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  #61  
Old March 31st, 2012, 23:12
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Re: Joel's multipurpose XJ build (rocks/boulevard)

that is once sexy skid plate!

IMHO it doesn't need to come that far back, but since you wanted to protect your fancy exhaust I guess it had too.

frame stiffeners do a lot more than spread the load out of a skid, they are a good idea for any unibody rig that is going to be flexing and used offroad, and all you would need to do is add the holes in for your side mounts, and possibly slot the mounting holes in your skid just a bit..

I would also find a way of tying in the rockers to the frame rails once stiffened. seems to me a pretty hard hit on them could bend the door sill pretty bad.
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  #62  
Old April 1st, 2012, 07:34
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Re: Joel's multipurpose XJ build (rocks/boulevard)

You're exhaust and skid plate look awesome!!
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  #63  
Old April 1st, 2012, 17:19
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Re: Joel's multipurpose XJ build (rocks/boulevard)

idk about skids replacing frame stiffeners, i think it might spread the load a bit... but i dont think it will do enough to substitute frame stiffeners... idk if it would be worth going for the risk. thats what i think/would do. but just my $0.02
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  #64  
Old April 1st, 2012, 23:49
frijolee frijolee is offline
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Re: Joel's multipurpose XJ build (rocks/boulevard)

Thanks guys, I appreciate the compliments. To be honest I kinda thought some folks were going to chew me out for way overthinking what I'm building (apparently I've been reading too much on pirate4x4). Personally I don't believe you can overthink a build but maybe that's just me.

As to the topic at hand, can someone please explain how frame stiffeners are supposed to work? I looked up some pictures and it looks like you're just plug welding the heck out of plates that install on three sides of the frame rails.

My problem is this: U-sections--the basic shape of the reinforcements--are pretty inefficient at resisting twisting loads (which I believe is the problem). If you're trying to optomize torsional resistance wouldn't a box be far stronger? Has anyone tried filleting the rails open so you could shove a full rectangular tube in there and/or reinforcing the floor on the top side of the "channel" of reinforcement? Is the floor sufficient to complete the "box" section such that heavy walls on three sides is enough?

As a first step, I think I'm more likely to try tying my mid skid into the welded in drip rails. That way the floor vs. skid becomes something of a box. It's a little unscientific but my hatch creaks quite a bit when flexing out. I assume if I can get the floor and underside of the jeep carrying more twisting load the creaking will be less.

I still may go ahead and do some sort of frame stiffering around the suspension locally. Note, I was reading about how some XJs crack at the front suspension pick up points so I could see how plating that helps with vertical loads from the pounding as well as twist. I'm not trying to reinvent the wheel but my impression is that there are more effecient ways to reinforce the frame and I at least want to think through the implications of changes. Heck, a triangulated internal cage with gusset plates tying in the a,b,c pillars would be the most efficient, I just don't think I want that in a Jeep.

Thoughts?

Last edited by frijolee; April 1st, 2012 at 23:59.
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  #65  
Old April 2nd, 2012, 00:03
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Re: Joel's multipurpose XJ build (rocks/boulevard)

Quote:
Originally Posted by frijolee View Post
Can someone please explain how frame stiffeners are supposed to work? I looked up some pictures and it looks like you're just plug welding the heck out of plates that install on three sides of the frame rails.
essentially yes. what the stiffeners do does is create a thicker frame rail that will resist flexing, crushing, and denting much more.

also, it gives you quite a bit more meat to weld bracketry for suspensions an armor to.

Quote:
My problem is this: U-sections--the basic shape of the reinforcements--are pretty inefficient at resisting twisting loads (which I believe is the problem). If you're trying to optomize torsional resistance wouldn't a box be far stronger? Has anyone tried filleting the rails open so you could shove a full rectangular tube in there and/or reinforcing the floor on the top side of the "channel" of reinforcement? Is the floor sufficient to complete the "box" section such that heavy walls on three sides is enough?
most frame stiffeners are just an L shape that wrap the outside and bottom of the existing unibody rail.. any number of other things have been done, wrapping all 3 sides, cutting off the unibody and building a frame, etc. the cheapest, easiest and most efficient form of frame stiffening is the HD offroad eng. style. a peice of plate, bent to wrap the bottom and outside of the rail, plug welded like a mofo to essentially join the two pieces of metal into one.


Quote:
As a first step, I think I'm more likely to try tying my mid skid into the welded in drip rails. That way the floor vs. skid becomes something of a box. It's a little unscientific but my hatch creaks quite a bit when flexing out. I assume if I can get the floor and underside of the jeep carrying more twisting load the creaking will be less.
thats not gonna help much. all those holes you use to attach the skid are going to flex and wallow out. bolt on frame stiffeners don't really work unless you use a ton of through bolts and crush sleeves. ask actionfab he designed something like that. with your welding skills, a set of stiffeners would be simple for you.


