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71 521KC Dually Flatbed Build


bob72gts

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So here is what I am starting with.

 

521s008.jpg

 

521s004.jpg

 

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521s001.jpg

 

Paid $40 for the pair.

 

The red-ish one is in better shape and has an engine so it will be the builder. The silver-blue one is the donor (Victim)

 

The L16 was supposedly rebuilt, but it never got installed properly. It is missing some bolts and is not even sitting on the mounts right now. Also it has been left without an oil filter, oil cap, or air cleaner for about 10 years. I see a tear down and inspect in my future.

 

521s013.jpg

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Here is a shot of the wheels and tires I am using on this project.

 

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Immediate plans are....

 

Get the 2 frames spliced together about 12" longer than original.

 

Finish widening the bed so that I can cut off everything above the body line and start building the flat bed.

 

Make the cab filler panels for the KC section using donor doors.

 

MOAR LOWER 4" rear and 3" front combined with the tire size difference and the extra weight of the new bed should sit level.

 

Future plans....

 

Get the brakes working

 

Pull the L16. Clean it and verify it's freshness.

 

Dreams.....

 

SD22T http://nissandiesel.dyndns.org/viewtopic.php?p=3727#3727

 

5 speed

 

Paint

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This is my flatbed dually.

100_0145.jpg

The frame has been lengthened 24 inches.

The kingcab truck I posted a photo of with the stepside box is a SD25 diesel, where did you get a SD22T engine, or are you planning on making it yourself? It will fit, but it is tight. I will check that link about the engine now.

DSCN0153.jpg

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How much are you going to add to the cab? I added 14 inches to mine.

DSCN0522.jpg

 

I was thinking 12" stretch would give me a total of 14" from back of the door to the back of the cab, but maybe I should go a little more. On a 620KC it is only 12" from the door to the back of the cab which is 9 1/2" longer than a standard cab. I know I want it longer than my 620 KCs but I don't want to go too far.

 

 

Are you making the whole box wider? I wish you were closer, I like seeing these mods in person. Are you using dually adapters, or custom six lug dually wheels?

 

First I am making the whole box wider then I am cutting off the top 8" or so. After I ad the flatbed there will still be a functional tailgate that will access a storage area under the flatbed. The storage area is the original bed floor and wheel tubs

The wheels are dually adapters with a large 5 bolt pattern

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but are they custom 6 lug dually rims?

 

The adapters go fron 6x5.5" to the 5 lug pattern you see in the pick. Same bolt pattern as old VWs but VW wheels wont fit the adapters.

 

The company that made these wheels also makes adapters to use 8 lug dually wheels on a 6 lug truck, but those are way out of my price range.

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Are the wheels 14", 15", or 16"? I looked at that SD diesel turbo thread, I seen that a couple years ago, they were having issues then, I went the other route, I bought a SD22 engine in austrailia with a VE type injection pump, I just haven't got around to putting it on the engine yet, I plan on doing it to mine also. I dropped my 521 kingcab onto a 1982 datsun 720 diesel kingcab frame, it gave me all the upgrades, PS, disc brakes, ect. I also used the 720 diesel wiring harness and wired it into the 521 instrument cluster, I used the 720 tilt wheel also, it's a lot of work putting a project like this together.

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Depending on the wheel size(14-15-16"), you will need to pick your rearend gearing carefully, I am running 14" wheels on my 720 diesel dually, with P195/75R14 tires, I have 370 gears in the rear now, the 437 gears that were in my 521 just would'nt work, your floored almost just to do 60mph.

100_0070.jpg

I have a lot of custom trucks, too many actually. :lol:

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why not use that 79 kc frame you were selling a bit ago?

 

Several reasons actually.....

 

The 620KC frame is shorter than I want.

 

The 521 bed mounts are WAY different than the 620.

 

I have test fit the front wheels on my other 79'. Because of the added track width on factory disc trucks the wheels stuck out of the fenders. I REALLY hate that.

 

By combining the 2 521 frames that I have I get a 3rd pair of cab mounts that are already in the right place to support the KC section and properly align with the bed.

 

Last but not least I can build it without pulling the cab off of the red truck, which is pretty important since I am doing most of it alone.

 

 

 

 

By the way the 79' and 77' KC frames are still available, but will be cut for scrap if not sold soon

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can you swap the front 620 suspension onto the 521 or get it so you get the disk brakes, it would be a shame to shell out more $$ to get disk brakes when you got stuff right now to do it and stay 100% datsun parts. That is ofcourse if you want disk brakes

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can you swap the front 620 suspension onto the 521 or get it so you get the disk brakes, it would be a shame to shell out more $$ to get disk brakes when you got stuff right now to do it and stay 100% datsun parts. That is ofcourse if you want disk brakes

 

I think I will stick with drums on this one. How ever I will probably swap it over to the 77' parts that I have. That way I will get the larger wheel studs, dual master cylinder, and front wheel bearings that you can actually get at the parts store.

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One of the 521 kingcabs around used the 79 620 kingcab frame, it was a 10" cab extention i think, but I could be wrong on that length, there are four 521 kingcabs out there that I know of, my 14" is the longest so far I beleave. Z chopper, using the 620 disc brake hardware on the 521 isn't as easy as one would hope, lot of modifacations needed, my 521 flatbed has them. The 720 kingcab has 6 cab mounts, same as the 521 standard cab, when they extended the cab, instead of putting another cab mount back there, they put a rubber pad at the very back that rests on the frame, it allows the rear part of the cab to move around, I put nothing back there, it just hangs a quarter/half inch above the frame.

