Exhaust Bolts Seizing in Aluminum

B

Bart_

Carpal tunnel level member
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I've got a 30 year old 5 hp 4 stroke Briggs flathead. The muffler rotted out again. It uses about 1 1/2" 3/8" dia shoulder bolts with a 1/4-20 tip. One bolt broke free the other snapped/seized. Upon closer inspection the same bolt had seized/snapped last time too because I found a 4 quadrant scooping out of the aluminum such as one would do to get access to a stub for vice grips plus heat/wd. Have vague recollection of doing that. This time it snapped at the surface, at the bottom of the scooped depression so no repeats on that procedure. I decide to do nut plus mig welder - weld bolt tip/top to inside of nut, torque on nut. 6x failure!!! So I'm relegated to drilling out on center - my tiny drill bits refused to bite. Even the center punch divot seemed shallow. So I went up 3 different drill sizes till the drill bit could take the necessary pressure to bite without threatening to snap like spaghetti. Bonus, now my hole wandered off center. Using good cutting oil.

There was a tiny amount of galvanise white that came off the nuts. 3 of them went full red thru mask. Is there a chance I hardened the crap out of the bolt welding onto it? Maybe the not-biting drill bits work hardened the hole surface. Maybe I'm getting old and feeble. Maybe the cylinder heat heat pattern pushes one to seizure and not the other?

? ideas?

Off center isn't necessarily a failure sentence. If it's mild you turn the bolt remainder into a crescent and lose some thread on one side. Not great but workable for low load situation.

I'm going to resume the drill fight tomorrow. Blowing it and re-engining - no thanks.
 
Bart_ said:
I've got a 30 year old 5 hp 4 stroke Briggs flathead. The muffler rotted out again. It uses about 1 1/2" 3/8" dia shoulder bolts with a 1/4-20 tip. One bolt broke free the other snapped/seized. Upon closer inspection the same bolt had seized/snapped last time too because I found a 4 quadrant scooping out of the aluminum such as one would do to get access to a stub for vice grips plus heat/wd. Have vague recollection of doing that. This time it snapped at the surface, at the bottom of the scooped depression so no repeats on that procedure. I decide to do nut plus mig welder - weld bolt tip/top to inside of nut, torque on nut. 6x failure!!! So I'm relegated to drilling out on center - my tiny drill bits refused to bite. Even the center punch divot seemed shallow. So I went up 3 different drill sizes till the drill bit could take the necessary pressure to bite without threatening to snap like spaghetti. Bonus, now my hole wandered off center. Using good cutting oil.

There was a tiny amount of galvanise white that came off the nuts. 3 of them went full red thru mask. Is there a chance I hardened the crap out of the bolt welding onto it? Maybe the not-biting drill bits work hardened the hole surface. Maybe I'm getting old and feeble. Maybe the cylinder heat heat pattern pushes one to seizure and not the other?

? ideas?

Off center isn't necessarily a failure sentence. If it's mild you turn the bolt remainder into a crescent and lose some thread on one side. Not great but workable for low load situation.

I'm going to resume the drill fight tomorrow. Blowing it and re-engining - no thanks.
Click to expand...
Yes, welding it can harden it. Reverse thread bits could help. Could use a small bit to drill out along side the stuck bolt, then step up in size when retapping.

Could try heating the case/surround. Aluminum heats readily compared to steel.

Cold could also work. I had good luck with liquid nitrogen on stuck mounting bolts that were salt welded to the aluminum casings when working at Cummins as a gen tech.

Photos?

Lastly, find an aluminum welder guy to patch the ears back up (if I'm reading the situation right). Cut it out, weld it back, retap.

That's a lot of work.
 
It is rather likely you hardened the bolt while welding. If you can find a source locally for cobalt drill bits, they should cut through the hardened bolt without any real trouble. Just be careful, because cobalt drillbits are brittle, if you start leaning on them sideways at all they will snap right off.
 
Well, Tom, I went with your suggestion: EDM - Extraordinary Drilling Maneuvers :)

Looks like the hardening was pretty shallow and at the end of yesterday I just broke through it, off center maybe .125 bit. I've done recentering before its a pita if at all possible. While your hole is shallow, redrill same smaller bit at maybe 45 to 60 degrees into the thick edge, Then upsize a bit to catch some overhang. Then go back down and try to deepen the new on-center. Still quite shallow. Then upsize and use the new oncenter to hold the bit as you upsize nearly on center. Then I downsized again running the hole till I broke through the end and clunked onto the blind bottom of the casting. STOP!!! Pooch the casting and all's for nought. Depending on your fussiness, change to single stepping up until you break into the bolt/block thread interface on the thin side. Then there's more finesse. 1/4-20 tap on a small T handle. The hole was only .187 or .190 not .203 tap size so you have to bit by bit try to bite bits of steel bolt out of the hole without overly gouging the softer aluminum casting and without taking too big of steel bite and breaking the tap. tap, clean, tap, clean.... Sometimes the bolt shell will break free at this stage. Mine didn't. I couldn't even tell if I cut it all out. Don't care - an adequate thread formed! Sometimes the bolt shell will break free during drilling. final steps - Qtips for debris removal, nickel antiseize.

Chances are I pooched the cutting edges on the first small dill bits. Bites because they're gold colored (titanium?) coated nicest set I have. Small center drill really pooched too. The first tiniest drill did manage to make/cut some fine particles in sacrifice.

The waterbath requirement for edm and surgeon's stable hand, if you had edm machinery to start with - interesting. Horizontal hole still on the equipment - kinda nope.
 
EDM in aluminum is setting you up for corrosion seizure - page 7 order of magnitude greater corrosion rate. doh.



What lead to this rabbit hole was seeing a big blurb of white corrosion powder with chips come out at a certain stage in my drilling. Then I read that EDM falls on its face when a simple grit impurity is encountered in the metal its cutting (electric arc gouging). So I figure crusty rust buildup on the steel and magic chemistry product corrosion powder probably fall into this category.

Be damned if I can even find how a crust of rust affects EDM. Anyone know?

I envision a mig-like probe that is non-conductively holding an electrode tip the required thousandths of an inch off the surface, flooding distilled water out the tip locally at the arc. voila, localised edm hole-side-file device. subject to the crud issue of course


edit - been done before, not exactly my concept but what, couldn't cost more than a couple hundred$ ? ;)


you have to do watch on youtube. sorry
 
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