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Date:         Wed, 6 Aug 2003 22:29:58 -0500
Reply-To:     John Rodgers <j_rodgers@CHARTER.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John Rodgers <j_rodgers@CHARTER.NET>
Subject:      Re: Torque wrench usage
Comments: To: don spence <dspence@OANET.COM>
In-Reply-To:  <BBE7546A-C843-11D7-AB3C-003065A72624@oanet.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Don, excellent write-up on the subject of torque.

However, I still maintain --- no lube unless specified. Makes sense to me, and is as I was taught at A&P Mechanic school by some old dudes that built Wilber and Orville' first flyer. (joke about "authority"). This is not to say never use lube, it's just that that there are times wihen it's right and times when it's not. The "as specified" is extremely important and the concept should be judiciously applied.

regards,

John Rodgers Birmingham, AL

don spence wrote:

> John's comments re lubricating (or not) nuts and studs before torquing > raised a question or two so off to the web. > On Wednesday, August 6, 2003, at 10:53 AM, John Rodgers wrote: > >> A a matter of good >> mechanical practice, the the torque values on bolts and nuts are >> established with no lubricants, and when a lubricant is added, it >> changes the parameters of the established torque for the part. So >> lubricants SHOULD NOT be added except where specified by the >> manufacturer. > > > > WEB search results: > 1: For greatest accuracy, use a thread preparation, either grease, > lube, or an appropriate grade of Loctite, on the threads of the bolts > you wish to tighten. > > 2: When using a torque wrench there are some basic preparatory steps > to consider. First, make sure the threads of the fastener and the > mating hole are clean and free of rust, dirt, carbon and goop. Debris > in the hole or on the threads will cause galling of the threads and > give an inaccurate torque reading. Secondly, if no special sealers or > instructions are given for torque applications are given, use a small > dab of high temperature grease on the threads and where the fastener > head contacts the part. Use of this lubricant will keep the fastener > from sticking and reduce the possibility of galling and stripping. In > addition the grease will assure the proper tension of the threads to > the mating parts when the correct torque is applied. It will also make > the fastener easier to remove in the future. > > > Now you ask; why should I use an accurate torque wrench? Well lets > talk about torque and its properties. You see, nuts and bolts are held > together by tension or elasticity. Some bolts are measured via stretch > but we will discuss that issue some other time. Threads provide a > continuously inclined plane, which creates a wedge for the bolt when > you tighten the nut. Like a rubber band, metal is elastic, and will > stretch a little as you tighten a nut. If you over tighten a nut you > will go past the limits of the metal's elasticity and strip the > threads. If you under tighten, the bolt will not stretch and thus will > loosen more easily through normal use. A torque wrench allows you to > tighten the bolt and nut to the correct tension, so it will stay in > place without loosening. > > 3: Torque is simply a twisting or turning motion around the axis of > the nut or bolt. Torque wrenches measure resistance to rotation. This > resistance can be correlated to, but is not a direct measurement of, > fastener tension. Generally, the higher the resistance to rotation, > the greater the tension on the threaded fastener. > > Typically, some type of lubrication is desired in the thread and at > the bolt head. Without lubrication, a higher twisting resistance is > felt by the torque wrench. The torque wrench reads only this > resistance to rotation, it does not directly read the tension in the > bolt. Be sure to check manufacturers suggestion on lubrication; many > manufacturers require a certain weight of oil or other liquid. > > Another option for thread preparation is a thread locking compound, > such as from Locktite®, Wurth®, and Devcon®. This is a fluid that is > applied to clean threads. The fluid provides some lubrication during > torque. When sealed from air, the fluid hardens and expands as it > cures. This provides resistance to loosening and also forms a seal to > water and corrosion. Thread locking compounds can be useful when parts > cannot be fully torqued. Thread lockers should not be used to replace > proper torque and thread pre-load when clamping load is important. > Generally, the service removable grades are used, such as Locktite® > #222 or #242. > > Cross threaded parts will cause more resistance than correctly aligned > threads. A torque wrench is unable to distinguish this problem. Don't > do something stupid and torque down a cross-threaded head bolt! If > you do, we're transferring you to a Ford group. > > It is important to understand torque unit specifications. Be sure you > read the manufacturers suggested torque requirements; remember, 125 > in/lbs is NOT the same as 125Ft/lbs! Don't screw up and break something. > > The most common reason for threaded fasteners loosening is simply that > they were inadequately secured during initial assembly. Vibration, > stress, or use/abuse usually will not cause a properly sized torqued > fastener to loosen. > Now you ask; why should I use an accurate torque wrench? Well lets > talk about torque and its properties. You see, nuts and bolts are held > together by tension or elasticity. Some bolts are measured via stretch > but we will discuss that issue some other time. Threads provide a > continuously inclined plane, which creates a wedge for the bolt when > you tighten the nut. Like a rubber band, metal is elastic, and will > stretch a little as you tighten a nut. If you over tighten a nut you > will go past the limits of the metal's elasticity and strip the > threads. If you under tighten, the bolt will not stretch and thus will > loosen more easily through normal use. A torque wrench allows you to > tighten the bolt and nut to the correct tension, so it will stay in > place without loosening. >


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