Kinda got carried away..... M1028 rebuild

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Sharecropper

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There may still be a few P400s out there somewhere for sale, but gosh I would hate to see the price. GEP is working on new vehicle concepts so maybe they will restart P400 production someday.
 

Sharecropper

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My NP241 arrived today from Mark Bendler at Kodiak Truck. I decided to go ahead and purchase another transfer case instead of re-using my original Np208 so that I could get everything mated together before installing the P400/700R4 into my truck. I made the decision to source a rebuilt NP241 because this model transfer case was an improved/strengthened model which superseded the NP208 in the late 1980's. The NP241 has a stronger case, stronger chain, and is pressure oiled, unlike the NP208 which relies on the chain to splash-lubricate the internal parts. After I decided to go with a NP241, I then began researching the best place to get one, and the best place to get one rebuilt. I found Mark Bendler at Kodiak Trucks in North Prairie, Wisconsin kodiaktruck.com . Mark is extremely knowledgeable and experienced in rebuilding mechanical components and got his start in the industry when he built and campaigned the monster truck Kodiak. Mark found an excellent used 1990 NP241 unit which had the mechanical speedometer assembly to mate with my M1028 cable. He then sourced a Slip Yoke Eliminater (SYE) kit from Tom Woods in Utah https://4xshaft.com/ . Mark also added additional needlebearings on the main shaft, something he said GM should have done from the factory. The rear case half is new, as is all bearings and chain. All I need to do is change the speedometer driven gear to make my speedometer read correctly. I will post a separate thread on this.

DSC_0770 (2).JPGDSC_0772 (2).JPGDSC_0773 (2).JPGDSC_0774 (2).JPGDSC_0775 (2).JPG
 

OldIronsides

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Awesome build man.

I used a P400/4L80e/NP205 set up. It does suck for all that. It could be easier, so consider this. Programable electronic speedometer makes proper speedometer gear irrelevant. In case you run into issues with your aforementioned route.
 

Sharecropper

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Awesome build man.

I used a P400/4L80e/NP205 set up. It does suck for all that. It could be easier, so consider this. Programable electronic speedometer makes proper speedometer gear irrelevant. In case you run into issues with your aforementioned route.
Thanks Arlen. Mark Bendler found a good '91 NP241 with the mechanical speedometer to rebuild so I am good to go. I had rather have the mechanical speedometer anyway, because my goal for the entire project has been to eliminate as many electronics as possible. That is why I went with a built 700R4 instead of a 4L80E - no electronics. Also why all my gauges will be mechanical, not electric.

Question - were you able to source your P400 new, or was it used?
 

Sharecropper

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Rutjes

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Just found this last night, thought some of you might like to know. Rock Auto seems to be selling blocks.


Not P400 but 506 and 599 according to the description. The block pictured is a 506 that carries the Navistar diamonds though...
 

Lostforwords

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Just found this last night, thought some of you might like to know. Rock Auto seems to be selling blocks.


Not P400 but 506 and 599 according to the description. The block pictured is a 506 that carries the Navistar diamonds though...


Is it close to the P400? Seems like SOB to get that might as well just get a LBZ hehe.
 

Sharecropper

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Is it close to the P400? Seems like SOB to get that might as well just get a LBZ hehe.
In my opinion, no it is not close to the P400. The ad indicates that it is a remanufactured engine, probably assembled by Jasper or one of the other outfits out there from used parts. In contrast, the P400 engines were developed by GEP to power the new upfit HMMWV which weighs over 15,000 pounds due to the addition of body armor. All P400 engines were designed, engineered, and assembled with brand new parts to power the heavier vehicle. Unfortunately GEP lost the U.S.Government contract for the future HMMWV. It is my understanding that a quantity of P400 engines, which were crated and in GEP’s inventory, were released to the public after they lost the contract. I consider myself extremely lucky to have acquired one of these engines. My only regret is not buying more than one.

