Air Filters
Operating conditions play an important part in deciding how frequently it is necessary to service the air filter. If you are working in dusty conditions then the air filter should be attended to every day, as indicated under "Preventive Maintenance".
If not already fitted, you should consider the fitting of a 22 in water gauge RESTRICTION INDIAVSOR in the air trunking between the air filter and the engine induction manifold. It indicates by means of a visual signal when the air filter element needs servicing.
A means of visual signalling for the "Rotopamic" type air filter failure is the use of the "DUST SIGHT". A window in this device becomes cloudy when the system has failed, but this type of indicator is usually only used with the two stage extreme heavy duty filters.
The type of air filter fitted to the vehicle or machine depends upon the manufacturer of the equipment. Usually, guidance for the method of servicing is shown on the body of the air filter, but the following advice will also help.
Dry Type Two Stage "Cyclopac"
1. Body Assembly
2. Element Assembly
3. Nut and Gasket Assembly
4. Clamp Assembly
5. Baffle Skirt
6. Cup Assembly
N1
(Fig. N.1)
The dust bowl collects the heavier particles which are thrown out by the centrifuge path of the air. This dust enters the bowl by the slot in the baffle plate. The level of dust in the bowl must not be allowed to reach to within half an inch of this slot in the baffle plate.
With horizontal installations the slot in the baffle is located at the top.
Renew the element or clean by back flow air pres-clamp. Remove the baffle from the interior of the dust cup by lifting it out, which gives access to the dust for removal. The element can be removed by releasing the wing nut.
Replace the element or clean by back flow air pressure no more than 100 lbf/in2 or washing in a non-foaming detergent as recommended by the air filter manufacturers. Allow the element to soak for at least ten minutes and then gently agitate. Rinse the element with clean water and allow to dry. Do not use oven heat.
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There is a danger that some of the dust remaining in the element after it is washed will be pulled through into the engine if the element is replaced in a wet condition. The reason for this is that the water acts as a carrier for the dust. |
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Inspect the element by placing a bright light in its centre. Any pin holes, thin spots or ruptures render the element unfit for further use. This cleaning procedure reduces the effective life of the element.
With all dry type elements, they should be renewed after six cleanings or once a year, whichever occurs first.
Dry Type Two Stage "Cyclone"
N2
(Fig. N.2)
The AUTOMATIC DUST EJECTOR should always be kept clean and the lips of the rubber ejector checked to see that they close but do not adhere together.
To service the element, unscrew the clamping screw and remove the element retaining strip. Remove the seal plate (if fitted) and element.
If the element is contaminated by dry dust, clean by carefully tapping by hand or by directing low pressure compressed air on to the clean side of the element. If the element is contaminated by oil or soot, it can be cleaned by washing in a suitable non-foaming detergent. After washing, rinse out thoroughly by directing clean water to clean air side of element and allow to dry-do not oven dry.
Inspect cleaned element by placing a bright light inside and looking through element. Any thin spots, pin holes or other damage will render the element unfit for further use.
The element should be renewed after six detergent washes or annually, whichever occurs first. Clean the inside of the filter body and dry thoroughly. Inspect joints, hoses and clips and renew where necessary.
Re-assemble filter ensuring that all joints are leak proof.
Extreme Heavy Duty Two Stage, with Multiple Elements "Rotopamic" (Fig. N.3)
N3
(Fig. N3)
The "Rotopamic" type air filter may be fitted where the application is designed to work in heavy concentrations of dust and a restriction indicator must be fitted.
The air filter elements are replaceable and no attempt should be made to clean or re-use dirty elements or cartridges.
For cartridge replacement, unclamp and remove the moisture eliminator or pre-cleaner panel, pull out the dirty cartridges and insert the new ones.
Refit the pre-cleaner.
Never use petrol (gasoline) for cleaning any of the air induction system.
