Page:Motors and motor-driving (1902).djvu/200

168 (c) There is a possibility of the compression also blowing past the piston-rings. This can generally be detected by listening attentively with the ear close to the cylinder at fault, and turning the starting handle or fly-wheel slowly—a gentle hissing will be heard at intervals. The cause of this is generally the sticking of the rings in their grooves. The remedy is to wash out with paraffin so as to free them for their whole circumference. If they still leak badly, the piston should be taken out and new rings fitted, especially if the engine has been over-heated at any time, in which event

(d) the cylinder-head joint, if there is one, may have warped and the compression may be escaping from one cylinder to the other, and into the water space; water in turn will probably find its way into the cylinder, and being converted into steam, will interfere with the working of the engine and rust the valves. Little spots of rust on the valves will indicate what is happening, and the cylinder-head joint will then have to be re-made—a matter for an expert.

No Compression at all.—If on trying to start the motor no compression at all is felt on one cylinder, there may be a valve stuck open through a breakage or gumming (see later), or else the ends of the piston-rings may have by chance arrived opposite one another, thus allowing the compression to slip through the spaces. When this occurs, the rings should be freed by letting in paraffin and running the engine a bit on the other cylinder or cylinders if possible; the rings will probably soon change their position—they are purposely allowed to move round so as to wear evenly.

Apparent Excessive Compression.—There may, especially on a cold morning, appear to be so much compression that the engine can hardly be turned; this stiffness is really due to the drying of the oil on the walls of the cylinder. To avoid this a copious dose of paraffin should always be injected when stopping the car after a day's run, and a few turns given to the engine by hand.

Note.—It is most essential for every motorist to insist on having proper and convenient means fitted on his car for washing the cylinders with paraffin or petrol, both to facilitate starting up and to keep the piston-rings in good order.