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Thread: Plenum repair

  1. #1
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    Plenum repair

    Any of you guys have done a plenum repair on a car? I need to graft a donor piece into my rusted out plenum.Name:  20210821_111028-min.jpg
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  2. #2
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    Re: Plenum repair

    get your replacement part first and look at it and see which way is the easiest to fit and trim it to yours.
    lincoln 125sp
    dayton 250 ac/dc
    miller 211 w/spool gun
    ahp 200 sx tig
    lotos ltp5000d
    kubota b3200 FEL BH
    of course duramax diesel

  3. #3
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    Re: Plenum repair

    You can't weld in a replacement unless it reaches beyond the rusted out area. I have concern you will have to attempt some portion on rusted out stuff, that won't work.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

  4. #4
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    Re: Plenum repair

    240/260z ?
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  5. #5
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    Re: Plenum repair

    Quote Originally Posted by duramax-rob View Post
    get your replacement part first and look at it and see which way is the easiest to fit and trim it to yours.
    I think the third photo is the replacement?

  6. #6
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    Re: Plenum repair

    might want to replace it at windshield post and rocker and make panels to cover rest of floor. and any other rusted out parts on replacement part. might be easier also. if it is a datson z those were rust buckets.
    lincoln 125sp
    dayton 250 ac/dc
    miller 211 w/spool gun
    ahp 200 sx tig
    lotos ltp5000d
    kubota b3200 FEL BH
    of course duramax diesel

  7. #7
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    Re: Plenum repair

    I was thinking of tacking the donor to the vertical piece in front of the windshield pinch weld. Only problem is I dont see how I can get that seam water tight. Even brazed I think water could get in the seam. Water would get into the plenum which is no biggie, just a rusted joint issue.Name:  donor (2).jpg
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  8. #8
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    Re: Plenum repair

    If you can get to clean material where the weld will be free of rust; choose your cuts. I want a butt weld everywhere, except where the manufacturer used an overlap with spot welds. There, drill out the spot welds.
    Take your time, use progressively more precise tools to cut. Your goal is to have a fit with a hair width or less.
    I'd then be torn between a gas weld & a TIG weld on steel butt welds of 20 gauge or so.

    Again, if you hope to weld rust, all bets are off.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

  9. #9
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    Re: Plenum repair

    Sealing isn't a big issue. The big question is how much you have to replace to be working with all good metal again. If you need to seal it up after spot welding, you can coat the gap with 3-M seam sealer or give it a layer of fiberglass if it isn't visible after assembly. If it does show, go over the fiberglass with a skim coat of bondo and finish as you would any other body work. That's a uni-body car. The rust isn't just affecting appearance, it's affecting the strength and integrity of your car's chassis... keep that in mind when inspecting it for rusted components.
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  10. #10
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    Re: Plenum repair

    Quote Originally Posted by whtbaron View Post
    Sealing isn't a big issue. The big question is how much you have to replace to be working with all good metal again. If you need to seal it up after spot welding, you can coat the gap with 3-M seam sealer or give it a layer of fiberglass if it isn't visible after assembly. If it does show, go over the fiberglass with a skim coat of bondo and finish as you would any other body work. That's a uni-body car. The rust isn't just affecting appearance, it's affecting the strength and integrity of your car's chassis... keep that in mind when inspecting it for rusted components.
    & don't be afraid to put a backer plate behind a particular strength important joint. You can successfully weld a wider gap with a 2" wide backer plate on the side you can't see. Still don't want a sheet metal butt joint more than 3/32". First drill a series of holes in body metal along the edges of the backer to plug weld there. Be thorough with the seam sealer to keep water out.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

  11. #11
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    Re: Plenum repair

    you will have to butt weld the joint where you think you will have a sealing problem area. that to ensure that you have the same thickness uniformity as original. like where the windshield sits but just below you can lap weld or butt weld with backer plate.
    lincoln 125sp
    dayton 250 ac/dc
    miller 211 w/spool gun
    ahp 200 sx tig
    lotos ltp5000d
    kubota b3200 FEL BH
    of course duramax diesel

  12. #12
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    Re: Plenum repair

    Its really a tricky proposition. This is not a 57 chevy where you can buy every part. This is a rusty jap car, plenum not available. In a perfect world i would replace the whole plenum but......the pinch weld is perfect and its acting like a tie beam. So i was thinking of putting the complete donor plenum over the existing plenum. Sounds dumb but i think it could work and be strong.

  13. #13
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    Re: Plenum repair

    Quote Originally Posted by johnfin View Post
    Its really a tricky proposition. This is not a 57 chevy where you can buy every part. This is a rusty jap car, plenum not available. In a perfect world i would replace the whole plenum but......the pinch weld is perfect and its acting like a tie beam. So i was thinking of putting the complete donor plenum over the existing plenum. Sounds dumb but i think it could work and be strong.
    You really need to blast clean this mess to see what is left that you could actually weld to.

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