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AIRPLANE MOTORS. 61

armature a different distance from the pole pieces, and may have considerable effect on the working of the magneto.  The breaker points should be clean and smooth.  If we find them badly burned we can true them up with a jeweler's file and re-adjust them so that they open the correct distance or separate the correct distance.  However, if they are badly burned, we should endeavor to get another magneto, because the fact that they are burning shows that the condenser is not working properly. 
13. I have found by experience that we can tell more about the actual strength of a magneto by the appearance of the spark-plug points than by any other means we have on the field.  The correct distance between spark-plug points for Bosch magneto and Dixie magneto is 1/64" or .015"; fora. Berling magneto, .030".  As long as these spark plugs are properly adjusted, if the magneto is up to full strength, the heat of the spark will burn these points to a whitish appearance between the tips, and when the magneto begins to get weak from any cause it will fail to burn the plugs in this manner.  Also, if the spark-plug points are too wide apart, this whitish appearance will not be noted.  I have found that by carefully watching the spark-plug points I have often been able to remove a magneto which was becoming weak before the engine had missed a shot, in this way [[italics]] preventing [[/italics]] trouble.  Also, suppose that in an eight-cylinder motor seven of our spark plugs show this white appearance between the tops and the eighth does not.  If all the plug points are adjusted equally, this will indicate that the insulation in this spark plug is defective, and usually if you break open such a spark plug you will find a crack in the porcelain which will usually be blackened by smoke.  This will prove that you were right in removing the plug. 
14. Remember that in ignition work it is the [[italics]] heat of the spark rather than the size [[/italcis]] of the spark which counts.  If you are out somewhere with a motor and find that the magneto is becoming weak and have no replacement for it, you can generally cause it to burn the spark-plug points white by closing the points together slightly; for instance, closing them in to .010"; in this way you will be able to keep the magneto in commission for several hours longer, sometimes six or ten hours longer.