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  #1  
Old 05-02-2010, 04:35 PM
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FSJ Frame Strength for a Diesel Swap

The recent posting created by Songman about the purchase of a 1990 Dodge Cummins 6BT as a donor for a FSJ Diesel project has prompted me to revisit this topic of Frame strength.
http://www.ifsja.org/forums/vb/showthread.php?t=121301

There is a debate (I would like to say a it's a HUGE debate, but I am sure there would be debate over the size of the debate) about FSJ Frames

Some say the FSJ frames are not strong.
They say the frame is not deep enough and not boxed enough and the material is not thick enough and is soft like butter to use for a Cummins 6BT.

Other say these frames are as strong as any other frame of the same era.

I would like discuss this more and other than just opinions (which are great for a discussion), I would love some more factual evidence.

I've dreamed of a Diesel FSJ for a long time.
Short of struggling to keep a roof over my head, I have not been able to move beyond the planning stage.

I've desired a Cummins 6BT, but the simplicity of the GM 6.2 Diesel swap have caused me to change my plans.
However, the source of this 1st gen Cummins 6BT is being to grow.
A person can find them in others places, like in School Buses and med duty trucks.

But, before anyone can address the issues related to the a Cummins 6BT, a person needs to have a good foundation, a good frame.

One factor is how would one use a 6BT powered FSJ.
A 6BT powered Wagoneer may lead a different life than a J20 tow rig.

Allow me to share my plans (fools fantasy) for a 6BT powered FSJ.
I would like a recovery rig, long range tow rig, dually rear axle, on board air (easy bolt on for a 6BT) and my flat bed would hold a 5th wheel hitch.

What I do with such a rig?
I want to be able to leave NE Indiana and head to the Southwest to collect those toys, like a 70 Nova, 67 Mercury Cougar, 71-74 Javelin, Jeep Forward Control, Fox Body Mustang (for Nathan) or a whole host of other interests that I have.
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2005 Grand Cherokee Limited - HEMI! Current Daily Driver
1982 J10: Current Project, goal to be roadworthy in 2017: No Cab Brow!
1981 J20: Commercial flat bed. Long term Project: RUST! No Cab Brow!

Quote:
Originally Posted by Jayrodoh
...but if it works, I wouldn't touch it.
Quote:
Originally Posted by Lindel
Best laid plans, yada yada yada...
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  #2  
Old 05-02-2010, 04:43 PM
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1983 j10 1983 j10 is offline
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the easiest way to do that would probly be to find a dodge and put the fsj body on it. and since your doing a flat bed it would be pretty easy.
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  #3  
Old 05-02-2010, 07:22 PM
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I am partial to M715 frames. They are a bit stronger, boxed to a larger extent, have reinforcements that civilian frames don't have and have a built-in suspension lift that makes engine fitment a lot easier.
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Last edited by Mikel : 05-02-2010 at 07:47 PM.
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  #4  
Old 05-02-2010, 10:07 PM
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76FSChief 76FSChief is offline
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Glad to hear that I am not the only guy that has dreamed about a diesel Jeep. I am in the middle of the swap as we talk - engine, transmission and transfer case are all mounted up.

Originally I wanted to go with the original frame but people told me that I wouldnt be able to. Then I started thinking about doing the Dodge frame but after talking to a dealer out in Ontario I decided to go with my original idea. He said all that is necessary is a little reinforcement of the frame and your good to go - they have done the swap a few times with no customer complaints.

Anyways I am going to get a thread going for the build, and if I can help you out in anyway just let me know.
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  #5  
Old 05-02-2010, 10:12 PM
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Even though the particular truck I was interested in got sold, I am still interested in this swap so will watch with interest. I'm on the lookout for an affordable donor.
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  #6  
Old 05-02-2010, 10:24 PM
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vintagetrks vintagetrks is offline
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Would you have to beef up the frame for a GM 6.2 swap. I would think the only reason a fellow would have to beef the frame up for the cummins is the higher torque. Because it would seem to me that the GM 6.2 would be a heavier engine than the 6bt but I'd bet the 6.2 does'nt produce near the torque of the 6bt. Just a thought.
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  #7  
Old 05-03-2010, 03:22 AM
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HOOT says:
Buy a truck you like and morph it into a FSJ knock off. I finally got fustrated when after years of work my J20 got destroyed on Its maiden trip after being rebuilt. Diesel was to come later after the Honcho was back on the street. No longer with a tow rig I was at square one not to mention the money loss. So after long debate I went outside the Jeep world for a truck,something I have never done in my life and I was 45 years old. Picked up a somewhat well taken care of '95 F350 and did a refresher on it. The power and drive is unbelieveable not to mention the safety as well. Yes I could of made my J20 back to this type of tow ability and stable road manners but I didn't see that happening with the struggles the past couple of years.

My neighbors roll their eyes as the see me wire tying a razor or muscle grill to the Ford sizing it up. It can be done, like dropping in a different drive line its all just a matter of fabbing. Only in this case I'm keeping factory driveline and changing its skin as much as possible.

