I still don't understand... You are saying that the procedure used for both drip counts is precisely the same and that you just vary the drip count by changing the pressure of hand pumping? I thought that one needed to be very meticulous, operating careful adjustments by rotating the IP, in order to arrive at a precise drip count...
How is it possible that, following exactly the same procedure for both, the two drip counts are interchangeable without varying anything else? I don't get it... Can someone help me understand this concept, please?

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1979 240D, W123, 105K miles, stick, white w/ tan interior.

The reality is that the flow goes from "all to nothing" very quickly as the IP is adjusted (rotated.) From a practical standpoint, the timing will be very close to correct if the IP is dripping (ie: forming droplets) at any rate.

It will make a lot more sense when see it for yourself.

If what you are saying were true, then what's the point about rotating the IP by small increases until getting exactly to a given precise count, which is very much an important step in all the tutorials on IP timing I've read so far? One would just set the degree number on the balancer (with cams in the proper position) and move the IP until getting ANY count... However, there are very distinct rates for doing this: 1 drop/sec, 1 drop every 20 secs, etc. I doubt that your answer is it...
Will someone with some solid technical (as opposed to practical) background step in and clarify this for all of us, please...

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1979 240D, W123, 105K miles, stick, white w/ tan interior.

What you are seeing is the #1 IP plunger closing the fill port of the injector barrel....the drips are indication of the very threshhold of beginning of pressurization in the fuel element .....The drips are an indication that the fill port is almost completely sealed by the upward travel of the plunger...As the fill port is blocked by the upward moving plunger...no more drips...
In actual operation the only escape for the now pressurized tiny column of fuel is out of the IP fuel line to the injector...
One forum member uses a bucket suspended above the engine full of diesel to maintain a constant pressure to the IP fuel chamber to get the drip count the same every time.....that is how I am going to do it from now on...
Hand pumping is too variable for a constant pressure....
If you have studied this stuff like it looks like you have...you are going to be extremely close to what spec calls for....once you do it it will make more sense....

__________________
1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)

I appreciate all the stuff you have written, but it still does not address my specific question. For instance...

Let's suppose that, using your strategy, we use a bucket suspended above the engine full of diesel to maintain a constant pressure to the IP fuel chamber to get the drip count the same every time... (thereby eliminating the variability inherent in hand pumping which makes it an unreliable procedure): are at this point the two drip rates (1 drop/sec and 1 drop every 20 seconds) still interchangeable?!? How is it possible that they be so? It doesn't make any sense at all...

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1979 240D, W123, 105K miles, stick, white w/ tan interior.

I got this information from an authorized Bosch IP service shop owner with about 30 years of experience....there may be some more qualified people for this topic... but I have been ok with the info from Bosch Injection service professionals...
I think the procedure may be over emphasized in shop manuals just to get as close to port threshold closure as possible since this is mostly a field procedure with simple tools...The original procedure was the high pressure test method which involves a lot of expensive Bosch test equipment...
If you want to be dead on timing specs. then an electronic timing device can be used to check dynamic timing with engine running...I also like to be as close as possible to spec. so I understand the need for good info....
You may be surprised when the drip count is where it is supposed to be.. but when put on a dynamic timing device it shows to be off a bit...In these cases I would go with the dynamic test results...

__________________
1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)

The flange IP setting for 1 drip every 20 secs or 1 drip every sec is probably so close to actual IP adjustment.... that whenyou tighten down the IP it may vary that much anyway....
Try both drip counts if you want to see if it does much...
You could call several Bosch shops and see what they say....
I thought I was the only one that worries about this stuff and cannot sleep for thinking about it....but that is a good thing when it comes to our oil motors...

__________________
1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)

Again, it's not about being obsessed with precision... It's about understanding how those two very different rates can be interchangeable... Please read my words, don't just assume you know what I am asking...
Some tutorials advise 1 drip every 20 secs... If you are getting one drip every 15, for instance, you are supposed to keep adjusting the IP until you get it right... 1 drip every 20 secs! Others say 1 drip/sec, and also ask for strict adherence to this rate. How in hell can these two different rates be interchangeable in order to get to the same end result? That is precisely my question...

__________________
1979 240D, W123, 105K miles, stick, white w/ tan interior.

Don't get me wrong... As I said in my first post, I got the procedure down and feel confident about going ahead and doing it...
My question is a conceptual one... It's not at all about getting as precise as possible in the timing... It's just about understanding how it is possible that, using exactly the same procedure, two different drip rates of measurement are interchangeable within that same procedure... Understand what I am saying?
I would like to comprehend how utilizing the 1 drop/sec method is interchangeable to using the 1 drop/20 secs method, because it seems absolutely illogical to me... I think maybe something is escaping me, and would like to understand what that is...

