Wait a minute. I'm very unfamiliar with anti seize threading lubricant. Can somebody start from the top and explain it all to me? I used anti size on the threads of the spark plugs I just installed on a ford 302 in a pickup. I used my usual "two finger tight," compress the crush gasket torque spec. Is there need for worry?

 

There are a variety of compounds that may be applied to threads. However, it is worth noting that the torque specs given in the manual are "clean, dry" specs - after each name, there will be a percentage in parenthesis, like this (90%). That is the amount of the book torque value you'll use with that particular lubricant. For instance, if you see (80%) and the book "clean, dry' spec is 40 pound-feet, you'll use 32 pound-feet instead.

If the manual calls for a specific lubricant, use that particular lubricant and torque value! Examples are the #11 cylinder head screw (coat with PTFE paste, torque to 100 pound-feet) and the harmonic damper screw (clean engine oil, 80 pound-feet.)

Threadlocker Compounts (100%) - These compounds are available with various properties and strengths, and are used to prevent screws from loosening under vibration. LocTite is a trade name of Permatex, but it's also generically used for the category in general. Fingernail enamel may also be used as a low-strength threadlocker compound, particularly on adjustment screws (I also often use it on screws on firearms.)

Room Temperature Vulcanising (RTV) (100%) - Same stuff you use to bolster a gasket. You can put this on screw threads to either provide a low-strength threadlocker or to seal the threads against liquid intrusion - I've also used it on undercar screws to help pprevent rust. It's more effective than using LocTite for this purpose (LocTite does prevent screw seizure and helps to prevent rust. RTV is better in some applications.)

PTFE "Teflon" Paste, A/K/A "Pipe Dope" (90%) - Available at your local hardware store, plumbing section. I stopped using PTFE tape a long time ago - I kept wrapping it around the wrong direction. Using PTFE paste makes this a non-issue. PTFE may also be used as a thread coating to help prevent corrosion - I commonly use it on thermostat housing screws or water pump mounting screws that protrude into the water jacket. RTV will also work for this application, however.

Engine Oil/Chassis Grease (75-80%) - Typically specified for use somewhere, they may generally be used interchangeably. Typically used as a handy method of increasing tensile preload in the fastener without needing to put more torque (turning force) on the screw head.

Anti-Seize Lubricant (A/K/A "never-seez") (50%) - This is used in environments where screws are subject to highly corrosive environmentsl, where threaded surfaces are made from dissimilar metals, and the like. Highly useful undercar. However, it is highly lubricious (?) and tensile preload increases rapidiy in relation to applied torque.

What's the difference between "torque" and "preload?"

"Torque" is the turning force applied to the head of the fastener, and is often used as an indirect measure of applied tensile preload. Where possible, the very best way to measure installed preload is by direct measurement of screw elongation - performance connecting rod big end screws & nuts are typically torqued not by using a specific value of turning force, but by measuring with a "stretch gage" and trying to achieve a specific elongation value. (Current ARP catalogue, ca. p72. www.arpbolts.com for explanation.)

"Preload" - or "tensile preload" - is the tensile (pulling) force placed on a screw when installed. This is achieved by applying a turning force ("torque") to the fastener head, and the inclined plane action of the mating threads (a thread is essentially a ramp wrapped around a shaft.) Torque is an indirect measure of this - and is notoriously inaccurate (clean, dry torque can vary by as much as +/-20-25%, this margin of error decreases as friction between mating threads is decreased.)

Preload may also be set using a "torque angle" method - where you set the screw's initial torque to a specific (low) value - which reduces potential error. Then, the fastener is turned a specific angle to finish the preload. This method is inherently more accurate, since it relies on a relatively small initial value measured indirectly (which seriously reduces the error,) and the the "lead" of the screw (amount the screw advances for each full turn - viz. a 1/4"-20 UNC screw will advance 1/20" - or 0.050" - per one full turn of the screw.) This is a much more direct measurement of tensile preload force

Why is tensile preload force so important? A threaded fastener remains installed primarily due to interference forces between the internal and external threads - and more tensile preload means more interference between the two threads (This does presume that the threads proper are not deformed...) Also, the installation preload provides clamping/sealing force on the join - which is important when sealing against a fluid (water pump, cylinder head gasket, thermostat housing, &c. Also indirectly used to seal things like hose clamps and such - while the preload acts on the sealing surface a bit indirectly, it's still important.)

Fastener engineering is a bit more complex than it first looks - different materials have different desirable properties, and yo uhave to account for environment, required sealing action, relative strengths of materials (both differing materials and wrought v. cast materials,) and a number of other factors. I don't understand anywhere near all of it, but I'm trying!

 

I see there is a lot to learn here. I really need a torque wrench. Is it good to always use anti-seize as a general rule of thumb? I do a lot of wrenching, and worry about stripping aluminum. Can you give me some specific advice, especially when doing general maintenance?


Thanks

Rob

 

My rule of thumb is if it doesn't get Loctite it gets Anti-Seize but I live in MN where rust and seized bolts are a major concern. Of course there are some exceptions to that rule like internal engine fasteners.

 

"A" torque wrench? If you do a lot of work, you need at least two and possibly three (each drive size - 3/8" is mandatory, 1/2" is useful, 1/4" helps with small work - like sump screws and Cardan strap screws.)

I don't like to put screws in dry, but what I do use depends largely on the screw and application. I usually put RTV on the threads of sump screws, LocTite on Cardan scrap screws, never-seez on suspension fasteners (never-seez will not make a fastener back out - if it backs out, you didn't torque it right,) RTV on valve cover screws (and other small screws - it's enough to hold it in place, not so much that you can't get it out. 1/4" is the lower limit for LocTite #242, most people can't readily get LT #222, so a substitute is useful,) and the like.

Experience will tell you what you want to put where, and the manual will also tell you in some cases (as can replacement screws themselves. For instance, if you go get a Cardan strap kit, you'll see a blue substance on the screw threads. DO NOT CLEAN THIS OFF! This is threadlocker - and it's necessary! Ditto replacement flywheel/flexplate screws, most torque converter screws, and replacement clutch cover screws. If it's not there, it will be before I put the screw back in the hole!)

If you're not sure what to use, do feel free to ask! If I give you an answer, I'll tell you what I use and why I use it - but most people will at least tell you what you can/should use on the screw (my "never install a screw dry" rule comes from hanging out with the A&Ps at Aretz when I was younger...)