Jerrys Old Engines in South Africa

Testing & calibrating the Lister 5/1 Diesel Injector.
26th September 2009.
(This article is aimed at those who are still learning about the diesel system - like me)


Someone on the lists suggested that I document this for others to follow - so here goes - first the preamble.

I was fortunate enough to be in the right place at the right time when my good friend of more than 40 years, Trevor Gebhardt, retired a few months ago. He presented me with 3 diesel injector tester/callibrators while "cleaning up" his shed in readiness for retirement.

Trevor did his apprentiship as both a "Diesel Mechanic" and an "Auto Electrician" many years ago, and, although he had already "left the bench" and moved on to greater things years before I met him, he retained his knowledge and equipment, as well as acquiring more of both along the way. Interesting is that, during his time on the bench, he was often called upon to work on Lister and Petter engines.

Anyway, back to the subject. Those testers that he gave me were an incredible gift (thanks Trevor) but I'm not experienced in diesel so, until I got an engine that I could use them on they stood on a shelf in my workshop.

Well, then the Lister 5/1 "followed me home" !

   Trevor was probably just as excited as I was and actually "itched" to get his hands on the diesel parts (although, he never mentioned it - I could just see)! After 40 years one begins to get a bit if insight into these things !

Well, earlier this week Trevor paid me a visit and showed me how to strip and clean the diesel pump and injector. He then insisted on coming back to show me how to test/calibrate them. Thanks Trevor.

Today was the day so, at last, I'll tell the story.

The first thing to do was to get one of the testers working (remember that they had probably not been used for more than 40 years). Trevor got stuck into this with gusto and within about an hour he let out a "Whoop" of satisfaction (as well as a fine mist of diesel all over my workshop). It worked!

Trevor then explained the whole thing to me and this article (at last) is what I learned. A quick note to "experts" - my explanation is for those of us who do (or did) not know much about the diesel system - the words and terms I've used are possibly incorrect but the article is written for "newbies" like me.

What you should know/understand before even starting is the following (this part for "newbies" like me). A simple explanation of the diesel system :

The diesel system, although similar in operation to the "gas engine" (which provides an externally generated spark to ignite the "fuel/air" mixture) works by compressing air to such an extent that the temperature of that compressed air is great enough to ignite the diesel vapour injected. That is why it does not need a "spark" - the "hot air" ignites the diesel vapour.

A "gas" (petrol to all except the Yanks) engine sucks in air from the atmosphere on the "inlet stroke" and mixes it with "gas" (petrol or whatever) vapourised by the carburettor (all on the "inlet stroke"). It then compresses it on the "compression stroke" and once maximim compression is attained an external force (magneto etc.) provides a "spark" which ignites that mixture and forces the piston down (power stroke).
  A diesel engine works by sucking in air (no "gas vapour' at this time - only air from the atmosphere) and compressing it to such a degree that the temperature of this air rises to a point where it is capable of igniting the vapourised diesel oil. At this time the "ignitable gas or vapour" needs to be introduced into the combustion chamber (that little bit of space left at the top of the cylinder).

    That is where the "diesel pump and injector" come into play. The "timing" is set to "inject" the diesel into the combustion chamber at the point of "maximum compression" (when the air compressed in this space is at it's hottest).

The diesel pump and injector now have to inject a diesel vapour into this very high pressure area so it is essential that the pump and injector are operating at much higher pressures to be able to do this. 

A vapour will ignite much sooner and burn more efficiently than a liquid so, the pump and injector must be capable of injecting a stream of "vapour" as opposed to a stream of "liquid" into the cylinder. For this reason, diesel components for the pump and injector are manufactured to extremely high tolerances and a calibrator is used to  "test" and "set" the injector for optimum results.

That's it in a nutshell. I hope you enjoy the article as much as I enjoyed learning about it.

Click on any pic to see a larger version - use your "back" button to return

C.A.V. Diesel jnjector tester

On the left is a pic and description of the C.A.V Diesel injector tester/calibrator.

The injector is connected to it by means of the pipe shown and the hand lever is pumped to force the diesel into the injector under pressure.

Once the pressure in the injector is high enough it "cracks" open and diesel is expelled through the nozzle. The guage shows at what pressure this is happening. If necessary, the injector is adjusted until it opens at the correct pressure.

The pic to the right shows the injector opening at 75 Atmospheres (which is too low a pressure) and the spray pattern can be seen to be a "stream" and not a "mist" or "vapour".
(Note that this all happens in a split second - some pretty nifty camera work was called for to capture it!)

The old Lister manual I have specified 75 Atmospheres but this was obviously too low. A quick phone call to Lister expert, George Botha, established that Lister had later changed this spec. and the correct setting for our altitude was 155 Atmospheres.

Here Trevor adjusts the injector to make it open at a higher pressure. The adjustment simply applies more pressure to the spring inside the injector.

Here the injector is opening at the correct pressure of 155 Atmospheres (see guage - allow for the error of parallax as my camera is held to one side).

Note now that the spray is no longer a "stream" but a "vapour" as it should be. The injector is now ready for use.
It's actually very simple if you have the right equipment!

Thanks Trevor for the tester as well as taking the time to show me how to use it.

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