Measurement Of Engine Speed - Mitsubishi 4DQ50 Service Manual

In appearance the flange looks identical to that of our conventional type hand
timer, but has inside two legs that project in the same phase with flange teeth and keep
contact with the curves surfaces of the flyweights. In these legs are machined the other
seats for timer springs. Each timer spring is held in the said pair of seats, that is, in the
bearing pin by one end and in the leg by the other. These major components are housed
in timer case, which is screwed to the flyweight holder.
Fig. 3·33 A shows the time at a standstill. Being free from centrifugal force, the
flyweights do not lift at all and timer springs are now longest in their setting length.
Fig. 3·33 B illustrates how the timer works at the max. engine speed. Centrifugal
force is now making the flyweights lift. In the picture the letter B indicates flange
leg, whose phase with the pump driving shaft of the engine is designed to remain
constant. So the lift pulls bearing pin A over the distance E, which results in turning the
pump camshaft on the driving shaft so as to put ahead the injection timing.
(A) ATA STANDSTILL
(B) AT MAX. SPEED
Fig. 3-33 Timer flyweight
The timer for Model 4DQ50 Engine is intended for clockwise revolution and
provides a max. angle of lead of
eO
as measured on the pump camshaft. At a standstill, it
keeps the injection slowest.
The automatic timer was assembled with 150gr. of grease inside and unless leaked
by chance, needs not be refilled. When the timer disassembled, change grease for new
one.
4-9 Measurement of engine speed
1) A drop of engine speed below the specified level will disturb the engine
working up to the given efficiency, while a rise above it will cause the
overrunning of the engine itself or of the vehicle it drives. Therefore, both max.
and rated speeds must be always as specified.
2) As mentioned befQre, pneumatic governor governs engine speed in one-to·one
proportion to the percentage of Venturi opening, hence permits the engine to
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