Oil Bath Air Filters (Fig. N.4)
N4
To service the oil bath type filter, the lid should be removed and the element lifted out. The oil in the container should be drained out and the dirt and sludge thoroughly cleaned out with a proprietary cleaning fluid or Kerosene. Refill the container with clean new engine lubricating oil to the indicated level. The woven filter element should be cleaned in a bath of Kerosene. Do not use petrol (gasoline) as this highly volatile fuel could cause explosive damage within the engine. The indicated filling mark level should never be exceeded, otherwise oil can be drawn up into the engine which could lead to uncontrolled engine speeds, and excessive engine wear.
The heavy duty oil bath air filters are usually fitted with a centrifugal pre-cleaner mounted on top of the main cleaner, this should be removed and the air inlet vanes in the bottom plate of the assembly, the ejection slots on the side of the cone and the vanes in the outlet tube, cleaned of dust and dirt. The detachable element is accessible by lowering the oil container which may be attached by clips or a pinch screw clamp.
Thoroughly clean the container and refill to the indicated level with new engine lubricating oil. The separate element should be cleaned in a Kerosene bath.
The upper element which is permanently attached inside the body should be periodically cleaned by washing in a Kerosene bath. Drain the element thoroughly before reassembly and do not use petrol (gasoline) for cleaning purposes.
Tractor Type Air Filter (Fig. N.5)
N5
The air filter container should be removed, cleaned and recharged with clean new engine lubricating oil to the level mark every 50 hours. The lower gauze filter should be removed and cleaned. The larger gauze in the main body of the filter should also be cleaned.
Under extremely dirty conditions attention to the filter should be given more frequently. It is important to note that the filter oil container must never be filled above the indicated level.
Fuel Filters
The fuel filter is of the paper element type, and no attempt should be made to clean the element. It should be renewed when periodical maintenance is being carried out.
The filters fitted to earlier engines have a separate element positioned inside a bowl whereas filters fitted to later engines have an encapsulated element held between the filter head and the filter base.
The period for changing the element will largely depend upon the quality and condition of the fuel available. Under normal conditions the element should be renewed as given in Section C. This period should be decreased if unavoidable contamination of the fuel is experienced.
To Renew Earlier Type Filter Element
N6
N7
1. Remove filter bowl as in Figs. N.6 and N.7.
2. Discard the dirty element. Remove the lower element sealing washer, seal seating and spring from the bowl.
3. Clean the inside of the bowl and centre tube.
4. Fit the spring and seal seating to the bowl. Examine the lower seal, renew if necessary and refit to the bowl. Place the new element in position in the bowl.
5. Ensure that the element and bowl seals are in good condition, if not, fit new seals.
6. Refit the bowl to the top cover.
7. Vent the fuel system.
To Renew Later Type Filter Element
1. Thoroughly clean the exterior of the filter assembly.
N8
2. Holding the filter base, unscrew the setscrew in the centre of the filter head and lower the base and filter element (Fig. N.8). Discard the filter element.
3. Thoroughly clean the filter head and base.
4. Inspect the sealing rings and renew if damaged in any way.
5. Place the base squarely on the bottom of the new filter element and offer up the element squarely to the filter head so that the top rim of the element locates centrally against the sealing ring in the filter head.
6. Hold in this position whilst the securing setscrew is located and screwed home.
1. Pulsator Diaphragm
2. Lift Pump Cover
N9
7. Bleed the fuel system as detailed on Page N.9.
Fuel Lift Pump
Testing the Pump in Position
1. Disconnect the outlet pipe (lift pump to filter) leaving a free outlet from the pump.
2. Rotate the engine. There should be a spurt of fuel from the outlet port once every two revolutions.
Pressure Checking of Fuel Lift Pump in Position
Fit a 0-10 lbf/in2 (0-0,7 kgf/cm2) or 0-70 kN/m2 pressure gauge to the outlet of the pump. Ensure that there are no leaks at the connections between pump and gauge. Crank the engine for 10 seconds and note the maximum pressure on gauge. If the pressure recorded is less than 75% of the minimum production static pressure shown below, then rectify the pump. Also observe the rate at which the pressure drops to half the maximum figure obtained when cranking has ceased. If less than 30 seconds, rectify the pump.
