Advice On How To Tig an Aluminum Engine Block

  1. schunter1969 Member

    Messages:
    15
    Location:
    USA, Carolina
    Hello I am rebuilding a 1989 Yamaha 115HP Outboard motor. When I was taking the motor apart I removed a bolt 1/2" in diameter 1/2" in length. When I removed the bolt the raised insert that the bolt threads into broke apart on one side (see pictures). It's considered a "plug" the hole is used for mounting a brass fitting with a nipple to run tubing from the motor to a pressure transmitter. This is only done when trying to diagnose a cooling issue. Outboard motors are water cooled, the foot of the motor has a small impeller the sucks water and pushes it through the engine block and then the water spits back out into whatever water the boat is in. In all my years working on boat motors I have never had to do this. To confess I should have never taken the plug out, I was just working away unbolting everything from the block.

    The rest of the block is great, the sleeves just need honed. So I am trying to save it. My plan of attack is take a solid aluminum rod, cutting it to 1/2" in length, and welding in place of the bolt. I still have the broken part of the raised nipple. So I plan on just putting it back into place and welding everything together.

    I have a Linde Heliarc 250 HF welder. I know I will have to prep the welding surfaces, preheat the block, and weld in small increments as to not over heat the block and cause further damage.

    What material should the solid rod be, 4036 or 5052 Aluminum? Pure Tungsten electrode? 4036 or 5052 filler material?

    Any advice is welcomed.
     
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  2. slim_boy_fat

    slim_boy_fat Forum Supporter

    Would something like JBWeld do the job, or is it under too much pressure when in use for diagnostics? :dontknow:
     
  3. schunter1969 Member

    Messages:
    15
    Location:
    USA, Carolina
    At full throttle it will have 12 psi but lets say 20 psi to be conservative. Its going have some heat going across it and I do not think jb weld would work forever.
     
  4. henry Kadzielski Member

    Messages:
    300
    Location:
    Australia Wollongong
    .

    Good morning schunter1969. This is cast but should be good material and can be welded with a mig. Clean up the surfaces wash with acetone, you can also grind out the threads and just weld it from there. There is no reason that you couldn't redrill, tap and put the plug back in after the welding. I would use a good pulse mig start inside the hole and work your way out. Dosn't seem too difficult from what I can see:thumbup:
     
  5. dobbslc

    dobbslc Member

    Messages:
    1,966
    Location:
    Hertfordshire UK
    If it's a multi cylinder engine do the other cylinders have the same test port? If so you could then just fill it with weld and use another port for pressure testing as the cooling system would be running at the same pressure throughout I would think.
    I'm not boat expert though but have " fettled " a few Yamaha two strokes in the past!
     
  6. gt6s Member

    Messages:
    378
    Location:
    Newtownards Co Down Northern Ireland
    You could TIG the hole up completely then even re tap if you felt it necessary.

    Laurence
     
  7. Brad93

    Brad93 M J B Engineering

    Messages:
    2,134
    Location:
    Essex
    You wont overheat it with 250 amps, give it a bit of preheat, 50-100 degrees c just to get the arc going a bit easier. Id
     
  8. Rig Pig

    Rig Pig Member

    Messages:
    2,407
    Location:
    Narrwich! U.K.
    Looks like they is enough meat there to re-tap without welding, if it's just a test port you could put a reducing bush in to leave a usable but smaller port.
     
  9. addjunkie

    addjunkie Forum Supporter

    Messages:
    1,902
    Location:
    Northumberland. Reet oot in the sticks
    You could also fix that with devcon or belzona plastic metal type products then drill and retap ive done a few water cooled dirt bike motors in the past.
     
  10. schunter1969 Member

    Messages:
    15
    Location:
    USA, Carolina
    @addjunkie I have been reading about belzona. Do you think I could just put a bunch of Belzona in the hole, reinsert the bolt and broken pieces, and then put Belzona inside the small channel before the plug hole to completely seal it? I saw that it can be sanded down and painted so I could make it look pretty decent. Would I have to worry about a piece of it breaking off in the water channel? I do not believe this would affect the cooling. See picture
     
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  11. Richard.

    Richard. Member

    Messages:
    11,526
    Location:
    Hertfordshire.
    I have repaired lots of little parts like that and more often than not the tiny piece that's broken off isn't worth faffing with.
    I'd build that up with 4043 filler rod re drill it out the next size up above the existing thread and re tap a brand new thread for a new bolt. Take your time with files and you'll get its shape back perfectly.
     
  12. RichardM Member

    As above and get the gasket surface skimmed as it will distort when you weld it.
     
  13. Done loads of stuff like this, no need to bother with pre heat. just take your time and build it up a bit at a time
     
  14. addjunkie

    addjunkie Forum Supporter

    Messages:
    1,902
    Location:
    Northumberland. Reet oot in the sticks
    With belzona i would just build it up as Richard describes with weld, file it up, re drill and tap. Id put a bit of tape or somethin to stop it going inside. Or file it off once set. But if you have ac tig..thats exactly whats its for
     
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