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237 Posts
Discussion Starter #1
First of all, don’t attempt to do this. P-pumping the 6.7 is a bad idea for many reasons that I will point out later.

The reason I needed to do this is to incorporate the PTO option. For my truck, I needed to use a gear driven air compressor for my air bag and brake system. I also need to use a gear driven hydraulic pump for my full hydraulic steering. The new 24v motors and the 6.7s don’t have the option for gear driven accessories. To do the conversion, a 5.9L 12v gear case and gears are needed which only fits a mechanical injection pump.

I could have used a 12v motor to start with but decided to go with the 6.7L motor. Since I have a street legal monster truck that weighs in at 14,000 lbs dry and rides on 53” tires, I wanted the larger displacement so that it is more efficient at pushing the behemoth down the road.
 

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237 Posts
Discussion Starter #2
Here are some of the pitfalls for doing the 6.7 p-pump conversion:
1) 12v gear case is needed and doesn’t fit
2) All 12v gears are needed.
3) Cam will not drive a mechanical lift pump
4) Block has different mounting holes. Custom brackets needed to support pump and accessories.
5) 6.7L head does not have clearance for the P-pump
6) 6.7L pulleys will not fit the 12v gear case
7) Oil pan will not fit
8) Injection lines will be custom
9) Injectors will need to be replaced
10) Valve cover will not fit
11) You loose the ability to control the variable turbo
 

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Discussion Starter #3
The first thing I did was to remove all the gears and gear housing. All gears have to come out and get replaced with helical cut 5.9L gears. The gears in the common rail 5.9 and 6.7 are straight cut gears. The earlier 5.9L motors all had helical cut gears. The crank gear is a real pain to remove while in the block. I had to build a custom puller to get it to come off. The 5.9 cam gear can press back in place of the 6.7 cam gear. Same goes for the crank gear. The oil pump gears can be pressed off and on or the entire pump can be replaced.
 

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Discussion Starter #4
Holes had to be drilled in the block to accommodate the 94-98 5.9L gear case. Many of the holes were the same but there were about 7 holes that had to be drilled and tapped. In addition, the 5.9 and 6.7 have different dowel pins to locate the gear case. The dowel pins are critical for locating the gear case. If the gear case is not located correctly, then the gear lash between the cam gear and the pump and accessory gears will be wrong and could cause damage. I opted not to use dowel pins. They are for alignment purposes only. Once the case is bolted on and sealed, the dowel pins are no longer needed. This took some really careful measurements and a bunch of trial fits to get right. I also had to pay attention to the alignment of the gear case bottom is in alignment with the block so that I get a good seal on the oil pan.

I used the 5.9L gear case as an alignment tool for the new holes. To get the case to center on all the bolts, I used o-rings on the bolts. I then used a plate of steel and a mag drill to drill the holes. I learned that the 6.7 block is thin in some areas where the new holes need to go and drilled into the water jacket. This is not a huge deal since some loctite or permatex can be used to seal the threads.
 

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Discussion Starter #5
The 6.7 had hollow dowel pins on the bottom of the block/gear case. These were no longer needed and had to be filled. I used some socket head cap screws to fill the holes and machined them to fit flush with the block. In addition, there was another bolt hole that was no longer needed in which I used a set screw with a slot cut in it to fill in the hole. I also used permatex to seal the screws in the holes. The pictures show the screws before I cleaned the excess permatex off which is why they look so bad. This allows for a good seal on the gear case gasket.
 

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Discussion Starter #6
Now came the tricky part. The injection pump had to be fitted to get the gear lash correct. As it turned out, the 6.7 head doesn’t have enough room for the P-pump. The early 24v and the 12v have room cast in the intake plenum to allow for the fit of the p-pump. On later motors, the intake plenum has been opened up quite a bit. A few options can be used here. One is to use an earlier 24v head. Another option is to cut the plenum off and go with a custom plenum. I liked the plenum the way it is and didn’t want to take the head off. I opted to cut and patch the plenum. I would have preferred to weld it, but that would require the removal of the head.

The pictures show where I cut out the plenum in the location where the pump would interfere.
 

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Discussion Starter #7
I made a patch that fit the inside of the plenum. It is made out of 3/16 steel plate and used a torch to shape it. I tapered the edges of the patch so that there would be little turbulence. I drilled and tapped the plenum and bolted the patch into place using JB weld to seal it. I like how it turned out. It is far less restrictive than the earlier heads.