To Clean the Pump Chamber
1. Remove the fuel lift pump cover and pulsator diaphragm (Fig. N.9).
2. Clean the sediment chamber and check the diaphragm for condition.
3. Refit the diaphragm and cover. Tighten the securing screw just sufficiently to make a tight sealing joint.
4. Vent the fuel system.
To Remove the Pump
Lift pumps which are in a upright position (with the top cover uppermost) are fitted to later engines. These are secured with four studs, nuts and spring washers and two keeper plates fitted vertically between the washers and the outside face of the pump mounting flange.
1. Disconnect the pipes.
2. Remove the pump and joint.
To Dismantle the Pump (Fig. N.10)
1. Before dismantling, make a file mark across the two flanges for guidance in re-assembly.
2. Separate the two halves of the pump.
3. Remove the diaphragm by unhooking it from the rocker arm link. The diaphragm spring can now be withdrawn.
4. Drive out the rocker arm pivot pin and withdraw the rocker arm, spring and link.
5. Dismantle the priming lever by removing the lever retaining pin.
6. Remove the valves by levering from their locations. Remove the valve gaskets.
7. Remove the pump cover and pulsator diaphragm.
Inspection of Parts
1. Check the diaphragm for hardening or cracking and examine the pull rod for wear at the point where it connects with the rocker lever link. A stem seal fitted over the daiphragm shaft may be found on some applications and should be renewed if worn.
2. The diaphragm spring should be renewed if corroded or distorted. Ensure the new spring has the same colour identification as the original.
1. Pulsator Cover Screw
2. Pulsator Cover Washer
3. Pulsator Cover
4. Pulsator Diaphragm
5. Cover Screw
6. Cover Screw Washer
7. Cover
8. Valve Gasket
9. Valve Assembly
10. Diaphragm Assembly
11. Diaphragm Spring
12. Body
13. Rocker Arm Spring
14. Rocker Arm
15. Link
16. Rocker Arm Pin
17. Primer Pin
18. Primer
19. Sealing Ring
20. Primer Spring
N10
3. The valves should be replaced. The two valves are identical and may be used for inlet or outlet (Fig. N.10).
4. Examine the rocker, arm, link, spring and pin for wear.
5. Check the pulsator diaphragm for condition.
6. Examine the flanges of the two pump halves for distortion. If necessary lightly linish to restore flatness.
To Re-Assemble the Pump
1. Fit the new valve gaskets and valves to the body. The inlet valve must be fitted so that it can open to admit fuel. The outlet valve must be fitted in the reverse position to the inlet valve. Valves are retained by retaining plate or alternatively by staking in six places with a suitable punch.
2. Fit the pulsator diaphragm and cover.
3. Insert the rocker arm pin through its hole in the body, at the same time engaging the link and the rocker arm. Tap the rocker arm pin in until it is flush with the pump body. Stake the casting in three places each side to retain the pin.
4. Place the diaphragm spring in position.
5. Place the diaphragm assembly over the spring, the pull rod being downwards, and centre the upper end of the spring in the lower diaphragm protector washer.
6. Press downward on the diaphragm and make sure that the downward tag on the lower diaphragm protecting washer is on the priming lever side of the body. This tag is required to be in the hole of the body ready for fitment of the priming lever. Engage the diaphragm pull rod with the link and at the same time match up the holes in the diaphragm.
7. Push the rocker arm towards the pump until the diaphragm is level with the body flanges. Place the upper half of the pump into position as shown by the file mark on the flanges. Install the screws and washers and tighten only until the heads just engage the washer. Release the rocker arm and push on the spaded end of the rod so as to hold the diaphragm at the top of the stroke, and while so held tighten the securing screws diagonally.
