Removing stuck ss screw from aluminum

Hi, everybody. Been out of touch for a few weeks due to rootkit trojan on computer and no time to mess with it, so turned off wireless
and let it sit. Just re-staged yesterday. Been building a wooden fence to hide my canoe trailer (bullshit HOA rules).
Anyway, next project is refurbing if possible the trim-tilt unit on my bay boat. This is a 1999 Yamaha 150 hp 2-stroke. Took it to the fixit shop near where we keep the boat (about 200 miles to the coast), their fix is replace the whole dang thing for over 2 boatbucks plus labor. Figured it was worth a look a that price, plus the trim-tilt is easy to remove as a subassembly, so I brought it home.
So far, I've got the motor/gear pump off. Corrosion in the threads is bad, as you'd expect for something on the bracket of a marine outboard. One cap screw broke off, leaving a decent stub. Others were stubborn as grim death, but eventually yielded to lots of heating and PB blaster, alternating over a few days. The broken cap screw has yet to yield. Continuing the same treatment, a little fire, a little PB Blaster. This is into a flat machined surface sealed by multiple o-rings for the different passages. Leak was at this interface.
Worst case, I can buy the new unit and save the labor costs. But it's worth a lot if I can get the bolt out. I'll probably helicoil the holes and use a good antiseize if successful. Realistically, if the boat lasts another 20 years, it'll be somebody else's problem (I'm 61).
Am I missing any good tricks? I remember something about dissolving steel and leaving the aluminum for broken taps with alum, but will it work on stainless? Thanks.
Pete Keillor
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On 7/27/2012 11:00 AM, Pete Keillor wrote:

I've had better luck with Kroil than PB. Use the same heat/Kroil cycles and get it as hot as you dare. A few good whacks with a hammer might help break the bond.
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On 7/27/2012 10:26 AM, Tom Gardner wrote:

Only think I could possibly add is this... It will take time for Kroil or PB to work, LOTS of time. Maybe days. Maybe lots of days. Be patient.
But I'd strongly warn against the hammer. It's highly likely that the threads in the aluminum will be damaged. Maybe beyond repair...
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Richard wrote:

See his comment above your response ...
--
Snag
Learning keeps
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On 7/27/2012 5:15 PM, Snag wrote:

I'm 62.
If the threads get torn up the boat won't last 20 minutes.
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wrote:

Good point, but the threads are already suspect due to the amount of corrosion. By the way, somebody asked what size, 5/16". I'll have to evaluate the resulting wall thickness if I drill out and tap for helicoils. First guess is it'd be ok, and with appropriate antiseize, less likely to have the same problem next time.
The trim/tilt is pretty easy to service otherwise. It attaches with a big pivot pin at the bottom of the outboard mounting bracket and a shorter one at the tilt yoke at the top of the tilt ram. Plus the electrical connection. I can see why they just sell the whole thing. The environment is about as nasty as it gets, so getting any bolts loose on the thing is probably always this kind of job.
I've got some time, the fishing won't get really good again until late September or October. Too many folks and boats on the Galveston Bay system in the summer. I wouldn't even consider going out on a weekend. But October - December is magic, cooler weather and water, crowds gone, fish biting with the higher tides and currents.
Thanks for the input, everybody
Pete Keillor
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On 7/27/2012 1:01 PM, Richard wrote:

Unlike a gorilla playing golf, one CAN temper one's enthusiasm with a hammer. How about a few light love taps?
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wrote:

Agreed. I've done that. I'll keep at it with the heat, juice, etc.
Pete
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On Fri, 27 Jul 2012 10:00:18 -0500
<big snip>

You didn't say how big this is (diameter). If it is big enough I would recommend drilling it progressively larger until you are in jeopardy of hitting the threads. That is after giving up on the heat/penetrating oil attempts. Then I would use a dremel or die grinder to open it up out to the thread area in a couple places. Should be able to pick out whatever is left at that point.
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Leon Fisk
Grand Rapids MI/Zone 5b
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Trick I have used to remove broken exhaust studs from aluminum cylinder heads is to weld a nut to the broken stud. It takes a few tries, the heat from welding helps loosen the stud. If you can weld inside a stainless nut to the broken bolt, use a socket on it when it cools to a dull cherry color. the welding does not stick to the aluminum. Last time I did that I was on a stud with a broken easyout in it. Patience is the key. Luck and good beer helps. Darcy
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On Sat, 28 Jul 2012 07:49:19 -0600, "CNC Solutions"

<snip>
Thanks, I'll keep that in mind as a last resort. I'd have to get a bottle of argon (need anyway) and practice my tig technique first. I've munged the threads, but that's no problem since I'd be welding the nut on. Press one on with the arbor press, hit it with the tig.
Pete
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On Sat, 28 Jul 2012 09:21:09 -0500, Pete Keillor

After weeks of heat and juice, I practiced up and welded on a stainless nut this morning. Out came the broken bolt. The aluminum thread corrosion doesn't look that bad. I think I'll just go back with a good antiseize.
Now I can get on with ordering the pins to make the cylinder end wrenches (6.5mm and 4.5mm pins, 35 and 32mm hole circles). It remains to be seen if they'll come out easily. The main leak was at the pump interface, so if they don't, I'll likely clean it up, assemble with new pump o-rings, fill it with Dexron II, and see how it behaves.
Thanks, everybody.
Pete Keillor
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You are excellent. We never doubted you.
Christopher A. Young Learn more about Jesus www.lds.org .
After weeks of heat and juice, I practiced up and welded on a stainless nut this morning. Out came the broken bolt. The aluminum thread corrosion doesn't look that bad. I think I'll just go back with a good antiseize.
Now I can get on with ordering the pins to make the cylinder end wrenches (6.5mm and 4.5mm pins, 35 and 32mm hole circles). It remains to be seen if they'll come out easily. The main leak was at the pump interface, so if they don't, I'll likely clean it up, assemble with new pump o-rings, fill it with Dexron II, and see how it behaves.
Thanks, everybody.
Pete Keillor
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