CAST IRON CAMS.

Star (Christchurch), Volume LXIV, Issue 931, 29 November 1933, Page 11

CAST IRON CAMS.

American Experiments With Special Alloys. A development concerning which news reaches us from the United States of Amenra, seems to present features that "IfA Drove of interest to automobile engineers. 3t has been found that great strength and toughness can be secured Ju a superheated electric furnace cast iron containing certain specific alloying + a . t: it.uents. It is understood that' the total carbon content is low and that nickel and chromium both enter into the composition of these alloys. Experiments are being conducted in the use of these cast-iron allov* for automobile cams, and even for'erankvast iron has, of course, been used for many years for cams of one sort and another, these have mostlv been of the type embodied in comparatively slow-moving machinery and in in which the stresses and rubbing velocities are not high. It is understood, however, that experiments are going forward in the use of cast-iron cams in the ordinary motorcaT engine. If so, considerable interest attaches to the experiments No inforI s available as to the method attaching the cams to the that 1 * , thous j} tins IS evidently a matter that demands careful attention. Presumably the cams, are fitted singly or in ‘2 a steel shaft, for which a able * w,de cbo * ce of materials is availReduced Costs. Special experiments were conducted in evolving the cam iron, the objective to i? et , materia l giving the highest machinable hardness, without brittle- , ness, of course. It is understood that considerable difficulties were experienced in finding just the riglit'al'.ov This would appear to indicate that manufacture of the iron needs to be \ery carefully controlled. Three per cent nickel was finally found to give the best results, the cams so produced giving a Brinell hardness in excess of 250 and being homogeneous m quality, free from hnrd spots, and machinable without difficulty. The sponsors of the new method affirm that not only does the scheme offer mamiiacturing advantages in the way of reduced cost, but that better service is rendered in operation, particularly in matte r of superior resistance to Iron of the requisite high strength and toughness is secured from a superheated electric furnace, and in addition to the alloy constituents it is essential that there be a low total carbon content. , -,, as been further proposed to use the chilling method for hardening those parts of the cams subject to the greatest loadings. The chill depth, it is stated, can be regulated by varying the nickel and chromium content. Botn these alloying elements have been found to increase the hardness at the point of cnill. It has also been found possible with certain alloys to harden the cams by a reheating process. Possibilities for Crankshafts. It is understood that, in general, the developments may be regarded as being sufficiently promising in the camshaft experiments to suggest the possibility of employing a similar material for crankshafts. It is stated that a martensitic iron in the cast or heat treated state will quite possibly prove suitable crankshafts. It is confidently stated that so far as the experiments have been carried at present satisfactory results have been secured.. In considering the question of crankshaft design for production by the new method it would presumably be necessary to employ the built-up construction. It might be advantageous to be ahle to combine cast iron and steel in this way, so providing webs of the requisite elasticity, in combination with the frictional advantages of the iron in the pins and journals. Shock and torsionai resisting qualities in the material or the webs are, of course, obviously essential. GRINDING THE VALVES. One of the Simplest of Overhauls. Many motorists are apprehensive about undertaking jobs in the garage which seem to be of a technical nature. There is, for example, the matter of grinding in the valves, an operation which is advisable after the mileage recommended by the makers of the car. We will assume that the head has been removed and that the valve has been removed. In the first place, let me advise you to do one valve at a time. If you take them all out there is a chance that you will get them mixed and obviously a valve which has become well bedded into its guide and has adapted itself to its seating is better in its own than in any other setting. First, the edges of the valve which make contact with the seating should be smeared with a little valve grinding compound. The special tool which is provided in the equipment of most cars should be used to hold the valve and with this the valve should be turned on its seating with a light semi-rotary movement backward and forward. The position of the valve should be altered from time to time so as' to provide for even grinding all the way round. After two or three minutes of this operation, the valve should be removed and the faces smeared again with a small quantity of the paste. Repeat this several times, wiping the valve so that you may observe the gradual disappearance of the ** pit ” marks. When you have satisfied yourself that the valve face is nicely smooth and that no more “ pitting ” obtains, blacken the face by holding it over a carbon flame, such as a candle. Then insert the valve again, press it lightly on to its seat and remove for inspection. If even contact is indicated, then you may rest assured that the valve has been well reconditioned. Having completed the job it is most essential that you should clear the valve and its guide of any paste. This is best done by washing out with petrol. It is important that every particle of the gritty compound should be removed, for if any remains, it will, j when the engine is restarted, eat into ! the guides and impair the efficiency of j the valves. ; If, on removal of the valves you find j that the seats are badly burned—this I may be clue to maladjustment of the • valves so that they do not seat proi Perly—not all the grinding in the world ! will bring them back to usable con- | dition. Loss of compression will have S warned you of the likelihood of burned j valves. In this case a new valve must ;be fitted. Grinding will recondition j valves which have ‘become slightiv ! pitted, but it will not remedy a badly burned face. The most convenient method of valve grinding is to lie the cylinder head on a bench of convenient height with the , valve heads toward you. Then remove the valves one by one, completing the I operation on each one before remov- ! ing another.