Quote:
I still may go ahead and do some sort of frame stiffering around the suspension locally. Note, I was reading about how some XJs crack at the front suspension pick up points so I could see how plating that helps with vertical loads from the pounding as well as twist. I'm not trying to reinvent the wheel but my impression is that there are more effecient ways to reinforce the frame. Heck, a triangulated internal cage with gusset plates tying in the a,b,c pillars would be the most efficient, I just don't think I want that in a Jeep.

Thoughts?
I agree with stiffening around your suspension, just make sure you spread the load as much as possible. the BDS crossmember does a good job, but everything helps.

cages can stiffen the chassis quite a bit, but you have to tie them into something somehow and the easiest and most effective way to do it is to stiffen the unibody first.
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  #66  
Old April 2nd, 2012, 06:36
troy5118 troy5118 is offline
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Re: Joel's multipurpose XJ build (rocks/boulevard)

I love that someone would go that overkill on an exhaust for a Cherokee

Here's what I did.








Those frame rails don't pick up any torsional strength from the weld on stiffeners but it does keep them from getting smashed on the trail and act as a nice attachment point for suspension parts, crossmembers, and a cage.
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  #67  
Old April 2nd, 2012, 08:03
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Re: Joel's multipurpose XJ build (rocks/boulevard)

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Originally Posted by troy5118 View Post

Those frame rails don't pick up any torsional strength from the weld on stiffeners.
i beg to differ. it's the main reason for doing it. i noticed a big difference when i did mine just driving on the street. these jeeps tend to crack all over if you don't do them and wheel a lot.
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  #68  
Old April 2nd, 2012, 08:54
troy5118 troy5118 is offline
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Re: Joel's multipurpose XJ build (rocks/boulevard)

What size of stiffeners are you using? Mine are 10ga and it runs from the front of the frame clear to the front leaf spring eye. If I flex the Jeep the rear hatch won't even open. I'm sure with thicker material you'd gain stiffness but I'd rather put that extra weight into a hybrid cage.
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  #69  
Old April 2nd, 2012, 09:18
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Re: Joel's multipurpose XJ build (rocks/boulevard)

3/16", i wasnt exactly concerned about the extra 5.6lbs per pair if it keeps my unibody straight and crack free.
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  #70  
Old April 2nd, 2012, 14:52
frijolee frijolee is offline
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Re: Joel's multipurpose XJ build (rocks/boulevard)

Vanimal,

Can you explain a bit more what you noticed as different with the addition of frame stiffeners? I found your thread on them. I’m still not following how a partial fortification of two parallel tubes in line with each other and separated by a sheet metal floor can dramatically impact the torsional stiffness. There’s no triangulation so it’s basically just the twisting resistance of each member. I’m guessing quite a bit of load goes through the roof so I can certainly see the upside to a cage.

Also, my math says these should be heavier than you suggest. If I assume two faces armored with 3.5” of wrap each, 3/16” thick, 60” long (a guess) I come up with:

2 x 3.5 x 0.1875 x 60 x 0.284 lbs/in^3 I come up with 22.4 lbs per side not 5.6 lbs per pair.

I’m not saying these don’t work, I’m just saying I think it’s an inefficient approach. It may still be the frame best fortification that can be done simply. I’m curious if anyone has done any before and after testing. (IE compare deflection of an open hatch when flexed on a repeatable obstacle.)

BTW: I can’t very well add these under my skid since the total side to side distance is now fixed… I’d have to cut that the attachment plates on my skid and re-weld them and I’m definitely not eager to do that. One way or another I’m doing something different.

Gotta think about this some more.
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  #71  
Old April 2nd, 2012, 16:36
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Re: Joel's multipurpose XJ build (rocks/boulevard)

Most commentary I've read suggests that while the off the shelf type frame stiffeners help in the short term and offer a lot of improvement, long term the same creaks come back.
My personal theory is that when you add fresh, de stressed steel to the body it will stiffen it up. When that steel gets stressed through vibration & flex, it starts to lose its stiffness & begins to flex / creak again.
Generally, to add stiffness to add structure.
Figure out what sort of a cage you want & add stiffeners if you need them for attachment points. I would't count on them to stiffen the chassis for long.

They also protect against rocks, which on my jeep is a total non-issue but YMMV.
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  #72  
Old April 2nd, 2012, 16:54
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Re: Joel's multipurpose XJ build (rocks/boulevard)

Quote:
Originally Posted by frijolee View Post
Vanimal,

Can you explain a bit more what you noticed as different with the addition of frame stiffeners? I found your thread on them. Iím still not following how a partial fortification of two parallel tubes in line with each other and separated by a sheet metal floor can dramatically impact the torsional stiffness. Thereís no triangulation so itís basically just the twisting resistance of each member. Iím guessing quite a bit of load goes through the roof so I can certainly see the upside to a cage.

Also, my math says these should be heavier than you suggest. If I assume two faces armored with 3.5Ē of wrap each, 3/16Ē thick, 60Ē long (a guess) I come up with:

2 x 3.5 x 0.1875 x 60 x 0.284 lbs/in^3 I come up with 22.4 lbs per side not 5.6 lbs per pair.

