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Old 12-06-2021, 08:42 PM   #1
diesel burner
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My 71 K20 Cummins swap

I started this project back in 2013 when I purchased a 71 K20 from a local plumber/electrician for the sum of $2000. They were originally asking $4000 for it, but the seals between the transmission and tansfer case were out and they were wanting to be rid of it. It had a 350/350 set up from the factory and a service box that dated back into the 50's. it had carried that loaded service box around most of its life, so the springs and bushings were pretty well shot.My first order of business was to fix the leaking seals and put new springs under it. I put Rough Country 2.5 inch springs in the front and ordered factory 7 leaf replacements from SD truck springs for the back.
Here are some pictures of it when i bought it.
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71 C10 Cheyenne 396, turbo 400
71 C20 Custom Camper 383,tko 600,14 bolt project
71 K20 Custom,Cummins,NV4500,NP205,dana 60F,dana 80R
06 GMC sierra 2500 extended cab duramax,allison
05 Toyota Corolla (commuter)
18 Chevy Tahoe RST (wifes car)
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Old 12-06-2021, 09:18 PM   #2
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Re: My 71 K20 Cummins swap

I knew when I bought this K20 that I wanted to do a Cummins swap and started reading up on what it would take. There were quite a few threads on here that inspired me and I read every word of them and studied the pictures religiously. I started looking for a donor vehicle and then life happened and I was set back a few years on finding a Cummins. In the mean time the 350 started burning oil badly so I pulled it and the transmission/transfer case out and put in a 383/nv4500/np241 setup. I also pulled off the service box and built a flatbed for it. I could have found a bed for it but a flatbed fits my needs better and I don't have to worry about the paint matching.
During this time frame I also managed to find a Dodge Dana 60 from a first gen. I built a new front crossmember with spring hangers and core support mounts out of 5/16 T1 steel, I did this to compensate for the wider spring perches on the dodge dana 60
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71 C10 Cheyenne 396, turbo 400
71 C20 Custom Camper 383,tko 600,14 bolt project
71 K20 Custom,Cummins,NV4500,NP205,dana 60F,dana 80R
06 GMC sierra 2500 extended cab duramax,allison
05 Toyota Corolla (commuter)
18 Chevy Tahoe RST (wifes car)
08 HD Roadglide
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Old 12-06-2021, 09:33 PM   #3
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Re: My 71 K20 Cummins swap

In 2017, I got back on track and found a donor pickup on CL. It was a 96 dodge 2500 that someone had shortened the frame on, it was 2wd, but it had a Cummins and NV4500. Only had 155000 miles but wouldn't hardly run, had a terrible miss..... After looking it over, I decided to bring it home. Someone had put bigger injectors in and a new lift pump, didn't have any of the fuel lines tight. Leaking fuel everywhere.... Anyway, I paid $3500 for it and felt pretty good.
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71 C10 Cheyenne 396, turbo 400
71 C20 Custom Camper 383,tko 600,14 bolt project
71 K20 Custom,Cummins,NV4500,NP205,dana 60F,dana 80R
06 GMC sierra 2500 extended cab duramax,allison
05 Toyota Corolla (commuter)
18 Chevy Tahoe RST (wifes car)
08 HD Roadglide
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Old 12-06-2021, 10:09 PM   #4
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Re: My 71 K20 Cummins swap

