Alternator removal from a 1987 2.5L resulted in a broken bolt in the intake manifold and one in the alternator.
Using a screw style remover in the intake bolt resulted in a chunk of the intake boss breaking away.
So far, the alternator bolt has defied removal attempts.

Should steel screws into aluminum have anti-sieze or thread locker or something else applied?
How do coatings affect the torque specs which I understand are applicable to dry threads?

quote Originally posted by David Hambleton: Should steel screws into aluminum have anti-sieze or thread locker or something else applied?

IMO... anti-seize. Absolutely.

quote Originally posted by David Hambleton: How do coatings affect the torque specs which I understand are applicable to dry threads?

Again IMO... perfect torque readings aren't critical for many (most?) bolts on an engine.

We touched upon appying proper torque to various bolts Here.

[This message has been edited by Patrick (edited 07-30-2013).]

quote How do coatings affect the torque specs which I understand are applicable to dry threads?

Most anything you put on the threads (except possiably valve grinding compound) will act a a lube on them. Larry

The only things I torque to specs are bearing caps, heads, intake manifolds.

I use copper anti sieze on almost all of the typically stubborn bolts.. It makes them so nice to get loose again. Case in point, I finished my swap and put the cradle in 2 years ago, and had to drop the cradle this last weekend to swap out transmissions and it took me all of an hour to get the cradle out. I want to give a medal to whoever invented that stuff..

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Build thread for my 88 + 3800NA swap

Obviously a steel bolt in aluminum threads is a problem for stripping out the threads, but it is also a problem for galvanic activity. But there are many types of steel as well as aluminum. Is the steel plated? Very likely, and depending upon what with, it may or may not be a good match for aluminum. Most platings will make it a better match, but if it is stainless steel, it is likely not a good match, although some are. Without knowing the exact materials, it is hard to say exactly what to use.

I think you can see though, that a material that will make stripping the threads less likely (a thread locker) and something that will decrease galvanic activity (plating) would be a good idea. Or something that does both.

quote Originally posted by David Hambleton: Should steel screws into aluminum have anti-sieze or thread locker or something else applied?

Excellent questions. I highly recommend using anti-seize on all threaded fasteners unless something else is specified by the manufacturer, but especially where dissimilar metals are involved.

quote How do coatings affect the torque specs which I understand are applicable to dry threads?

Most published torque values for threaded fastener assemblies assume clean and dry threads, but some specify clean and lightly oiled threads, while some require a specific thread locker or sealant.

Anything you apply to threads ... anti-seize compound, oil, thread locker, or sealant ... affects the torque to use for a given fastener. (Actually, torque is a pretty poor way to determine optimum fastening tension, but it's relatively easy to measure and has a long body of historical data to support it.) Most high-quality manufacturers of such thread compounds conduct tests and publish data on how each product affects torque requirements. The thing to look for in the specs is the "torque coefficient" ... usually called the "K Factor" or sometimes the "Nut Factor." If you can't find a published K Factor, I would call the manufacturer before using that product.

For reference, the K Factor for clean and dry threads varies somewhat with fastener material (steel alloy, plating, etc.) and cleanliness, but it's a number usually in the range of 0.20 to 0.22. In comparison, when applied to clean threads the rated K Factor for the anti-seize I usually use (standard Never-Seez™) is 0.13. This means that when using Never-Seez the torque should be reduced to about 65% (i.e. 0.13 / 0.20) of the value specified for clean and dry threads. For me, "2/3" is easier to remember than 65% and it's still close enough.

In actual practice I tend to reduce specified torque to about 75-80% when using Never-Seez on an all-steel threaded joint (steel bolt and steel nut, or a steel screw in an iron or steel casting). On the other hand, aluminum castings have less strength margin and are easier to pull the threads out of, so with bare aluminum (with no thread inserts) I will usually dial in no more than the 65% figure ... and even then I will approach it cautiously.

Be careful. If the manufacturer specifies the use of anti-seize, oil, thread locker, or sealant on a fastener before assembly (e.g. the head bolts on a Fiero V6), then the published tightening torque value already takes the K Factor of the thread treatment into account.

Incidentally, anti-seize compound is not a lubricant and it should never be used where oil or grease is specified. On the other hand, threaded fasteners lubricated with oil or grease before assembly, even when properly torqued, are more likely to loosen in service than those assembled dry or treated with anti-seize only.

Bottom line: Use anti-seize, look for the K Factor, and always use a torque wrench. It's much easier to overtorque small fasteners when tightening "by feel" ... with or without anti-seize ... than is it to undertorque them.

[This message has been edited by Marvin McInnis (edited 08-02-2013).]

Thank you.