DEFEATING ILER GREMLINS
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• Operators in Rural Areas are Discouraged from Using Oilers Because They Do Not Understand the Technique of Maintenance : This Article, Based on Practical Tests, Explains It
By Laurence J. Cotton, M.I.R.T.E.
pROVIDED that it is properly maintained, the oil engine normally requires far less attention than a petrol engine, and the little servicing needed with the fuel-injection equipment can be tackled by any fitter of average intelligence. Fleet operators can afford to employ specialists to track down and cure the alleged " gremlins " of an oiler, but to the user with one oil-engined lorry among a number of petrol-engined vehicles, maintenance might be an expensive item because little might be known of the injection equipment.
It is the operator working in the more remote parts of the country who mostly complains of oiler maintenance costs, and he may quite easily deter other operators in the area who are contemplating the purchase of oil-engined vehicles. From inquiries I have made many of these complaints originate from entire lack of, or at the best poor, maintenance, and in other cases little was known of fault-finding diagnosis or knowledge of injector servicing.
Fewer Overhauls Apart from the fuel-injection equipment there is little difference between an oil engine and a petrol unit except for the materials used and the physical dimensions. In comparing the small oil engine with its contemporary unit, the potential life should be at least equal, with the possibility of far greater mileage between overhauls for the oiler because of its lower piston speed. An exception is to be found in petrol engines having specially treated cylinder bores that afford an unusually low rate of wear.
Provided that oil changes are made at the prescribed intervals and the oil and fuel filters receive regular attention, the life of the compression-ignition engine should indeed be the longer because there would be less dilution of the lubricant by unburnt fuel.
Using the Perkins range of oil engines to exemplify a maintenance system, B6 there is the normal daily inspection of water and oil levels in the
radiator and sump, and check on fan-belt adjustment and battery electrolyte level, and greasing of the water impeller every 1,000 miles. These are normal tasks for both oil and petrol engines.
It is recommended that the sump oil should be changed overy 2,000 miles and the felt element of the lubricant filter removed and cleaned. At the same time the oil in the air cleaner should be inspected and the level topped up or the oil changed if necessary. Once again, this is routine maintenance, but thc period is perhaps shorter than that laid down for the petrol engine.
An. additional task at 2,000 miles is to clean the pre-filter of the fuel lift-pump, this on the Perkins engine being of the bowl pattern with a close-mesh gauze. The life of the fuel-injection equipment depends almost entirely on the cleanliness of the fuel, therefore the user should carry out any such maintenance tasks at the periods specified.
To determine what this involved. I performed the routine tasks of fuel-filter maintenance on a Seddon 7-tonner. which was rather an early model and less accessible in its engine components than the more recent types. The fuel lift pump is attached to the injection pump, being operated by the plunger camshaft. and, on the vehicle used, the primary filter was easier to reach from below.
10 Minutes' Work It took less than a minute to slacken the toggle screw and remove the bowl, after which the gauze and bowl were rinsed in a tin of clean paraffin. with emphasis on the cleanliness of the tin and of the paraffin.
As a precautionary measure, a new rubber sealing washer costing Id. was fitted between the bowl and housing when reassembling; any air leak at this point would cause air locks in the fuel
supply. The bleed screw on the injection pump was opened and the lift pump operated manually to ensure that the fuel system was free of air. I would allot 10 min. as a maximum for attention to the fuel precleaner.
At 5,000 miles the intermediate fuel filter is scheduled for attention, this unit being housed adjacent to the engine and having a bowl and element retained by a single setscrew. This again is a 10mm. task for removal, washing, replacing and bleeding the supply free of air.
A felt filter element is used, which is cleaned in paraffin or petrol and replaced at I0,000-mile intervals. With the Perkins R-type engine, and some of the P series, the final filter has a paper element and no intermediate filter is required.
Every 10,000 Miles At 10.000-mile intervals it is prescribed that with the Perkins engine the crankcase ventilation pipe, air cleaner. sump strainer and the gauze of the lubricating-oil filter body, should be cleaned and the felt element replaced. Additionally the felt element of the intermediate fuel filter should be replaced and the gauze strainer in the exhauster banjo connection cleaned. Two hours' labour should be ample for such routine tasks.
