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Thread: Rear subframe reinforcement. Weld vs. Epoxy

  1. #26
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    I'll fuel the fire:
    I'm doing this job now. Last night was welding, tonight is grinding Tomorrow night will be painting and cleanup. Saturday will be re-assembly and if all goes well the car will drive Sunday. I would have MUCH rather been able to epoxy last night... quick cleanup tonight and have the car back and driving by tomorrow night or Saturday worst-case.

    I wonder how many e36 owners have had subsequent cracks/issues due to poor welding? Welding is an art, not a science. Epoxy is a pretty K.I.S.S. with a X:X ratio of hardener to resin. Some even self-mix. Both bonds get out what you put in --meaning prep work is similar with welding and composites work.

  2. #27
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    Does NZ or Australia have guerilla glue ?
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  3. #28
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    Yea, But we only get the Gorilla variety..imported some guerrillas from south america to rebuilt build my cars interior in 2014, still have their glue left over, but the blacks windscreen sealant works better I hear.
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    Last edited by MisterM52; 06-21-2019 at 08:10 AM.
    "So we've come to the conclusion that BMW just has parts laying around they decide to throw on cars for no reason."

    Interest on a Very Budget Supercharger Build??



  4. #29
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    M52, are you old enough to remember the titanium Russian subs?

  5. #30
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    I know where you are getting at but that was military grade stuff, not the off the shelf wall mart consumer commercial stuff you and I can buy and far from the 3M stuff as well.
    "So we've come to the conclusion that BMW just has parts laying around they decide to throw on cars for no reason."

    Interest on a Very Budget Supercharger Build??



  6. #31
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    Thank you, your position is quite clear.

    OP,
    The schmucks at Dow sell a range of products branded betamate to the schmucks at jaguar, Audi, BMW, Opel, etc to do exactly what we are talking about. I'm not sure if this technology is available to the shade tree mechanic, or appropriate in this application, but certainly worthy of more research and consideration.

    When welding was groud-breaking, the same arguments were used when compared to riveting.

  7. #32
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    I welded mine on my e46 and clutched dumped and beat the piss out of it with no issues... you don't just weld the outline your also weld rossest in each place.

  8. #33
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    For what it's worth, the front plates on my E46 are metal-epoxied in place. They have survived 2 years and 30k miles of a welded diff and solid aluminum bushings.

    The reason epoxy/JB weld works in this situation is because the plates are only in compression, no tension or shear stresses. Anyone who speaks out against this solution is just guessing it won't work. I guarantee they haven't actually seen first-hand that it will fail.

  9. #34
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    Quote Originally Posted by MisterM52 View Post
    I dont think you could find a single person in NZ or Australia who would put these on using any kind of Epoxy.
    I've spent a decent amount of time in Auckland (RNZYS) over the years and I'm pretty sure I could dig up a glue head Kiwi or three on your North Island that would try to epoxy a lubed condom on their d**ks if they thought it would make them last longer. No idea about Aussies, they are a different breed all together.

  10. #35
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    Weld vs epoxy? I have seen many poor welds fail (and cause additional problem when done wrong) and many improper epoxy fail too. Has anyone flown on an airplane recently? Anyone buy a modern bike. Epoxys are used everywhere. Even on new cars. The trick is to have the dissimilar material stay bonded under the stress they are placed under.



    Automakers are using more aluminum and exotic composites, which cannot be welded together but have to be glued with adhesives that will not lose their strength and can hold together parts even at top speeds and high pressure
    http://www.autonews.com/article/20130617/OEM01/306179993/automakers-spread-more-glue-to-eliminate-weight-rattles

    Just do it right...
    While analysts predict the amount of glue used in new cars will grow by more than a third in the next 5 to 10 years, the report also calls out the dark side of cutting edge construction techniques. For instance, the 2010 Ferrari 458 Italia had a notorious tendency for spontaneous combustion, which turned out to be a result of a melt-prone glue used to adhere heat shields to wheel arches.
    Ferrari's solution? Good ol' fashioned metal rivets.


    Last edited by gc325is; 02-27-2016 at 07:34 PM.

  11. #36
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    Quote Originally Posted by gc325is View Post
    Just do it right....