When I got the dodge home we realized that the miss was more serious, evidently PO had driven it with a bad injector until it damaged the pump. Number 4 had a cracked barrel in the pump.....
I pulled the drive train out of the dodge and started analyzing what I had, PO had resealed the front cover and fixed the KDP.... But in doing so created a bigger leak on the back of the motor, appears he didn't get the cam gear hot enough to slip it onto the cam all the way.... so he tried driving it on with a hammer..... drove the soft plug out of the back of the block. Can you say Gusher..!!!!!
For the next couple years I was just plugging along cleaning things up, resealing the motor,got the P7100 rebuilt, changed transmission over to 4wd, figured out that I got a Dana 80 with my dodge purchase. That made me happy, I figured it was probably a Dana 70 But tag said 80......That was one of the first things I swapped out, went for a year or so with no 4wd because my front dana 60 had 3.54 gears and my stock HO 52 had 4.10. The dana 80 had 3.55s to match the front.
The biggest thing holding me back was a transfer case. I had sold the np205 with the turbo 350 that came in the K20 and didn't think the np241 was strong enough for a Cummins. So i had been patiently searching for a round bolt pattern 205 and finally found one in winter of 2019.
I work on a farm, it keeps me really busy April thru November, so I really only have winter months to work on it. December is my time off and January and February i only work 4 days a week.... so in 2019 I wasn't quite ready to take the plunge. to be continued.......
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71 C10 Cheyenne 396, turbo 400
71 C20 Custom Camper 383,tko 600,14 bolt project
71 K20 Custom,Cummins,NV4500,NP205,dana 60F,dana 80R
06 GMC sierra 2500 extended cab duramax,allison
05 Toyota Corolla (commuter)
18 Chevy Tahoe RST (wifes car)
08 HD Roadglide
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Old 12-07-2021, 09:18 AM   #5
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Re: My 71 K20 Cummins swap

Very nice truck and great work on it so far! I'm in to watch! Bad deal on the engine but at least it had a D80!
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1972 Chevy Longhorn K30 Cheyenne Super, 359 Inline 6 cylinder, Auto Trans, Tilt, Diesel Tach/Vach, Buckets, Rare Rear 4-link and air ride option Build Thread
1972 GMC Sierra Grande Longhorn 4x4
1972 Chevy Cheyenne Super K20 Long Step side tilt, tach, tow hooks, AC, 350 4 speed
1972 C10 Suburban Custom Deluxe
1969 Chevy milk truck
1971 Camaro RS 5.3 BTR STG3 Cam Super T10
1940 Ford 354 Hemi 46RH Ford 9" on air ride huge project


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Old 12-07-2021, 12:28 PM   #6
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Re: My 71 K20 Cummins swap

Dieselwrencher, I'm ok with how it worked out, with a little horse trading I was only out $380 to have the P7100 rebuilt

So in 2019 I found a core support at a swap meet that was in decent condition and I started modifying it for the dodge radiator and aftercooler. My goal was to repurpose as much of the dodge as i could to keep expenses down. I had studied Ryanroo's build extensively and even though his pictures were blurred out by photobucket I copied his idea as best I could on the core support. I was able to get the 2nd gen aftercooler in without modifying it.
During this time frame I also ordered the frame boxing and motor mount kit from Rob Bonney Fabrication. I wanted to have as much stuff as possible ready to make the swap go smoothly when I finally do it. This pickup is my daily driver and I didn't want it out of commission any longer than necessary, although I do have other vehicles to fall back on.
I also ordered a 4" Diamond Eye exhaust kit for a 1st gen dodge, I figured it would be the closest thing to fitting.
While the motor was out, I pulled the head off and did a valve job replacing the umbrella seals. Pulled the pan and checked bearings, pulled the cam to check for damage, pulled the gear housing off and put new gaskets in everywhere. Then I painted the motor Chevy Orange..... I didn't take any pictures of it out of the pickup. I painted the exhaust manifold and hot side of turbo with high heat black(surprisingly after almost a year of driving it still looks like new)
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71 C10 Cheyenne 396, turbo 400
71 C20 Custom Camper 383,tko 600,14 bolt project
71 K20 Custom,Cummins,NV4500,NP205,dana 60F,dana 80R
06 GMC sierra 2500 extended cab duramax,allison
05 Toyota Corolla (commuter)
18 Chevy Tahoe RST (wifes car)
08 HD Roadglide
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Old 12-07-2021, 12:52 PM   #7
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Re: My 71 K20 Cummins swap

So now I'm caught up to 2020.....
In November of 2020 I jumped in with both feet, out came the 383, NV 4500,NP241 and everything else. I pulled the front clip and removed the bed. Started cleaning the frame so I could box it in and weld in motor mounts
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71 C10 Cheyenne 396, turbo 400
71 C20 Custom Camper 383,tko 600,14 bolt project
71 K20 Custom,Cummins,NV4500,NP205,dana 60F,dana 80R
06 GMC sierra 2500 extended cab duramax,allison
05 Toyota Corolla (commuter)
18 Chevy Tahoe RST (wifes car)
08 HD Roadglide
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Old 12-07-2021, 12:55 PM   #8
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Re: My 71 K20 Cummins swap

