Motor mounts from stock shackles

[Vanimal]

Yall are trippin. Just because there's room doesn't mean it needs a gusset. 1.5" square tube that stands less than 1.5" off the base, and it needs to be braced? Guess I should have machined it from a solid block. The stock block bracket will break first.

Quick, tell this guy his v8 is going to fall out the first time he starts it up:
http://www.naxja.org/forum/showpost.php?p=245598654&postcount=8

don't post your crap up if you're going to get butt hurt when you get an opinion. nobody said it was junk, we were just offering a suggestion.

you're obviously new to fabricating, we are not.

 

[souske]

Whatever dude, run em. It really doesnt matter to me, as long as I am not on a trail run with you when they break. Not a fun trailside repair.

 

[Vanimal]

the issue is not the up and down support of the square tube, it's the side loading that is only going to be supported by the welds. as the motor twists it's going to attempt to push the round section sideways off the top of that piece of square tube. an angled brace would help to keep that from happening.

There is a reason nobody else's motor mounts are built the way you built that one. much better than your first attempt but it really should have an angled brace on it as stated above.

this is exactly the issue, if you look at the link that you yourself posted, the tubes in his motor mounts are basically tangent to the rotation of the crank, so that they have to do very little work to handle it. yours are more perpendicular to that plane, making the welds and tube do all the work.

 

[srimes]

This makes sense to me, and is what convinced me to try again:

Geometry, mostly. If there is much sideways force on them (cornering and hitting a pothole, wheeling) the vertical pieces of metal will bend. Since you have both tipped the same way, even the weight of the engine combined with a rough road will flex the vertical pieces, even if it isn't enough to bend them, repeated flexing will fatigue the metal until they break loose.
.

the issue is not the up and down support of the square tube, it's the side loading that is only going to be supported by the welds. as the motor twists it's going to attempt to push the round section sideways off the top of that piece of square tube. an angled brace would help to keep that from happening.

There is a reason nobody else's motor mounts are built the way you built that one. much better than your first attempt but it really should have an angled brace on it as stated above.

Engine torque will mainly load the mounts vertically, as I understand it. There are side loads, fine, that's why I redid it. So what is going to fail? Kastein explained on the last ones: upright plates flex and fatigue. These new ones are boxed. So now tube can't take any cantilevered forces? Welds can't handle any shear? Come on. One could make the argument that the tube I used is too small or too thin, but that isn't what you said.

this is exactly the issue, if you look at the link that you yourself posted, the tubes in his motor mounts are basically tangent to the rotation of the crank, so that they have to do very little work to handle it. yours are more perpendicular to that plane, making the welds and tube do all the work.

Think you're confused about the force directions. Plus his are stressed supporting the engine vertically, and they are much longer (3x or so) so will see much more stress at the base of the tube.


I can take criticism and admit when I'm wrong. But you have to explain or prove it first, and no one has done that yet concerning the new mounts.

 

[Vanimal]

This makes sense to me, and is what convinced me to try again:







Engine torque will mainly load the mounts vertically, as I understand it. There are side loads, fine, that's why I redid it. So what is going to fail? Kastein explained on the last ones: upright plates flex and fatigue. These new ones are boxed. So now tube can't take any cantilevered forces? Welds can't handle any shear? Come on. One could make the argument that the tube I used is too small or too thin, but that isn't what you said.




Think you're confused about the force directions. Plus his are stressed supporting the engine vertically, and they are much longer (3x or so) so will see much more stress at the base of the tube.


I can take criticism and admit when I'm wrong. But you have to explain or prove it first, and no one has done that yet concerning the new mounts.

we did explain it. if i cared enough to prove you wrong i could model it up in solidworks and run cosmos on it to give you real numbers, but i dont have that kind of time.
The forces are rotational, not just straight up. think of a ratchet or a come-along, it doesnt matter where the pawls are, it maters how they're oriented. look at the tiny pawls on a ratchet, they are miniscule. but they take the forces of people putting hundreds of ftlbs of force on them because the way they are positioned. the way he has the motor mounts on the 5.3l MJ are directioned to take the force of rotation. yours are not.

