Page:Motors and motor-driving (1902).djvu/199

Rh will be more likely to start an engine than hours of slow 'grinding.'

3. Having now ascertained that neither the Ignition nor the Carburation is to blame, if the motor still will not go we must look for the failure in either the compression or one of the moving parts.

Compression is the life and soul of a modern high-speed internal combustion engine.

When the engine is in proper working order, and being turned by hand, a considerable resistance should be felt at the alternate back stroke of each piston; this back pressure should require a considerable effort to overcome when the handle is being turned slowly. If the compression of any cylinder leaks, that cylinder will not give off its full power.

How to Locate a Leak of Compression.—If there is a loss of compression, a slight hiss will generally be audible when the handle is turned. In order to find out where the leak is, a lighted taper may be held over the cylinder in different positions, while the engine is being turned slowly; the flame will be turned on one side on meeting the leak; or soap and water may be painted about the cylinder head, and bubbles should soon indicate the presence of the leakage.

Possible Sources of Leakage.—(a) A leakage will generally be found at the junction of such fittings as the ignition tube, induction valve, valve cover, sparking plug, compression tap, or other attachment connected with the interior of the cylinder or combustion chamber—probably a washer blown out or a nut loose will be the cause.

Should, however, the leakage not reveal itself under the above tests, it is probable that

(b) the exhaust or inlet valves are 'pitted' or coated with deposit, and consequently permit a loss of compression past their seating; if this is so, they should be taken out and ground on their seats with fine emery powder and oil, or paraffin, till they bed properly; the engine may then have to be run for some time before the leakage ceases. See also that the valve springs have not grown too weak.