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THE GROWING USE OF CYLINDER LINERS.

17th July 1928, Page 53
17th July 1928
Page 53
Page 53, 17th July 1928 — THE GROWING USE OF CYLINDER LINERS.
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A Feature of Design or of Subsequent Alteration which Simplifies Maintenance and Secures Longer Engine Life.

IN recent years the practice of fitting cylinder liners for the purpose of correcting wear or damage to the bores of cylinders of commercial petrol engines has grown considerably and it is now followed by several of the largest passenger-carrying companies in this country. The practice has many definite advantages over the alternative method of grinding the cylinder to a larger diameter and fitting an oversize piston.

It has repeatedly been found, especially where there is a limited number of spares available, that a certain amount of confusion always arises when several standards are used. One often finds the standard cylinders in stock, but no pistons, or there may be secondstandard pistons but no cylinders, and the same difficulty persists with the piston rings. Another point is: One has to carry much larger stocks whenever more , than one standard of fitting is adopted. Using the liner method obviates the fitment of oversize pistons and rings, and only one standard need be stocked. • ' The method which has found favour for fitting liners is the outcome of some years of experiment and experience. The cylinders are bored out from 3 mm. to 6 mm. larger in diameter (according to the thickness of cylinder wall) than the original bore. The liners are machined all over, the outside being ground .001 in. to .002 in, larger than the bore of the cylinder to allow for tight fitting. The bore of the liner is left for grinding and is finished after being pressed into the cylinder. To safeguard against any possibility of endwise movement of the liner, a small flange is provided on one end of the liner ; this flange fits into a recess about 3 mm. or 4 mm. deep machined in the cylinder.

If the cylinder be of the detachable head type, the recess will come at the top of the cylinder and the head being tightened down on this flange will prevent any movement. In the case of the integral head type the recess will be at the bottom of the cylinder, and the flange of the liner will be a little larger in diameter than the piston bore of the crankcase.

Another great point is that the liners are always replaceable when they become worn or damaged by a gudgeon pin and at very little cost, since the cylinders have already been bored out to take them.

From the point of view of economy this process has much to recommend it. To fit liners is cheaper than to supply oversize pistons. There is another point worth considering : that if anything should happen to one bore the fault may be corrected by the fitting of a new liner without having to interfere with the other • bores, whereas by the old method all cylinder blares would have to be ground and new pistons fitted.

In addition to the advantages mentioned, there is a great increase in the mileage or life of lined cylinders

A comparison of the microstru used for cylinder work and (rig showing in the latter case an ev as compared with that of the ordinary unlined cylim ders. The liner being of iron, centrifugally cast, it has far better wearing qualities, owing to the much better distribution of free carbon or graphite.' The two photographs which are published on this page show the difference between the microstructure of an ordinary grey cast-iron, as generally used for cylinder work, and that of a centrifugally cast liner, the magnification in each case being the same, namely, 70 diameters.

Some very useful figures have been taken from the records of a large number of cylinders, and they may here be set out :—

New cylinders fitted as received from maker (not lined).-362 blocks tested, average miles per .001 in. wear 1,735.

'Cylinders fitted with steel liners.424 blocks tested, average miles per .001 in. wear 1,172.

Cylinders fitted With centrifugally cast-iron liners.991 blocks testea, average miles per .001 in. wear 2,903.

Experiments

were carried out with steel liners over a considerable peilod ; these were found to be very unsatisfactory.

In comparing

these results it must not be forgotten that cylinder wear varies with the design of the engines and depends largely upon the conditions under which the engines have to run, but the comparison still holds good as between lined and unlined cylinders. In all the instances mentioned the lubricating oil was similar.

It will be obvious that, as the result of securing this

increase of life with lined cylinders, a large saving is effected by the lesser number of times that the cylinder need be removed owing to cylinder wear, whilst a better oil consumption is obtained on account of the piston becoming less sloppy or slack, because of the better wearing qualities of the liner.

Some commercial manufacturers in this country, alert in detecting the requirements of those whose business is to operate either public service or road transport fleets, are meeting this growing demandfor higher wearing qualities in cylinders by incorporating in their design centrifugally cast liners in the cylinders. Some manufacturers are fitting what is called a wet liner, which provides for cylinders cast separately from the block atul fitted so that the water comes in direct contact with and around the liners themselves, a suitable joint being provided to prevent any water getting into the crankcase or cylinder bore. One of the advantages of this liner is that its employment permits a much simpler cylinder to be cast, dispensing with the complex core work for the water-jacketing and enabling the foundry to concentrate with greater ease on the production of a sound block casting and leaving the wearing properties of the cylinder to be provided for in the centrifugally cast liner. cture of (left) grey cast-iron as ht) of a centrifugally cast liner, en distribution of the graphite.

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