    [/URL]While analysts predict the amount of glue used in new cars will grow by more than a third in the next 5 to 10 years, the report also calls out the dark side of cutting edge construction techniques. For instance, the 2010 Ferrari 458 Italia had a notorious tendency for spontaneous combustion, which turned out to be a result of a melt-prone glue used to adhere heat shields to wheel arches.
    Ferrari's solution? Good ol' fashioned metal rivets.

    http://www.autonews.com/article/2013...weight-rattles
    Although some are loath to admit it, a fair amount of automotive development is advanced through trial and error. I once had the directory of safety engineering at a European automaker storm off on me after I asked him how they addressed that in their supercomputer modelling.
    Last edited by johnf; 02-28-2016 at 03:25 AM.

  12. #37
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    most body shops use 08115 (panel bond) to replace and or supplement welding on body panels, im a bodyman i would be lost without panel bond. not sure id use it for anything more than body work though

  13. #38
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    Anybody that says epoxy isnt as strong needs to explain and then go tell nasa...

    I can show you pictures of bad welds also, but epoxy is stronger than any part you will find on a bmw. I have the same question. I had an engineer do it on my z3 in 2 spots and all but 1 weld has held. If you don't have a degree or a high understanding of work like this, don't just spit out responses. Rivets and epoxy will be far better than welds. Or call nasa and tell them they are wrong. Or show me the math. Welding is cheap, that is why it is done.

  14. #39
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    I am an engineer (Probably not a good one, but whatever) and reading through this thread has been interesting to say the least. There are some good points and the assumptions are fairly reasonable. Epoxy like they use on the Lotus ect, is not off the shelf stuff, it costs $150 a tube and I know that because I am looking into fixing a friends Elise race car. So as far as cost goes, welding is far cheaper than acquiring the proper adhesive. Welds are rigid and hands down WAY stronger than epoxy given an equal area to compare. Where the epoxy shines is when you have large surface planes mating. For instance, you have two piece of sheet metal with a 6" overlap, you can weld the two pieces at the ends, and even spot weld the mated plane, but you will never get to the level of strength the epoxy will provide over the 6" wide mated surface. This is not a question of "What is better" its more of a when and where to use these different materials and practices. For reference, I would never epoxy the sub frame, epoxying reinforcement plates? Sure, why not? Seems like a good application for epoxy, lots of surface area, probably does not need to be epoxied or welded to function but its not going to hurt. One last thing to think about, fatigue. The lotus epoxy stays kinda rubbery, its like a shore 60 urethane when dry, if the adhesive is rigid on flexing materials, the bond wont last long. You need to sit down and do some real math to understand exactly what mechanical forces are going to be applied to a part, how much strength the adhesive has, and how much surface area there is available for the bond.
    Last edited by FiberFast; 06-15-2019 at 10:44 AM.

  15. #40
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    I did the epoxy on my E36 328 1997 with 260,000 miles driven in the rust belt. That was back in 2017.
    One ear on the subframe broke and when I removed it to replace it I noticed that most of the spot welds around the threaded subframe bolt holes were rusting. The worst being the same referred on the E46 threads, I think it is front right but don't quote me.

    Have been meaning to do a DIY but life keeps interfeereing.
    The previous post is spot (!) on. In compression over large areas structutal epoxy is far superior to welding provided you do the prep work correctly. You have to read the 3M specifications. That stuff has a dozen restrictions and very specific prep that requires chemicals you never used. Mek comes to mind. I used 3M Scotch-Weld Epoxy Adhesive DP420 Black.

    If the metal is cracked you should weld the crack first. If you are there with the welder and the person welding is competent, weld the plates while you are there.

    If you do not understand the surface prep document do not attempt it. If you miss the surface prep it will fail. The following link is a download from 3M:
    https://multimedia.3m.com/mws/media/...s-dp420-lh.pdf

    It is much longer than simply welding the plate. If you have time, a techy side and time, by all means go for it.

    I tracked the car last week and when I inspect the plates they look like they were installed las week.
    Be careful. The product has a one year shelf life...
    Last edited by Franky goes; 06-20-2019 at 12:12 AM.

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