![]() Lead is the amount the valve has opened the steam port for admission when the piston is on a dead center. Its purpose is to allow the steam to be used expansively. Lap is the amount the steam edges of the valve overlap the steam ports when the valve is central. ![]() To the man building his first engine, and some of the more experienced ones as well, they are about as clear as mud and not too well understood. To a good many of the older (I do not mean in years) and more experienced Live-Steamers, these terms are clear and well understood. When talking about this subject, one will hear some of the terms mentioned, such as lap, lead, valve travel, steam ports, exhaust port, bridges and line in line. I realize that I am treading on dangerous ground here, as a complete answer to valve and valve gear problems takes a lifetime of study to master and a lot of technical study, in addition. It could be that an explanation and a sketch or two might be welcome. ![]() There are other things that enter the picture as well, but, if the valves and valve gear are right, the other conditions can be dealt with and usually corrected without too much trouble. Valves and valve gears can be the making or the breaking of the performance of any engine. ![]()
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