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Re: Torque and Torque wrenches

Posted: Tue Nov 22, 2022 5:44 pm
by Al Zim
I use to do engine work by SLAPPING IT TOGETHER! I always had leakage. Where possible parts that we use are checked on a thick piece of glass with fine Emory cloth WHAT A SURPRIZE.! Most of the engine we see now have the sump plate torqued more than 8 foot pounds and they are bent. EVERYTHING WE ASSEMBLY IS DONE WITH A TORQUE WRENCH. ZIMZ USES OUR TORQUE DUDE which makes 500 foot pounds of torque using a 3/8 inch torque wrench at 53 foot pounds of torque. You can purchase the VW torqueing device (it looks like ours) but it will need to be modified to fit the Porsche Flywheel Bolt and will not work on 356C disc brake axle nuts.
I have read accounts about adjusting valves...and we have taken EVERY rocker arm adjusting off the rocker. Usually one or two are jammed on the rocker because a long wrench was used to make sure they were tight and distorted the threads 13/15 pounds of torque is the specification. If the adjusting device cannot move in the rocker then how do you correctly adjust your valves.
Fasteners: 1963 was the start of fasteners with 13MM heads. Your 14 MM bolts are a minimum of 60 years old. Do you measure the stretch of the bolts to make sure that it has the correct strength?. In this case Millimeters is important. Engines get all the fasters replaced. Metallurgy is significantly better now
And the fasteners have smaller wrench sizes that allow. easier access. putting on the nuts on the studs for a Zenith Carburetor is much easier when they are 10mm in size. The foot is still 13 mm. ZIMZ

Re: Torque and Torque wrenches

Posted: Wed Nov 23, 2022 1:54 am
by DaveErickson
Here is an interesting video on fasteners. Might make you rethink torque specs.

https://www.youtube.com/watch?v=IKwWu2w1gGk

Re: Torque and Torque wrenches

Posted: Wed Nov 23, 2022 2:04 am
by DaveErickson
Al Zim wrote: Tue Nov 22, 2022 5:44 pm ZIMZ USES OUR TORQUE DUDE which makes 500 foot pounds of torque using a 3/8 inch torque wrench at 53 foot pounds of torque.
Al, why do you use an inherently less accurate method for torquing fasteners? Maybe a home hobbiest would use an uncalibrated and less accurate method, but I cannot see why a shop would do it.

-Dave

Re: Torque and Torque wrenches

Posted: Wed Nov 23, 2022 2:05 am
by DaveErickson
duplicate post

Re: Torque and Torque wrenches

Posted: Wed Nov 23, 2022 4:56 am
by Harlan Halsey
DaveErickson wrote: Wed Nov 23, 2022 2:04 am
Al, why do you use an inherently less accurate method for torquing fasteners? Maybe a home hobbiest would use an uncalibrated and less accurate method, but I cannot see why a shop would do it.

-Dave
Dave,
The answer is obvious: because the advantages of the geared system far outweigh the small decrease in accuracy. Or, put differently, the Torque Dude is far more accurate than these jobs demand.

Re: Torque and Torque wrenches

Posted: Wed Nov 23, 2022 2:09 pm
by Al Zim
Dave: did you ever use a 500 Foot Pound torque wrench to tighten the flywheel nut. You will need a friend to ballast the engine so it does not want to flip over, a flywheel lock and the torque wrench. Moving the wrench around is almost a 2 person chore and you will need to be BIG to make the wrench work properly.
THEN you have the rear axle nuts which means you need long bar to hold the axle from turning and no easy method to do that on disc brakes. Zim

Re: Torque and Torque wrenches

Posted: Wed Nov 23, 2022 5:46 pm
by DaveErickson
Harlan Halsey wrote: Wed Nov 23, 2022 4:56 am
DaveErickson wrote: Wed Nov 23, 2022 2:04 am
Al, why do you use an inherently less accurate method for torquing fasteners? Maybe a home hobbiest would use an uncalibrated and less accurate method, but I cannot see why a shop would do it.

-Dave
Dave,
The answer is obvious: because the advantages of the geared system far outweigh the small decrease in accuracy. Or, put differently, the Torque Dude is far more accurate than these jobs demand.
Thats fine if you are a home hobbiest. But a shop has to worry about liability and getting sued. If the shop manual calls for a torque of 385 ft.lbs., then a shop should use a method that can be traced back to standards. Nobody certifies a Torque Dude.

I had a wheel come off once. I had just had the tires balanced and was on the freeway on the way home. The rear fender was badly damaged and the wheel was bent, but I got off lucky. The installer admitted right away that he had gotten distracted by a phone call and had forgotten to torque the wheel bolts, so they were finger tight. However, just think if he claimed that he had tightened them and torqued them with a Torque Dude (or equivalent) and refused to accept responsibility. Do you think he would win or lose in a court of law? For the point of argument, assume you could use a torque dude for this job (it could have been the axle nut).

