Torque decrease for lubricated bolt

Perhaps I have that old saw wrong. No doubt that is why I broke it off

Torque specs are produced by committees like the SAE etc. for the different fastener types with a number of things in mind, among them litigation. A lot of lab work went into getting specs, look at what is at stake when talking about aircraft components.

So it is heavily tied into the companies that manufacture goods, they have to have their product hold together to avoid lawsuits, and they can not recommend specs that might see a mechanic damaging expensive equipment during repair or overhaul.

If you work in a Nuke plant you will see torque wrenches used on fasteners you would never think about, all so that in case something blows up corporations can say they are not responsible because everything was done to "spec".

Aside from that, a really experienced mechanic can work without a torque wrench. A bolt is simply a spring that has to have a rating so that it does not stretch more than a certain amount under load.

An experienced mechanic, torquing up a fastener with clean oiled threads, can feel the stretching of the bolt as it is tightened, he can also feel when the steel begins to yield, the point where it is stretched to the point that it will not spring back to it's original length when loosened.

The order of torquing bolts can also be learned and become intuitive quite easily. I am sure there are any number of old mechanics that could assemble any engine without a torque wrench or manuals and have the finished product give perfect service, perhaps even better than a neophyte mechanic who did the work by the book and might have missed details and earmarks of problems during assembly.

My retired neighbor across the street was a very professional mechanic for over half a century working for other companies rebuilding heavy truck engines for one, and he backs this up, and in turn he said he initially learned from an old mechanic that did work by feel.

So there can be some art involved in the best mechanical work where experience and aptitude can beat schooling and books.

Another example is how students of tool and die do everything by machine and computers these days, but the highest form of the art is still hand fitting of parts, making a part fit a surface plate by hand scraping so that when it is put on a magnetic grinder table it is not falsely pulled flat and unsuccessfully ground.....

This old story has been around for a hundred years -

Torque specs for an engine were determined by having a experienced mechanic assemble the engine. Instead of a normal wrench, they gave him a torque wrench. He paid no attention to it, just tightened the fasteners by feel. As he did that, a lackey observed and wrote down the reading on the wrench for each bolt he tightened. They then published those readings as the "torque specs" for the engine. True or not true? Who knows but sure seems possible.

FWIW Re engine oil for lubricant - In the era of the Norton Commando, US auto engine makers published the torque specs for the engines in the shop manual, specifically stating if the fasteners were to be assembled clean/dry or lubricated. If lubricated, the lubricant specified was almost always 30 WT motor oil. I say "almost always" because there were some bolts on some engines that penetrated the water jacket and those bolts were specified to have sealer applied as opposed to oil. So at the time, engine oil was commonly specified as thread lubricant for engine assembly.

The thing to keep in mind, torque is simply a resistance to rotation. Tension is the critical factor as applied to fasteners. Since most of us don't have the equipment to measure tension we use torque as a relative indicator of fastener tension. The measured torque is usually a spec of a fastener with clean, in most cases very lightly lubed threads, that has the specified tension. The only thing I would be afraid of with oiled threads is when torquing up a fastener in a blind hole with too much lube, enough to cause hydro locking. As for our Norton fasteners; no rust and chase both threads. That is, use a die and tap for both the male and female threads. If you oil, wipe down with a clean rag before installing. As for completely dry threads, I think that's an invitation for rust.

Cylinder head torque from an old diesel locomotive engine service manual: "One man on a 6' wrench" :lol: :shock:

But seriously, "lightly oiled" threads is the standard in industry. Moly grease, Nevr-Seez and such changes the game, whole other kettle of fish. DRY thread assembly is best reserved for MEANINGLESS threads like license plate bolts. Assembly of critical of fasteners DRY will give torque values way before reaching desired clamping force.

You will find dry-oiled settings have the same effect on the clamping force. A dry thread just as a greater resistance due to frictional forces. oil it and reduce the torque. the bolts stretch is the same. Tension and bolt grade varie's set screws and socket head cap screws are totaly differant, then full commercial "rolled" thread are up with the strongest. My old cummins had 500 lbs torque cyliner head bolts, the gasket is mild steel! a 4-1 multiplier was needed .

Rider wakeup and all's'ya'alls, I take all your reports as concerned advice not misleading or personally offensive and apologize for my meanly stated attitude. I do not for an instant think Norton did any research on torque values except maybe the rod cap bolts and just listed values for the rest by what prior trial and error testing found appropriate in various makes and models of engines and bicycles, which means there or errors in the manual. Guess how these errors in the manual get discovered by newbies... The main frustrating torque factors that makes following a set torque value about ridiculous in Nortons is they do not retain that torque clamp value after first warm up cool cycle, ugh, so what do ya do, if just re-torque to set value that just don't stay that way long? I loved the example proving my point of view, of manufacturer using an experienced mechanic's calibrated neurological sense to set down the numbers in print as if a real scientific objective method used to base our bantering on. There are videos of the facilities used to keep t-wrenches calibrated in assembly lines so how often are your's double checked for critical fasteners? Have ya ever had a Norton fastener let go below the listed value - I have, ugh. After finding crank bolts loose I now tend to stop only after breaking off the end wrench jaws, so can't defend against being a hamfisted FU even to myself so no offense taken by yo'alls polite reactions to my static.

concours said:

But seriously, "lightly oiled" threads is the standard in industry.

Click to expand...

That "lightly oiled" phrase is totally non-standard, lets not exxxxagerate here...

The factory workshop manual for my car, (only a couple of years after Commando) which is way more comprehensive than anything Nortons ever put out, has a complete list of torques for every bolt in the thing. It spells out in careful detail that all torques are quoted DRY - except a special few inside the engine and oilpump which are to be oiled and torqued accordingly.

