LD/LDT vs LDS Hydraulic heads

[JasonS]

I have wondered for quite awhile why there is a different hydraulic head on the LDS engines. I wasn't able to find any differences in the military or Bosch documentation. It wasn't clear why a different hydraulic head was specified for such a minor difference in horsepower. I have accumulated two LDS pumps (HD90101A) and two LD/LDT pumps (HD90100A) and finally took time to take the hydraulic heads apart. I don't have any meaningful answers but wanted to post this information since I don't believe it has been posted here before.

The diameters of the plungers are both the same (~9mm). However, the plungers are not exactly the same. The left one is the LDT and the right is the LDS. Both are sitting flat on a ruler. Notice the difference in the timing of the openings. Why?

I am also curious how to evaluate an injection pump's condition. If I hold the plunger in my hand to slightly warm it up, there is a definite increase in resistance to push it back in. When at the same temperature, the plungers slowly fall back into the barrels when lifted. Thoughts?

 

[JasonS]

Probably even less meaningful after noting that the cam determines the injection event and those are all the same.

 

[rustystud]

I have wondered for quite awhile why there is a different hydraulic head on the LDS engines. I wasn't able to find any differences in the military or Bosch documentation. It wasn't clear why a different hydraulic head was specified for such a minor difference in horsepower. I have accumulated two LDS pumps (HD90101A) and two LD/LDT pumps (HD90100A) and finally took time to take the hydraulic heads apart. I don't have any meaningful answers but wanted to post this information since I don't believe it has been posted here before.

The diameters of the plungers are both the same (~9mm). However, the plungers are not exactly the same. The left one is the LDT and the right is the LDS. Both are sitting flat on a ruler. Notice the difference in the timing of the openings. Why?

I am also curious how to evaluate an injection pump's condition. If I hold the plunger in my hand to slightly warm it up, there is a definite increase in resistance to push it back in. When at the same temperature, the plungers slowly fall back into the barrels when lifted. Thoughts?

The openings would change the timing slightly. Yes the injection pump cam determines the "initial" timing but the valving or openings fine tune it. Just like a distributer on a gas engine. The initial timing is set with the distributer to cam relationship but the weights and springs fine tune the timing due to RPM increase. Basically the same thing here. Timing needs to be able to advance when RPM's increase. We know from the spec sheets that the LDS has a higher RPM then the LDT so it also needs more timing at higher RPM's.
Now about the condition of the injection pump. If there is no major scratches or worn areas and like you already tested the fit with the warmth of your hand I would say it is OK. On the newer Cummins pumps the warmth of your hand would prevent the spool valve from even going back in. The clearances are that tight. Our pumps not so much.

 

[Floridianson]

Don't want to step on toes but the holes are the spill port. I don't think they would affect timing Rusty. It would allow the plunger to hold more fuel longer if the hole was higher. The control collar is what slides on the plunger and keeps the holes closed. When the control collar is down then the fuel spills out and no run. Collar rides all the way up we get WOT.

 

[JasonS]

I appreciate the insight, Rusty. However, both of these pumps had the same maximum governed speed: 2600 rpm. Only the LDS427-2 and LDS465-2 had higher governed speeds (2800 rpm).

I like the comparison to a distributor on a gas engine. However, on a distributor, the timing of the spark is solely controlled by the points/ reluctor position. The rotor/ cap has no ability to control the breaking of the primary coil current. The rotor only has to be passing by the cap electrodes when the coil fires. For the plunger rotation to affect the timing, it would have to also limit the flow of fuel to the injectors; how would this be possible without damaging the head?

 

[Wildchild467]

I have an LDT head on my LDS pump. It runs fine. There has to be a difference between them all but I'm not sure what it is.

 

[Floridianson]

Fuel to the injectors is controlled by the control collar. The lower the collar rides the more the spill port stays open through the plunger stroke. The higher it rides the longer the spill port stays closed and more fuel is delivered.

The plunger rotates. Sure seems like that would produce more wear but would not work correct if it did not. Dam getting old and good Meds from the hospital can make me look more like a Blonde than ever. Hay wait I am a blonde to begin with. One strike on me to begin with.

