The advance piston moves in the retarded direction. The pump will always be in the fully advanced position when cranking unless the throttle is at wide open
@Thewespaul you mean spring pressure holds the advance piston in the advanced position at rest and not pressurized?
The power side of the advance piston is the side of the pump opposite the LLA lever and servo valve/spring, correct? Transfer pressure pushes the advance piston in the direction of the lla lever and servo/spring IF flow is permitted by the servo piston by its position in relation to the passage supplying transfer pressure to the power side of the piston. Retarding it?
Non lla equipped ip advance function is a relatively simple spring acting against the advance piston. Someone tell me point blank that essentially the lla servo spring is doing the same general thing, along with the valve do-hickey and movement of spring.
This shows a roosa master with spring pressure holding the piston in the retarded direction. Is that also how the truck db2 with the lla are designed?
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5 psi delivered to the inlet allows the advance piston into the fully advanced position why? hydraulic pressure on the power side in the absence of rotational force to act against it overcomes spring tension. it will adjust by the accelerator's action on the servo valve relieving and restoring those 5psi but also changing advance piston return spring trim. Correct?
because during rotation the timer piston is forced by the plunger action in the retarded direction during rotation, the scenario (the one we're up against) changes. If the purpose of the lla is to provide advance during low transfer pressure pump states, may be what is being said by "it moves in the retard direction" is that the spring pulls on the timer piston towards the advance direction and transfer pressure moves it the other direction.
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interesting that I saw mention in the
service bulletin this comes from
that some engines require the advance. What would the characteristics of an engine that require it be?
the timer piston is acted on by the transfer pressures which are regulated by the servo valve in reference to its position in its bore against housing pressures. in the event of housing pressures being zero (advance solenoid engaged), transfer pressure more easily moves the advance piston IF the LLA servo position allows it I guess, but it isn't exactly metering the entire supply of transfer pressure to the power piston.
Edited to jump the youtube video to the point and finish a sentence lol