LDS465 (HD90101AR) and LDT465 (HD90100) hydraulic heads, the real difference.

[Jeepsinker]

After having my LDS hydraulic head crack, and since I have some spare bad LDT hydraulic heads laying around, i decided to pull both apart and compare. I've come to the conclusion that the only difference is in fact the plunger itself. I verified that the 90101AR plunger fits the bore in both housings equally well, and I will be installing the plunger in a good 90100 housing and installing the head back onto my injector pump for real world functional verification.
Link to my research thread with pictures here:
https://www.facebook.com/groups/52368678497/permalink/10155702453513498/

 

[Flyingvan911]

Interesting.

 

[gimpyrobb]

Why not post the info on a real military truck website that anyone can see? Some do not have bookface accounts.

 

[Jeepsinker]

Why not post the info on a real military truck website that anyone can see? Some do not have bookface accounts.

I probably will. It's way easier to post pics to Facebook than here. I was snapping pics and posting them as I went. While I have not posted a picture here in probably a couple of years, it used to be fairly troublesome from my phone ( I don't have a computer).

 

[gimpyrobb]

That makes sense, I do not like posting pics here from my phone either. I've heard it was easier with tappatalk, but I don't use it.

 

[rustystud]

After having my LDS hydraulic head crack, and since I have some spare bad LDT hydraulic heads laying around, i decided to pull both apart and compare. I've come to the conclusion that the only difference is in fact the plunger itself. I verified that the 90101AR plunger fits the bore in both housings equally well, and I will be installing the plunger in a good 90100 housing and installing the head back onto my injector pump for real world functional verification.
Link to my research thread with pictures here:
https://www.facebook.com/groups/52368678497/permalink/10155702453513498/

Actually the different plungers don't make any difference. They all travel the same distance on the cam lobe. The cams are the same in all the injection pumps so they are all putting out the same amount of fluid per stroke.
Now there are different pump Hydraulic Heads out there. Some with more output then others. I've just never been able to find them yet. That still doesn't explain the difference between the LDT and LDS Hydraulic Heads though.

 

[Jeepsinker]

Actually the different plungers don't make any difference. They all travel the same distance on the cam lobe. The cams are the same in all the injection pumps so they are all putting out the same amount of fluid per stroke.
Now there are different pump Hydraulic Heads out there. Some with more output then others. I've just never been able to find them yet. That still doesn't explain the difference between the LDT and LDS Hydraulic Heads though.

I took measurements with calipers. The fuel helix on the LDS plunger holds more fuel to distribute on the same stroke length.

 

[Jeepsinker]

I guess I'm going to have to post the pics here, buy my god is it a pain sometimes.

 

[rustystud]

I took measurements with calipers. The fuel helix on the LDS plunger holds more fuel to distribute on the same stroke length.

OK Garrett, stop and think here. On a engine cam if the valve opens up a certain distance will it open up further if the valve stem is longer ? No. It is all dependent on the stroke of the cam. So the plunger holds more fuel. Does all the fuel empty out on the end of the stroke ? No. You will just have extra fuel there. The only way to add more fuel is to 1) either have a wider plunger, thicker stem or 2) a cam with a more aggressive lift in the injection pump. They (American Bosch) did make several different pump variants, some with larger stem plungers. Those where for large industrial engines. Though I have wondered if the Hydraulic Head would transfer over to ours. Of course you need to find one of these injection pumps first.
Of course if someone had access to a quality machine shop, they could make a thicker stem plunger and hone out the bore of the Hydraulic Head to fit. That would be very interesting to try. Of course the engines cannot take much more fuel then they already do now. So I guess it is a mute point.

 

[Jeepsinker]

Ok, so why the different measurements the with a plunger the same diameter and length?
With my 90101AR head, I was running a max boost of 18psi, but when I installed the 90100 head onto my pump it was only providing enough fuel to give 5psi of boost max. It basically put me back at stock LDT465 fueling with zero adjustments from when I was running the 90101AR head. The idle was also about 300 rpm lower at idle. I had to turn mymain fuel up a few turns and bump my smoke cam up a few degrees just to get it back where i was before.
Now, when I get time in a few days here, I'm going to put my fuel settings back where they were, pull the 90100 off, install my 90101AR plunger in it, and see if it puts me back at around 15-18 psi of boost. The fuel porting between both heads is identical. The only difference I found between the two other than the plunger, is the center bolt in the 90101AR head is .020" longer from sealing surface to tip than the one in the 90100 head.

 

[rustystud]

View attachment Scan0229.pdfView attachment Scan0230.pdfView attachment Scan0231.pdfView attachment Scan0232.pdfView attachment Scan0233.pdf

OK Garrett, this took me an hour and a half to get this information together. If it was for anyone else I don't think I would have wasted my time.
So the first page is telling about the "smoke cam", and how it will increase fuel flow the higher the angle. The second page shows the settings for the "smoke cam" for the different applications (LDS-LDT) . The third and fourth pages shows how "American Bosch" used different widths of "plungers" to increase fuel flow. (Just so you know they didn't use anything special in the Hydraulic Head) The fifth page (last one) shows the difference in the LDS and LDT pumps fuel flow at different RPMs . The difference is very slight. Now if you compare the "smoke cam" settings for the different pumps you will see the LDS is set at 100 degrees while the LDT is set at 48 degrees. This difference of fuel flows is directly tied to the different "smoke cam" settings.
Now why you are experiencing different power levels between Hydraulic Heads I don't know. Maybe the linkage settings got changed. After rebuilding four different injection pumps and tearing down over 12, this is the only differences I found between the LDS and LDT pumps. Yes there is different governor springs and advance springs. I posted that information in my "Injection Pump rebuild thread" .

 

[Jeepsinker]

Well rusty, I certainly appreciate you spending the time on my behalf. However, I do think this is one of those things I have to answer for myself. I saw a drastic difference in performance between the two heads, the plungers have slight variations, and te 90101 center bolt is a hair longer, which would make the stroke slightly shorter or compress the fuel more I'd think.
Seeing what I have seen so far, I have to believe there is some reason that the 90101 head was used on the LDS pump instead of simply using the HD90100 on all the multifuel pumps across the board. I have verified differences in the plunger, no matter how small they may be, so there is no question whether they are different in any way or not.
Also note, there was no change in the linkage settings until I had to bump the fuel up to compensate for the lower output of the 90100. It was a simple hydraulic head swap with before and after comparison.

 

[rustystud]

Well rusty, I certainly appreciate you spending the time on my behalf. However, I do think this is one of those things I have to answer for myself. I saw a drastic difference in performance between the two heads, the plungers have slight variations, and te 90101 center bolt is a hair longer, which would make the stroke slightly shorter or compress the fuel more I'd think.
Seeing what I have seen so far, I have to believe there is some reason that the 90101 head was used on the LDS pump instead of simply using the HD90100 on all the multifuel pumps across the board. I have verified differences in the plunger, no matter how small they may be, so there is no question whether they are different in any way or not.
Also note, there was no change in the linkage settings until I had to bump the fuel up to compensate for the lower output of the 90100. It was a simple hydraulic head swap with before and after comparison.

OK then. Keep us posted on your findings.