Highest temp to heat aluminum casting to remove stuck fastener?
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  1. #1
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    Default Highest temp to heat aluminum casting to remove stuck fastener?

    I have a broken starter bolt in a '95 Ford auto trans case I need to remove. I have a nut welded to the end of it and it's been soaking in Kroil for a few days, still no love. The hole is open ended, so I believe the bolt is corroded fast in the tapped hole from road deicer and salt. Next step is to heat the casting to try to release things. It's in a awkward place in a truck and access is limited from underneath, of course. I plan to heat the casting with a torch, and want to use a temp gun to gauge how hot to make it, because I can't just hover my hand over the case to feel the temp and guess at it. If I screw up the case I'll make a major job out of a minor one. Drilling it out would be very difficult because of the location so this is my best hope.

    How hot can I make the cast aluminum case without taking all the strength out of it afterwards? I know certain cast heads have a few hundred degree limit before they loose a lot of stability, is this also the case here? In the past I just heated and estimated by feel, I need some digital data for this job.

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    If heat treated (or naturally age hardened), 350F will start to soften/weaken same.
    Last edited by johnoder; 10-22-2013 at 07:10 PM. Reason: add on

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    Plus, the problem is when it is heated, it's softer. The bolt may pull the threads with it. Can you maybe help it along by rapping it with a hammer? Gently, of course. Might upset it a bit. A friend of mine uses a burp gun, then heats it up and melts bee's wax into it. Seems to help....plus it smells good!
    Lucky me, I've got a tap disintegrator.

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    Thanks guys. I thought it was higher than 350° but I can work with that. I am worried about pulling the threads out with the bolt, but at least that would be better than drilling off center and having half the bolt still in the hole. It's been rattled pretty good, I used a big air chisel to knock the head off the 3/8-16 bolt to get the starter off to begin with. I've never tried the beezwax trick but I hear it's effect is comparable to Kroil. At present it's so tight I have doubt whether anything can penetrate the corrosion to have an effect. I've welded 2 nuts on and twisted them back off so far, so the bolt has been pretty hot - I was hoping that would grow the hole a little, it's always helped in the past in cast iron.

    I have a tap disintegrator too, I just wish it was the size of a pocket knife so I could get it in there to work. This bolthole is far enough up in the truck that when I put the tig torch up in there I almost can't see the bolt to weld onto it and my eyes are so far away I need surgeon's binoculars on the welding helmet. Been thinking about making a drill bushing jig to bolt to the other starter bolt hole and use a 45° drill motor to poke through the bolt with a series of drills. I also find myself fantasizing about flipping the box truck up on it's side with the forklift so I can get to this a little better...

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    When I was heating aluminum heads to put seats & guides in, I wouldn't let the temp get higher than 320*. I was using a thermal oven to heat the whole head also.

    Ron

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    Heat it up (to below 350, I'm assuming) and then toss water on it. Thermal shock should help loosen it.

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    Quote Originally Posted by Sean the Dog View Post
    Heat it up (to below 350, I'm assuming) and then toss water on it. Thermal shock should help loosen it.
    I would modify this by NOT tossing water on it. Spritz water on it. When it sizzles on the aluminum ( like frying in a pan ) turn the nut you welded to the bolt. Worst case is you use a longer thru bolt with a nut on it ( Grade 8 please )

    Ron

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    Standard aluminimum alloy heat treatment tables..... assorted mixes and alloys and combinations.

    All Alloys start going mechanically soft by about 280 - 320*C... maybe a lower critical limit of 250*C for some die casting alloys containing lots of zink etc.

    Stick to ~200*C max.

    You can also heat the bolt right up to a red heat, and let it cool, as that will make it expand fast in the hole and then kind of crack the binding between it and the aluminimum alloy.

    Use the tighten slightly to break the bind technique, before undoing....

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    DO NOT heat that bolt red hot in aluminum. Cast iron-- OK. Not aluminum. too much heat will transfer to aluminum housing softening it.

    Ron

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    Left hand drills to minor diameter of thread try to make sure it is on center if you can get up in there to do it maybe a right angle drill would help. Not the easiest way but it works.

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    just thinking: the hole is open ended, so you might try to heat up the bolt with current from a welder.

    also, try a mix of acetone and atf (3:1) instead of kroil.


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