained supreme. The material, lent itself readily to modern manufacturing methods and as it was amenable to chrome plating and various surface treatments a constantly improving product could be produced economically.

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