Re: Torque and Torque wrenches

Posted: Wed Nov 23, 2022 6:26 pm
by Martin Benade
Getting it accurately to 385 ft- lbs may not be terribly important considering that most of the experts have their own pet number, from a little to a lot tighter than factory specs. None of them arrived at scientifically, but they work.

Re: Torque and Torque wrenches

Posted: Wed Nov 23, 2022 6:31 pm
by Pete Indelicato
+1 to Martin--don't over think it.

Re: Torque and Torque wrenches

Posted: Wed Nov 23, 2022 6:58 pm
by Mike Wilson
Interesting videos, Dave. Thanks for posting them.

Mike

Re: Torque and Torque wrenches

Posted: Wed Nov 23, 2022 7:34 pm
by David Jones
385 is pretty much an arbitrary number considering that the chances are that you will have to torque it to where the cotter pin will be able to be inserted.

Re: Torque and Torque wrenches

Posted: Thu Nov 24, 2022 12:15 am
by Rudy Bernhard
Today's flywheel nuts are stronger than the ones that were around when they set the 385 pounds number. Crank material might just be better also. These are good things for those that choose to just use an air ratchet for that final tighten...
And remember it was probably those guys who discovered that bad batch of flywheel nuts years ago. Risk is related to the likelihood of failure times the consequence of the postulated failure. Mass of flywheel, pressure plate rotating at 6000 rpm being released from a crank. Sounds like severe consequence, so take care to keep the failure probability low. Its lots worse than oil leaks from over tightened sump nuts. Use a torque wrench.

The final torque calcs for a tight tolerance torque multiplier can be calculated from the torque of the input torque wrench. For industrial applications precision torque multipliers exist. Not sure what tolerance the torque dude that Al manufactures has. If I remember the original torque dude had the math included in the instructions. There was a bad batch of the ones used in the VW market years ago. They were trash. Used a dude borrowed from a friend who bought one of Al's and it seemed to be tighter in the gears than my decade's old one. Did a beautiful job removing the flywheel nut. Up to the user to decide which tool for which use. Lets see... 1500 miles per year driven, slightly under-torqued flywheel nut... might find out in about a decade, and by then the new owner will likely decide to rebuild the engine, or replace a leaking flywheel seal. Not a common failure you hear much about these days these days. Anyone got a story of what happens when a flywheel decides to leave a crank?

Re: Torque and Torque wrenches

Posted: Thu Nov 24, 2022 3:42 am
by Harlan Halsey
Rudy,
You may not be aware that the #1 journal diameter increases as the torque on the gland nut increases. If you over torque the gland nut way beyond the spec you run the risk of binding the journal. Around 400# is probably the practical limit no matter how strong the material.
BTW that video posted by DAVE is interesting but irrelevant for us. Porsche engines stay together long beyond 100,000 miles, and I would venture to say that failures due to fasteners which were properly assembled, loosening are unknown.
Bolt stretch is critical with Carrillo rod bolts, so they are assembled using a stretch gage. Stock 356 bolts are less critical, so we get away with torque where Porsche has provided the spec.

Re: Torque and Torque wrenches

Posted: Thu Nov 24, 2022 12:59 pm
by Rudy Bernhard
Harlan, great info. Another reason to use the proper torque and tools to tighten the flywheel nut. Thanks, Jacques, for starting this thread!

Re: Torque and Torque wrenches

Posted: Thu Nov 24, 2022 3:08 pm
by Don Gale
Gentlemen: I hate to get down into the weeds with this one, but it struck me as a bit odd that an overtorqued gland nut could swell the diameter of the crank journal enough to affect the bearing clearance . . . so, being the anal retentive OCD ADHD engineer that I am, with too much free time on my hands, I had to model it:

In rough ballpark terms, torque T = .2 * d * Ft
where T = applied torque (convert to in-lb)
d = nominal bolt diameter (in)
Ft = resulting tensile force (lbf)
.2 = an approximate combination of a bunch of coeficients.

Extracting the tensile force from a torque of 385 ft-lb produces Ft = 21,000 lbf

Apply 21,000 lbf to the end of the crank at the flywheel face
crank1.jpg
Evenly apply 1/5th of 21,000/cos30 (assume 60 degree threads) to each of the first five thread faces in the opposite direction
crank2.jpg
Results show a radial growth of 0.0009", slightly less than 0.001" where the nominal clearance should be 0.002-.003" on the diameter.
crank3.jpg
Will the crank bind in the bearing? Perhaps if the clearance is tight to begin with and the gland nut is way overtightened

Just for grins, I looked at the stress in the threads and they are very close to yield, assuming material = 4340 normalized steel
crank4.jpg
Edit: modified model with dowel pins and refined meshing:

Swelling of the crank journal is slightly reduced from previous run (stock gland nut torque = 385 ft-lb).
(Exagerated deformation display scale)
crank5.jpg
Internal crank thread stresses are still high, approaching yield:
crank6.jpg
(FEA method = SolidWorks Simulation Premium, 2017 version)