Bolt stretch

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: Harold_V, websterz, GlennW

User avatar
SteveM
Posts: 6524
Joined: Mon Jun 27, 2005 6:18 pm
Location: Connecticut

Re: Bolt stretch

Post by SteveM » Wed Aug 08, 2018 5:14 pm

John Hasler wrote:
Wed Aug 08, 2018 1:49 pm
This needs to be emphasized. The goal when tightening a bolt is to achieve a specific amount of tension in the shank, not to reach a specific torque. The torque is just a convenient but indirect (and inaccurate) indicator of tension.
I remember the head bolts on a car that tightened to a specific (but low) torque and then you turned them a specified angle (like 1 quarter or half turn).

The bolts were NOT reusable.

My dad had a car that SPECIFICALLY called for oiling the studs and then torquing to the spec.

Steve

User avatar
Rich_Carlstedt
Posts: 1437
Joined: Sat Dec 21, 2002 12:16 am
Location: Green Bay Wisconsin USA

Re: Bolt stretch

Post by Rich_Carlstedt » Wed Aug 08, 2018 5:15 pm

SteveM wrote:
Tue Aug 07, 2018 9:05 pm
The lug nuts on a Toyota Sienna are M12 x 1.5.
The manufacturer spec is 80 ft-lbs, which produces a predetermined (but unknown to me) bolt stretch.
The dealer put them on with 130 ft-lbs.
Is there any way with just that information to calculate if the bolts have been excessively stretched?
Steve
Wow, that is an incredible amount of over torquing for a thread !
Inform the dealer immediately ! I have worked a lot with Bolt torques on dies when employed
Stretch , or deformity cannot be determined without knowing the stud material composition and strength.
Even so, consider this: Lubricated threads and bolt/nut face reduce torque requirements by 15 %
The finest bolts/screws you can buy are made by Unbrako ( IMHO after many yrs experience and experimentation)
Use their specs for the highest level of performance for most fasteners
Please go here
http://www.unbrako.com/images/downloads/engguide.pdf
Start at page 39
Note that Meteric fasteners are graded DIN 8 or 10 or 12 ie.
The best being DIN 12.9
Note the "required strength - 1220 Mpa , which is 177,000 pounds Tensile Strength here in America
Now read down to Unbrako's standard for bolts 16 mm and under and you see1300 Mpa or 189,000 pounds tensile ( quality !)
Now go to the next page (40) and read the Torque value for a Unbrako screw
The 12 mm is rated at 1200 inch pounds, or 100 Foot Pounds of torque
Note also that the torque will induce a 800 Mpa Load on the fastener ( footnote on page)
Note on same page that the "YIELD" point is at 1170 MPA ( which is 46 % higher than max torque of 800 Mps is given)
This is imperative info because once yield is reached, the threads deform and failure is imminent as the torque value decreases
So if we apply the above to your notes-- we have a torque point of 130 FtPounds versus a possible failure point of 146

You do not know the strength of the stud, but I personally doubt it is equal or better than an Unbrako IMHO
What I am concerned with is your personal safety and decided to post commercially available info and reasonable logic rather then my calculations or opinion for your consideration.

Rich

User avatar
BadDog
Posts: 4513
Joined: Wed May 17, 2006 8:21 pm
Location: Phoenix, AZ

Re: Bolt stretch

Post by BadDog » Wed Aug 08, 2018 6:12 pm

Best bet is to insist the tire shop use a torque wrench. I've made THEM loosen and retorque in front of me when they don't, or there is any question of honesty. Angered more than one service manager, but better than me being out on the road and having to change a tire by hand. I know it's a compromise, but I will accept use of a torque bar. And yes, if it's not a dire emergency, I stay and observe. Having worked as and with professional wrenches, I've seen enough that there are very few mechanics I trust with my vehicles.
Russ
Master Floor Sweeper

User avatar
liveaboard
Posts: 484
Joined: Sun Dec 08, 2013 1:40 pm
Location: southern Portugal
Contact:

Re: Bolt stretch

Post by liveaboard » Wed Aug 08, 2018 6:40 pm

I had the left rear wheels come off my fully loaded Mercedes 5 ton van while driving down the road.
No one to blame, I put them on myself.
After decades of that sort of work, I didn't think such a thing could happen to me, but it did.
It was a bit frightening.
Apparently it's not uncommon with those vans, the under engineered lug nuts have to be torqued just right or else; KABOOM
Anyway, now I have a nice snapon click torque wrench and things are all rosy.