 

[souske]

I guess the fact the factory, Brown dog, MORE, and Jeeperjohn all thought it was important to address this would be enough explanation for me. Oh well, Im just a guy with a jeep, none of that fancy book learnin' to tell me your design will work well.

 

[srimes]

we did explain it. if i cared enough to prove you wrong i could model it up in solidworks and run cosmos on it to give you real numbers, but i dont have that kind of time.
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The lever arm from the bolt to the base of the upright tube is 2", and that's ignoring the side of the bottom channel. Not a long lever arm.

If you did run fea on it you'd see that it's plenty strong. If the numbers show otherwise I'll buy you a 6 pack.

The forces are rotational, not just straight up.

How much rotational force will transfer through that single bolt and bushing? Practically 0.

 

[souske]

Rotational in respect to the crank centerline

 

[Vanimal]

Rotational in respect to the crank centerline

this.
think beyond the motormount, grasshopper.

 

[zebvance]

3 bolts isn't really that much to hold the mount on, and they're in a stupid pattern. That's my opinion on it anyways...

For what it's worth, I've wheeled multiple jeeps with only two bolts in the passenger side, and the only time I've broken the mount off the block is when I got super bad deathwobble in my stock MJ doing about 50. By the time I got it to stop wobbling the mirrors weren't pointing the right direction, the steering wheel was no longer centered, the tires had scrub marks on them, and the passenger side motor mount bracket had torn off the block. Scared the hell out of me.

Puts a Whole now meaning to DEATHWOBBLE. I would poop myself. Im glad I still dont have it in my mj. I need to replace my tie rod ends, but Im afraid to because I have heard of people replacing stuff that needed attention and creating death wobble.

 

[zebvance]

Sorry for the Off topic post above btw.

Any way I just got my iron man mounts and I truly feel Like the are the best design out there. Very solid on every side. The use thicker steel than the brown dogs and they have way more support bracing on every side. I can see why andy has a lifetime warranty on them now. After buying these I will never have to buy new ones again. And when it comes to replacing motor mounts, Its a job I want to do right the first time and never have to touch them again.

 

[zebvance]

Pure Beef. 1/4 plate

 

[souske]

Looks nice. Does he offer a rubber version?

 

[zebvance]

Yes

http://www.ironman4x4fab.com/Jeep_Mo...nts/XJ_MM.html

After several years of Building super tough motor mounts we decided to build the toughest!
As with all of our products our mission is to provide the absolute toughest parts available. We are continuing this With the new 4.0 Monster Mounts

-They are designed for all XJ, MJ, YJ, And TJ applications with the 4.0 Engine.

-These mounts are built with a 1/4" lift to relieve drive line angles without affecting clearances.

-Laser cut from high tensile 1/4" steel and precision formed for absolute accuracy.

-CNC Machined, Dom tapered bushing sleeve, (no cheap rolled sleeves like the other guys that split and wear.

-Fully precision pulse welded construction for flawless and unmatched strength.

-88 Durometer Poly with progressive pre-load for unmatched poly life and much smoother operation than most poly MM kits.

-All mounts come with grade 8 hardware, locking fasteners, and a black powder coat finish.

-I guarantee these mounts for life! http://www.ironman4x4fab.com/warranty.html

-These mounts are designed for all types of racing and high horsepower applications. They also work fine in stock applications to replace floppy stock mounts.

Check them out here at our site: http://www.ironman4x4fab.com/Jeep_Mo...nts/XJ_MM.html

 

[zebvance]

Accidentally no I, I got his uca and lca's bushing offers with these sorry. Here is the link thought.
http://www.ironman4x4fab.com/Products/MM.html

 

[kastein]

I would run your latest fixed version. Looks pretty ok to me, the stock ones are certainly weaker. I would probably put gussets on because I think it looks better and is obviously a bit stronger, but as long as your welds are good I wouldn't worry at all about what you have now. Especially since it looks to me like you used c channel as the baseplate.