I had to do a small amount of grinding on the pump. In addition, the oil inlet fitting on the injection pump had to be changed out to a banjo style fitting due to the tight fit.
 

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Discussion Starter #9
Here is the injection pump oil line and clearance I had to do. I had to trim off some of the shaft that sticks out and a little of the housing where you see clean metal. The oil fitting was switched out to a banjo. I even had to machine some of the banjo bolt down a little.
 

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Discussion Starter #11
To supply oil to the injection pump, I tapped into the oil pressure sender. Luckily, the oil pressure sender brass fitting is extra long. All I had to do is cut off the same amount of material as the thickness of a new banjo fitting. I had to drill some extra oil holes in the banjo bolt where the banjo fitting aligns. Oil will come out of this port and tee off to both the injection pump and the air compressor.
 

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Old Jarhead
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587 Posts
Very interesting build project, you have going there. Good Luck.
 

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Discussion Starter #13
The timing pin in the back of the gear case will not fit with the block so I decided to just get rid of it. I put a freeze plug in place of the timing pin and set screws in the threaded holes with loctite to seal the threads.

There were a couple of spots on the block that needed to be ground to fit. One on the upper portion of the block was a stud hole that protrudes out of the block. For some reason I didn’t get a picture of it. It had to be ground down to fit the gear case. The other spot is pictured. This one only needs to be ground to fit an air compressor.
 

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Discussion Starter #14
In this picture, if you look closely at the front of the intake plenum, you can see that I trimmed off the front portion of the intake manifold flange. It really serves no purpose other than a spot to bolt a bracket or a wire harness. This trim really is needed to access to the bolts that hold the injection pump on.

I also removed the electronic injectors and put in the 98.5-02 style injectors and hold downs. I kept the 2008 delivery tubes. From pictures, I noticed that the 98.5-02 style fuel delivery tubes have a tip that is more pointed. I took my delivery tubes and put some Prussian blue on the tip. I then test fitted the delivery tube into an injector to see if there was a solid sealing surface and there was. One thing to note is the 6.7L delivery tubes stick out of the block a little bit further than the 98.5-02. This makes installing the fuel lines a pain in the butt and requires a little bit of bending. The injectors are new aftermarket matched set of 7x14 injectors for 98.5-02 that have a pop pressure setting for the P-pump. The P-pump pop pressure is lower than the common rail. The shop that sold the injectors had no problem setting the pop pressure and didn’t charge extra for it.

I also went ahead and installed ARP head studs.
 

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Discussion Starter #15
This is a picture of the 94-98 5.9L cam gear compared to the 6.7L (common rail) cam gear. The earlier cam gear is considerably wider for good reason. The earlier gear had to drive the accessory as well as the injection pump. The gears will interchange on the cam.
 

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Discussion Starter #16
Once I got the gear lash exactly where I wanted, I drilled some holes and used roll pins to as a temporary alignment method.
 

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Discussion Starter #17
Now I got the gear case sealed to the block, I needed to build an injection pump support bracket. The 6.7L block has different stud holes than the 5.9L, so I had to make a custom bracket to support the P-pump. There isn’t much to tie to so I used the fuel pump cover and some holes lower on the block as mounting points. The strange thing about the fuel pump hole is that it is located in a different spot than the 5.9L. Since 98.5 and on, the cams did not come with a lobe to drive a mechanical fuel pump. So why was the fuel pump hole relocated???? The cover for the fuel pump hole was used as an oil return line from the valve cover. When the air compressor is installed, there is no room for the oil return tube. I just cut the tube off and plugged it. I routed the oil return to a spare dipstick hole on the bottom of the block.
 

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Discussion Starter #18
Now here is the real reason that I went through all this trouble. (The air compressor and hydraulic pump). I fabricated a support bracket for the air compressor shown in the pictures. The air compressor is a Bendix tru flo 550. The hydraulic pump mounts directly to the back of the air compressor, which is not shown. The hydraulic pump won’t fit just yet because the left motor mount is in the way. I will eventually have to fabricate a left motor mount.
 

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Cowboy AKA Equality State
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890 Posts
Awesome build!! Love the looks of the older Chevy/GMC trucks!! :thumbsup:

Just one question... When you opt to park in the compact parking lots, how do you go about digging out a Prius or Beetle when it gets stuck between the tires?? :confused013: :hehe:
 
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