Some manuals refer to using a wire brush on the threads of bolts, to ensure they are clean and dry.

The dry vs. oil argument can never be settled conclusively unless you have the equipment to measure tension. A stress gauge device such as a Skidmore is used for measuring fastener tension. Once you've measured tension with the same applied torque, both dry and oiled, you'll have proof of what happens. Some "experts" swear dry, while others say oil needs to be used. Since there seems to be satisfactory results with either, my best guess is there is not a great difference.

I do know from experience that all bolts used in structural steel erection are lightly oiled, primarily for rust prevention. Sometimes a Skidmore is used to calibrate the air impact used to tighten these bolts.

Actually what we want in engine fasterners besides not coming loose is the even clamping force all around and no measure of bolt torque or stretch can reveal this but there are pressure sensitive thin pads somewhat like carbon-ink paper that leave impression of the clamp forces across the whole mating surfaces. Examples show extra color near bolts and lack of it between. With this info one can configure surface grind off and bolt tension for best compromise in our elastic engines.


http://www.sensorprod.com/glossary/bolt ... -force.php

The tension that does the job and maintains that, is correct. How you arrive at it, well thats the 64000 dollar.

This is an interesting thread.

Heinz Kegler worked for Norton for many years and then as a master mechanic with Cummings Diesel.

I met him when I moved to Albuquerque 20 years ago and spent a lot of time with him in his home shop
after he retired.

He was truly Old School in the sense that as we worked on my Commando doing the total rebuild he would call out the fastening tension to me as we went along.....he would say Just Nicely Snug on that little nut or
Hard and Firm, or Really Muscle Hard on those head bolts and the same on all four around the plugs. He knew the softness of each thread and the sized and different metal of the fastener components. I never, ever, saw him use a torque wrench.

I suspect he would have been one of those guys referred to up thread who would set the tension by hand and then someone else would measure it and write it down and later it would be in the specs as the proper amount

Was Heinz "wrong" for relying on his 60 years of experience and not a calibrated torque wrench?

I don't believe that for one minute, but I do get why nowadays on more critical fasteners it IS proper and best to look up the torque and grab the wrench to get it right.

All I am suggesting is that we all differ in both mechanical feel and experience and also that much of wrenching is as much of an art as it is a science. Some of the criticism on this thread is unjustified.

Then there is the alternative method of specifying bolt preload as snug-tight followed by x degrees rotation, granted this appears to be more common with torque to yield bolts but it still eliminates a few variables.

What about a bolt and a stud and nut in the same situation ?
If friction were based on thread engagement,what of that same bolt (high) and a nut (low) ?
Rotation value but what of a fine verses coarse thread on the same diameter fastener ?
What of the friction at the contact area under the bolt head or nut (with or without a hardened washer,not to mention the face condition of the part itself)
It is about stretch is it not,not to low that a bolt would loosen,not to high that it would yield and fail or pull threads.

Who torques Norton cylinder base nuts or those on the head studs ?
That then comes back to rotation from seated with or without lubricant ?

Or not.

I envy you iup3dn and thank you for sharing Heinz experience. Not everyone will reach this self assured state, but own a Norton long enough and you may tend too. Shop classes should have kits of fasterners and screws, to let students break some and bugger the driver slots and try sealing leaks in tanks for a feel of what they may face in future - sans calibrated wrench.

He was truly Old School in the sense that as we worked on my Commando doing the total rebuild he would call out the fastening tension to me as we went along.....he would say Just Nicely Snug on that little nut or
Hard and Firm, or Really Muscle Hard on those head bolts and the same on all four around the plugs. He knew the softness of each thread and the sized and different metal of the fastener components. I never, ever, saw him use a torque wrench.

Click to expand...

What did the Nut say to the Bolt...




Bolting science sight that may or may not apply to this thread.
http://www.boltscience.com/pages/junkertestvideo.htm
http://www.boltscience.com/pages/vibloose.htm

Ah!! Common sense, assuming that its got some lube??
cheers
wakeup[/quote]

The trouble with common sense is that it is not very common
Bradley

Ugh Bradley there is great confusion and mis use of the word-term "common" with "normal".

Truths on torque wrenches to refresh common sense if in doubt. How many cycles of tightening is standard for say head bolts? How much per tightening round do ya apply? Do ya just crank on a fastener to test or break free first?
How many lb ft in a dropped wrench before its suspect? Why ya should really have two even if only using one.
http://www.circletrack.com/techarticles ... ewall.html

OK I give up, you should never use a torque wrench, do it by feel like hobot says, oh that's what I said too.
For what its worth my torque wrench has never been dropped, was calibrated before I retired (and did not need adjustment at that time) is always slackened off to remove any tension in the system, etc etc etc.
Hobot, if you don't like torque wrenches just say so. I'll carry on doing it my way, you carry on doing it your way. Reality is they aren't that far apart, except I'm probably less concerned than you seem to be.
cheers
wakeup

Perhaps it could be commented that there is a VERY big difference between Joe Worker bolting together motors in the factory by feel.
And the average owner, who might bolt together 2 or 3 motors in their lifetime.

Torque wrench makes a lot of sense, with page of torque values, if you don't do it all that often.
Or aren't too familiar with how tight things should be.

Can recall doing a caterpillar tractors head bolts.
300 ft/lbs.
Thats a lotta muscle.
If that number wasn't in the owners book, not many would do them up tight enough ??
Head warps if not tight enough...

If the torque numbers are available, use em !!??