 

[rustystud]

View attachment Scan0154.pdf

Fuel to the injectors is controlled by the control collar. The lower the collar rides the more the spill port stays open through the plunger stroke. The higher it rides the longer the spill port stays closed and more fuel is delivered. No rotation on the plunger just up and down catching as much fuel as the control collar allows.

OK, first lets all get on the same page. What I see is the "spill holes" on the plunger are higher on the LDS and lower on the LDT plunger. Do we all agree on this ? If that is so then according to the TM when the spill hole clears the edge it drops all fuel and even though the plunger is still moving up no more fuel in being injected. Then if the holes on the LDS are higher then the LDT that would mean more fuel is being delivered and consequently the timing would be advanced or allowed to be advanced.

 

[rustystud]

I appreciate the insight, Rusty. However, both of these pumps had the same maximum governed speed: 2600 rpm. Only the LDS427-2 and LDS465-2 had higher governed speeds (2800 rpm).

I like the comparison to a distributor on a gas engine. However, on a distributor, the timing of the spark is solely controlled by the points/ reluctor position. The rotor/ cap has no ability to control the breaking of the primary coil current. The rotor only has to be passing by the cap electrodes when the coil fires. For the plunger rotation to affect the timing, it would have to also limit the flow of fuel to the injectors; how would this be possible without damaging the head?

I though my "analogy" was pretty good. I never mentioned the distributor cap which would correspond to the Hydraulic Head. As far as the "rotor" goes, yes it does effect the timing of a gas engine. The positioning of this rotor either before or after the caps electrodes effects where the spark is going just like the plunger and the fuel. Now since the rotor is controlled by a "moveable plate" in the distributor it is just like the "plunger" in our injection pumps. I suppose you could use the points/reluctor as the plunger in the "analogy" but I like the rotor visual more. Now remember Jason this is just an "analogy" not a "tit for tat" kind of thing.
Now about the higher RPM's your right, I keep getting the LDS465-1 mixed up with the LDS465-2 . Now the more fuel allowed by the higher spill ports would give increased power just like a larger 4 barrel carb gives a big block engine with just a small 2 barrel carb. Another "analogy" there, did you catch that ?

 

[Floridianson]

The sleeve is the correct term not the control collar but some of you know me. Old and on drugs. Would be interesting to know when the fire really begins in the combustion cycle. Or how far up the cylinder is to set the fuel off. Looking from a gas engine stand point if the spark does not happen then nothing happens. So we can advance or retard the spark. Seems with a diesel we can advance the fuel going in or keep adding after the fire begins and keep adding with the piston going down. To me if the hole is higher on the plunger then the fuel is added longer in the plunger stroke. I might call it the duration of the shot as it does not start it any sooner but if it does anything it just holds the plunger fuller longer. Now for injectors and for how soon they pop lets look at the book and the LDS injector. It starts to pop at 2800psi. and from what I have been reading and people say when tested the LDT injector pops at 3500 psi. So does that mean the LDS is more advanced on it release. I still don't see how the LDS with a slight placement of the spill ports would affect timing. Seems like it would just allow more fuel to be added longer in the plunger cycle. Then I guess that could thought of as timing. I stand corrected after thinking and looking at the head I have yes the plunger does rotates of course as well as go up and down. ADHD child. Seems like that would cause more wear but I'm good not Great. Plus loosing what little gray matter I have. Owell good thread and I am off to packing for the Ga. rally hope there is good weather.

 

[rustystud]

Floridianson you still have plenty of brain cells popping ! Your one of only a few on this site that has a good grasp of how the injection pump really works, so don't sell yourself short. I also know about the effects the pain pills have. Somedays its amazing I can even remember I have a wife and child !

 

[JasonS]

Measuring vertically from the top of the plunger, the only difference between the plungers is the height of the groove around the plunger; about 0.012 taller on the LDT head. The vertical location of all ports is the same. I don't the means to easily measure the "timing" of the ports.

 

[rustystud]

Measuring vertically from the top of the plunger, the only difference between the plungers is the height of the groove around the plunger; about 0.012 taller on the LDT head. The vertical location of all ports is the same. I don't the means to easily measure the "timing" of the ports.