NOTE: The edges of the diaphragm should now be flush with its two clamping flanges. Any appreciable protrusion of the diaphragm indicates incorrect fitting.
8. Fit primer to side of body and retain with the pin. Clip on priming lever spring.
9. Test the pump to ensure that it is working correctly.
To Refit the Pump
1. Refit the pump to the cylinder block.
2. Reconnect the fuel line and vent the system of air as detailed on page N.9.
Fuel Injection Pump
Description
The fuel injection pump is of the D.P.A. distributor type. It is a precision built unit incorporating a simple hydraulic governor or one of the mechanical flyweight type.
The pump is flange mounted and is driven from the engine timing case.
NOTE: Unless the necessary equipment and experienced personnel are available, dismantling of the fuel pump should not be attempted.
To Remove the Fuel Pump (Hydraulic Governor)
1. Remove the high and low pressure pipes from the fuel pump.
2. Disconnect the stop and throttle controls and remove the return springs.
N11
3. Remove the fuel pump (Fig. N.11).
To Refit the Fuel Pump (Hydraulic Governor)
1. Replace the fuel pump ensuring that the master spline on its quill shaft will enter the female spline in the driving plate.
N12
2. Position the fuel pump so that the scribed line on the fuel pump flange aligns with the mark on the fuel pump gear adaptor (Fig. N.12). Secure the pump to the timing case. To check accuracy of mark on fuel pump adaptor plate, this may be ascertained in accordance with instructions for marking new adaptor plates given on Page K.7.
3. Refit the high and low pressure pipes to the fuel pump.
4. Re-connect the throttle and stop lever controls and attach the return springs.
5. Vent the air from the fuel system (Page N.9).
6. Adjust the maximum and idling speeds (Pages N.8 and N.9).
To Remove the Fuel Pump (Mechanical Governor)
1. Remove the high and low pressure pipes from the fuel pump.
2. Disconnect the stop and throttle controls and remove return springs.
N13
3. Remove the timing case front cover inspection plate (Fig. N.13).
4. Remove the three setscrews which secure the fuel pump gear to the fuel pump
5. Remove the fuel pump from the timing case ensuring that when the fuel pump gear leaves the shaft it stays in mesh with the idler gear otherwise the fuel pump timing will be affected
To Refit the Fuel Pump (Mechanical Governor)
N14
1. Replace the fuel pump ensuring that the slot in the pump hub is aligned with the dowel in the gear.
2. Position the pump so that the scribed line on the pump flange aligns with the mark on the timing case (Fig. N.14). Secure the pump to the timing case. To check accuracy of mark on rear of timing case, this may be ascertained in accordance with the instructions for marking a new timing case given on Page K.6.
3. Secure the driving gear to the fuel pump shaft with the three setscrews and spring washers, ensuring the dowel is properly located in its slot (Fig. K.14).
4. Fit the timing case inspection cover.
5. Refit the low and high pressure pipes to the fuel pump.
6. Re-connect the throttle and stop lever controls and attach the return springs.
7. Vent the air from the fuel system (Page N.9).
8. Adjust the maximum and idling speeds.
Fuel Pump Gear
For details of fitting a new fuel pump gear see "Timing Case and Drive"
To Re-set the Fuel Pump Timing
On the fuel pump rotor, inside the fuel pump are a number of scribed lines, each one bearing an individual letter. A timing circlip is positioned inside the pump and has to be set so that when the appropriate scribed line on the fuel pump rotor aligns with the scribed line on the circlip (Fig. K.13), it denotes commencement of injection (static timing).
NOTE: On later engines the scribed line on the circlip has been deleted. On these engines the scribed line on the rotor should be aligned with the end of the circlip which has the straight edge, (Fig. K.12).
