“SUN” SERVICE STATION

Sun (Auckland), Volume III, Issue 716, 16 July 1929, Page 6

“SUN” SERVICE STATION

rpHB ’Motordora' section ol The Sun includes in its service to readers a JL Queries and Answers Department, the object o! which is to give accurate tnlprmation regarding mechanical and touring subjects Whatever the particular puzzle may be In either diagnosing Irritating troubles, or motoring information of any kind, "Headlight” will endeavour to help, or refer the point to men who are recognised automobile experts In their respective lines All communications must be accompanied by the inquirer's name and address (not tor publication). and sent to THE SUN “Service Station, Motordom." THE SUN Auckland Answers will appear weekly In this column

“Wobbler."—Having an Oldsmobile, 1927 model, that has started a wheel wobble. I would be pleased of your help- The wheel is the one on the opposite side to the steering wheel. If the road ts a little rough the wheel starts to wobble, although X have tightened the nut on the axle as tight as it will go. This does not appear to be a real wheel wobble as that always affects both wheels at once. I would suggest an examination for a bent rim. wheel or stub axle “A.”—l have had trouble on two occasions recently from the insulators on the spark plugs splitting, and shall be glad to know the cause. * * • (1) The principal cause of splitting is bending the centre electrode to set the gap. This sets up a strain in the wire which upon heating, will t.tud to break the insulator. The shell electrode should always be the oua which is moved in setting gaps. (2) The other cause is excessive heat, which may be due to having: (a) Too lean a mixture: fh) valves sticking or not seated properly: (c) spark plug too hot for the service required. “Dodge Owner.”—l have a Dodge Sedan which has done only 12,000 miles, a 1927 model, four-cylinder engine. I have a knock of backlash, I would say, in timing gears, when the engine is running. Upon putting a piece of wood against the fan, driving pulley on pump and generator shaft I stop the noise. I stopped the engine and got hold of pulley, and X could move pulley; that Is, move gear in camshaft

gear wheel backward and forward, and by adding a little more pressure I could move camshaft timing wheel backward and forward in crank timing gear wheel, ft shows up mostly when coming clown a hill, for ail Uio world like a universal knock, but, of course, it’s in the timing gears; I am positive of this. What could I do or what is the trouble? This is a not uncommon knock in the Dodge, and is caused either by excessive backlash between the pump shaft gear and camshaft gear, oi by end play in the pump shaft itself The first ca.n sometimes be cured by letting the gears further into mesh, or, if this is not sufficient, by replacing the pump shaft gear, which is of the fabric type. The second trouble cu». he ou* --d by fitting a spring thrust washer to the pump shaft, or by rebushii.g the shaft. I would not advise you to tackle either job yourself or you will be only striking trouble, as the pump shaft gear housing is awkward to get on and off. “Spark.”—Why is it necessary to have the different types of spark plugs with different lengths of insulator projecting into the firing chamber of the plug? To control the rate of heat flow from the gap of the plug to the cooling medium, which is either water «»r air. The rate of heat flow depends on tielength and shape of insulator from the spark gap to the inside gasket. A long projection mak s a hot plug to be used in engines which develop comparatively little heat. These are usually designated as cold engines. A short projection, on the other hand, makes a cold plug, intended for use in hot, high-compression engines, where it is necessary to dissipate e extra heat at a rate sufficiently rapid to avoid overheating of the ha- r The application of hot s o : in a given engine depends both on' the heat characteristics of the engine and the service required.