So then there is no difference in the amount or length of time the fuel is spraying. Hmmmmm. Then what is the difference in the LSD vrs the LDT injection pump then ?

 

[rustystud]

Well I guess I'll have to take mine apart and see for myself. I bought two LDS and two LDT pumps last year and have been planning on rebuilding them some time this winter. I've just been racing to get all my other outside projects done before winter sets in. I'm still planning on the "Great Alaskan Expedition" next year. We'll see if I make it.

 

[Floridianson]

Thanks for not rubbing my face in it Rusty for as many times I rode your azz and did not even at least pull your hair is was nice too see your post. I can use any excuse I want but I clearly did not think on the post about rotation. Stupid thing is I had a new Head right in my hand when I post.

As for you you are one of the group of mechanics here on SS that has been there done that and know what you are talking about. Your post's are respected and very helpful. You would make a good teacher. Now me no way I could teach in less I could keep my mouth shut and the student just watches what I do and learns. As for verbal instructions or having to write them down forget it.
What about my question on the injectors popping sooner could that cause advance?

 

[rustystud]

What about my question on the injectors popping sooner could that cause advance?[/QUOTE]

Yes it could. It's just like advancing the spark in your gas engine. Both cause early ignition of the fuel.
Also thanks for the kind words.

 

[Floridianson]

Then also the timing button on the bottom of the HH would be a way to make small timing change right?

 

[Squirt-Truck]

Isn't the fuel delivery volume significantly different LDT vs LDS?

A faster pressure rise will make the injector open earlier, but time is limited to get an efficient burn, longer is not realistically better, we have to keep in mind that is primarily a vaporization ignition engine not an atomization ignition engine. The slower burn severely limits the time available for injection. Remember the LDS 1A engine uses a single hole injector just to minimize atomization effect. (And smokes badly.) Adding more fuel post initial burn well past TDC just drives up the EGT.

Just a thought.

 

[gimpyrobb]

In today's world, why throw something like thought in there?!

 

[rustystud]

Isn't the fuel delivery volume significantly different LDT vs LDS?

A faster pressure rise will make the injector open earlier, but time is limited to get an efficient burn, longer is not realistically better, we have to keep in mind that is primarily a vaporization ignition engine not an atomization ignition engine. The slower burn severely limits the time available for injection. Remember the LDS 1A engine uses a single hole injector just to minimize atomization effect. (And smokes badly.) Adding more fuel post initial burn well past TDC just drives up the EGT.

Just a thought.

All the later injectors have two holes. One small and the other noticeably larger. One throws a mist out and the other a stream of fuel. So that totally negates your injector issue. The Multifuel engine works by creating a "slow" burn thus being able to burn such fuels as engine oil which requires a longer burn time. All engines (gas or diesel) burn fuel that is "vapor" ours just gets there in a different way. The amount of fuel sprayed only has the effect of allowing more "power" . It has nothing to do with "timing" . By changing the "point" of injection you change the timing so starting the flow of fuel earlier you are basically advancing the timing of the ignition. In a diesel engine it is heat generated by compression that allows ignition so you can "inject" the fuel and start the timing process as soon as the piston is coming up to TDC (top dead center) . Of course if you inject to soon or to late you will hurt power. So the trick is to find the "right" spot to inject the fuel. That is why the engineers have already found that out and put the specs in the TM showing where and how to time the injection pump. Of course as we all know they go with the broadest application and the actual power of the engine can be increased if you know how. Since we know the LDS makes more power then the LDT engine we are trying to figure out what they did.
Since we are talking about "increasing" the injection point (timing) your premise of not enough time is not valid here. Granted if you allow the burn to continue past TDC you will lose power or at least just waste fuel and yes cause higher EGT's. Also since the "burn" time has been factored in by the engineers and is pretty constant it is also not a factor here. We are not talking about changing timing by vast amounts, just small increments. That is enough to cause the horsepower to increase to the amount we are talking about here between the LDS and LDT engines. Of course a cam and rocker arm change is necessary, as we know they did. We're just trying to figure out the amount of change they did to the injection pump.