Van didn't roll, but it was dicey. Got carried to a nearby free parking area on the southernmost tip of Europe, and got new lug bolts from Mercedes after a couple of days. the brake drum lost some metal, but was still usable. One wheel needed to be replaced too.
The police found one of my wheels in the bushes a mile up the road and brought it to me! Good guys.

User avatar
BadDog
Posts: 4513
Joined: Wed May 17, 2006 8:21 pm
Location: Phoenix, AZ

Re: Bolt stretch

Post by BadDog » Wed Aug 08, 2018 7:11 pm

Yeah, I did that too. My son and I were doing brakes on our light duty K5 rock-crawler/expedition rig 35" tires on 1 ton axles, 8 lugs per wheel. I put the wheel on and ran the nuts down just to take up the slack with an air ratchet (LONG threaded studs/nuts), he was following me with the torque wrench, and he was to tighten them in a fast criss-cross pattern. Not sure what happened, but I had gotten to the point working with him (about 16 years old) that I trusted him (working on vehicles at least) and no longer double checked everything.

He drove it to work that night and made it about 5 miles before turning into the parking lot as the back left wheel just came completely off. He said he felt it just as he was turning in and just had time to think, "I need to check that when I get parked" before the back left corner dropped. When you are making a hard right and the back left 35" tire falls off, the tip-up is very dramatic, or so I'm told. He said he had a momentary panic moment as it triggered memories of our Rock Buggy (42" tires) going over backwards climbing a waterfall. :D Thankfully it didn't do a corner-over, but that 1 ton drum did take a chunk out of the asphalt (no damage, thing weighed about 70 lbs for just the drum), and I'm pretty sure he'll never forget to tighten a wheel again...
Russ
Master Floor Sweeper

User avatar
liveaboard
Posts: 484
Joined: Sun Dec 08, 2013 1:40 pm
Location: southern Portugal
Contact:

Re: Bolt stretch

Post by liveaboard » Thu Aug 09, 2018 2:23 am

We were going about 50 mph when the wheels came off. Odd thing is that I didn't feel them wobbling, damage to the lugs and mounting holes indicated they'd been loose for a long time. We'd driven 2,000 miles from across Europe since I mounted them.
Not huge tires + wheels, but substantial enough to total a European car if there had been a head on collision. Luckily it was late at night and the road was empty.
We traveled another 100 yards with the drum rolling on the road as I eased it to the shoulder. Yee Haw! What a rush.

John Hasler
Posts: 868
Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: Bolt stretch

Post by John Hasler » Thu Aug 09, 2018 8:24 am

My father had the right rear come off a Michigan Bell company van while he was going about 60 on a paved rural road. He came over a rise, started to brake lightly as he started down a small hill, and saw the wheel pass him. The van stayed on three wheels until he had rolled nearly to a stop. The lugnuts had been left loose when the Chevy garage service the van a week earlier.

I was very lucky *not* to have a wheel come off my IH544 tractor (7000 lb, 18-28 tires filled with 900 lb of solution). The hubs spline onto the axles and are retained by huge washers and single 3/4" grade 8 bolts torqued as specified in the manual. There is rarely any reason to remove them, and I never had. I spent some time mowing ditches (tractor tilted 30 degrees), unhitched the mower, and parked it. As I walked past the left rear after dismounting I happened to glance at the hub. No washer. Broken bolt.

I fixed that (fabricated the washer: IH wanted some ludicrous price for it) and checked the other side. Grade 2 bolt, overtorqued.

