6646441 Volvo.Penta Disc

Structure and Operation
Fuel System (Flow of Fuel)
* The feed pump, which is driven by the driveshaft of the injection pump, draws up the fuel from inside the fuel tank and sends it through the fuel filter, where dust and other impurities in the fuel are filtered out.* The filtered fuel is then sent to the injection pump, where it is pressurized and sprayed out through the injection nozzles into the combustion chamber.* The leak-off fuel from the injection nozzles returns to the fuel tank through the leak-off hose and fuel return pipe.* When the internal fuel pressure of the injection pump exceeds the limit, the overflow valve opens to allow part of the fuel to return to the fuel tank.Fuel Filter
* The fuel filter removes impurities in the fuel through the fuel filter cartridge and also separates water from fuel.* The water that has been separated from the fuel collects at the bottom of the fuel filter. A water separator sensor is installed in the fuel filter, which activates the warning lamp on the meter cluster when the water reaches a certain level.* The water can be drained through the drain port by loosening the drain plug.* A priming pump is provided at the fuel filter head. The priming pump is used for air-bleeding the fuel system.Injection Nozzles
* The injection nozzles are of a throttle type, in which the injection starting pressure is determined by the thickness of the adjusting shim.* When the pressure of the fuel forced into the nozzle by the injection pump (the pressure inside the nozzle tube) presses upon the pressure-receiving surface and overcomes the spring force, the needle valve rises and fuel is sprayed out of the nozzle. * When the pressure acting on the pressure-receiving surface no longer overcomes the force of the spring, the spring pushes the needle valve up and fuel injection is instantly stopped.* Any excess fuel passes through the space between the needle valve and the nozzle to the fuel leak-off pipe, and returns to the fuel tank.Injection Pump
* The injection pump is a compact, lightweight type and has a distribution system that can cope with high revolution operation.* The distribution system is a type that distributes fuel to each cylinder by a single plunger. Fuel to be distributed is filled within the injection pump and lubricates each part in there.Injection pump body
* Drive shaft drives feed pump, cam disc and plunger simultaneously. Plunger spring presses the plunger and the cam disc against roller.* The rotation of cam disc which is driven by drive shaft drives face cam in a rotary movement on roller, creating a reciprocating movement of plunger, which eventually forces the fuel into the cylinder.Governor
* The rotation of drive shaft is transmitted via drive gear to flyweight holder gear to turn flyweight holder.* Flyweight holder is supported by governor shaft. The four flyweights installed in the holder open outward due to the generation of centrifugal force.* The movement of flyweights pushes governor sleeve, and governor lever toward the right as illustrated.* Governor lever consists of corrector lever, tension lever, and start lever.Automatic timer
* The automatic timer is a hydraulic type and consists of timer spring, timer piston and roller holder pin.* Timer piston makes a reciprocating movement inside the injection pump housing. At the end of low pressure side, timer spring is installed and at the end of high pressure side, fuel pressure prevails. The piston is activated by alternating changes of force between the two sides.* Roller holder pin is installed between timer piston and roller holder and converts the reciprocating movement of the piston into the rotary movement of the holder.* As roller holder moves its position, the timing of the lobe of cam disc going over roller changes, and this controls the fuel injection timing.Feed pump
* The feed pump is a vane type and consists of rotor installed inside the injection pump chamber, vanes and liner in the pump housing.* Rotor is fixed to pump drive shaft and has four vanes. Liner is installed eccentric to rotor. Due to this arrangement, when rotor rotates, vanes spin outward due to the centrifugal force generated and adhere to the inner side of liner, creating four chambers partitioned by the vanes. The capacity of the chambers varies as the rotor rotates. When the capacity of the chamber expands, fuel from fuel tank is sucked in, and as the capacity contracts, fuel is compressed to be forced out into the injection pump chamber.* Regulator valve opens when the pressure for fuel delivery generated by the feed pump is higher than the standard value; in the process of increasing the engine revolution, this lets the fuel return to the inlet port of the feed pump, thus controlling the fuel pressure in the injection pump chamber within the standard values. Fuel-cut solenoid valve
* The starter switch turns the fuel-cut solenoid valve ON or OFF electrically opening or closing the valve for fuel passage which is connected to inlet port of plunger barrel. Starter switch at ON or SFuel-cut solenoid valve is electrically active and magnetized to push up spring and armature, opening fuel passage. Starter switch at ACC or (OFF) or LOCKDemagnetization takes place by which action armature is pushed down by spring, and fuel passage is closed and no fuel is delivered to plunger, making the engine inoperative. Troubleshooting
General Inspection and Adjustment
Inspecting and Adjusting Fuel Injection Timing
Service standards (Unit: mm) Tightening torque (Unit: N m {kgf m}) Special tools [Inspection]* Remove the rocker cover. * Bring the No. 1 or No. 4 cylinder piston to the top dead center (TDC) on the compression stroke by the following procedure.* Rotate the crankshaft in the illustrated direction so that the notch on the crankshaft pulley is aligned with the "0" mark on the timing gear case.
* Do not turn the crankshaft pulley in the wrong direction (counterclockwise), as this may cause damage to the tensioner that is adjusting the tension of the timing chain on the idler sprocket and