| July/August 1981

  • Slow-burning mixtures.
    Slow-burning mixtures.
  • The Jacobson valve sear.
    The Jacobson valve sear.

  • Slow-burning mixtures.
  • The Jacobson valve sear.

Box 25, Pavilion, New York 14525

From the valve-gear side of the engine, the valve-gear shaft is driven by a pair of spiral gears from the main engine shaft, and its speed is, of course, one-half the speed of the latter. The exhaust-valve is operated by a cam, while the inlet valve is actuated by means of an eccentric.

The valve-gear is shown in detail in the figure below, and it will be observed that the regulation is effected by means of a release gear by which the inlet valve is disengaged and closed at varying points of the stroke, to suit the load. To some extent, the cylinder is scavenged with pure air in order to prevent, as much as possible, any back-firing due to slow-burning mixtures.

The operation of the gear is as follows:

The inlet valve I is opened by means of the rocker R when the pick-blade P on the end of the eccentric rod E, lifts the end of the rocker arm, and the valve becomes opened more and more, until the roller D rides up on the trip block T, the position of which is controlled by the governor. It is evident that the further the trip block is moved to the right the earlier in the stroke the valve will trip.

As soon as the main inlet valve opens, air will be admitted to the cylinder from the air port, for scavenging purposes. The gas valve G has a sliding fit on the main valve stem and is held closed by the spring Z, until the collar C, which is solid on the valve spindle, moving down, forces the valve to open against the spring pressure back of it. The position in which the valve is drawn is such, it will be observed, that the main valve is opened to some extent for the admission of air, and the collar C is just touching the hub of the gas valve to effect its opening, in unison with the main valve, as the latter is further opened. S is the main valve spring, the function of which is to close the main inlet valve, and to hold it closed against the partial vacuum that will be created in the cylinder at light loads.