Torque and Torque wrenches

356 Porsche-related discussions and questions.
Message
Author
User avatar
Jacques Lefriant
356 Fan
Posts: 4203
Joined: Mon Dec 06, 2010 1:50 pm
Location: National City Ca

Torque and Torque wrenches

#1 Post by Jacques Lefriant »

Hi Al and Brad
i will not use capitals but i admit to not using torque wrenches on occasions. In some cases the use of torque wrenches could be detrimental since the book value could be in error and some torque wrenches don't prove feedback. in situations where the strech can not be determined a combination of initial torque and angle will provide more equal loading. lubrication is an important consideration to establish the loading and torque value to use. experienced technicians have no problem using feel in most cases on say a sump plate. there have been some you tube videos that rate commercially available torque wrenches for accuracy and consistency. for hi torque requirements i prefer a beam type for feel and for consistency a clicker one.
j
Last edited by Jacques Lefriant on Mon Nov 21, 2022 9:43 pm, edited 1 time in total.
 

User avatar
Jacques Lefriant
356 Fan
Posts: 4203
Joined: Mon Dec 06, 2010 1:50 pm
Location: National City Ca

Re: Torque and Torque wrenches

#2 Post by Jacques Lefriant »

Hi
Only 95 views and no reply? i would think this topic would generate a civil discussion and be beneficial to the individuals that never used a wrench.
j
Thanks Rudy i hope you did not imply i was a wise guy OK you got me.
 

User avatar
Rudy Bernhard
356 Fan
Posts: 107
Joined: Fri Apr 03, 2009 4:01 pm
Location: Atlanta area

Re: Torque and Torque wrenches

#3 Post by Rudy Bernhard »

I agree with Jacques. Look in your toolbox. Wrench lengths vary with the size of the fastener, shorter for smaller sizes, to allow for the lower torque for common fasteners using the feel from the hand of the experienced mechanic. It also lessens the likelihood of stripping the threads.

Torque is not twisting, as is commonly believed. Critical torque values are specified for applications where minimum clamping force is necessary to hold parts together in service with their expected loads. Each fastener's stretch supplies the force using the same laws as a spring. Tightening the lubricated, threaded fastener will stretch the bolt or stud the required amount to provide the clamping force without taking the fastener to plastic deformation. If you over torque you will feel the nut or bolt suddenly turn with a smaller force, and the fastener has likely failed in a way that the required clamping force will not be provided.

Even use of torque wrenches can give a false sense of security if too large of one is used. Smaller ones result in higher accuracy for smaller torques. Yeah, mechanical engineers do the calcs, but frequently suck at putting the calcs into practice.
60 Super Cab, 63 S90 Cpe
#311

User avatar
Martin Benade
356 Fan
Posts: 9533
Joined: Wed Nov 23, 2011 10:52 am
Location: Cleveland, Ohio

Re: Torque and Torque wrenches

#4 Post by Martin Benade »

Torque is twisting force, specified for bolt tightening because it’s easy to measure even though it’s relationship to clamping force is quite sketchy.
I’ll admit there are times I’m confident enough not to use a torque wrench, not that I can do better that way, but I can do “good enough”.
Cleveland Ohio
62 Cabriolet
56 VW
02 IS 300
04 Sienna

User avatar
Wes Bender
356 Fan
Posts: 3965
Joined: Wed Aug 27, 2008 10:54 am
Location: Green Valley, AZ

Re: Torque and Torque wrenches

#5 Post by Wes Bender »

I think anyone who has used torque wrenches will develop a feel for various torque values. I own three torque wrenches over varying sizes. I pull them out and use them if I think the torque is critical, for example, alternately torquing head bolts. For tightening of most common fasteners I use the torque wrench that resides on the end of my arm. I limit torque by using use a twist of my wrist when tightening sump plates or carb cover bolts. After a visit to the local tire shop for new skins on my Tacoma, however, I always drag out a torque wrench and recheck their work. I've had them stretch a few wheel studs in the past and I also may need to remove the lug nuts alongside the highway.
Some days it's just not worth chewing through the restraints.....

User avatar
Rudy Bernhard
356 Fan
Posts: 107
Joined: Fri Apr 03, 2009 4:01 pm
Location: Atlanta area

Re: Torque and Torque wrenches

#6 Post by Rudy Bernhard »

Martin, you are correct, and I stand corrected. The force required to turn the nut or bolt is determined by the normal force to the bolting surface times the coefficient of sliding friction between the nut and the surface. As the bolt or stud stretches, the normal force increases, and the force required to continue turning the bolt or nut increases. Since lots of things can impact the coefficient (lubrication, surface roughness), Lookup Tables are commonly used to relate the torque value to the stretch so calculations using the coefficients are not necessary for common materials. But the function is to stretch the bolt or stud a defined amount using a pitched thread.

You can get the same effect through other methods like using thermal expansion on large studs, and then just snugging the nut down when the right amount of lengthening is achieved as measured by a dial indicator. when the heat causing the thermal expansion goes away, the stud is in tension. But we are not assembling turbine generators here.

But now everyone's eyes are glazed over...
60 Super Cab, 63 S90 Cpe
#311

User avatar
Martin Benade
356 Fan
Posts: 9533
Joined: Wed Nov 23, 2011 10:52 am
Location: Cleveland, Ohio

Re: Torque and Torque wrenches

#7 Post by Martin Benade »

I forgot the number I read but I think the variation in stretch at a given torque is huge due to all the variables. Even though it’s used a lot torque is a terrible way to assess clamping force.
Cleveland Ohio
62 Cabriolet
56 VW
02 IS 300
04 Sienna

User avatar
Jim Clement
356 Fan
Posts: 1134
Joined: Tue Oct 26, 2010 10:46 am
Tag: 1957 356 A Coupe
Location: Calgary Alberta

Re: Torque and Torque wrenches

#8 Post by Jim Clement »

I am an not as experianced as many of you, I try and use a tourque wrench when ever I can and can find the values.
I always use one on my wheels, and Wes - yes, I find the tire guys are all over the map, sometimes they are like 2 times the correct value..
 

