PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
adjacent to the splines. The weight and spider thrust plate, located
between the flange and the timing device housing, carries the back thrust of
the flyweights and prevents housing wear.
(4) The sliding gear has internal lefthand helical splines at one
end and internal righthand helical splines at the other, and meshes with
the external splines of both the weight and spider assembly and the timing
device hub. Correct assembly of the spline train is ensured by a wide land
on both the hub and weight and the spider assembly. The sliding gear has a
missing tooth on each set of internal splines to receive the wide lands.
Three arms extend from the outer surface of the sliding gear to provide
seats for the three timing device springs. The force on these springs is
controlled by a sliding gear spacer.
c. Operation (figure 61 on the following page).
(1) As the engine rotates the weight and spider assembly, centrifugal
force opens the flyweights from their collapsed position against the force
of the three timing device springs.
(2) As the flyweights swing out, the sliding gear is forced toward
the timing device hub.
(3) The longitudinal movement of the sliding gear on its helical
spline causes a slight change in the rotational relationship of the
injection pump to the engine, causing injection to begin slightly earlier in
a. Purpose. Diesel engines are very difficult to start in cold
weather. This is due mainly to the low volatility of the fuel. The two
most popular methods of assisting a diesel engine in starting are:
(1) Preheating the induction air in the intake manifold so that
adequate vaporization will take place for combustion.
(2) Injecting a fuel into the engine that remains volatile enough in