Torque & Lubricated Threads


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Torque & Lubricated Threads

Postby cbx4evr » Fri Jul 13, 2012 11:15 am



I subscribe to the RockAuto Newsletter. Interesting article detailing a home garage experiment with torque and lube. it's not scientific and sometimes it's better that way. HAve permission to share this.


My Garage Experiment


I tend to put anti-seize compound on most bolts. After struggling to remove a frozen fastener, I want to make sure that it is easier to remove the next time. I have read that the problem with smearing anti-seize compound on nuts and bolts is that it makes it too easy to over-tighten even using a torque wrench. The torque specifications in repair manuals are usually written for fasteners that are relatively clean or “dry.”

The right torque is essential for the success of many repair jobs. Cylinder head bolts sometimes have a torque specification that requires both a torque wrench and a torque angle meter to measure a subsequent rotation of the fastener by a set number of degrees. Fel-Pro recommends that a “torque-to-yield” cylinder head bolt never be reused because “chances are great that it has already exceeded its elasticity barrier and won’t spring back to properly seal the engine.” What if even the most careful torque measurements on new parts using the best tools is thrown out the window by a dab of anti-seize compound?

I decided to clear off a corner of my workbench for a quasi-scientific investigation! I cleaned a new bolt, washer and nut to make them “dry”, clamped the nut in a vise and marked the position of the bolt head at points between 25 to 65 ft. lbs. of applied torque (34 to 88 Nm). Then I put anti-seize compound on the bolt and measured the torque necessary to bring the bolt head back to the dry positions. With the anti-seize compound, I found that 31% to 44% less torque was needed to turn the bolt head to the dry position. For example, 45 ft. lbs. of torque on the anti-seize coated bolt turned the bolt head as far as 65 ft. lbs. of torque on the dry bolt. The dry/anti-seize conversion ratio became very non-linear when I put 65 ft. lbs. (88 Nm) of torque on the anti-seize covered bolt. The bolt head turned far past (remember this is quasi-scientific!) the dry 65 ft. lb. mark indicating that the bolt head was probably now cutting into the washer and/or the bolt was stretching.



After my experiment, I looked at bolt manufacturer data and found they generally recommend roughly 25% less torque (compared to dry) on fasteners lubricated with anything (oil, grease, etc.) and roughly 40% less torque on fasteners coated in anti-seize compound.

I am still a big fan of anti-seize, but I am going to more carefully consider the torque specifications for each bolt. Many, if not most, of the bolts I install are hard to access and impossible to get a torque wrench on. Most fasteners have likely been inadvertently lubed by the penetrating oil I used to help remove them, transmission fluid, the grease on my gloves, etc. With those hard to get to bolts, I can only use the manufacturer torque specification as a ball park figure to calibrate the pressure I feel in my hand and wrist when I turn the wrench. Manufacturer torque specs in the repair manuals are usually a range rather than an exact number so now at least I know to usually aim for the low end of the torque range.

I will forego the anti-seize compound and/or follow the part manufacturer’s installation instructions when I work on torque sensitive sealing applications like cylinder heads. It is worthwhile to remove more parts so the torque wrench has access and make an extra effort to clean fasteners and mounting holes. I will also be more cautious when bolting together dissimilar metals like aluminum to steel. My garage experiment showed me how easy it would be to inadvertently distort or crack parts while tightening lubed fasteners to the high end of a torque specification range. My test bolt looks the same to me, but it likely painfully “exceeded its elasticity barrier” when I applied the anti-seize compound and 65 ft lb. of torque.

Tom Taylor,
RockAuto.com


"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

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Re: Torque & Lubricated Threads

Postby WingAdmin » Fri Jul 13, 2012 5:28 pm

I read that as well today, interesting. I'm going to assume in future that Loctite is considered a "lubricant" and adjust my torque levels accordingly.

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Re: Torque & Lubricated Threads

Postby fixbikes » Fri Jul 13, 2012 9:47 pm

Neat experiment, as I am also a great believer in antisieze compounds. Guess I will now be a little more cautious.
Something else to keep in mind, depending on manufacturer and location, the manual will specify a locking compound, a sealant (some holes are open to the cooling jacket), and sometimes for lightly oiled bolts. In these cases, I don't think the touque spec should be adjusted.
Many years back, I was taught that tourque is actually a measurement of bolt stretch, which is approximated by a tourque wrench, which actually measures friction and resistance. (For what it is worth, the same instructor would also go slightly nuts over calling it a "bolt" instead of a cap screw.)

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Re: Torque & Lubricated Threads

Postby bustedwing » Sun Jul 15, 2012 10:10 pm

I too am a firm believer in the use of anti-seize due to the fact I am basically lazy. But I did notice that you were using a soft grade bolt and washer in your tests and that will make a difference in stretch and warp in both.Head bolts I have never re-used but that is just because I was trained that way in heavy equipment repair.But anti-seize is a lifesaver when it comes to many common parts .And care is needed to make sure the parts stay together without over-torquing.Thank you for the eye opener.


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