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  1. #1
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    Lower Unit Oil Leak: Fix with Epoxy?

    After taking my modded XR6 gearcase out of storage yesterday to install it on my boat, I realized that it was leaking oil, and there was a bubble on the side where the oil was leaking from. I bought this gearcase back in October of last year from a S&F member as a freshly built unit (billet carrier/ cut down SM gears, etc.), and I noticed when I got it that it had a small bubble on the side, with a small trace of gear oil, which I assumed might have been from a very slight leak where the original oil drainplug was (I actually have no idea where that would be), and the leak was caused by the drop in air pressure in the cargo hood when it was air-frighted to me.
    I contacted the vendor and was assured that the unit was solidly built and sound, so I put it in storage until I was ready to use it.
    Now, yesterday when I took it out to cut a slot for the shifter linkage and to fit the 12” adaptor plate on it, I noticed oil on the side of it and saw that the bubble was much bigger, so it’s obviously been leaking just sitting in the box.
    I used a screwdriver and ripped the epoxy bubble open and it was saturated with gear oil (you could smell it too) and I scraped it down to the aluminum underneath (it came off easily), but I can’t see any leak, so it must be small.
    I’m thinking of putting some low air pressure inside the case through the air vent and see where that pushes oil out, to figure out where the leak is.

    So, here’s my question:
    If there is a small pin-hole or crack in the case (it has some pretty deep gouges in the aluminum from a grinder), can I repair that with a good epoxy? If so, what works best, in terms of strength and being impervious to oil seepage?
    Or do I need to get it welded? If so, can I take the chance to have it professionally welded while it’s still together?
    Can’t believe I’m having to do this sh!t after what I spent on this unit.

  2. #2
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    The hard part will be getting the area totally oil free for epoxy to stick or even weld to stick. Would try epoxy first, grey Marine Tex or Belzona would be first choices on epoxy.

    Dave
    1980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
    1988 BAJA Sunsport 186, 96 225 Pro Max
    79 12' Auminum, 95 Merc 9.9
    RIP Stu
    "So many idiots, so few bullets"

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  4. #3
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    Thanks. I’ll drain the oil and would clean everything good with acetone to make sure there’s no oil residue.

  5. #4
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    Quote Originally Posted by Dave Strong View Post
    The hard part will be getting the area totally oil free for epoxy to stick or even weld to stick. Would try epoxy first, grey Marine Tex or Belzona would be first choices on epoxy.

    Dave
    JB WELD i works good has never failed me. fixed a large case hole,worked great.

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  7. #5
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    Quote Originally Posted by KIRCHNER View Post
    JB WELD i works good has never failed me. fixed a large case hole,worked great.
    I actually already have some of that in my garage. Have always had good results with that too.

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  9. #6
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    Here’s what my fancy $3800+ XR6 L/U looks like under the three layers of filler, not sure whether it’s all epoxy, and/or Bondo and fiber-strand/filler… The green chunk is the bubble that lifted off.
    Click image for larger version. 

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    Note the puddle of oil that seeped out overnight.

    Click image for larger version. 

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    I pressurized it with low air pressure and sure enough oil started to leak out. It’s leaking in two spots where it was welded to fill in the original water pickups. One looks like a hairline crack in the welding, and the other is a bubble or pinhole in the weld. The crack leaks a pretty significant amount of oil when you put just a little air pressure in it, so that’s the main problem. It’s pretty visible when you look at it up close too.

    Here’s a close-up, with the two problem areas circled:

    Click image for larger version. 

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    Last edited by CI STV; 08-03-2021 at 08:17 AM.

  10. #7
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    I bought a big pack of JB Weld today. I’m hoping that it will hold and not allow any oil seepage.

  11. #8
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    ...time for a new housing...

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  13. #9
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    3800 for a coned xr lower unit??
    The epoxy might be enough to stop the leak
    Probably cracked from having water freeze in the pickup cavity
    Should fill that cavity with epoxy also


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  15. #10
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    Quote Originally Posted by FUJIMO View Post
    ...time for a new housing...
    Really? Sh!t! I haven’t even run this one yet. The guy I bought it from says he does them all the time for a bunch of big name racers, and that this one was was freshly built and never run. I guess that means it wasn’t tested too. There’s no such thing as a new housing with these things anyhow, is there?