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I think I will stick with drums on this one. How ever I will probably swap it over to the 77' parts that I have. That way I will get the larger wheel studs, dual master cylinder, and front wheel bearings that you can actually get at the parts store.

 

 

Mike sells spacers that allow the use of 620 front wheel bearings on the 521.

http://community.ratsun.net/topic/30876-320520521-inner-bearing-spacers-15pr-shipped/page__view__findpost__p__461698__hl__mklotz70__fromsearch__1

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One of the 521 kingcabs around used the 79 620 kingcab frame, it was a 10" cab extention i think, but I could be wrong on that length, there are four 521 kingcabs out there that I know of, my 14" is the longest so far I beleave. Z chopper, using the 620 disc brake hardware on the 521 isn't as easy as one would hope, lot of modifacations needed, my 521 flatbed has them. The 720 kingcab has 6 cab mounts, same as the 521 standard cab, when they extended the cab, instead of putting another cab mount back there, they put a rubber pad at the very back that rests on the frame, it allows the rear part of the cab to move around, I put nothing back there, it just hangs a quarter/half inch above the frame.

 

Wayno I think the cab proportions on a 720KC are just about right for what I want. Could you measure the length of your door and the length of the KC section and let me know? I would measure one myself, but I don't know of any in this town and the closest boneyard is about 60 miles away.

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I am not sure exactly what you want me to measure, rough guess(spent 10 minutes measuring), is if you used a 1980 datsun 720 kingcab frame, as it has the L20b engine mounts for sure, but the napZ engines probably have the same engine mount surfaces, as it just uses differant hardware to mount the engine, you would need to extend the cab approximately 10 1/2 inches if using the stock 521 box. This measurement includes the inch gap between the cab and box. I usually spend a couple hours on measurements before I commit to doing any cutting. If I had planned on a flatbed not using any part of a 521 box, I could have extended the cab 18 inches on the 720 kingcab frame and still used the stock kingcab fuel tank, any longer and the stock tank won't work and you also are real close to where the frame starts upward for the rear axle clearance. The 720 frame e-brake system doesn't modify well, if you extend the frame, you need to change how it works. Oh yea, I have never tried to mount a 521 box on a 720 frame yet, I used the stepside box on that project, that's why I extended my cab 14 inches, if the frame had been shorter, the cab extention would have been shorter. I base all my measurements on wheel centers front to rear as I want the wheels to be centered in the wheel wells, if you make a flatbed from scratch, most these measurements do not matter. I cannot see how this will help you, but, my 521 KC measures from the front of the door to the back of the cab, 54 1/2 inches with a 38 1/4 inch door, the 720 KC is 60 1/2 inches with a 40 inch door, the distance from the center of the front wheel to the rear of the 720 KC is 80 1/4 inches. Let me know if this helps you, or if you need anymore measurements. wayno

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Wayno 720KC front of door to back of cab 60 1/2" with 40" door, those are the measurements I was looking for. Thanks.

 

So to get the same proportions on my 521KC I would need to build it with a 19" KC section which would work out to about 17" stretch.

 

I don't know if I have enough good sheetmetal in my donor cab for that, but I guess I will just build as big as I can using what I have. Wish me luck

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Are you going to try to stretch it 17 inches on a stock 521 frame? That can't be done on a stock frame, unless you mod the cab extention. If your going to stretch the frame and use the stock box bed, then for every inch you stretch the cab you have to stretch the frame the same, inch for inch. I stretched my 521 14 inches and it is still almost 4 inches shorter than the 720 KC body/cab, that's why I have some extra room left over the 720 KC fuel tank.

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17 3/4 inch stretch will put the front wheel centered in the wheel well, and it would just clear the 720 KC fuel tank sitting on a 720 frame, this doesn't even take into account the rear box, if your going to make it a flatbed, I suppose the box bed could be shortened to fit in the space available.

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Are you going to try to stretch it 17 inches on a stock 521 frame? That can't be done on a stock frame, unless you mod the cab extention. If your going to stretch the frame and use the stock box bed, then for every inch you stretch the cab you have to stretch the frame the same, inch for inch. I stretched my 521 14 inches and it is still almost 4 inches shorter than the 720 KC body/cab, that's why I have some extra room left over the 720 KC fuel tank.

DSCN0683.jpg

DSCN0684.jpg

17 3/4 inch stretch will put the front wheel centered in the wheel well, and it would just clear the 720 KC fuel tank sitting on a 720 frame, this doesn't even take into account the rear box, if your going to make it a flatbed, I suppose the box bed could be shortened to fit in the space available.

 

I am using 2 521 frames, a few feet of 4" C channel, and some plate steel to do my frame stretch. The bed will be stock length with the stock fuel tank on the original mounts of the rear frame section. The bed will be about 18" wider than original with the top sides cutoff at the bottom of the wrap-around body line which is where the top of the flat bed deck will be. A tailgate cut down to the same height will be in the stock location on the original bed. Then I will build stake sides for both sides and across the front of the bed.

 

I know it might sound confusing, but there is a plan and as the project progresses all will be revealed. I didn't get to work on it today but I hope to get the bed roughed out tomorrow.

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