Every 20,000 miles the final fuel-filter bowl should be cleaned and the element renewed. This element consists of a series of felt pads built up on a perforated support tube. The filter requires no other attention apart from partial draining of the bowl every 5,000 miles to remove sediment.
No great knowledge of oirengines is required to perform the routine tasks so far dealt with. and the first specified period for attention to the injection equipment is at 20,000 miles when it is recommended that the injectors, sometimes termed atomizers, should be cleaned and checked. The fuel-injection pump requires no maintenance because, apart from the initial supply of lubricant introduced into the housing during 'assembly, it remains topped up by oil fuel which leaks past the plungers. Any surplus drains off via an overflow pipe.
Injector cleaning and checking can be accomplished without expensive test equipment, but it is suggested that the special cleaning kit should be used. The injector is removed by freeing the feedpipe union-nut and releasing the two holding-down nuts, after which it can be prised from the cylinder head. After washing the injector in paraffin the carbon deposit should be cleaned off the nozzle with a soft-brass wire brush. It is preferable to check the spray and opening pressure of the nozzle on an injector test machine which costs f:12 10s., hut if the operator has not invested in such equipment the injector can he tested summarily on the engine.
Improvize0 Tests
Engine manufacturers do not usually recommend improvintion for testing injectors, but provided certain precautions are taken, there is no reason why the nozzle should not be tried initially on the engine. The feed pipe should be disconnected at the pump and refitted so that the • injector can be attached outside the engine.
Care must be taken fo avoid bending the pipe when doing this because internal scale might be freed, which would score the working parts of the
nozzle. As the pressure of the spray from the injector is sufficient to penetrate the human skin suitable precautions should be taken to keep the spray away from the hand,
After the injector is connected, the engine can be started and run for a few seconds to observe the spray characteristics. If there is any indication of the passing of a solid stream of fuel, the injector will require stripping, cleaning and the opening pressure reset after . assembly. The method will be explained later, In routine maintenance no attention is required for the injection pump. and apart from an examinaiion of the injectors for spray characteristics there is no regular servicing corresponding to the attention which has to be given to the carburation and ignition equipment of the petrol engine.
It is good policy to "leave well alone " when operating an oil-engined vehicle because, normally, it is exceptionally trouble free, and the first indication of pending trouble is usually shown by difficult starting from cold. Road stops are few and can usually be traced to shortage of fuel in the tank, or air-locks caused by loose pipe connections. Lack of power on hills may
be caused by the fuel-supply-pump diaphragm becoming porous or by dirt under the fuel-delivery valve.
Drivers should be instructed"on the .procedure to adopt for ridding the supply line of air following fuel short
age at the injection pump. After ensuring that there is fuel in the tank the bleed screw at the injection pump should be released and the hand primer operated until fuel flows freely without trace of air bubbles. Following the tightening of the bleed screw, the engine should start.
The symptoms of air in the fuel supply line are equivalent to misfiring in a petrol engine, the result being uneven running and loss of power. Apart from this, I would advise that no further knowledge should be imparted to the driver of a vehicle employed on local work.
A porous lift-pump diaphragm, or a faulty filter relief valve in the fuel system might not proclaim themselves by misfiring but might be first denoted by poor pulling on hills. A check can be made by removing the plug from the top of the filter case and priming the lift pump. If the level is not raised to overflow point fairly rapidly, or falls when the pump is not being primed. the fault is in the lift pump or relief valve.
A method of checking that I recommend when poor starting from cold is experienced is first to make sure that there is adequate fuel in the tank and then to bleed the supply system at the pump to ensure freedom from air lock. Assuming no improvement, the injection-pump timing should be checked by turning the flywheel to No. 1 t.d.c. firing point making sure that the scribed lines on the pump coupling and pointer coincide.
Wear in the pump coupling or chain drive would retard the injection point, and there is the possibility that the Fig adjusting screws may have worked loose. If the engine still refuses to start after any corrections have been made, the injectors should be checked for spray characteristics, and for pressure if test equipment be available. It is unlikely that one faulty injector in a four-cylindered engine would be the cause of non-starting.
