Torque and Torque wrenches

356 Porsche-related discussions and questions.
Message
Author
User avatar
Al Zim
Registry Trustee
Posts: 3433
Joined: Fri Mar 14, 2008 9:14 pm
Location: FT.WORTH/DALLAS TEXAS

Re: Torque and Torque wrenches

#16 Post 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
www.allzim.com 
356 Parts and Services

DaveErickson
356 Fan
Posts: 1464
Joined: Sat Oct 26, 2013 9:34 pm
Location: Monterey, CA

Re: Torque and Torque wrenches

#17 Post by DaveErickson »

Here is an interesting video on fasteners. Might make you rethink torque specs.

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

DaveErickson
356 Fan
Posts: 1464
Joined: Sat Oct 26, 2013 9:34 pm
Location: Monterey, CA

Re: Torque and Torque wrenches

#18 Post 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
Last edited by DaveErickson on Wed Nov 23, 2022 2:06 am, edited 1 time in total.

DaveErickson
356 Fan
Posts: 1464
Joined: Sat Oct 26, 2013 9:34 pm
Location: Monterey, CA

Re: Torque and Torque wrenches

#19 Post by DaveErickson »

duplicate post

User avatar
Harlan Halsey
356 Fan
Posts: 1742
Joined: Fri Mar 02, 2012 2:05 pm
Location: No Cal SF Peninsula

Re: Torque and Torque wrenches

#20 Post 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.

User avatar
Al Zim
Registry Trustee
Posts: 3433
Joined: Fri Mar 14, 2008 9:14 pm
Location: FT.WORTH/DALLAS TEXAS

Re: Torque and Torque wrenches

#21 Post 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
www.allzim.com 
356 Parts and Services

DaveErickson
356 Fan
Posts: 1464
Joined: Sat Oct 26, 2013 9:34 pm
Location: Monterey, CA

Re: Torque and Torque wrenches

#22 Post 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).

User avatar
Martin Benade
356 Fan
Posts: 9539
Joined: Wed Nov 23, 2011 10:52 am
Location: Cleveland, Ohio

Re: Torque and Torque wrenches

#23 Post 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.
Cleveland Ohio
62 Cabriolet
56 VW
02 IS 300
04 Sienna

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

#24 Post by Pete Indelicato »

+1 to Martin--don't over think it.
1963 T6 couple #212891, motor #*KD*P*730464

User avatar
Mike Wilson
Classifieds Monitor
Posts: 9494
Joined: Tue Apr 15, 2008 4:37 pm
Location: SW Los Angeles

Re: Torque and Torque wrenches

#25 Post by Mike Wilson »

Interesting videos, Dave. Thanks for posting them.

Mike
Mike Wilson
Lomita, CA
'63 B coupe

User avatar
David Jones
Classifieds Moderator
Posts: 6920
Joined: Tue Mar 25, 2008 6:32 pm
Tag: I wish I knew as much as I think I know.
Location: Kentucky

Re: Torque and Torque wrenches

#26 Post 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.
If I had known I would live this long I would have pushed the envelope a little harder.
Cymru am byth
David Jones #9715

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

Re: Torque and Torque wrenches

#27 Post 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?
60 Super Cab, 63 S90 Cpe
#311

User avatar
Harlan Halsey
356 Fan
Posts: 1742
Joined: Fri Mar 02, 2012 2:05 pm
Location: No Cal SF Peninsula

Re: Torque and Torque wrenches

#28 Post 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.

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

Re: Torque and Torque wrenches

#29 Post 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!
60 Super Cab, 63 S90 Cpe
#311

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

#30 Post 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)
Last edited by Don Gale on Mon Nov 28, 2022 12:50 pm, edited 2 times in total.
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"

Post Reply