When a pump requiring attention is removed from an engine, it may not need a complete Overhaul. The pump can be set up on a testing machine to locate the particular faults, and repairs or adjustments are made on the basis of the test results.
An injection pump consists of a large number of fairly small parts, which should be separated out into divide trays during dismantling. The person dismantling the pump must be familiar with the detail of the pump’s construction. He will identify the parts as they were being dismantled and subject them to a visual inspection to ensure that they are satisfactory for further use.
Many parts of the pump are mated assemblies, which has been lapped together during manufacture. These must keep together and in the even of either part having excess wear, the assembly must be renewed.
All dismantled components must be closely inspected. Any component that shows signs of fretting, damage, wear, corrosion, cracks or distortion must be discarded and replaced with new part.
During pump overhaul, all O-rings, seal, gaskets, tab washers and locking devices that are removed should be renewed. Protection sleeves should be used when installing seals to prevent damage. All seals must be coated in clean test oil prior to assembly so that they do not operate dry and become damage as a result.
Overhaul procedures vary considerably for different pumps. Some general points relating to in-line pumps will be covered below. This will also assist with knowledge of pump construction.
In-line pump Overhaul
Figure 23.8 shows an injection pump fitted with diaphragm-type feed pump. As a first step in dismantling, the feed pump is removed. The side covers, which is secured with two Philips head screw, can then removed.
The body of the pump, which carries the pumping element, is bolted to the main pump housing by Allen-head bolts. These are removed and the pump body, complete with the pumping elements, is separated from the main housing.
The pump body, separated from the housing, is shown in figure 23.9. The illustration shown a plunger removed from its barrel. The delivery valves are unscrewed from the top of the pump body and then the elements can be removed. The components part of each pumping element must be kept together.
They must not be inter-mixed. The tappets, which are located in the main pump housing, are removed (fig 23.10) and then placed in the individual containers. The parts of each tappet are kept together and the tappet must be replaced in its original position in the housing when the pump is reassembled.
The pump has an automatic-advance mechanism on the front of the crankshaft. This ia removed to gain access to the governor housing which can then be removed as shown in figure 23.11. Further dismantling removed the governor linkage and spring from the pump housing. The camshaft is withdrawn from the housing, completed with the governor assembly, as shown in figure 23.12.
Only the main points have been indicated to show the general approach to pump dismantling. The components can be further dismantled into their smaller parts. All parts are normally cleaned in test oil and examined for visible signs of wear or damage. The plunger and barrel are lapped fit and are checked for evidence of wear or scoring.
Reassembly follows the reverse of the sequence used for dismantling. Cleanliness is most important, particularly during assembly. The components of the pumping elements, such as the barrels and plungers, should be assembled “wet” with clean test oil. Figure 12.13 illustrates a complete pump in part section. Reference should be made to the illustration to identify the main parts of the pump, and also to gain an appreciation of the detail of its construction.