LDS VS LDT and the real differences

gimpyrobb said:

Yeah, it was a joke.


Must have missed the "bazinga" part. (maybe over your head too)


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Hey quite playing with my hair ! Also I like Dan Fogelberg ! I was at his last concert here in Seattle before he died.
Oh by the way sent you a PM.

I found something interesting while cleaning my "FDC" today. There is a groove cut in the shaft hole for the piston that looks like it will fit an 'O' ring ! I measured this cut-out and it is 0.290" . That is 0.040" over the shaft size of 0.250" (1/4") .
According to the "Parker" catalog the 'O' ring #5-583 will just fit that. Though it will be a little tight. I should also check out some Metric sizes.
I have to wonder why they machined or built into the "mold" this cut-out. Was this originally designed to hold an 'O' ring ? Since it seals so well without the O-ring they just left it out to save a little money ? I'll try and install the O-ring when I rebuild this unit and see what happens. If it works then that would solve the whole leaking FDC problem.

I found out why there is a circular groove cut into this area. There is a very small hole drilled from the groove to the exhaust port. This passage then creates a small vacuum to help suck out any fuel that goes down the piston shaft. This passage in my housing was blocked that's why I didn't see it at first. After I sandblasted it I found it. I wonder if the main reason most FCC's start to leak is because this hole gets blocked or that the shaft hole just gets too worn out and the drilled passage is not able to suck out all the fuel. I still plan on installing an 'O' ring there and see what happens.

Well after tearing down 3 Injection pumps and measuring everything I can honestly say the only difference between the LDS and LDT pumps I found is the different springs for the governor assembly and the settings on the "Smoke Limit Cam" . The smoke limit cam adjusts the amount of fuel flowing at different RPM's .
So this means that the only differences that we know for sure between the LDS and LDT are "rocker arms" and "engine cam" . The rest is just adjustments on the pump and timing. Yes I know there is only one engine cam listed "now" but back in the day there where "three" listed. We just don't know what their dimensions were (lift, duration, opening, etc...) .

rustystud said:

Well after tearing down 3 Injection pumps and measuring everything I can honestly say the only difference between the LDS and LDT pumps I found is the different springs for the governor assembly and the settings on the "Smoke Limit Cam" . The smoke limit cam adjusts the amount of fuel flowing at different RPM's .
So this means that the only differences that we know for sure between the LDS and LDT are "rocker arms" and "engine cam" . The rest is just adjustments on the pump and timing. Yes I know there is only one engine cam listed "now" but back in the day there where "three" listed. We just don't know what their dimensions were (lift, duration, opening, etc...) .

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...also, turbo, and more piston cooling oil squirters, timing, and lower compression pistons, correct?

I think it would be good to pin it down in a list and maybe make a sticky, can't read the whole thread every time.

DavidWymore said:

...also, turbo, and more piston cooling oil squirters, timing, and lower compression pistons, correct?

I think it would be good to pin it down in a list and maybe make a sticky, can't read the whole thread every time.

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The piston squirters are all the same in the later engines. The lower compression pistons where in the smaller multifuel. The LDS and LDT both used "C" and "D" turbos as far as I can see. The earlier LDS used that funky turbo (cannot remember the number) until the 1960's in the 5 tons. Then it appears they used the "D" turbos. Maybe some 5 tonners can weigh in here on that. Also the output out of all three of those turbos are so close it makes no difference at all in engine performance. So that basically leaves the timing which is different between the LDS and LDT.
So again the rockers and cam and injection pump springs and injection pump adjustments and engine timing are all that is different. At least as far as I can see.

rustystud said:

The piston squirters are all the same in the later engines. The lower compression pistons where in the smaller multifuel. The LDS and LDT both used "C" and "D" turbos as far as I can see. The earlier LDS used that funky turbo (cannot remember the number) until the 1960's in the 5 tons. Then it appears they used the "D" turbos. Maybe some 5 tonners can weigh in here on that. Also the output out of all three of those turbos are so close it makes no difference at all in engine performance. So that basically leaves the timing which is different between the LDS and LDT.
So again the rockers and cam and injection pump springs and injection pump adjustments and engine timing are all that is different. At least as far as I can see.

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I believe the turbo is the 4LE-354 if I remember correctly. Have one in my '62 parts truck. Thinking about swapping it and the rockers to my '70 driver and adjust the smoke cam, maybe timing. I'd like to do the IP springs eventually too. The LDS exhaust sounds awesome, curious to see what makes the difference.

DavidWymore said:

I believe the turbo is the 4LE-354 if I remember correctly. Have one in my '62 parts truck. Thinking about swapping it and the rockers to my '70 driver and adjust the smoke cam, maybe timing. I'd like to do the IP springs eventually too. The LDS exhaust sounds awesome, curious to see what makes the difference.

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Could be the cam. I would like to have a LDT and LDS cam side by side and compare lift and duration. That is of course if they are still original and not the replacement cams which were all the same. Also the LDS injection pump springs allow the engine to spool up faster. Could make for an interesting sound.

i finally scored a set of lds intake rockers and when i get the time to install them i am going to try to have something to compare before and after, probably going to be some runs recording egt and boost maybe up the big bridge, i don't expect to see full benefit without turning up the fuel as air alone doesn't make power

winfred said:

i finally scored a set of lds intake rockers and when i get the time to install them i am going to try to have something to compare before and after, probably going to be some runs recording egt and boost maybe up the big bridge, i don't expect to see full benefit without turning up the fuel as air alone doesn't make power

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Record using the "stock" LDT rockers first, then using the LDS rockers. That way we can have a base line to go from.

winfred said:

i finally scored a set of lds intake rockers and when i get the time to install them i am going to try to have something to compare before and after, probably going to be some runs recording egt and boost maybe up the big bridge, i don't expect to see full benefit without turning up the fuel as air alone doesn't make power

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So did you ever do it?


I’m wondering about camshaft part numbers...might look into my LDS

I was dismayed to find it didn’t have LDS rockers. It does sound cool.