3. Timing the Ignition.

My colleague, Mr. Oliver Mitchell, has pointed out to me that it is often impossible to tell directly when the piston is exactly at the top of its stroke, and he recommends a study of the accompanying Valve Setting Diagram (Figure 71). From this it will be seen that it is sufficiently near to bring the engine first of all to such a position that the exhaust valve has just closed; then make a chalk mark on the flywheel and give the engine one complete turn round; the piston will then be in the firing position if the flywheel is turned a shade backwards. Another method would be to retard the ignition fully and time it so that the spark occurred one complete revolution after the inlet valve had just commenced to open. When either valve is closed its tappet can be felt to be free, the amount of freedom depending upon the clearance between the tappet head and valve stem.

Fig. 71.—Diagram of Valve Setting.


INDEX

(PR. 1315.)
Butler & Tanner Frome and London

Transcriber's Notes