User avatar
Greg Bryan
356 Fan
Posts: 3055
Joined: Sat Oct 04, 2008 1:05 pm
Location: San Pedro, CA 90732 Fallen Leaf, CA
Contact:

Re: Torque and Torque wrenches

#9 Post by Greg Bryan »

I would say if you are not an experienced mechanic, use a torque wrench. The tendency is to overtighten (I was an autoshop teacher in a former life). More fastener failures are caused by over-tightening than under-tightening, although not exclusively. I don't think you can estimate anything much over say 36 ft lbs.
I've been fooling around with cars since the '60s and tend to do a lot of hand tightening but not on critical fasteners such as rod bolts, flywheel nuts, head bolts, etc. It would be interesting to do an experiment and see how close one can come to a target torque value.
Greg Bryan

User avatar
Rudy Bernhard
356 Fan
Posts: 107
Joined: Fri Apr 03, 2009 4:01 pm
Location: Atlanta area

Re: Torque and Torque wrenches

#10 Post by Rudy Bernhard »

Also reuse the original German hardware whenever you can, not just for appearances. For the most part they are well made. The amount of 'Bogus' fasteners out there is staggering. Even at the proper torque values the poorly fabricated, wrong strength steel fasteners are failing. Buy replacement hardware from a source you trust to supply qualified automotive grade hardware, not just the local chains.

Always use the required hardened steel washers and thread lubricant in joints where torque is specified to minimize the variations in stretch that Martin mentioned.

Stainless threads, even lubricated, will gall easily while tightening. Keep your original carbon steel fasteners, stainless is not necessarily an upgrade. Stainless and Carbon Steel together in a joint can also set up a corrosion cell if moisture is present, and can lead to localized rusting.

Don't over torque the screws in your Porsche's electrical parts, or mechanical assemblies, either. Hooking up those pliers to the screwdriver's shaft for more force while tightening isn't a good idea either. Distorted fuel pump, Carb bodies or fuse boxes anyone?
60 Super Cab, 63 S90 Cpe
#311

User avatar
Rudy Bernhard
356 Fan
Posts: 107
Joined: Fri Apr 03, 2009 4:01 pm
Location: Atlanta area

Re: Torque and Torque wrenches

#11 Post by Rudy Bernhard »

Jacques, I prefer beam type torque wrenches for smaller fasteners, where i am more likely to be able to read it accurately. I use click type for larger fasteners, and I use a torque screwdriver (click type) for many electrical connections. But I have never had any of my garage tools checked or recalibrated as I did for the at work tools. Contributes to Martin's variations.
60 Super Cab, 63 S90 Cpe
#311

User avatar
Carl E. Klem
356 Fan
Posts: 30
Joined: Mon Jan 24, 2022 10:30 pm
Tag: Keeping going keeps me & my cars going :
Location: Santa Cruz, CA

Re: Torque and Torque wrenches

#12 Post by Carl E. Klem »

61 years ago when I was 16 years old I asked an old time mechanic how much I should torque the head bolts on my Model A Ford. He said he torques them until the hair on his arm stands up. I then bought my first torque wrench. My question now is, where do I get my torque wrench calibrated? The only time this even occured to me was a few years ago while getting new tires at Costco. They store their torque wrenches on a machine that checks calibration between each use. I think of this each time I use and trust my torque wrenches.

User avatar
Wes Bender
356 Fan
Posts: 3965
Joined: Wed Aug 27, 2008 10:54 am
Location: Green Valley, AZ

Re: Torque and Torque wrenches

#13 Post by Wes Bender »

Carl, find a dealer for the brand of torque wrench you own and they can send it in to be calibrated. In theory, you could put together your own calibration check. All it would require would be a known weight on a specific length arm that was attached to a shaft that you could turn with the torque wrench. Checking it in about the middle of its range would suffice for a quick check.

I would also submit that a torque wrench will not be as accurate near the ends of its range. For this reason, I try to use the middle two thirds of the range and is the reason I have three wrenches. My smallest is intended for bicycle shop use.
Some days it's just not worth chewing through the restraints.....

User avatar
Don Gale
356 Fan
Posts: 920
Joined: Wed Jul 26, 2017 6:27 pm
Tag: Black A's Matter
Location: Albuquerque
Contact:

Re: Torque and Torque wrenches

#14 Post by Don Gale »

I bought a digital torque adapter at Harbor Freight when it was on sale and used it to "calibrate" all of my click-type and lever-type and dial torque wrenches. It can also be used directly stand alone. It came with a certification sheet, don't recall specifics but it was tested to be within 1% or less when packaged.
torque_adapter.jpg
1958 356A 1600 Super Sunroof Coupe
former 1966 Euro 912 Sunroof
former 1978 Intermeccanica Speedster w/'68 912
Member Since 1983, #4039

"Nostalgia isn't what it used to be"

Pete Indelicato
356 Fan
Posts: 362
Joined: Mon Apr 13, 2020 2:42 pm
Tag: 356 owner
Location: Yountville, CA

Re: Torque and Torque wrenches

#15 Post by Pete Indelicato »

We used to have a saying in the Budweiser maintenance shop--"We're not making a watch and it's not going to the moon"--(we had a former NASA engineer)--don't over think it. For most cases tight is tight, just don't want it to fall off.
1963 T6 couple #212891, motor #*KD*P*730464

Post Reply