Where only one or two oil-engined vehicles are to be maintained it would be reasonable to hold a spare injector complete, and to avoid delay should a second injector fail, it would be as well to hold a replacement nozzle. If a new injector shows a poor spray or maybe no spray on engine test, the trouble is probably in the injection-pump delivery valve. This, however, is an uncommon failing, and one that can be virtually eliminated by giving attention to the efficient filtration of the fuel.
If the pump timing is correct, the fuel supply free from air and the injectors .working efficiently, failure to start might be traceable to poor compression or lumped valve timing. Whilst the latter is unlikely to be the cause, I have found that with a single-tooth jump the engine will start but lacks normal power. If not corrected and a second tooth is jumped there is danger of the valves fouling the pistons at the top of the exhaust stroke, which would involve an expensive repair.
An engine which idles erratically may require injector attention, but if it surges, or hunts as it is sometimes termed, the fault would be in the vacuum governor diaphragm. To check the action of the diaphragm the three screws and the side plate of the injection pump are first removed to expose the rack, and the vacuum pipe to the governor detached.
The stop lever operating the rack should then be moved to the off position, and a finger placed over the diaphragm-housing unit to seal it. When the stop lever is released the rack should return slowly to the full-throttle position.
If there should be any air leakage at the housing joints or diaphragm, the rack will move more rapidly. Replacement of a faulty diaphragm is a job best left to the experienced fuelinjection equipment specialist.
Injector stripping, cleaning and assembly require no great skill, but the work must be done on a clean ' bench and all parts thoroughly cleaned before assembly. Assuming that a faulty injector is replaced by a spare one, there is little delay in putting the vehicle back into service, and the defective unit can be examined at leisure.
Injector trouble is usually denoted by poor starting from cold, knocking in one or more cylinders, loss of power. overheating or smoky exhaust. The knocking might be so marked as to be mistaken for a loose connecting-rod big-end bearing. With a dry injector, however, the sound is more hollow. Tracing a faulty injector is similar to the procedure adopted in the case of a defective sparking plug, each cylinder being cut out in turn when the engine is running at idling speed. In the case of an oil engine the pipe at the injector is loosened. If after slackening the nut, the engine speed remains constant this denotes a faulty injector.
The nozzle is held in place by a screwed cap which can be released by a set-spanner. There is a tool made to hold the injector and special spanners are available to fit the cap and cover, but I would not consider these as essential for the maintenance of one or two sets of injectors.
When the cap is released the nozzle can be lifted from the injector body, and the first point is to observe whether both mating surfaces are clean and bright. The nozzle valve should be withdrawn for examination and cleaned with the soft-brass wire brush supplied in the cleaning kit. The nozzle itself should have all carbon scraped from the, interior and the sac at its base, and the holes cleaned out using the tools provided.
Ready for Assembly After washing, the components are ready for assembly and test. The cap over the adjusting screw at the top of the injector should be removed, and the locking nut slackened in readiness for setting to the correct pressure. If the injector spray is still wet or streaky, or drops of fuel form on the tip, the defective nozzle should be replaced.
There is no remedy if the norile valve is scored or tight in its housing, but as a last resource the faulty valve and its seat can be very lightly lapped in with a metal polish. This method does not meet with the approval of the makers because in initial machining the valve and its seat are ground to slightly different angles to provide a hair-line contact. Lapping the two together would, of course, broaden the contact face.
My experience has been that a light touch with metal polish as the grinding agent will often move an obstinate piece of carbon or take out any slight pitting in the valve or seat. Few faulty injectors fail to respond to this treatment, and if the spray characteristic is restored they will probably continue to give satisfactory service.
The axioms for trouble-free operation of an oil engine are—keep the fuel clean, observe scrupulous cleanliness in handling components of the injection equipment and change the lubricating oil at the specified intervals. Never use cotton waste or a fluffy wiper when cleaning the injectors, filters or pump, and do not lift the heads unless some mechanical fault, such as loss of compression, is reported. The oil engine ,s best left alone, and provided the parts are well lubricated with clean oil, it does not suffer burnt valves or other "top end" troubles.