The historic weakness of 6.2/6.5 engines has been in the bottom end around the main bearings and associated castings. The design of the P400 solved this inherent weakness by the addition of a cast iron girdle between the block and oil pan with newly designed main bearing caps integral to this girdle, which is massive in itself and 3 inches tall. Additional strength was achieved by utilizing a forged crankshaft, forged connecting rods with cracked-joint technology, forged pistons with ceramic coated top surfaces, hardened valve guides and seats, and improved cooling and lubrication passages.

There is no way to obtain these features in a remanufactured engine assembled with used parts.

I hope this helps in understanding exactly what a P400 is.
 

Lostforwords

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In my opinion, no it is not close to the P400. The ad indicates that it is a remanufactured engine, probably assembled by Jasper or one of the other outfits out there from used parts. In contrast, the P400 engines were developed by GEP to power the new upfit HMMWV which weighs over 15,000 pounds due to the addition of body armor. All P400 engines were designed, engineered, and assembled with brand new parts to power the heavier vehicle. Unfortunately GEP lost the U.S.Government contract for the future HMMWV. It is my understanding that a quantity of P400 engines, which were crated and in GEP’s inventory, were released to the public after they lost the contract. I consider myself extremely lucky to have acquired one of these engines. My only regret is not buying more than one.

The historic weakness of 6.2/6.5 engines has been in the bottom end around the main bearings and associated castings. The design of the P400 solved this inherent weakness by the addition of a cast iron girdle between the block and oil pan with newly designed main bearing caps integral to this girdle, which is massive in itself and 3 inches tall. Additional strength was achieved by utilizing a forged crankshaft, forged connecting rods with cracked-joint technology, forged pistons with ceramic coated top surfaces, hardened valve guides and seats, and improved cooling and lubrication passages.

There is no way to obtain these features in a remanufactured engine assembled with used parts.

I hope this helps in understanding exactly what a P400 is.


I did not know that! Now I must get one! Are they easy to spot? I guess the likey hood of finding one in the junkyard would be zero to none. How much you want for yours =]. Maybe I could source one from a wrecked HMMWV
 

chevymike

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I did not know that! Now I must get one! Are they easy to spot? I guess the likey hood of finding one in the junkyard would be zero to none. How much you want for yours =]. Maybe I could source one from a wrecked HMMWV
Good luck! I don't think many were made and not sure any made it into HMMWV's. If you happened to find a new one, I had seen prices of $12,000. This is the ultimate 6.5 series engine but sadly they stopped producing almost as fast as they started.
 

Sharecropper

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I did not know that! Now I must get one! Are they easy to spot? I guess the likey hood of finding one in the junkyard would be zero to none. How much you want for yours =]. Maybe I could source one from a wrecked HMMWV
To my knowledge, there are no new P400 engines available. In the past 4 years I have seen only 1 used P400 on ebay, and it looked like it had been run hard. Mine is not for sale. You may want to reach out to Leroy Linza in Houston. A couple years ago he purchased the last P400 long blocks GEP made available. He may have one left or might know where one is. His number is 713-408-0423. info@leroydiesel.com .
 

richingalveston

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That rock auto motor is a standard 6.5. not an optimizer or gep. And yes it is most likely built with used parts.
I don't think Leroy has any p400's left.
I believe you can still get a new GEP
 

cruzer747

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how long til that oil turns black? ;P Super jelly.... I just bought a low mileage '01 3500HD (116k) donor truck for my work truck with a 506 block. has the smaller cap bolts but damn if it does not have two cracks already starting to run. I am going to cobble it back together anyways :/ I would have added a girdle as preventative but at this point I am going to leave it be as I have read some horror stories of the 3 point girdle and I dont have the time or money or patience to fab a 5 point girdle.

That P400 really is pretty, gotta be nice knowing the thing isnt going to just s#!t the bed on ya.
 

nattieleather

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I thought all the GEP engines had the redesings in them? that was one reason that GEP went into business was to make 6.5L diesels for HMMWV and that all of the blocks made by them had upgrades over the GM blocks. Yes no?
 

richingalveston

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yes, gep was redesigned. just because it is a 506 block does not mean it was a gep. need to look at the forge markings to determine if it is a gep for sure. need to have the Navistar logo which is two triangles back to back for an old gep.
The new gep motors are from a different forge.
 
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