Edit: fwiw I think I already did say something about those 5.3 motor mounts. I worry about 1. The way the plate he attached the DOM to is butt welded onto the stock sheetmetal frame brackets and 2. What happens if he airs it out? That's pure downforce not rotational force and will kill those mounts without a crossmember under the engine tying them together.

 

[srimes]

Thanks for your input.

The base is 2" tube (1/4 wall) cut in half to make channel. The top of the channel to the bushing sleeve is only about 1/2 inch.

I think the welds are OK. I'm still new at it and I'm sure it could be better, but I think I burned them in pretty good (miller syncrowave 250).

I agree on the 5.3, especially because the mounts are long. Orientation matters too.

 

[Darky]

Thanks for your input..

Three other people give you advice on how to make them even better and you complain and discount them for not knowing anything (even though one of them works with metal for a living...) and then you get one compliment saying they're good how they are and that's what you go with? I mean, kastein knows his stuff, but so do Vanimal, Grimm, and souske.

 

[srimes]

Three other people give you advice on how to make them even better and you complain and discount them for not knowing anything (even though one of them works with metal for a living...) and then you get one compliment saying they're good how they are and that's what you go with? I mean, kastein knows his stuff, but so do Vanimal, Grimm, and souske.

Kastein explained WHY my 1st attempt was flawed. I respect that. Vanimal and Souske impressed me as not knowing what they were talking about, and wouldn't go into detail. Maybe they have made stuff that works. Great. But if they can't explain why something won't work I can't learn much from that. Grimm I respect. Don't understand his reaction as he didn't expand much. My impression is he briefly looked at it and thought it looks different, and didn't bother to look closer.

I'm not looking for popularity. I want to understand reality. Explain the flaws with concepts, models, or examples. I'll listen. I admit when I'm wrong. In my first attempt (using the shackle) I somewhat copied popular aftermarket designs. I recognized that it was weak containing sideways forces, but figured it was ok as it was a common design. When Cal showed the failed aftermarket piece that was the first I had seen or heard of, and Kastein explained why it happened. So I made a new mount with a new design.

I'm not a mechanical engineer, but I am and engineer. Went through statics and mechanics of materials. I understand the basic concepts. Not all that experienced in the Jeep world; do deal with real world material stresses. I work in manufacturing. Ever see 2" square solid steel fail? I have. Multiple times. And that was only holding up about 5000 pounds. Had the steel examined and its properties looked quite good. Never should have failed, but it did. I understand the difference between theory and reality. So show me examples. I'll listen.

Just saying, "That isn't the popular way to do it. It'll fail," doesn't convince me. Tell me why.

Anything could be stronger. Doesn't mean it needs to be. Brown Dog mounts don't fail. I think my mounts are stronger than Brown Dog's. Tell me why they aren't. I'm listening :smoker:.

 

[GrimmJeeper]

it's not that I didn't bother to look closer, I don't need to. the mounts are subject to rotational forces from the torque applied by the motor on the mounts, this is why the stock mounts fail the way they do (disintegrating the rubber on the drivers side moreso than the passenger side). The problem with your mounts is you are relying entirely on the strength of the metal that was added with your weld and the bond between the two surfaces to deal with this force. There is more going on than just gravity pulling the motor straight down. I would expect to see your mounts crack the welds where the riser meets the bushing sleeve eventually. It may not happen now, or soon, but it most likely will happen. I'm just trying to save you some more work down the road.

Triangles are strong. this is the basis of all fabrication work. take a tennis ball and duct tape it to the end of a stick and wiggle it around. I don't care how short your riser is it is still subject to the laws of physics. You seem set on your current design so all i can do is applaud you for having the guts to try something new. Just a word of advice for your next project if you are going to ask for advice maybe try drawing it up on paper first before making the actual part, it may save you some time and headaches later.