Iím not saying these donít work, Iím just saying I think itís an inefficient approach. It may still be the frame best fortification that can be done simply. Iím curious if anyone has done any before and after testing. (IE compare deflection of an open hatch when flexed on a repeatable obstacle.)

BTW: I canít very well add these under my skid since the total side to side distance is now fixedÖ Iíd have to cut that the attachment plates on my skid and re-weld them and Iím definitely not eager to do that. One way or another Iím doing something different.

Gotta think about this some more.
i said 5.6lbs heavier than the 10ga, and your assumptions on the sizes are off.
the frame rails twist and bend, not just become out of parellel. they're just thin sheetmetal. and as i'm sure you know, the more it flexes, the weaker it becomes. it's best to stop some of the flexing before it starts because there is no going back.
even just driving on the street, when i take a hard corner it's much easier to spin the inside tire, which means the torsional stiffness is definitely greater.
Even when i did subframe stiffeners on my mustang, it greatly reduced flex.

obviously a cage, if done right, will increase stiffness even more. but frame stiffeners definitely help and are well worth the effort.

as for opening the hatch and doors when flexed out, i had no problems with that before i had the stiffeners, and i doubt they would make that worse.
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  #73  
Old April 3rd, 2012, 13:33
frijolee frijolee is offline
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Re: Joel's multipurpose XJ build (rocks/boulevard)

I’m going to leave the frame stiffener discussion for a bit to circle back and talk about the mid skid some more. (If you have further thoughts on stiffeners, feel free to post up).

Mid Skid Heat Management

One question I had in designing the mid skid was whether it would be able to shed enough heat while only have having about 1/2" of clearance top and bottom and air flow limited to the tunnel around the pieces fore/aft.

When I took the plates over for water jet cutting I built in a whole series of pilot holes under the cat and muffler just in case I needed to open part of it up to improve the airflow. Well it turns out I did have a heat issue but it wasn’t a problem with it radiating through the floor like I thought it might be (it’s warm but not much more than it used to be.) Instead the issue was the transmission handling the trapped heat.

A couple weeks after getting the skid installed I was hauling a mattress set on the roof while driving on the freeway. I was rocking about 75 mph up an incline just steep enough that the trans was shifting back and forth trying to decide which gear it wanted to be in. All of a sudden, I look back and I’m puking grey smoke and a lot of it. It scared the heck out of me. Still, the motor sounded fine and I was only a few miles from home so I slowed way down threw on the hazards and limped it in.

Upon investigation the bottom of the Jeep from transfer case back was coated in a film of red oil. The smoke seemed to be from the oil that coated the cat and muffler.



Forward of this point everything was dry, which confused me for a while. I started wondering if I’d blow a rear main seal at the driveshaft (red likely meant trans fluid), but despite the yoke being coated I couldn’t find a definite source of the oil. I even strapped a clean paper towel around the yoke since that seemed to be the most likely culprit. A few days later it was still spotless.

I started doing a little digging here on and found a couple threads where folks were talking about a transmission overheat causing it to burp transmission fluid out of the main seal. I know this is supposed to have a breather but I can’t guarantee that mine isn’t plugged from driving on dusty trails.

Anyways, that conclusion surprised me a bit since I do have an external trans cooler but driving up a several mile steady state hill with extra wind resistance (mattresses up top) , the trans shifting back and forth, plus a gigantic skid that was limiting airflow and I seems to have been enough. I don’t even know how big a burp of fluid I lost, but the trans fluid level looked fine (and no sign of water or other contamination.)

It was the best theory I had to go on and since this might have been caused by a confluence of factors I decided to go ahead and add vent holes. BUT since I now wanted to keep the trans in cooler air I added them all the way across instead of just under the cat and muffler. It took ~200 1.5” holes… I dropped 5.5 lbs doing this.






My friends now call it “the cheese grater”. It still seems to slide over rocks just fine.

-Joel

P.S. Troy, thanks for the exhaust pics. It looks really nice. I dig the fact you were creative in looking for what you could recycle while still focusing on keeping it clean, tucked tight, and functional.

Last edited by frijolee; April 3rd, 2012 at 13:55.
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  #74  
Old April 3rd, 2012, 17:12
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Re: Joel's multipurpose XJ build (rocks/boulevard)

thats a lot of holes.

methinks you could benefit from making a deeper pan with airflow holes
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  #75  
Old April 3rd, 2012, 18:00
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Re: Joel's multipurpose XJ build (rocks/boulevard)

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Originally Posted by rockclimber View Post
thats a lot of holes.

methinks you could benefit from making a deeper pan with airflow holes
Yea, and also use something like a B&M 70298. Place it in a good spot and it will help to keep the AW4 high temperatures in check.

Great build,...plenty of attention to details. Every thing come together pretty like a painting by an experiance artist. How come I am not that creative?,...
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1996 XJ; 4.0L; AW4; NP231; SYE; D30 and D44; ECTED; 4.10 gears; 30X9.5 -15 BFG/AT/KO; 3" lift; Rusty's LCA; JKS ADJ UCA; Kevins ADJ Track bar; Drawtite Front Receiver; Dual Electric Fans; Dual Battaries.
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