The other day I changed spark plugs on my 2002 Z28. It has kooks headers so I was able to access the passenger side plugs by removing the starter and changing #8,6,4 from under the car, the other 5 plugs I can access from the top.

I always place a tiny dab of permetex anti-seze on the plugs. When I remove the starter I dont normaly bother placing anti-sieze on them. This time when I removed the bolts the short one was pretty hard to remove. I was surprised how much torque it took to break it lose. So I figured perhaps the threads were slightly galled. So I found a tap that fit that thread from work and I cleaned out the threads a little. Nothing came out, I was expecting to see some shavings etc. Normally I am not this ****, but the thought of stripping a thread in my block wasnt exciting me. This time I decided to place a small dab of anti-seize on the starter bolts and reinstall the starter. I noticed that the short bolt snuged up fine but the long bolt now took a little more torque than I figured it would require but eventually it snuged up (phew I thought I had striped it)

It wasnt until the next day that it dawned on me that I probably shouldnt have tighetened the starter bolts up as much as normal because the anti-sieze may have an effect on them. I never install starter bolts with a torque wrench but the next night, since the car is still op on jackstands in my garage I would place a torque wrench on them and se what they clicked at. I was pretty close, both about 35 ft/lbs I think GM says 37 ft/lbs for starter bolts but then I wondered if I should have reduced the torque value because I assume 37 ft/lbs is a dry value.

I did some searching online to see huge long winded debates about how much torque to reduce using anti-seize and it seemd like 20% is the majical number. So if LS1 starter boltes are supposed to take 37 ft/lbs dry thats only 29 ft/lbs, thats not much to strip threads.

Since I couldnt get the answer I wanted at work today I saw a 3/4" thick piece of 6061 (which is pretty soft aluminum) and I drilled and tapped 10 5/16-16 holes in it and I torqued 5 down with a torque wrench until they striped dry and 5 with antisieze. I did this by torqing until it clicked and moved the wrench up 0.5lbs at a time until it wouldnt click where it would just rotate, signifying its striped. Here are the results I got. Values are in ft/lbs.

 

Wow... Props for actually doing empirical testing on this! Thank you!

 

I've never heard anything about reducing torque values while using antiseize. The idea is to use a small amount to minimize galling of threads and the seizing of bolts, and the added benefit is multiplying (improving) the clamping force.

Typically torque values aren't anywhere close to the failure point (as you tested). Personally i've never had any issues with anti seize (a GOOD quality with a high metal content) and pretty much use it religiously as i've had all kinds of bolts seize up in the past. And that's using it at the suggested torque values, everything from brake/wheel assemblies, to spark plugs and pinion bolts.

 

Of couse it does! ALL torque values are threads clean and dry unless otherwise specified.

 

Which causes stripping

Also, you are correct that bolts are only tirqued to 75% of their yield strength

 

You have reduced the friction between the threads (i.e. so you don't have to overcome it to achieve the same clamp/pull).

 

nice test. thanks for doing this.

 

I'll tell you what else effects torque, the amount of times the bolt is turned to get to the torque value.

Try this take a bolt and torque in two steps then mark its position and loosen it. Next torque it to full value in one step and see the difference position.

Also try torquing a bolt standard two step with and without oil marking its final position both times.


I personally like to use a little oil on threads and reduce the torque settings by 15% or so. This link will tell you more http://raskcycle.com/techtip/webdoc14.html

 

I learn something new everyday.

 

Great analysis. This is very cool, and I've wondered the same thing as well.

 

As one turns a bolt and develops torque, it is stretching the bolt like a piece of spaghetti, putting strain on the bolt and increasing the friction between the threads. This increased friction helps keep the bolt from backing out.

Anti-sieze is essentially little glass ball bearings. I expect that those glass ball bearings are filling the voids/gaps between the threads. Maybe the reduced space between the threads is allowing more strain to be built up in the bolt with less torque. I say "maybe" because this is really making my brain hurt and I have my textbooks (with torque/strain calculations) packed away in storage.

Mechanical Engineers - jump in here!

So... if this is what is happening, the anti-size would also change the friction coefficient of the threads. (I imagine that the little ball bearings would reduce that friction.) Thus, even if torque is compensated to get the correct strain in the bolts/threads the friction may be reduced (and the bolts ability to stay in the right place.) if anti-size is used in a place where its not needed or designed for.

 

Little ***** you say....youre scarin me.

 

google "torque to yield"

http://www.enginebuildermag.com/Arti...uetoangle.aspx

http://www.motor.com/magazine/pdfs/112009_02.pdf


the % number i am familiar with for reducing torque value when using anti-sieze or other thread lubricant other than basic oil is 30%, and those numbers tend to show that. 1 - (43.7/60) = 0.27.

using 30% reduction is safe because it will prevent you from blowing out the threads. but the % will vary depending on the fastener materials, whether it's a bolt into a hole, or a nut on a stud.

 

Just read a short atricle in Popular Mechanics about this (April 2011, pg 106-107). According to the article, O2FORM is correct. Furthermore, adding lube to threads may require reducing the torque applied from 20-50%!!!. Antiseize does prevent galling and I put it on stuff too - sparkplug threads etc. Stuff like that often says 1/2 to 3/4 turn once seated as a guide so...

 

Thanks for doing the test its good to know

 

*****: What the hell you need ball bearings for?
Fletch: Awww, come on guys, it's so simple. Maybe you need a refresher course.
[leans arm on hot engine part]
Fletch: Hey! It's all ball bearings nowadays. Now you prepare that Fetzer valve with some 3-in-1 oil and some gauze pads. And I'm gonna need 'bout ten quarts of anti-freeze, preferably Prestone. No, no make that Quaker State.

 

correct!

 

I learned some thing today,thank you.