The dire warnings about getting dirt into the fuel pump and injector do not prevent you stripping down your own pump etc if you have a siezed rack or other problem, but once you have scored a pump element plunger, it will be scrap - you have been warned ! The basic unit injection pump as fitted to Lister CS,CE,CD and others is a pretty simple bit of kit, and will dismantle and re-assemble very easily. It is also a robust bit of kit which can be maintained by most engine men.
DISMANTLING PUMP AND INJECTOR
A few tips on general removal / dismantling:-
1) NEVER EVER hammer or knock a seized rack, as you will quickly destroy the fragile element inside the pump. Leave it to soak in WD40 and take your time about it.
2) Always use two spanners when removing the injection pipe from the pump or injector, one to hold the pipe nut and the other to stop the bit it is screwed on to from turning. If you have a seriously rusty joint, heat it up with a blowtorch but do not get it too hot as the pipe will suffer. At the worst, the pipe may have to be scrapped to save the injector/pump to which it is attached.
3) Keep all bits away from other engine parts, as there are some fine pieces in there which will quickly get lost.
4) Get a couple of small plastic boxes to hold dismantled parts, and put half an inch of fresh diesel in the bottom to keep the bits from going rusty. Use one for newly dismantled parts and the other for cleaned up parts. DONT use paraffin, which absorbs water and leaves rust everywhere.
5) Clean all or as much as you can of the surface dirt from the pump/injector before dismantling. To dismantle the standard pump, you only need to undo the top delivery valve housing and remove the lower cam bucket circlip, and everything drops out ! BUT-
The relative position of the governor rack to the pump element will affect the output of fuel relative to the position of the engine governor arm. If you alter this relationship then you may find that your engine is ungovernable ! The pump element is normally marked with a dot on the small rectangular head which contacts the cam bucket, and there is also a mark on the rack or housing to line this up with. If you are not sure, then get something to mark the rack and element with which will enable you to re-assemble the two together in the same relative position. Pattern elements do not always have the mark, and while diesel repair houses can assemble the things with their eyes shut, the likes of us will get it wrong !
Once the bits are out (and you have taken note of how they are assembled haven't you ?) they can be cleaned and inspected. The delivery valve and spring in the top housing are there to act as a non-return valve and to make sure that the supply shuts off with a bang when the pressure falls from the pumping element. If the spring is intact and the valve face is clean and bright without any pitting, then it is OK to re-use. The element has two pieces, the inner plunger and the outer housing. The diameter of the plunger is reflected in the part number, the most common size is 5mm or 7mm for Lister 3/1 and 5/1 respectively. Thus you will be able to start identifying pumps from their element size. The fit between the two pieces is the make or break of the whole thing, and as long as the wearing surfaces are bright with no long scratches down the length of either, then they are re-usable (as far as eye inspection can tell)
Re-assembly is the reverse of dismantling, making sure that the cam bucket is free and lubricated, and the element alignment in the main body is correct.
The rack gets a lot of stick from the governor arm, and if the hole at one end is elongated and sloppy, you will not get decent speed control. Better to open the hole up and bush it or use a larger cotter pin. If the rack is sloppy in the pump body, you can get the holes line bored and bushed back to size (11mm) or look for another pump body.
The operation of the pump element always seems a mystery to 'outsiders', but like most things is very simple:
The element has a spiral groove cut in it's outside diameter, that has a connecting hole through to the inner pumping cylinder. The element is rotated in the pump housing by the rack, and there is a relief port in the body of the pump that will communicate with this spiral groove in certain positions of element height in the body and rotation. When pumping fuel at full throttle, the element is rotated to the full extent of the rack and each pumping stroke will eject the full volume of the element plunger and cylinder. Allowing for losses, this is pretty repeatable, so the speed / fuel relationship is very tight, subject to load.
If the engine governor decides that it wants to lower the speed, the the rack is pulled back (or forwards, depending on the governor configuration) and the element is rotated in the pump body. This time, the spiral groove will meet the spill port in the pump body and fuel pressure will fall away before the end of the pumping stroke, thus limiting the amount of fuel pumped. Note that the pump stroke is unchanged, just the volume has been reduced.
This constant stroke/variable volume system was the basis for the original successful Bosch pump, and forms the basis for probably 99% of injection systems. The repeatability of the fuel injection is what makes diesels so economical, and why their speed governing is so good in relation to fuel volume regulated petrol engines. The problem with carburettors is that the volume of fuel varies with air flow over the main jet in the carb venturi, and this in turn is affected by fuel and air temperature etc etc.
