In-line injection pump service

Removing and replacing injection pumps

Pumps may be mounted on a bracket attached to the engine crankcase and secured by bolts in the base of the pump. Alternatively, they may be provided with a flange on the front end of the pump which is bolted to a flange on the rear of the timing case. The pump is removed by first disconnecting the control linkages, the fuel line, all the injector pipes and leak-off pipe (if fitted) and then unbolting the pump from the engine. Care should be taken that dirt does not enter the pump. Before removing the pump, timing marks should be identified as they will be needed when the pump is being reinstalled.

Dismantling or repair of the injection pump should net be attempted expect where special workshop facilities are variable. These are not normal workshop operations.

Installing and timing injection pumps

Before the injection pump can be replaced, it is necessary to set the engine for correct injection timing. A timing mark will be provided on each engine. This might be located on the flywheel and be accessible through an inspection hole or cover, or it might be on the crankcase pulley.

The engine must be set on the timing mark with no.1 cylinder on the compression stroke. This is the point where injection should commence. For example, in a particular engine this could be 20 degrees before TDC.

The injection pump must be also be set for correct timing as it is mounted to the engine – it must be set in the position where it is just starting to pump fuel to the injector on no. 1 cylinder. On many pumps, this position is identified by a timing mark and pointer on the pump. An example for an in-line pump is shown in Figure 23.1.

With both the engine and pump set to their correct injection positions, the pump can be mounted to the engine, the timing marks checked (Fig. 23.1)

And adjustment made where this is required. Figure 23.2 shows an adjustable coupling. The driving member (1) is connected to the auxiliary drive shaft from the timing gears. The driven member (2) is attached to the injection-pump camshaft. The driving member can be adjusted in relation to the coupling by loosening the securing bolts and moving it in the slotted holes.

When checking timing, all timing checks and adjustment should be made after the engine has been turned in the direction of normal rotation. This will take up any slack in the drive train between the crankshaft and the injection pump.

The general procedure for timing in-line injection pumps has been indicated above but the actual procedure can vary with different engines and different types of pumps. Caterpillar timing, also timing and adjusting unit-type injections are covered in separate chapters. Distributor pumps are also covered separately.

Timing marks

For the purpose of injection timing, there are two different sets of marks provided on most engines:

  1. Engine timing marks – marks on the crankshaft pulley or other rotating part which show when injection should commence, i.e. degrees before TDC.
  2. Pump timing marks – marks on the injection pump to show just when the plunger is commencing delivery of fuel to the injector.

When both sets of marks are correctly aligned, the pump will commence delivering fuel to the injector at exactly the right time. That is, it will be timed to the engine.

Engine timing marks

These are related to no. 1 cylinder with the piston on compression stroke unless specified otherwise by the manufacturer. The timing marks can be located on the flywheel, crankshaft pulley, vibration damper, or auxiliary drive pulley, depending on the particular engine.

Two examples of timing marks are shown in Figure 23.3. In (a), the TDC mark and a degree scale for injection timing are marked on the edge of the vibration damper. The specified timing mark (e.g. 12 degrees) is lined up with the pointer on the timing case cover. In (b), the timing marks are located by removing a small inspection cover bolted to the flywheel housing.

In lager engines, a “barring” tool is used to rotate the engine while setting the timing marks or performing other adjustments. The barring tool is often in the form of a small gear which is installed temporarily to the flywheel housing. The gear is meshed with the flywheel ring gear and turned by a lever or ratchet handle (Fig.23.4).

Pump timing marks

One mark is provided on the injection pump housing and another on the member of the coupling attached to the injection-pump shaft. When the two marks are aligned, the plunger of the pumping element for no.1 cylinder will be in the position where it the position where it is just starting to deliver fuel to the injector of no. 1 cylinder.

Figure 23.5 (a) shows the marks on a pump and coupling with a timing device. This is an open coupling which enables the marks to be easily seen. The coupling in Figure 23.1 is enclosed in a housing and a cover has been removed so that the timing marks on the pump and coupling flange are visible.

Figure 23.5 (a) shows the marks on a pump and coupling with a timing device. This is an open coupling which enables the marks to be easily seen. The coupling in Figure 23.1 is enclosed in a housing and a cover has been removed so that the timing marks on the pump and coupling flange are visible.