The next step was test fitting the motor.....
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71 C10 Cheyenne 396, turbo 400
71 C20 Custom Camper 383,tko 600,14 bolt project
71 K20 Custom,Cummins,NV4500,NP205,dana 60F,dana 80R
06 GMC sierra 2500 extended cab duramax,allison
05 Toyota Corolla (commuter)
18 Chevy Tahoe RST (wifes car)
08 HD Roadglide
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Old 12-07-2021, 01:02 PM   #9
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Re: My 71 K20 Cummins swap

After hours of measuring and eyeballing from every possible angle I was satisfied with the placement of the motor and tack welded the mounts in place. Seems like I had the motor in and out 50 times, not a lot of fun.
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71 C10 Cheyenne 396, turbo 400
71 C20 Custom Camper 383,tko 600,14 bolt project
71 K20 Custom,Cummins,NV4500,NP205,dana 60F,dana 80R
06 GMC sierra 2500 extended cab duramax,allison
05 Toyota Corolla (commuter)
18 Chevy Tahoe RST (wifes car)
08 HD Roadglide
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Old 12-07-2021, 02:26 PM   #10
Dieselwrencher
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Re: My 71 K20 Cummins swap

Very nice work!
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Ryan
1972 Chevy Longhorn K30 Cheyenne Super, 359 Inline 6 cylinder, Auto Trans, Tilt, Diesel Tach/Vach, Buckets, Rare Rear 4-link and air ride option Build Thread
1972 GMC Sierra Grande Longhorn 4x4
1972 Chevy Cheyenne Super K20 Long Step side tilt, tach, tow hooks, AC, 350 4 speed
1972 C10 Suburban Custom Deluxe
1969 Chevy milk truck
1971 Camaro RS 5.3 BTR STG3 Cam Super T10
1940 Ford 354 Hemi 46RH Ford 9" on air ride huge project


Tired of spark plugs? Check this out.
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Old 01-12-2022, 07:38 AM   #11
Dieselwrencher
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Re: My 71 K20 Cummins swap

It's funny you mention these. The AC pressure line on my VE24V Excursion has been leaking for years. I decided to address it this spring. Too bad my local shop I had my AC hoses made up closed. I couldn't find anyone who would crimp on any fittings on my hose or who could even find me a fitting. My drive line shop whom also deals with hydraulic parts, sourced me these same type of fittings and I was able to fix my line. It has been on there all summer with no issues. I was leery at first but from the research I've done they hold better than a crimped fitting.
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Ryan
1972 Chevy Longhorn K30 Cheyenne Super, 359 Inline 6 cylinder, Auto Trans, Tilt, Diesel Tach/Vach, Buckets, Rare Rear 4-link and air ride option Build Thread
1972 GMC Sierra Grande Longhorn 4x4
1972 Chevy Cheyenne Super K20 Long Step side tilt, tach, tow hooks, AC, 350 4 speed
1972 C10 Suburban Custom Deluxe
1969 Chevy milk truck
1971 Camaro RS 5.3 BTR STG3 Cam Super T10
1940 Ford 354 Hemi 46RH Ford 9" on air ride huge project


Tired of spark plugs? Check this out.
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Old 01-12-2022, 01:02 PM   #12
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Re: My 71 K20 Cummins swap

Here are some pictures of the fittings I used. The single line is the pressure line to the steering box, I just reused the steel line that connects to the steering box and attached a new hose to it. The triple lines are from hydroboost, the return line is still factory. The other two have new hoses attached to the factory steel lines
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71 C10 Cheyenne 396, turbo 400
71 C20 Custom Camper 383,tko 600,14 bolt project
71 K20 Custom,Cummins,NV4500,NP205,dana 60F,dana 80R
06 GMC sierra 2500 extended cab duramax,allison
05 Toyota Corolla (commuter)
18 Chevy Tahoe RST (wifes car)
08 HD Roadglide
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