I have a utility bed I bought for the Jeep. It's a Reading and as anyone knows it looks nothing like a Jeep even when its on a Jeep. So I found a use for my factory fiber glass rear flares no one wanted to buy. I also have a set of rear J truck tail lights that will be grafted in place of the round Reading lights. My J truck rear bumper will most likely be installed as well, although there is a sweet after market step bumper I want also. Since I prefer the looks of a brow truck I'll most likely put a Lund visor on it for the unibrow bliss.
It's a factory crew cab so now I'll have my sleeper unit as well that I wanted. All I have to haul is me and Annie, and she prefers shotgun. I picked up a killer topper for it from a TX member on here(Thanks Jason).
This thing can pull the house of its foundation and still get me to the Dairy Queen for a sundae. Capable of hauling gooseneck or bumper pull and able to do it cross country like a Sunday drive.
I have about $3000 more into this as I had into my J20 and it was still sporting the 360 motor, dana 44/60 SRW 3:73 gears and regular cab with 8' bed.
I now have 7.3 (brace yourself Derek) Turbo !! diesel, with overdrive, crew cab, Sterling 10.25 dually,4:10 gears, with a locker and dual fuel tanks.
Soon it will have the utility bed and other Jeep stuff as I get time to work it over. It may never be a Jeep but it has an older Ford style that I like, and most of all so far very dependable after being worked fairly hard the last year or so. 20,000 miles on it in less than a year and it sits for week or more at a time as I have a different daily driver car that gets all non hauling type driving.

So turn your J trucks into diesels if you want but its my love for getting back behind the wheel of my Honcho and wanting to take it back to its homeland in the Southwest that forces me to change tow rigs, even if it means being towed by a Ford to get there.
Now if they only had a F350 site as nice as this one is.....
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1980 J20 Utility bed truck. Factory cab and chassis truck. Many new mods for it but it will look all stock.
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Last edited by HOOT : 05-03-2010 at 04:10 AM.
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  #8  
Old 05-03-2010, 04:26 AM
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The PIG Smith The PIG Smith is online now
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Quote:
Originally Posted by vintagetrks
Would you have to beef up the frame for a GM 6.2 swap. I would think the only reason a fellow would have to beef the frame up for the cummins is the higher torque. Because it would seem to me that the GM 6.2 would be a heavier engine than the 6bt but I'd bet the 6.2 does'nt produce near the torque of the 6bt. Just a thought.
IMHO, No, you would not.

First, the GM 6.2L Diesel is about 750# fully dressed compared to the Cummins 6BT which is about 1200# dry.

You are correct, the torque from a 6.2L is nowhere near that of a Cummins 6BT.

The 6.2L is about the same size and only slightly heavier than a small block Chevy.
So, if the FSJ frame can handle the size, weight and power from a hot SBC, then the 6.2L is not a problem.

The issue as I understand it is the FSJ frame would not hold up to the excessive weight and the torque from a Cummins 6BT.
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2005 Grand Cherokee Limited - HEMI! Current Daily Driver
1982 J10: Current Project, goal to be roadworthy in 2017: No Cab Brow!
1981 J20: Commercial flat bed. Long term Project: RUST! No Cab Brow!

Quote:
Originally Posted by Jayrodoh
...but if it works, I wouldn't touch it.
Quote:
Originally Posted by Lindel
Best laid plans, yada yada yada...

Last edited by The PIG Smith : 05-03-2010 at 07:00 AM.
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  #9  
Old 05-03-2010, 08:10 PM
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WHSII WHSII is offline
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Bumper

Hello Hoot.

Now before you graft a good J10 bumper on a Ford, Lets talk.

If it is 5 1/2" tall, and in good shape, I might be able to make it worth your while.

Thanks,
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Dad's J10, Honcho, 1980 Sport Side
Build http://www.ifsja.org/forums/vb/showthread.php?t=118144

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  #10  
Old 05-03-2010, 10:11 PM
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I wrote this the other night but I guess it didnt post:
For what you want to use the rig for Pig Smith, I think you would either have to box the whole frame, or swap the dodge frame underneath (which seems easier *if* you have the tools for it, big IF).
I am now looking towards the 6BT as well, but my Wagoneer would be a daily driver for me and wouldnt be towing anything.
I am anxiously waiting 76FSChiefs build thread
And speaking of the rig 76FSChief mentioned, it was done by overlanddiesel at overlanddiesel.com
I emailed the guys asking questions and didnt get too specific answers but this is what they emailed back:

"Hello Josh,

The frame was plated and reinforced in key areas. A crossmember plate was later installed to tie the frame rails together as well as act as a slam-guard for the front differential to oilpan. The Jeep already had a 4" lift but it sagged 2" after only a few months. 2 additional J20 leaves were added to each pack and it hasn't settled since. Hope this helps. Send us pics when you are done! Love seeing other swaps. ......."