Figure 23.5 (b) shows the marks for an injection pump with a front-flange mounting. The flange is bolted to the rear of the taming gear case. The timing drive is enclosed in the timing gear case and an inspection cover has to be removed so that the mark can be seen.

Because of the enclosed design of the pump drive, the pump coupling cannot be aligned directly with a mark on the pump housing. Instead, two intermediate mark are used: a mark on the coupling is the first aligned with an pointer on the timing cover and the marks on the timing gear case are really transfer marks which would not be necessary if the coupling was accessible and its marks could be aligned directly with the mark on the pump housing.

The above are but two examples of timing marks on injection pumps. In other incases, the pump driving gear may have timing marks or marked teeth. In cases where the drive is enclosed, the marks will usually be accessible only after removal of an inspection cover or plug from the timing case or pump housing.

Timing marks will always be provided on the engine, and in most cases, also on the injection pump, or where doubt may exist, the pump can be spill timed as discussed in the following paragraphs.

Spill timing a jerk type pump

If a jerk type pump has no timing marks, the point at which injection commences will have to be found. This is the point where the plunger, moving upwards in its barrel, has just closed off the fuel inlet port and pumping is about to commence. The procedure is as follows:

  1. Set the engine with no. 1 cylinder on compression stroke, and with the engine timing mark in line with the pointer.
  2. Disconnect the injector pipe for no. 1 cylinder from the delivery valve on top of the pump, unscrew the delivery valve holder and remove the delivery valve, spring and volume reducer from the holder.
  3. Refit the delivery valve holder (without the valve, etc) and then fit the “gooseneck” spill pipe to the delivery valve instead of the injector pipe. This is shown in figure 23.6.
  4. Operated the priming lever on the fuel lift pump to obtain a continuous flow of fuel from the spill pipe. (If the fuel supply to the pump has been disconnected, the pump must first be primed and bled). If a flow cannot be obtained, the pump must be rotated a little.
  5. With the injection pump drive coupling loosened or removed, turn the injection pump flange slowly by hand in the direction of rotation. The plunger will rise on the pumping stroke and cut off the inlet port in the barrel and thereby cut off the flow of fuel from the spill pipe.
  6. Remove the spill pipe and delivery-valve holder. Replace the delivery – valve holder and refit to the injection pump. The delivery – valve holder must be torque to the correct setting. If it is too tight, the barrel can distort and cause the plunger to jam.
  7. As the pump is being turned, the flow of fuel from the spill pipe should be carefully observed. As the rising plunger progressively closes the inlet port in the element, the fuel from the spill pipe will gradually decrease to a drip. The pump should be turn very slowly towards the final stages to identify the instant that the inlet port is fully closed. This is refer to as “spill cut-off”. This occurs when there is no drip from the spill pipe during period of about 15 seconds.
  8. The pump drive coupling must now be secured in this position – that is, Whit the engine on its timing mark and the injection pump at spill cut- off position.
  9. Remove the spill pipe and delivery-valve holder. Replace the delivery – valve holder and refit to the injection pump. The delivery – valve holder must be torque to the correct setting. If it is too tight, the barrel can distort and cause the plunger to jam


Couplings are provided with some flexibility to al low for small differences in alignment between the pump and the engine. One design of coupling was shown in Figure 23.2.

A different type of coupling is shown dismantled in figure 23.7. Couplings of this type consist of two flanges with a non-metallic insert between them. Apart from providing a semi flexible coupling, the toothed insert enables the timing to be set to the approximate position when the pump is mounted to the engine. The left-hand flange is tapered and keyed to the injection pump shaft. The right – hand flanges is bolted to a drive flange, which is keyed, and clamp to the engine’s auxiliary drive shaft. The bolt holes in the drive flange are slotted so that the injection timing can be accurately set.

Injection-pump servicing

Any work that has to be carried out on injection pumps which goes beyond removal and replacement or on the vehicle adjustments requires special facilities. These include a dust – proof room, an injection pump testing machine and special tools. Also required are specification data related to pump adjustment, torque settings of bolts and screws, and performance figure for testing purposes- for each model of pump. Pump work also calls for cleanliness and accuracy, with attention to detail.

While injection pump repair and overhaul are outside the normal scope of a mechanic’s work, he should be aware of the general procedures that are carried out during pump overhaul. The following paragraphs are only intended to give an appreciation of the scope of pump overhaul work and are not given as overhaul procedures.

2 thoughts on “In-line injection pump service

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