Mr Ron
Posts: 1582
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: Bolt stretch

Post by Mr Ron » Thu Aug 09, 2018 11:27 am

Thank you for the correction. One time I rented a car at the airport and drove it on the freeway for about 5 miles before the left rear wheel came off. I had just enough time to see the wheel in my side mirror starting to wobble and was able to pull over on the shoulder before the wheel overtook me and continued down the road sans car.
The problem with most mechanics is: they use an impact wrench on the wheel lugs with no idea how much torque has been applied. Un-torquing and re-torquing with a proper torque wrench may be too late as the studs may have already reached their elastic limit.
Mr.Ron from South Mississippi

User avatar
warmstrong1955
Posts: 3127
Joined: Thu Mar 18, 2010 2:05 pm
Location: Northern Nevada

Re: Bolt stretch

Post by warmstrong1955 » Thu Aug 09, 2018 11:41 am

Mr Ron wrote:
Thu Aug 09, 2018 11:27 am
Thank you for the correction. One time I rented a car at the airport and drove it on the freeway for about 5 miles before the left rear wheel came off. I had just enough time to see the wheel in my side mirror starting to wobble and was able to pull over on the shoulder before the wheel overtook me and continued down the road sans car.
The problem with most mechanics is: they use an impact wrench on the wheel lugs with no idea how much torque has been applied. Un-torquing and re-torquing with a proper torque wrench may be too late as the studs may have already reached their elastic limit.
Same thing happened to me with a rental I got at the Spokane airport, but it was the right wheel. Had to walk about a mile to retrieve the tire & wheel, borrowed a lugnut of the other three that were still on the car....and checked 'em to see if they were tight while I was at it.

Bill
Today's solutions are tomorrow's problems.

User avatar
liveaboard
Posts: 484
Joined: Sun Dec 08, 2013 1:40 pm
Location: southern Portugal
Contact:

Re: Bolt stretch

Post by liveaboard » Thu Aug 09, 2018 12:48 pm

well this is a lot of wheels coming off a lot of cars [+ trucks]. I guess it's more common than I imagined.

I recently added an impact wrench to my home workshop. It gets within a whisper of my torque wrench, but of course I always check now.

On my tractor I just haul on the lugs with a 4' lever.

User avatar
ctwo
Posts: 2673
Joined: Tue Mar 27, 2012 12:37 pm
Location: Silly Cone Valley

Re: Bolt stretch

Post by ctwo » Thu Aug 09, 2018 1:10 pm

I've never heard of wheels coming off due to snapped lugs, but I have heard endless stories of tire shops over-torquing. I just drop my calibrated foot onto the wrench for the final torque (I actually just use my hand with the wrench horizontal.).

I didn't think click wrenches worked both ways. I have been specifically told not to use a torque wrench to remove bolts, as that will affect its calibration. But, if it is a two-way clicker, I would repeat the experiment with the nuts properly torqued and compare loosening torque. I think marking the location of the nut works too, as long as they were not over-torqued to yield.
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

User avatar
warmstrong1955
Posts: 3127
Joined: Thu Mar 18, 2010 2:05 pm
Location: Northern Nevada

Re: Bolt stretch

Post by warmstrong1955 » Thu Aug 09, 2018 1:18 pm

Checking is a more than good plan. Impacts are a disassembly tool, and a 'rough' assembly tool only.
Wheel fasteners come loose on a lot of heavy equipment too!
Generally due to using only an impact, and with Budd nuts, because they were not centered when the wheel was installed.

I had a rule at the places I worked, that all wheels will be torqued with a torque wrench. No exceptions. Having a wheel come loose on a 8 yard LHD, or any piece of equipment, wrecks the wheel, the studs, and can damage the hub. Not to mention the time it takes to fix all that stuff, and loss of availability.

FYI....some clickers work both ways....and some do not. My Protos do. I have an old Craftsman that doesn't, and a newer one that does.

Bill
Today's solutions are tomorrow's problems.

Post Reply