  16. #11
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    Quote Originally Posted by Aaronhl View Post
    3800 for a coned xr lower unit??
    The epoxy might be enough to stop the leak
    Probably cracked from having water freeze in the pickup cavity
    Should fill that cavity with epoxy also
    Yep, it has a billet carrier and cut down SM gears, supposedly. It actually cost me $4250 with overseas air freight and then 27% import tax, so I have like $5,400 invested in it. So, yeah, I’m p!ssed about this.
    I’m not sure what cracked it, but there’s no way it should be leaking oil, since it was professionally built. The cavity appears to be welded up and the two leaks are in the welded area. I have no choice to try to epoxy it and hope that it holds.

  17. #12
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    Can I assume that case will be run in saltwater? Grand Cayman can't have fresh water big enough to run fast boats in?

    A bondo conned case in saltwater will be a never ending maintenance job. It will just keep bubbling and peeling and popping chunks. Epoxy will last a little longer but water will still eventually get behind it and pop chunks loose.

    I don't think you'll have much luck trying to seal those leaks with any type of epoxy, jb, marine text,. I might still try though if I couldn't get access to a competent welder.
    Give them a slight v grind and put the case under a slight vacume to help draw the epoxy into the crack, after you clean, clean, clean, then clean again.

    Down side is if this doesn't work it will make it a much bigger nightmare to weld later on.
    ANTI40​It's just an idea.

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  19. #13
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    There are products that will seal that leak. Seals all comes to mind and I’m sure there are others. It’s not any kind of epoxy nor does it have strength but it will stop the leaks.

    if it were mine I’d find someone with a spool gun and start laying in tacks and pressure test til it was leak free. Grind as little as possible to allow for fairing. Pressure test again to ensure it’s still leak free and then use epoxy over it. I haven’t had a lot of luck with regular jb weld when submersed. The marine jb weld works well but it’s approx 1/3 the strength or marine Tex which is excellent product in my brief experience with it. Holds strong and fully water proof.

    if the welder option is off the table if so some testing on scrap aluminum with seals all and epoxy over it and test for bonding. This way you get the leak sealed and hopefully the epoxy over it for strength.


    I have no skin in this game so I cannot comment on the build quality but those imperfections would be easy to miss during fabrication. Maybe a pressure test would have indicated these leaks but only if there was lube in it. It’s doubtful that a dry pressure test would have revealed that leak.

    I used this on a damaged transfer case on my plow truck that was leaking a steady drip. I smeared it on and filled it because snow doesn’t wait for repairs. It’s been three years and it’s still not leaking

    Click image for larger version. 

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    Hydrostream dreamin

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  21. #14
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    Many thanks, folks.
    Yes, it is going in saltwater, although only for short periods, since it’s a single seat race boat that I’m setting up for drag racing.
    That Seal-All stuff is something I looked at yesterday when I picked up the JB Weld. Good to know it works.
    I’m going to see if I can find a competent welder around here, but my worry is that when they try to “fix” it, they f@ck it up worse than it is. There’s a guy around here that welds leaky radiators and I got him to patch a hydraulic oil cooler on an excavator before and that worked. If that doesn’t work, I’ll try the epoxy.
    I know these flaws may have been hard to spot with the naked eye, but when you’re selling parts to racers, and you’re welding on an aluminum case that obviously needs to be leak-proof, I would expect at least a vacuum or pressure test after it’s assembled.
    I already have an old JC coned XR6 that was built in the 90s that doesn’t leak, and I stupidly opted to buy this unit because it was advertised here on S&F as a newly built unit, rather than rebuilding the old one.

  22. #15
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    Hard to see how thick that bondo is but maybe weld an aluminium plate over it?
    Because they might have gone overboard with the grinder with multiple thin spots!
    I thought the cayman islands where suppose to be a tax evasion paradise!?

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