Highest temp to heat aluminum casting to remove stuck fastener?

Mud · Oct 22, 2013

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.

johnoder · Oct 22, 2013

If heat treated (or naturally age hardened), 350F will start to soften/weaken same.

Ray Behner · Oct 22, 2013

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.

Mud · Oct 22, 2013

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...

ormachine · Oct 22, 2013

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

Sean the Dog · Oct 22, 2013

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

ormachine · Oct 22, 2013

Sean the Dog said:
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

TSI · Oct 22, 2013

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....

ormachine · Oct 22, 2013

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

scojen · Oct 23, 2013

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.

dian · Oct 23, 2013

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.

jim rozen · Jun 9, 2023

Heat gun, not torch.

BOB-OO · Jun 9, 2023

Heat to 300dF THEN spray your choice of penetrant. Hit it with an impact wrench(big) immediately after cooling w spray. Has never failed me. I've had to do it 3x on a rusty jeep, but they all come off.

I use a torch.

Garwood · Jun 9, 2023

I've welded dozens of aluminium bellhousings back together. That's way more than 350 degrees. No problems.

Aluminium needs heat treated so it can be machined. If you spot anneal it it won't hurt the parts integrity.

I would be concerned about heat damaging the front pump seal or valve body seal and That's it. The fluid in the trans should help wick heat away.

I've done the drill guide trick for exhaust manifold bolts and it's always worked good in the end.

Salt sucks!

jccaclimber · Jun 9, 2023

Decade old thread alert. I see a spammer building cred.

boslab · Jun 9, 2023

Cast Ali suffers from hot short, ( I beleive the old timers who named it after shortbread biscuits, least that was the theory of a curator of the British museum, sounds plausible) so when you stick the heat on it is getting more and more brittle as you ramp the heat up ( I did break an important casting once, an ass kicking followed, deservedly btw.
So heat by all means but don’t go thermonuclear on it.
Vibration may be helpful, also reverse forward etc has helped.
I’m inclined to drill the buggers out these days ( if there’s enough meat on the thing) and stuff a helicoil in, they work well, stainless bolts can be used instead, though arguments ensue as the position on the electrochemical series is similar that there’s no benefit on paper but I’ve found they seize less.
Often the shock heat of welding the nut is enough
Mark

john.k · Jun 9, 2023

Her indoors has been researching the melting points of various aluminium saucepans for decades now........I wouldnt care to ask about the documents though .

SIP6A · Jun 9, 2023

Mud said:
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've done this when you can't get the part off and under a spindle. If you can get your drill jig centered on the bolt and a drill up there I think that would be the way to go.

Also could you get a drill in from the other side? Then your drill jig could just be a short 3/8 bolt that you could screw in with a hole through it.

dgfoster · Jun 10, 2023

OK, you are not going to get that bolt out no matter what you do. It is fused in place by galvanic corrosion. I learned my lessons about that when working on my aluminum parts that had SS bolts in them and were for years exposed to seaspray. The nearly one-volt battery established by the aluminum-to-steel contact effectively welds the bolt into the part. If any method you try works, by all means inform us. Cuz, I think it is in there until milled out or dissolved chemically.

Denis

eKretz · Jun 10, 2023

dgfoster said:
OK, you are not going to get that bolt out no matter what you do. It is fused in place by galvanic corrosion. I learned my lessons about that when working on my aluminum parts that had SS bolts in them and were for years exposed to seaspray. The nearly one-volt battery established by the aluminum-to-steel contact effectively welds the bolt into the part. If any method you try works, by all means inform us. Cuz, I think it is in there until milled out or dissolved chemically.

Denis

That ain't no joke. I've told countless people about using antiseize on steel fasteners threaded into aluminum. Most of them ignored me and regretted it later. Just worked on a chipper/shredder that has steel fasteners into an aluminum housing. Half of the bolts had aluminum threads wrapped around them when they came out. Going to have to Helicoil every one of them because someone didn't use antiseize.

And I too believe the necroposter is getting ready to serve some spam. I'm watching you, buster.

Highest temp to heat aluminum casting to remove stuck fastener?

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