“SUN” SERVICE STATION

Sun (Auckland), Volume IV, Issue 1078, 16 September 1930, Page 6

“SUN” SERVICE STATION

* THE "Motordom” section of The Sun Includes in its service to readers a Queries and Answers Department, the object of which is to give accurate information 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 All communications must be accompanied by the inquirer's name and address (not for publication), and sent to THE SUN “Service Station, Motordom/* 'THE SUN Auckland. Answers will appear weekly in this column •

“Driver.” —l have an Essex sedan car, Challenger model, 1929, and it has developed a knock in the engine which sounds like a tappet. I have given attention to the valves, but cannot locate trouble. When engine is cold and first starts, the knock is distinct, but when engine warms up it is not so distinct. When car is pulling up-hill it again can be heard. The mileage on speedometer is under 11,000 miles. Perhaps you may be able to advise me how to locate knock or where to 100k..’ * * * Probably your trouble is piston slap. I remember peculiar noises in an Essex diagnosed as this complaint. As this car has aluminium pistons which expand considerably, they are looselyfitting when the motor is cold, and expand when the motor gets hot. Have new rings fitted if the trouble becomes worse. L.C.B. —Being a constant reader of the motor section in The Sun, I am writing to ask you if I could dye a motor-car hood. It is now a khakicolour, and has become very dirty and shabby. I would like to dye it black, so could you advise me the best stuff to use and how to use it. The car is a Morris-Cowley four-seater 1927 model so the car is not a very big one. Do you think that it will crack when the hood is folded back during the summer? * * * Merely to dye a hood in the ordinary fashion probably would diminish its waterproof qualities. Sevac hood dressing should achieve what you desire. It can be had at most stores, and is less likely to crack. “X.” —I have a Super X motor-cycle which has done only 4.000 miles. Can you tell me what is the cause .of the back plug continually oiling up; also how can it be remedied? The tappets and timing are correct, but the front cylinder gets hot and the back one oils up. If I tried a hotter plug in [ the back cylinder would it make any j difference? The trouble probably is the result

from worn or broken piston . ring’s in the rear cylinder, because a perfectly fitting piston and good rings will prevent oil reaching the 'plug, even when the engine is over-lubricated. A good plug suitable for an oily engine would minimise the trouble until it is convenient to effect repairs. “Buick.”—Can you help me to solve the following problem in regard to carburettor adjustment? My 1925 Buick is fitted with the usual Marvel carburettor. I find that when adjusted to idle smoothly on low throttle the engine does not get nearly enough air at touring speeds. On the other hand, if 1 adjust the air valve control so as to give maximum revolutions (hence, apparently, best mixture) on about one-third throttle (which would correspond to about 25 m.p.h.) it is impossible to get the engine to idle at all, the mixture at idling speeds being then far too lean, no matter how I adjust the idling control. All manifold intake connections appear to be O.K. I have changed the air valve spring and discarded the No. 57 main jet for th.p smaller ]\ T o. 125, but without any marked improvement. I am wondering (1) whether it is right to assume that the mixture which gives highest engine revolutions for a -particular throttle opening under no load is necessarily the best driving mixture; (2) whether it is likely that the difficulty arises from worn valve stems allowing air to pass on the suction stroke; (3) whether I should fit a still smaller jet or lower the float level; (4) whether it is too much to expect good idling and perfect mixture at all speeds from this, or any, type of carburettor. The trouble is evidently caused by the heat riser tube in carburettor manifold lieat-box being burnt out, leaving a slight hole, whereby air enters when idling, thus necessitating an extremely rich mixture to overcome the extra air entering at idling speeds. Xaturally, then, at high speeds the mixture is far too rich. The only cure is to have a new' heat tube fitted to the riser box.