Diesel Engine Injector Pump Repair

 
By 4 August 2014
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Other than periodically checking the oil level for in-line pump reservoirs and
adding rust inhibitor to the fuel before long-term storage, injector pumps require no
special attention. When loss of pressure indicates that the pump has failed, the
mechanic farms the unit out to a specialist for cleaning or repair.

While most mechanics would tackle Bosch VE, inline pumps are simple devices that can be opened for cleaning and elementary repairs. But the work requires patience and the highest possible levels of cleanliness. Plungers are lapped to their barrels and must be assembled as found. Nor should these sensitive parts be touched with bare fingers. Wear surgical gloves or use forceps. Tappets and other adjustable parts must be kept with their plungers. When disassembly entails loss of adjustment, the existing adjustments must be scribe marked. If at all possible, obtain a drawing of the pump before you begin.

Inline pumps come apart as follows:

• Unscrew the delivery valves mounted above each barrel and lay them out in sequence on the bench, which should be covered with newspaper to reduce the possibility of contamination.

• Most inline pumps incorporate a side cover for tappet access; others mount the individual plunger assemblies from above with studs. On those with side covers, rotate the camshaft to bring each tappet to the top of its stroke and shim the tappet. Withdraw the plungers from the top with the aid of a hooked wire or expansion forceps. Mark or otherwise identify the plungers for correct assembly.

• Inspect the lapped surfaces with a magnifying glass. Deep scores or pronounced wear marks mean that the pump has come to the end of its useful life. Over-tightening the delivery valves warps the barrels and produces uneven wear patterns. Water or algae in the fuel leave a dull, satiny finish on the rubbing surfaces. Loss of the sharp edges on the helix profile upsets calibration.

• A plunger should fall of its own weight when the barrel is held 450from vertical. Gummed or varnished plungers can make governor action erratic and accelerate wear on the helixes and rack.

• If you have the specifications, check the cam profile with an accurate (i.e., recently recalibrated) micrometer.

• Examine the rack teeth for wear. Figure 5-18 illustrates, in exaggerated fashion, the wear pattern. The rack should move on its bushings with almost no perceptible side or vertical play. Installation of new bushings requires a factory reamer.