To set the timing circlip, it is necessary to remove the pump from the engine and fix the position of the circlip by connecting No. 1 cylinder outlet connection (marked "W") to an atomiser tester and pump up to 30 atm (31 kgf/cm2 or 440 lbf/in2). Turn the pump by hand in the normal direction of rotation until it "locks up". The squared end of the circlip should now be adjusted until it lines up with the letter "A" for hydraulic pumps or the letter "C" for mechanical pumps, on the pump rotor.
To re-set the fuel timing the following procedure should be adopted:-
(a) Hydraulically Governed Pump
Ensure that the fuel pump circlip is correctly positioned as described previously.
1. Ensure that the fuel pump is correctly fitted with the scribed line on the mounting flange aligning with the mark on the fuel pump gear carrier (Fig. N.12).
2. Position the crankshaft so that No. 1 piston is at T.D.C. on compression stroke.
3. Remove the collets, spring cap and spring from the inlet valve of No. 1 cylinder and allow the valve to rest on the top of the piston.
4. With the aid of a clock gauge in contact with the end of the valve now resting on the No. 1 piston it will be necessary to position the crankshaft at the static timing position given on Page K.5.
5. Remove the inspection plate on the fuel pump enabling the rotor to be seen.
6. With No. 1 piston at the static timing point on its compression stroke, the scribed line on the fuel pump rotor marked "A" should align with the scribed line or straight edge on the circlip (Figs. K.12 and K.13). If it does not, release the fuel pump drive plate securing setscrews and turn the drive plate on the slotted holes, the required amount to bring them into alignment. Access to the drive plate is gained by removing the timing case front cover inspection plate (Fig. K.11).
7. When the fuel pump timing is correct, obliterate the mark on the fuel pump drive gear and re-mark the gear to correspond with the mark on the fuel pump drive plate (Fig. K.11).
8. Refit the spring. spring cap and collets to No. 1 inlet valve and refit the pump inspection plate and timing case inspection plate. Re-seal the inspection plate.
(b) Mechanically Governed Pumps
The procedure for re-setting the fuel pump timing on mechanically governed engines is similar to that used for hydraulically governed engines with the exception of the method of pump adjustment.
As there is no adjustable fuel pump drive plate on a mechanically governed engine, the adjustment is carried out by slackening the nuts on the pump mounting flange and rotating the pump body until the scribed line on the rotor, marked with the letter 'C' aligns with the scribed line or straight edge of the circlip (Figs. K.12 and K.13).
To Check Marking Angle of Fuel Injection Pump using Tool MS.67B
N15
1. Release screw (5, Fig. N.15) and remove splined shaft (6). If pump has a slotted hub, the splined shaft should be retained with the small splined diameter to the rear to locate in the centre of the hub.
2. Ensure that slotted pointer (2) is positioned with slot to rear of tool and chamfered sides of slot outwards. At this stage, slotted end of pointer should be kept well back towards body of tool. Ensure that the flat in the washer fitted behind the pointer securing screw (3) is located over side of pointer.
3. Release bracket screw (4) and set bracket so that the chamfered edge is in line with the relevant marking angle (see Page B.14).
N16
N17
4. Position timing tool on pump drive shaft with master splines engaged and tool locating on spigot (see Fig. N.16). With dowel drive pumps, locate splined shaft in hub, slide tool towards pump to rest on end of hub and lock shaft in tool (see Fig. N.17).
5. Connect No. 1 outlet of pump body to an atomiser test rig and pump up to 30 atmospheres (31 kgf/cm2) -440 lbf/in2. If pressurising valve is fitted this must be removed.
6. Turn pump in normal direction of rotation as shown on pump nameplate, until it locks.
7. In this position, slide pointer forward until it is halfway over pump flange and check that timing mark is central to slot in pointer.
Maximum Speed Setting
NOTE: The maximum speed screw seal of the original fuel pump must not be broken or tampered with in any way unless factory authority is first obtained. Failure to do so may result in the guarantee becoming void.