And to vintagetrks, the frame needs to be beefed up because of the torque and the weight. The 6bt is a HEFTY engine. IIRC MUCH heavier than the 6.2, exemplified by the sag they mentioned in above email
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  #11  
Old 05-03-2010, 10:22 PM
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seamus seamus is offline
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My 2005 cummins goes through front end parts like crazy,
it's my daily driver spends winters on stock height tires and
summer on 35's.
145000 kms and some parts have been replaced 3 times.
Don't underestimate the forces that these big tourquy
engines produce, and don't forget there is no kill like overkill.
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  #12  
Old 05-03-2010, 10:33 PM
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uglyjeep uglyjeep is offline
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Quote:
Originally Posted by vintagetrks
Would you have to beef up the frame for a GM 6.2 swap.

I haven't and I'm not going to.

I'm only a few PS pressure lines, radiator hoses, and a couple of wires short of running my 6.2 in my jeep. My springs aren't sagging considerably more than they were before the 6.2(but they were/are sagging very bad). I have a "custom" set of spring packs (that use the jeep front main leafs and leafs from some unknown trucks rear springs) that I'll put on when I put in my HD44.

Anyway, back to the topic. IMHO, a 6BT would need, at least, some serious reinforcement to the stock frame, even if the engine isn't tuned/hopped up. I think a 6bt would probably turn a stock FSJ frame into a pretzle over time (or very quickly...).
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  #13  
Old 05-04-2010, 05:12 AM
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I know this topic has been brought up before, so I did a search and IMHO, here is the best that I found on this topic:

FSJeeper commenting about FSJ frames:

http://www.ifsja.org/forums/vb/showthread.php?t=20184

http://www.ifsja.org/forums/vb/showt...t=14326&page=2

gotmike's Cummins powered Cherokee and speaks about his frame:
http://www.ifsja.org/forums/vb/showt...t=90702&page=2
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2005 Grand Cherokee Limited - HEMI! Current Daily Driver
1982 J10: Current Project, goal to be roadworthy in 2017: No Cab Brow!
1981 J20: Commercial flat bed. Long term Project: RUST! No Cab Brow!

Quote:
Originally Posted by Jayrodoh
...but if it works, I wouldn't touch it.
Quote:
Originally Posted by Lindel
Best laid plans, yada yada yada...
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  #14  
Old 05-04-2010, 06:18 AM
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I would also like to see where this topic goes....
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Old 05-04-2010, 12:33 PM
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From reading all these threads I think that boxing atleast around the engine bay would be the smart thing to. Possibly throw in a crossmember or some gusseting and you'd be set. Now to find shop prices on frame boxing......

Someone brought up a good point on one thread, how much torque does a slightly build 401 put out? And how much does one weigh?

If only i could find a 5.9 that was under 3grand
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Last edited by jMedia : 05-04-2010 at 01:42 PM.
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  #16  
Old 05-04-2010, 02:07 PM
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Quote:
Originally Posted by jMedia
Someone brought up a good point on one thread, how much torque does a slightly build 401 put out? And how much does one weigh?
Excellent point.
It's for sure that a hot 401's weight does not exceed the weight of a 6BT, however the torque is another issue.
Would the torque of a hot 401 put more (or less) stress on a FSJ frame than a stock 6BT with it's massive weight?
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2005 Grand Cherokee Limited - HEMI! Current Daily Driver
1982 J10: Current Project, goal to be roadworthy in 2017: No Cab Brow!
1981 J20: Commercial flat bed. Long term Project: RUST! No Cab Brow!

Quote:
Originally Posted by Jayrodoh
...but if it works, I wouldn't touch it.
Quote:
Originally Posted by Lindel
Best laid plans, yada yada yada...
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  #17  
Old 05-04-2010, 06:33 PM
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seamus seamus is offline
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Quote:
Originally Posted by The PIG Smith
Excellent point.
It's for sure that a hot 401's weight does not exceed the weight of a 6BT, however the torque is another issue.
Would the torque of a hot 401 put more (or less) stress on a FSJ frame than a stock 6BT with it's massive weight?


My first gen will weigh over 1100lbs, it will produce over 700 ft/lbs

My daily driver makes over 800 ft/bs
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Old 05-04-2010, 06:55 PM
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Quote:
Originally Posted by seamus
My first gen will weigh over 1100lbs, it will produce over 700 ft/lbs

My daily driver makes over 800 ft/bs

And your frame? I'm guessing stock. Which makes me happy I wonder if the "shake" of a diesel would be a factor as well
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  #19  
Old 05-04-2010, 10:00 PM
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Quote:
Originally Posted by jMedia
And your frame? I'm guessing stock. Which makes me happy I wonder if the "shake" of a diesel would be a factor as well

I just returned from a 300 mile in my 4BT-powered J300. I am utterly amazed at how smooth the engine is (I did raise the idle a bit).
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Old 05-04-2010, 10:54 PM
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Dang jealous of that 4bt. Wish I could, stupid CA. Next rig will be pre 76 or if first diesel craps out I'll put a 4bt next
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