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How a Special Gardner Oil ist Rebuilds Engines

13th August 1948, Page 32
13th August 1948
Page 32
Page 33
Page 32, 13th August 1948 — How a Special Gardner Oil ist Rebuilds Engines
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IWAS recently able to compare the methods used by fleet operators in the overhaul of oil engines with those employed •by a specialist engineering concern, F. G. Smith (Motors), Ltd., High Road, Goodmayes, Essex. Some nine Gardner units pass through the company's engine. reconditioning section each week and are completely rebuth in about a fortnight.

The first stage in giving a Gardner engine a new lease of life is to degrease the various components as they are dismantled. Special attention is given to parts that will ultimately call for machine grinding, as if any trace of greasy foreign matter be allowed to remain on the journals or crankpins of a crankshaft, for instance, the surface finish would be seriously affected.

As a matter of general policy, all crinkshafts are reground. the machine employed being a Van Norman heavy-duty crank grinder. Similarly, it is routine to test all crankshafts for soundness on a magnetic crack detector, so that there is no chance that a faulty shaft will be put back into service. Gardner engines are fitted with white-metal big-ends and bronze small-ends, and both these bearings are jig-bored exactly to size on a special machine, so that subsequent treatment by hand scraping is not necessary.

Before the rods reach this stage, however, they are tested for truth by the simple expedient of threading the big-end housing on to an accurately ground bar, the dial gauge being used on a test piece passing through the small-end. The whole set-up is, of course, mounted on a marking-off table.

Like the white-metal big-ends, the main bearings are not touched after thay have been line-bored. The Newton line-borers used are normally hand-operated tools, but as a steady continuous turning movement gives a better surface finish, they have, in this instance, been mechanized through the agency of a Flextol flexible drive. To couple up the power, the operative merely slips the dog-clutch coupling over the end of the boring bar, and controls the power as if he were using a portable electric drill.

The cylinders are treated according to the particular requirements of the customer. In certain cases undersize *30

liners are specified, so that the first rebore will bring the bores back to standard, leaving sufficient material for two further rebores. In the case of pistons, all well-known• makes are available, so that if an operator has a 'particular preference, his wishes are met.

Before the main bearings are bored, the cylinders are attached to the crankcase and this assembly is mounted on a " tray " which stays with the engine from then onwards. The fitting of the cylinders at this stage not only provides an accurately machined base for subsequent location purposes, such as during the boring of the main bearings, but imparts essential rigidity to the crankcase during the operation.

I was particularly impressed with the orderly sequence in which the various reconditioning operations were being carried out, and the fact that no operative was expected to manhandle any large component.

Careful Inspection

The section has a full-time inspector, and it is his job to examine the components after they have been dismantled and cleaned. It is he who lays down' the nature and the extent of the work to be undertaken on any of the components, and it is his responsibility to see, ultimately, that the work has been carried out to instructions. By adopting this system, the foreman is not concerned with such matters as the amount of metal which has to be taken off a crankshaft, or the limit of oversize on a cylinder bore.

On a rebuild of this nature, with which goes a guarantee covering 40,000 road miles, every component subject to wear or deterioration, mint be carefully examined and, if faulty, made good. As an instance, the carbon-type seal in the water pump is-lapped to a perfect fit, using a mixture of flour sulphur and oil between the contacting surfaces. the pump being finally tested on the machine that performed the lapping operation. During this test, the pump outlet is sealed, so that the only possible outlet for the water would be past the pump-spindle gland.

I quote this as an example of the degree of attention which is paid to small, but important, features. As another instance, there is the treatment of the engine piping. Vibration and time will harden a copper pipe to a stage where it may fracture, so to guard against this possibility all pipes are reannealed before being refitted.

There is a special department which deals with fuel pumps and injectors, the former, which are reconditioned if necessary, being calibrated on a Hartridge test bench. Injectors are tested for spray by the aid of hand apparatus, this type of tester being preferred to the mechanized form.

When an engine has been fully rebuilt it is subjected to a bench test. The unit is coupled to a 55 kW generator, each engine being run for a total period of four hours. It was in connection with this testing that I obtained another insight into the thoroughness of the service of F. G. Smith (Motors), Ltd.

During the tests the engine is coupled to an outside oil filter of large capacity, and after a batch of 20 engines has been tested the solid matter in the filter is extracted and examined to discover its nature. By adopting this procedure. it has been possible to conttol almost exactly the internal cleanliness of rebuilt engines.

I saw a filter paper on which the solid particles from the filter had been laid out, and the small quantity of foreign matter from 20 engines was a striking tribute to the scrupulous internal cleanliness of the engines that had been tested. I was told that every tenth engine was completely dismantled, after test, for examination, and that, in all cases, the sumps were removed and examined after the bench test..

The readings obtained are compared with the maker's own chart, and the job is considered good enough only when the curves more or less agree. There is no question that a Gardner engine rebuilt by this organization remains a genuine Gardner product, which is perhaps the best corn pliment I can pay to Mr. F. G. Smith, the company's chairman and managing director.

The spare-parts problem causes more anxious moments, perhaps, than the whole of the actual work involved in reconditioning a unit, but here, again, are excellent organization and planning, as I found the stores trays for major spares, such as chains, valves and push rods well stocked.


People: F. G. Smith

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