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Torque Wrench Means Large Tension Errors

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Blll Hires

11-28-2002 08:24:51




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When reading the many requests relating to "TORQUE" on the Discussion Form I would like to suggest going to the WEB Site, www.howstuffworks.com, and request "TORQUE", this does an excellent job of explaing torque/tension. Torque is correctly read as, lb-in, or lb-ft, not in-lb, or ft-lb. This is similar to saying Skil saw, not saying power saw, however the incorrect form will continue to be used. When the reading on the torque wrench is correct, it is possible to have errors from 20-50%. When you are tightening a sixty-year-old bolt, there are many variables to consider i.e., how mony times has the bolt been tightened/over tightened? Corrosion from acids and oxidation, heating and cooling stretches the bolt as the engine operates. Using taps/dies to chase/clean threads is one important item often ignored. Modern engines use tension/stretch and not torque as a measure for correctly installing fasteners. Some bolts are used only once and must be replaced with new ones each time they are removed. This is also true in some older engines.

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Farmered

12-02-2002 03:57:12




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 Re: Torque Wrench Means Large Tension Errors in reply to Blll Hires, 11-28-2002 08:24:51  
Whether you say ft/lb or lb/ft is a matter of personal preference. 2x3 equals the same as 3x2 no matter how you arrange it. Ed



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Irv

12-01-2002 11:12:53




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 Re: Torque Wrench Means Large Tension Errors in reply to Blll Hires, 11-28-2002 08:24:51  
I am no expert at this, but I work in an engine plant, and we use a torque angle scheme. This uses an intial torque and then so many degrees. Fasteners such as head bolts are only used once. If the head comes off for inspection, new bolts are used. Some types of thread coatings are used, depending on use. Irv



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Green_in_MI

11-29-2002 17:16:10




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 Re: Torque Wrench Means Large Tension Errors in reply to Blll Hires, 11-28-2002 08:24:51  
What really is important in measuring or describing torque, or any other engineering term is to get the units on the right side of the equations. Torque is a force multiplied through a distance which causes a twisting or torsion of an object. The order is not important, only what units are applied in their proper algebraic relationship is what counts. lb-ft, N-m, in-lb
same thing.



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Tom

11-28-2002 21:24:06




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 Re: Torque Wrench Means Large Tension Errors in reply to Blll Hires, 11-28-2002 08:24:51  
I am no expert, but it seems that in addition to cleaning, visual inspection, and thread chasing on each, it would help to coat it with that copper anti-seize compound. Would this eleminate or lesson thread friction during the tightening??



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Nolan

12-03-2002 08:11:09




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 Re: Re: Torque Wrench Means Large Tension Errors in reply to Tom, 11-28-2002 21:24:06  
SAE specifies that threads be clean and lightly lubricated. So in answer to your question about using a lube, the answer is yes.



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bob

11-29-2002 06:30:08




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 Re: Re: Torque Wrench Means Large Tension Errors in reply to Tom, 11-28-2002 21:24:06  
in power plant you alaways clean bolts before trying to torque them and you also have 2 charts for tightning one dry and one lub. even have difference from oil to neversieze. Yes on the larger bolts on turbine we measure stretch intead of torque But most bolts to be used on tractors and imp can be reused after cleaned and lub



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Bus Driver

11-29-2002 05:40:36




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 Re: Re: Torque Wrench Means Large Tension Errors in reply to Tom, 11-28-2002 21:24:06  
Adding thread lubricants makes a given torque reading place much greater tension force on the fastener. Unless the specs call for a lubricant, torquing to full value with the lubricants may cause the fastener to be stretched beyond design limits. The question then becomes one of how much to reduce the torque when lubricants are used. Any standard data on this?



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bob

11-29-2002 17:27:46




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 Re: Re: Re: Torque Wrench Means Large Tension Errors in reply to Bus Driver, 11-29-2002 05:40:36  
Don,t qoute me on this as don,t have book in house but figure about 70- 80 % torque on neversiesed bolts 90% on oil lub threads NOt 100% sure but close enough to not get oin trouble. Like someone said torque wrench only makes sure all are same tightness



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Skinner

11-29-2002 15:05:21




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 Re: Re: Re: Torque Wrench Means Large Tension Errors in reply to Bus Driver, 11-29-2002 05:40:36  
Yes, look around on the web. Clean dry threads have a friction rating of 1, neverseize reduces that to 0.16 which means if you use the same torque on the head of each bolt you are going to stretch the heck out of the one with neverseize.

I have torque charts at work and we use lubricants to act as torque multipliers from time to time.



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John Ne.

11-28-2002 19:31:51




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 Re: Torque Wrench Means Large Tension Errors in reply to Blll Hires, 11-28-2002 08:24:51  
Older equipment had heavier castings which gave more leeway in tightening, also thicker gaskets which were more forgiving. cleaning and oiling the threads like Taylor said is important, and if there is an error, all the head bolts will have the same errror. Besides, the torque wrench wasn't developed until 1935. John in Nebr.



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G Taylor

11-28-2002 11:58:44




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 Re: Torque Wrench Means Large Tension Errors in reply to Blll Hires, 11-28-2002 08:24:51  
That's why we use clean threads oiled with engine cam assembly lube after chasing the male and female threads. Stretched,questionable or one time fasteners are hurled. True torquing is not directly measuring fastener stretch/spring. These simple steps do however reduce most of the undesirable variables. The scary thing is nothing is usually used except a pipe wrench, vice grips or a ordinary wrenches by the home tinkerer as they assemble something. It's wonder that more fasteners are not broken,threads stripped,machines fall apart or equipment warps/leaks than what actually does. The engineers thankfully designed in some "tinker tolerance". Funny how it's the machine's.or manufactures fault when something goes wrong however.

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bill b va

11-28-2002 09:29:18




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 Re: Torque Wrench Means Large Tension Errors in reply to Blll Hires, 11-28-2002 08:24:51  

my i point out when you torque a bolt or nut you are not measuring how tight it but the amount of thread restistance .



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