So far as the admission and exhaust valves are concerned, the wearing of the cams, rollers, and lever-pivots is evidenced by a retardation in the opening of these valves and an acceleration in their closing.
The ignition, whatever may be the system employed, is affected by lost motion and is retarded. The engine appreciably loses in power, and its consumption becomes excessive.
Overheated Bearings.—Apart from the imperfect adjustment of a member, it may happen that the bushings of the main bearings of the ends of the connecting-rod,
and of the piston-pivot, may become heated because of excessive play, or of too much tightening, or of a lack of oil, or of the employment of oil of bad quality. The overheating may lead to the binding of frictional surfaces and even to the fusion of bushings if they be lined with anti-friction metal. In order to avoid the overheating of parts, it is advisable, while the engine is running, to touch them from time to time with the back of the hand. As soon as the slightest overheating is felt, the temperature may be lowered often by liberal oiling. If this be inadequate and if for special reasons it is impossible to stop the engine, the overheated part may be cooled by spraying it with soapy water.
If the overheating has not been detected or reduced in time, a characteristic odor of burnt oil will be perceived, accompanied by smoke. The part overheated will then have attained a temperature so high that it cannot be touched with the hand. Should this occur, it is inadvisable to employ oil, because it would immediately burn up and would only aggravate the conditions. Cotton waste should be carefully applied to the overheated member, and gradual spraying with soapy water begun.
In special cases where the lubricating openings or channels are not likely to be obstructed, a little flowers of sulphur may be added to the oil, if this be very fluid. Castor oil may also be successfully employed.
If the binding of the rubbing surfaces should prevent the reduction of the overheated member's temperature, the engine must necessarily be stopped, and the
parts affected detached. All causes of binding are removed by means of a steel scraper. The surfaces of the bushings and of the shaft which they receive are smoothed with a soft file and then polished with fine emery paper. Before the parts are replaced, the precaution of ascertaining whether they touch at all points should be taken. Careful inspection and copious lubrication should, of course, be undertaken when the engine is again started.
Overheating of the Cylinder.—The overheating of the cylinder may be due to a complete lack of water in the jacket or to an accidental diminution in the quantity of water supplied. If this discovery is made too late, and if the cylinder has reached a very high temperature, the circulation of the water should not be suddenly re-established, because of the liability of breaking the casting. It is best to stop the engine and to restore the parts to their normal condition.
It is well to recall at this point that if the calcareous incrustation of the water-jacket or the branch pipes should hinder the free circulation of water, cleaning is, of course, necessary. The jacket may be washed several times with a twenty per cent. solution of hydrochloric acid. After this treatment the jacket should, of course, be rinsed with fresh water before the piping of the water-circulating apparatus is again connected.