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How do you torque?
Posted by: 63 Spyder Ragtop ()
Date: January 12, 2020 05:39AM

When torquing to spec, particularly on aluminum, how do you torque? Do you torque to the spec on the first pull or do you up the torque in steps ie: say your spec is 80 ft lbs, do you torque to 30 lbs, then 60 lbs and the final pull to 80? I've always stepped and then check the final torque several times afterward. My reasoning is to get a gradual pull to allow the metal to adjust. Is this reasonable or a waste of time?

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Re: How do you torque?
Posted by: Caraholic4life ()
Date: January 12, 2020 05:50AM

Your method makes sense to me. It is the method I also practice when torquing almost anything regardless of the material the threads are in.
When gaskets are a part of the equation, I believe it is more important to follow this procedure in order to reduce the chances of distorting or potentially damaging the gasket or seal.

1962 95 F.C. Van
1965 Monza Coupe
Westminster, Maryland

MID ENG enthusiast &
prior Kelmark owner.

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Re: How do you torque?
Posted by: JimBrandberg ()
Date: January 12, 2020 06:35AM

I definitely do it in stages with a sequence.
When doing Corvair heads I go through several times with only the last few with the torque wrench, 25 and 30.
When doing a Corvair crankcase I go through the last 3 sequences with the torque wrench. I check the crankshaft rotation and beat on it with a rubber mallet in-between which may be folly but that's what I do because that's what I've always done.

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: How do you torque?
Posted by: racingguy2 ()
Date: January 12, 2020 07:26AM

From working in a lab which did extensive torque testing of threaded fittings, the proper way to torque a multiple thread system is to torque in stages. They recommend 75% torque, then 100%. For your example of a final torque of 80ft/lbs, you would torque in sequence to 60ft/lbs, let the material rest for a few minutes, then torque to 80ft/lbs. NEVER go back over and retorque at 80, as you will actually risk over-torquing, especially with a click type torque wrench. Also, bear in mind that break away torque plays a factor (basically the friction between the nut and the stud and the nut/washer/face), so you want to make your final torque in one smooth, non-stop motion. If you are getting that fingernails on chalkboard creaking noise, stop and reapply lube as you will not get an accurate torque this way. Lubrication plays a huge factor in break away torque as well. They recommended hydraulic oil, stressed that any oil would work, as long as you always used the same thing that the torque spec was developed with. In professional racing, a lot of people use ARP anti-seize, not because it is magic or special, but because it is consistent. (They develop torque spec's by measuring fastener stretch, which is actually a much more accurate way to measure tension. Torque is just a much more convenient estimate.) Also, be sure to lube the face of the fastener and washer as well as the threads!

When thermal cycling is involved, like an engine, the proper way to verify torque ISN'T to go back over the fasteners at 80ft/lbs, but rather to torque, thermal cycle, loosen below 50% torque, then re-torque in stages as above.
This of course is all different in torque-to-yield fasteners, but that's a complicated story for another day!

Hope this helps!

Eric
Plymouth, Michigan
74 Kelmark GT (Mid engine Corvair 140)
02 Maserati CambioCorsa Spyder
06 Porsche Cayenne
89 Jaguar XJS 12
86 Alfa Romeo Graduate (7200 miles!)
1902 Curved dash Olds
70 Fiberfab Avenger
57 Ford Custom 300 (factory 312Y)
80 Mercedes-Benz 450SL
05 Audi TT
Cylinder head and valvetrain engineer, PhD Nuclear Engineer
Originator of strange ideas and over-complicated solutions!

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Re: How do you torque?
Posted by: 63 Spyder Ragtop ()
Date: January 12, 2020 07:34AM

Yes, this helps immensely! I do have hydraulic oil in my garage and will use it. Thanks for the info.

Chris

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Re: How do you torque?
Posted by: dolomitefan ()
Date: January 13, 2020 04:28AM

When re-torquing a cylinder head on my Triumph I tend to back the nut/stud off slightly and then re-torq to avoid the overtorquing.

---------------------------------------------------------------
Mark Gibson, Staffordshire, England

1961 Corvair Greenbrier
1980 Triumph Dolomite Sprint
2009 Mazda MX5
2018 Infiniti Q30

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Re: How do you torque?
Posted by: Lane66m ()
Date: January 13, 2020 05:03AM

Unless lubricant is called out to be applied to hardware threads before torqueing, avoid the lubricant. threads should be clean and dry. Lubricant will change torque value on hardware when torque is applied.

Quote from website "lubrication of threaded bolts has lots of benefits, but with it comes the overriding concern that the lubricant will change the torque required to develop proper tension on the bolt—and how that could affect the integrity of the joint. Some estimate that adding a lubricant could reduce the required torque reading by up to 40 percent!"

[www.smartbolts.com]

Al Lane
Ellabell, GA 31308

1966 Monza Coupe, 110 hp, 4 Spd
1966 Monza More Door 110 hp, PG
1968 Camaro SS Coupe 350 CI 295+ hp PG
1964 Greenbrier Deluxe, 6 dr, 80 hp car engine, PG
1947 Farmall A tractor 15 hp


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Re: How do you torque?
Posted by: vairmech ()
Date: January 13, 2020 05:10AM

Eric described the absolute perfect way for torquing!

BUT

We do not live in a perfect world!

The Corvair case halves need to be torqued in 3-4 stages, I start at 20 lbs. ft., 40 then 60 lbs. ft., with a big rap of a hammer on an end web on the pan gasket side after each torque stage. You need to hear the crack of the hammer! The vibrations relieve the case stresses and unevenness causing crank binding. You should be able to grab either crank end and spin the crank with just a little drag. If you try to turn the crank before you hit the case and cannot, keep pressure on the the crank and then hit the case. All of a sudden the crank will turn free after you hit the case! There is also a specific pattern for the crankcase that has proven to work even better than the shop manual.

The heads are a little different story. Here you need to start low! I use the lowest setting on my click type torque wrench of 15 lbs. ft. Start on the top studs and then do an X pattern all the way across the head. This is NOT for each cylinder but the WHOLE head. You do not X each cylinder but continue the X pattern in a circular X across the complete head. My next step is less than the recommended step as i only go to 20 on the next step and do an X pattern again. Then I go to 25 lbs. ft. and finally I do 30 lbs.ft. Do NOT believe the shop manual for 38 lbs.ft.!
There is more to this though than I just described. You need to go back to the center cylinder and retorque after yo have went through even the 15lbs. ft. You will see the center nuts have become loose! You do each step until the torque does not change! Then go to the next step. On the final torque to check all fasteners you do not need to follow any specific pattern. If you do not do this then you run the risk of blowing the center head gasket.

What I have described is for stock steel gaskets, the copper gaskets are just as critical if not more so. Also yo think the heads are a solid mass? They are VAIRY flexible! That is why you need to be so careful with them.

Lastly is semantics! LOL when everyone talks about torque they say ft. lbs. Did any of you notice that I did Lbs. ft.? If you look it up that is the absolute correct way to talk about torque. Not that everyone will automatically change now, it's just one of my things.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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