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1979 240D, W123, 105K miles, stick, white w/ tan interior.

I appreciate the concern about conflicting info.....The difference between the two counts seems to be what source the info is coming from...(MB) (Bosch) (Haynes) (Bently) (Chilton)
I have noticed that some manuals for the older pumps have different counts from the newer ones...
Bosch may have a slightly different count from Mercedes for the same pump....I bet there have been some good arguments in the Fatherland over this topic with much cussing and beer drinking....
One drip every 20 seconds would place the timing a tad earlier than the one drop every 1 second...
I go with the earlier timing to compensate for wear of components....plus it seemed to have more power on the more advanced side of timing range on my older engines...

__________________
1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)

What do you mean "a tad earlier?" The difference between 1 drop/20 secs and 1 drop/sec is H-U-G-E, if you look at the fact that, when using the first method, if you are at 1 drop/23 secs, for instance, or 1 drop/17 secs, you are considered to be way off and are supposed to patiently keep trying until centering it at 1 drop/20 secs... If the two rates were considered to be so close as you say, the difference between, say, 1 drop/15 secs and 1 drop/20 secs would be considered negligible. But it's not, and this according to both methods. According to the 1 drop/sec drip rate method, for example, if you are at 1 drop/2 secs, you are considered to be off and expected to get it precisely at 1 drop/sec. So according to the directions given for both methods, the difference between 1 drop/sec and 1 drop/20 secs is considered to be H-U-G-E and not negligible as you say. Yet these two very different drip rates are adopted by different people to supposedly get precisely to the same end result... This is what does not make any sense at all to me and I thought I was perhaps not interpreting correctly at some point... hence my coming here asking for clarifications.

Well, I have asked my question. This exchange between the two of us, with me saying over and over the same thing and you doing the same, is not conducive to much... I don't think you understood my question well... which again is a conceptual one about the validity of method and not about how to do it in the best way possible... So, if someone understands what I am asking about and has an answer to that, I'm all ears...

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1979 240D, W123, 105K miles, stick, white w/ tan interior.

BINGO! What you are looking for is a drip. The point at which you get a drip rather than nothing or a stream is quite narrow. It might vary by a few degrees, but you will be plenty close enough if you are set for a drip.

If you are into hair splitting, then a piezo electric gizmo for a timing light will get it down to a frogs eyelash, but by getting this precise, you or no one else will ever be able to tell the difference.

My $0.02,

Larry,
As one who has been striving to get one of the "piezo" "gizmo"s working, let me belatedly announce that we finally have a working system... so to speak. I found that the piezo sensor we had that clamps onto the heavy fuel lines used on these vintage MBZs, I found our clamp sensor was apparently defective. So two new piezo clamps [ 6 & 5 mm] did the trick. We are using a Kent Moore "Tach-N-Time" meter I purchased on Ebay for ~$200. Let me point out that the standard inductive strobe light I initially used was NOT sensative enough but my Indy friend "Karl" the mad Hungarian has a "Snap-On" light that works with the meter every time now. Another part of this "show-n-tell" is that after using our timing meter/light on numerous 70(s) and 80(s) MBz diesels [ several at our last S.F. EastBay GTG in July]... after this considerable experience with our working meter/light, I can report that most cars have been found retarded 4 to 10 degrees or set at from 14 to 20 degrees BTDC. My Son's '80 300D IP was off by 11 degrees and once reset ~26 deg. BTDC the car's fuel mileage has improved about 15 %.

Let me say IMHO a practical accuracy for timing for us at present is ~ +/- 1 degree largely due to the limitations of being forced to make the adjustments "statically". Now IF only we could figure out a way to make the timing adjustments "dynamically" [ aka with the engine running ]!?
I'm thinking that we might try fabricating extra long HP fuel lines that would be used temporarily for IP timing adjustments. Such fuel lines would loop much higher and thus be flexible enough to allow the IP to be turned/ adjusted while the engine is running. "Yellit" and I have also talked extensively another yet to be successfully invented tool... some kind of attachable lever/bar/handle that would extend up and out of the engine well to increase the ease and accuracy of your IP adjustments! "Yellit" [Kevin] and I would appreciate any thoughts/ideas that you might have on either of the above described yet-2-B invented tools needed to add the ability of dynamic timing adjustments to go with our now functioning meter and timing strobe light!

Even with such tools, I think +/- 0.5 degrees would be the absolute best one should expect... and probably 1 degree is more practicable... so I truly hope Barry is correct that once we get this close to what he believes is the ultimate "sweet spot IP timing setting"... I hope his Glow Plug MiliVolt Method can then take over and together with our ideas for flexible test/adjustment fuel line and attachable lever/handle... then we will have a workable way to "tweak" these IPs/Engines probably somewhere near the 26 deg. BTDC mark!
Regards,