When fitting a replacement fuel pump, or in the event of the maximum speed screw having been moved, the maximum no load speed must be checked and re-set as necessary.
The maximum no load speed will vary according to application. For details, reference should be made to the code number stamped on the fuel pump data plate. The last four numbers in the code indicate the speed required, and in the case of the following example, this would be 3130 re/min.
Code Example:-AS62/800/0/3130
NOTE: If the fuel pump data plate is damaged or defaced so as to make it impossible to read the code, or if the code is not stamped on the plate, you are advised to contact your nearest Perkins Distributor or C.A.V. dealer, or alternatively, Service Department, Perkins Engines Limited, Peterborough, to obtain the correct setting.
NOTE: Under no circumstances should the engine be allowed to operate at a higher speed than specified or severe damage to the engine may result.
Idling Speed Setting
The engine idling speed is adjusted by the idling screw. With the engine warm, turn the screw clockwise to increase the engine speed and anti-clockwise to decrease.
The idling speed will vary, according to application. For details apply to the nearest Perkins Distributor o C.A.V. Dealer, alternatively Service Department, Perkins Engines Limited, Peterborough.
Priming the Fuel System
The air must be vented from the fuel system whenever any part of the system between the fuel tank and injection pump has been disconnected for any reason, or when the system has been emptied of fuel.
No attempt must be made to start the engine until the injection pump has been filled and primed as serious damage can be caused to the pump due to lack of lubrication.
Later filter elements are self venting and do not have a vent plug fitted on the top of the filter cover.
1. Drive Shaft
2. Fuel Outlet
3. Idling Screw
4. Maximum Speed Screw
5. Bleed Screw
6. Stop Lever
7. Fuel Inlet
8. Bleed Screw
9. Speed Control Lever
N18
N19
1. Slacken the air vent valve on the front side of the governor control cover (mechanical governor, Fig. N.19) or on the top of the control gear housing (hydraulic governor, Fig. N.18).
N20
2. Slacken the vent valve fitted on one of the two hydraulic head locking screws (Fig. N.20).
3. Where applicable, unscrew, by two or three turns, the vent plug on the top of the filter cover (Fig. N.21).
N22
4. Operate the priming lever on the fuel feed pump (Fig. N.22) and when fuel, free from air bubbles, issues from each venting point, tighten the screws in the following order:-
N21
1. Filter cover vent screw (Fig. N.21), where applicable.
2. Head locking screw vent valve (Fig. N.20).
3. Governor cover vent valve (Fig. N.18 or N.19).
N23
5. Slacken the pipe union nut at the pump inlet (Fig. N.23), operate the priming device and retighten when oil, free from air bubbles, issues from around the threads.
6. If the fuel pipe to the Thermostart cold starting aid has been drained, loosen the union nut at the starting aid and operate the priming lever until fuel, free from air, comes from the connection. Tighten the union nut.
7. Slacken the unions at the atomiser ends of two of the high pressure pipes.
8. Set the accelerator at the fully open position and ensure that the "stop" control is in the "run" position.
9. Turn the engine until fuel oil, free from air bubbles, issues from both fuel pipes.
10. Tighten the unions on both fuel pipes, and the engine is ready for starting. If the fuel has been drained from the thermostart feed pipe, the pipe must be disconnected at the thermostart and all air bled from the pipe before the thermostart is operated.
Priming Procedure after changing Earlier Filter Element
1. With the vent plug on the filter cover removed, and the union at the filter end of the return pipe (filter to tank) slackened, operate the feed pump priming lever until oil, free from air bubbles, issues from the filter cover vent.
2. Replace the vent plug, and continue to operate the priming lever until oil, free from air bubbles, issues from around the threads of the return pipe union.
3. Tighten the return pipe union.
4. Slacken the union at the filter end of the filter to injection pump feed pipe, and operate the priming lever until oil, free from air bubbles, issues from around the union threads.