EXCESS FUEL TOGGLE
The excess fuel toggle is fitted to all CS engines, and probably others as well. It allows the pump rack to go further when it is flipped over, thus giving more fuel than normal for cold starts. If the toggle sticks open, not only will your engine start well, it will also get too much fuel at full load, with possible expensive consequences. Make sure that the little weight is free to rotate.
The injector is another can of worms entirely, but is still quite simple to strip and repair. What you cannot do at home is reset the injection pressure, which requires a bench test rig.
STRIPPING is done from two ends: the top delivery edge filter and the bottom nozzle.
The delivery edge filter is contained in the tube which the injection pipe connects to. You can blow them out against the direction of fuel flow, but not much else. The Top cap covers the injection pressure adjustment screw, locknut and spring. Once out, the bottom nozzle cover can be removed and the nozzle taken out. The fit of the nozzle pin in the housing is as critical as the pump element plunger in the housing. Too much clearance will see increased leak-off of fuel back to the tank and loss of power. It is all relative though, and a clean system will deteriorate very slowly over time, especially if the filters are kept clean.
There are thousands of injector nozzles in use. There are one or two which will suit your particular engine, and mixing nozzles from different engine types will cause all sorts of problems.
To give an example, the CS Lister engines all used the same nozzle body, but the 3/1,5/1,8/1 all used different nozzles. If you take that series of older injectors, there are about 500 nozzles listed for the range of applications, and unless you have the equivalents and supercession lists, it is a bit of a minefield.
As I have access to a very good injection shop in our industrial estate, I leave all this work to Vince, who has graced these articles before. I do have a bench tester for injectors and could do my own if I wanted, but I feel that if you can strike up a good working relationship with a supplier, and Vince also does our works vehicles, then it is far better than struggling along trying to do it all on the cheap.
Vince also has years of experience and loads of old bits and pieces in his stores to fall back on, which I do not. He is CAV trained and has an excellent working knowledge of most injection systems. More importantly he is prepared to look at older units, which a lot of CAV agents will not.
Injection pipes are something which work or don't, but there are different sizes of pipe, with bore sizes which can affect your pump performance. Most pipes have about a 1mm hole down the middle of a 4mm body. If the pipe gets bent, this hole can become restricted, so do not bend your pipes with too small a radius !
New pipes can be either made up or adapted from other engines. Most threads are metric, and I have found that truck pipes are probably better as substitutes than anything else. For trucks you can substitute agricultural machinery etc.
FUEL FILTERS Once you have restored your engine and fuel tank, and you have got all the crap out, flush it through a couple of times to get rid of any residue. Fit a clean filter and bleed as normal. Those owners of CS engines with the old wick filter may be interested to note that I have devised a replacement filter conversion which fits the old filter housing and used a modern cartridge filter. The details will be made public soon, and the kit consists of a new filter and a conversion piece which fits the existing housing, thus retaining the appearance of the original.
Spares are still pretty good for older systems, with pattern and genuine nozzles and elements being easily obtained. Test plans for older pumps are a bit tricky, but I have had good responses from Lucas Service at Ipswich, although this was on an occasional basis: they may not be so good if swamped by loads of telephone calls and faxes.
Loads of Bosch-CAV pumps are still around, and this was the original set-up in the UK, as CAV made pumps under licence from Bosch in Germany.
The World Wars put paid to that, so CAV went their own way, much as the UK magneto industry did in the first World War. Bryce was another company which probably did more for the unit injection pump (single element pump) than anyone else, and then Simms got involved in the multi-element pumps. They all ended up as part of Lucas eventually, and the market in pumps now is starting to fall off as electronic injection systems come onto the market, mainly driven (no pun intended) by environmental concerns, just as fuel injection for cars became commonplace for the same reason.
For single cylinder engines, the unit pump is still king, with the Italians taking the bulk of the market with Bosch still involved.
HELP AND ASSISTANCE Queries and requests for help with injection problems can be sent to me either by e-mail or fax. Vince has asked if I could handle any initial queries for him, but is basically willing to help with repairs/spares, as long as he doesn't get too distracted from earning a living !
I have access (through Vince) to a large amount of data sheets and catalogues which cover most popular applications such as Lister and others, and will be happy to look up information for you all.
© Peter & Rita Forbes 1998