Wow! Thanks for the detailed and well thought out response
I'm a company mechanic in the salt belt. While I do some retail, most of my work is in house. I fix things every day that simply could not be fixed at retail. I've done a lot of this type of work. I'm not a machinist... I just stuck a lathe in my basement, so I soak up a lot of stuff here that I'm in no position to reciprocate. So when I stumble on something that is within my depth.... I try to offer solutions, as well as reasoning. Even if it's beyond the immediate need, it will be searchable, and probably applies to a lot more than the immediate need. So thank you as well, for all the stuff you've put up here that might be nothing to you, but I will search and find one day.
Is there some overwhelming reason against the high-temp, copper-based stuff?
Thanks,
Brian
It's not the right answer. The bolts will not freeze in place if you use the copper, but if you have to do this again in due time, which is not uncommon, you'll find that the aluminum holes are corroded back. Enough to matter? Crystal ball? The chemistry escapes me to some degree, but you have dissimilar metals-giving a galvanic "situation" there. Adding the third (the metal in the anti seize becomes a third dissimilar metal. Plus we add our own electrical current, so it gets crazy, way beyond any galvanic compatibility charts. At a level that's way over my head, there's several ways to use that situation to your advantage, be it to "moderate" a galvanic reaction, to act as a sacrificial anode, or to just be so "wrong" that it makes a damaged which is guaranteed to be softer than the parent metals. At a level that's not beyond me, nickel won/t damage the aluminum, and "eventually", and that's use case and environmental conditions, the copper will. Eventually. The next time apart, the aluminum holes would probably accept a new bolt, but the threads, probably still intact, will be eroded back such that they're oversized, with poor engagement. Excellent chance that they won't take torque when they are tightened at that next go-round.
How long are you gonna keep this? How fast did it rot the first time? Are you the first, or has this been done before? I see you found anti-sieze on the stuff you removed.... Somebody's been there. That's NOT factory on anything. Ever. Copper is better than nothing, as heli-coils are so easy to pop into an aluminum head, in situ, provided you have correctly placed holes (which you will). And they are a sound repair, with a stronger and more durable joint than the original. They're very very forgiving about some slight angular misalignment from the awkward manual drilling and tapping. And typically (I know folks hate to hear this.....), typically they have a similar pull out force than the time sert type (solid) inserts do in an ideal situation, but freehanded, with some ever so slight misalignment (or just crazy crooked if you like), the heli-coils shine above. So if you add in the "by hand" factor, and the solid inserts are not as good as the original. But anyhow, it's VERY repairable at a very low cost if you have no other choice, and of course that will apply if you have to go in again. The biggest risk being a straight up mistake with the drill. If you use copper, and you leave the new hardware there forever,t and never have to revisit this...... Just like original half failed hardware, you could never set up a "new" joint with it, but it worked fine as is, after the head, manifold, and gasket all got to know each other via some years of service and heat cycling. It's not gonna fall off. Not for that reason anyhow. The point of that being, recovering from "wrong" is a real thing, more work, more time, etc. but it is NOT something that's going to take the next repair to the next level in any way. It's very, very recoverable with no unreasonable extra tools or skillsets. So in my mind, it becomes a judgement call on your part. What are the odds you'll do this again? And can you fire in a heli coil freehand and get it kinda close? (If you got this far... I bet you could fire in a heli-coil freehand and get it kinda close...). So yeah.... Judgement calls and speculation sometimes come into play in that situation. If you have cause to live with a compromise, and a risk (not guarantee) of future with some known degree of managable (but real) aggrivation... Well..... There you go. Measure with a micrometer, mark it with a crayon, and cut it with an axe. If it has to get done, it has to get done.
One other thought I'm having... You might know this. I "assume" that you're going to torque these fasteners with a carefully calibrated click elbow, right? If so, (assuming it's an experienced click elbow) you'll probably be fine, but if you're actually gonna click the hardware like you oughtta.... Whatever brand of anti-sieze you have is gonna have published nut factors (K factors) for adjusting the torque. It's likely be something in the neighborhood of half to two thirds of the "standard" torque. That stuff is GREAT for fooling you into over stretching bolts, and with the uneaven heating/cooling of that area, and the very different coeficient of expansions.... Pay attention, and while it is a joint that abuses it's fasteners tremendously, it's low force (in the big picture), so if you know about it, you'll probably be plenty close enough.