5. Tighten the feed pipe union. The pump and filter are now filled and primed.
Atomisers
General
When replacing atomisers in the cylinder head it is essential that a new, correct type copper washer is fitted between the nozzle cap and the cylinder head.
A one piece collar type dust seal is fitted on earlier engines but later engines have an improved two piece arrangement which consists of a soft rubber sealing ring or sleeve and a rigid plastic spacer which presses down onto the rubber sealing ring.
NOTE: The rubber sealing ring is always fitted below the rigid spacer.
Tighten securing nuts evenly to 12 lbf ft (1,7 kgf m) -16 Nm.
Some engines are fitted with atomisers which use a top inlet connection. These can be fitted with the atomiser 180° out of position. In this position, the nozzle holes will not spray into the combustion chamber correctly and will result in loss of power and increased smoke emission. Atomisers with top inlet connections must always be fitted with the leak off connection to the fuel injection pump side.
Atomisers should be taken out for examination at regular intervals.
Refer to preventive maintenance, Page C.2.
The first symptoms of atomiser troubles usually fall in one or more of the following headings:-
- 1. Misfiring.
- 2. Knocking in one (or more) cylinders
- 3. Engine overheating.
- 4. Loss of power.
- 5. Smoky exhaust (black).
- 6. Increased fuel consumption.
- 2. Knocking in one (or more) cylinders
The particular faulty atomiser or atomisers may be determined by releasing the pipe union nut on each atomiser in turn, with the engine running at a fast "tick-over". If after slackening a pipe union nut the engine revolutions remain constant, this denotes a faulty atomiser. The complete unit should be withdrawn from the cylinder head and inverted, atomiser nozzle outwards and the unions retightened. After slackening the unions of the other atomiser pipes (to avoid the possibility of the engine starting), the engine should be turned until the nozzle sprays into the air, when it will be seen if the spray is in order. If the spray is unduly "wet" or "streaky" or obviously to one side, or the nozzle "dribbles" it may only be necessary to probe the nozzle holes to remove carbon.
NOTE: Care should be exercised to prevent the hands or face from coming into contact with the spray, as the working pressure will cause the fuel oil to penetrate the skin.
N24
NO ATTEMPT SHOULD BE MADE TO ADJUST THE INJECTION PRESSURE WITHOUT A PROPER TESTING PUMP AND PRESSURE GAUGE (FIG. N.24). IT IS QUITE IMPOSSIBLE TO ADJUST THE SETTING OF ATOMISERS WITH ANY DEGREE OF ACCURACY WITHOUT PROPER EQUIPMENT.
A perfect atomiser, when tested by pumping fuel through it in the open air gives a short "pinging" sound as the fuel emerges from the holes. After the atomiser has been in service for some time, the "pinging" changes to a crackling sound. It is not until the atomiser sounds "dead" that its condition is likely to affect the running of the engine.
Atomiser Identification
Atomiser identification codes as given on Page B.17 were originally stamped on a tab washer fitted under the spring cap locknut.
Currently, the atomiser code is stamped on the atomiser body.
Fuel Pipes
N25
For standardisation purposes, high pressure fuel pipe assemblies are now supplied with olives fitted as shown in Fig. N.25. The earlier type pipe assemblies with olives fitted in the reversed position are still satisfactory.
No two of the pressure pipes, from the fuel pump to the atomisers are alike.
(High pressure fuel pipe nuts should be tightened to 15 lbf ft (2.1 kgf m) -20 Nm.
If the union nuts have been over-tightened there is a risk that the olives will have cracked or been unduly compressed, when leakage will resut.
The working pressure which these joints must sustain is several thousand pounds per square inch.
If the union is tightened excessively the olive may collapse and split The same danger exists if the pipe is not square to and central with the union.
When changing an atomiser always remove the pipe entirely.