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Why Not Delay That Rebore? •

25th March 1938, Page 44
25th March 1938
Page 44
Page 44, 25th March 1938 — Why Not Delay That Rebore? •
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An Engine-reconditioning Service Utilizing Special Rings. Existing Pistons Made Oversize by Peening

TSIE use of special piston rings as a' .1 means for compensating for cylinder-bore wear is usually looked upon with a certain amount of scepticism, but why this should be so is not quite clear.

There are cases, of course, where a rebore is unquestionably called for, but many thousands of engines which are rebored could have had this major operation delayed for some thousands of miles or so by the use of special rings.

We were recently introduced to the Ramconizing process of engine reconditioning, for which the sole concessionnaires in this country are Messrs. Thompson's Cylinder Service, 266-8, Beulah Hill, Norwood, London, S.E.19.

In addition to the use of special rings, which, in themselves, prove effective in cases of moderate wear, this new service is extended to the treatment of existing pistons, so that results comparable to those obtained by a rebore and new piston can be looked for.

The design of the rings has received considerable thought and, in the case of both compression and scraper ring, an inner spring ring forms part of the unit. In order to provide for almost immediate bedding down, the ring face is given a one-degree taper, the widest portion of the ring being at the bottom.

A point in connection with the inner spring ring of the Ramco scraper ring is the provision of recesses on the lower edge. These provide for an unobstructed flow of oil through the ring slots and holes in the ring grooves. By arranging an inter-slot in the bridge pieces the flow of oil around the ring face is more or less metered, with the

result that there is never an excess of oil in one slot at the expense of others. The low radial pressure of the Ramco rings was particularly noted.

Regarding the piston-reconditioning side of the service, the method of resizing depends on the piston type. With a split-skirt piston, it is possible to use an expander, which is in the form of a spring ring of such conformation as to exert thrust where required, i.e., on the piston' faces at right angles to the gudgeon pin.

With full-skirt pistons, a peening process is used, a mechanical hammer operating on the inside of the piston, which is securely retained in a closely fitting steel sleeve to prevent deformation in the area of the hammer blows. By way of demonstration, a piston of standard size was, in a few minutes, given an oversize of .005 in. ; the readings, before and after, being taken by ourselves.

It may be mentioned that the object of so treating the pistons is to prevent rock, which, if allowed to take place, will quickly negative any efforts which may have been expended in the way of fitting special rings.

As an instance of what may be expected following engine reconditioning by the Ramco process, we may mention the case of a vehicle which was consuming engine oil at the rate of one gallon to 250 miles. Following treatment, we are told that the oil consumption dropped to one-tenth of a gallon for the same mileage.

We understand that the cost of such an overhaul is roughly half that normally charged for a rebore.


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