There is another leak of the same nature which is quite as expensive, and that is of lubricating oil. If you do not believe it to be prevalent or serious in extent, you have only to watch places where automobiles stand frequently along the curb and notice the pools of oil on the pavement. These come from leaky crank cases, transmission gear cases, rear-axle gear (differential) cases, or from a faulty distributor. In most cases it is only a matter of tightening a few bolts or connections occasionally; but with oil at present prices it is a serious matter.
Another leak which needs to be corrected frequently is at the valves. So much has been written about the care of valves that it would seem superfluous to refer to it, but regrinding and proper care pay big dividends in efficiency and should be on the regular program. There is a leak at the valve, however, seldom mentioned, though quite as serious as the others, which is due to worn valve stems.
The valve stems should fit snugly in the guides; if they do not, air will be drawn past the stem into the cylinder on the suction stroke and thin down the mixture so that the engine runs irregularly, unless more gasoline is supplied at the spray nozzle, and throttling down to a reasonable idling speed is impossible. If the exhaust valve guide is worn there will be a hissing sound that is objectionable.
The purpose of repeating this caution as to mixture thinning is to make it plain that wherever there is a leak between the carburetor and the cylinder it lets in air and thins the mixture so that it is necessary to feed in more gasoline to get a mixture that will fire and that is wasteful, for a mixture made anywhere else than in the carburetor is less efficiently accomplished.
The burned gases pass out through the exhaust valve side and in so doing often deposit small pieces of carbon, which keep the valve from seating properly and let perfectly good mixture escape. If not cleaned often, the heat and constant tapping of the valve against the seat will hammer the carbon fast to the valve or seat as though it had been fused there. Carbon must be scraped off frequently and as often as necessary the valve should be reground into the seat.
Piston rings which are not pinned often work around until the slots are in line and the mixture will blow through. If the rings will not stay in place a pin should be put in the ring groove on the piston to prevent the ring from working around and the slots should be staggered, so that no two are in line. Naturally the rings must be kept free from carbon or gum from the oil or they will freeze to the groove and leak mixture.
In older cars the cylinder may be worn oval, so that the piston and its rings do not fit. When the cylinder is oval the piston will not pump in the mixture properly, and when the explosion occurs much of the burned gas will be forced down into the crank case. One of the products of combustion is water, which is exhausted in the form of vapor. When it gets into the crank case and condenses, forming water, it collects under the oil. In cleaning out and replacing the oil, if water is found, it always indicates a tendency to oval in the cylinder. This is caused by the thrust of the connecting rod being against one side on the up stroke and against the other on the down stroke.
With everything else there may be a loss of gasoline by reason of poor adjustment of the carburetor. The adjustment should be such as to make the mixture as lean as possible and have it fire readily, and to have the float not too high. One sure indication that the mixture is too rich is when black smoke is given off. Black smoke always indicates excess gasoline—burning money. As has been told in another chapter, there is another kind of smoke to guard against, but if the owner will make sure that he is not exhausting black smoke he need not worry about the price of gasoline, and a little judgment and care will eliminate many of the items of upkeep expense.
CHAPTER XII
CARE OF THE TIRES
When a tire buyer is told by the dealer that a tire is guaranteed for so many miles, the manufacturer expects to make good—he expects if the tire falls down on performance to replace it, or at least make an allowance for the mileage short. As a matter of fact they do not have to do this on thousands of tires which are defective, for the reason that the auto owner has not kept his part of the bargain. Nine times out of ten this is because the user of the tire does not know how it ought to be treated and doctored and cajoled into doing all that it is expected to do.