Tightening torque values

[RichardHawkins]

I have not noticed anywhere in the service manual that tells us whether the torque values are for dry or lubricated conditions. Lubricant makes a huge difference to the tension exerted in the bolt. Does anyone have a definitive answer?

[types26/36]

Although I can't give you a definitive source, in my experience it is generally accepted that torque settings are with clean and lightly oiled threads, I was in the motor trade for many years and recall many times where this was the specified procedure.

[andyelan]

Hi There

I too would agree with what Brian says

Andy

[Galwaylotus]

Ditto except that it is always recommended that wheel bolts or nuts must be tightened DRY.

[types26/36]

Ditto except that it is always recommended that wheel bolts or nuts must be tightened DRY.

Yes, you are 100% right there!...........forgot about those

[GrUmPyBoDgEr]

Torque measurement values on fasteners is a rather crude method of defining the all important clamping force.
The torque values provided by car makers are based on long term experience based on new engines where non of the threads have become contaminated by oil.
Vital bolts such as bearing cap bolts, cylinder head bolts, flywheel bolts etc are high tensile bolts supplied with an oiled phosphor coating.
Other less vital bolts are zinc plated or a modern equivalent & supplied dry.
In a new build engine all bolts are fitted as supplied & tightened to the values that eventually appear in the workshop manual.
Any additional application of lubricant during today's assembly process would be too hit & miss (has it been oiled or not?) & would slow down & increas the cost of the process.
Generally speaking when rebuilding an engine where oil is present on/in the threads the same torque values apply & the additional amount of tightening due to the reduction of friction in the threads is well within the limits of the bolt & associated components.
Many times the given values will be needed to push the bolts into plastic deformation & that will generally happen to those bolts before the component being clamped becomes deformed, except for maybe aluminium components such as cylinder heads.

The above information is based on the experience I gained in the engine development department at BMW.

John

[bcmc33]

Ditto except that it is always recommended that wheel bolts or nuts must be tightened DRY.

No fastener should be applied dry ? i.e. without lubrication, in order to achieve the ?correct? design clamp load.

Other less vital bolts are zinc plated or a modern equivalent & supplied dry.

A slight correction here, John ? you should have said ?supplied with a dry lubricant?
In the days of zinc + passivation, the passivation was, in fact, the lubricant, and those without passivation went through a dry lubrication process. I am now too out of date regarding current practice, but the finish that replaced zinc + passivation (due to European regulations & IMDS) was also a lubricant.

[summerinmaine]

Any questions of this nature should be definitively resolved by Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook, infamously known as "Screw to Win."

[GrUmPyBoDgEr]

Ditto except that it is always recommended that wheel bolts or nuts must be tightened DRY.

No fastener should be applied dry ? i.e. without lubrication, in order to achieve the ?correct? design clamp load.

Other less vital bolts are zinc plated or a modern equivalent & supplied dry.

A slight correction here, John ? you should have said ?supplied with a dry lubricant?
In the days of zinc + passivation, the passivation was, in fact, the lubricant, and those without passivation went through a dry lubrication process. I am now too out of date regarding current practice, but the finish that replaced zinc + passivation (due to European regulations & IMDS) was also a lubricant.

I don't think so Brian; or maybe we're talking at cross purposes.
Yes the zinc or its modern equivalents could be called a lubricant because it helps in preventing galling in the threads.
But the passivation (silver or gold coloured chromate) process is used not as a lubricant but to temporarily enhance the corrosion properties of newly zinc plated components.
The necessary move away from zinc plating to more "acceptable" surface finish was a long & arduous process with many pitfalls.
The search for a cost effective alternative for zinc continues.
I remember aero engine bolts being cadmium plated, much nastier stuff for the guys working in the plating plants.

Wheel bolts usually have a phosphate surface finish, an anti galling finish
Elan spinner threads are brass onto steel, comparable to old fashioned exhaust manifold nuts, again a reduced galling combination.

Cheers
John

[bcmc33]

I don't think so Brian; or maybe we're talking at cross purposes.
Yes the zinc or its modern equivalents could be called a lubricant because it helps in preventing galling in the threads.
But the passivation (silver or gold coloured chromate) process is used not as a lubricant but to temporarily enhance the corrosion properties of newly zinc plated components.
The necessary move away from zinc plating to more "acceptable" surface finish was a long & arduous process with many pitfalls.
The search for a cost effective alternative for zinc continues.
I remember aero engine bolts being cadmium plated, much nastier stuff for the guys working in the plating plants.

Wheel bolts usually have a phosphate surface finish, an anti galling finish
Elan spinner threads are brass onto steel, comparable to old fashioned exhaust manifold nuts, again a reduced galling combination.

Cheers
John

John,

Perhaps I should have explained better - passivation was, of course, for corrosion protection and was, at some time followed by the dry lubrication process until some clever bugger discovered that the passivation was in fact a good lubricator. That clever bugger, not me, won ?1000 and and Escort car on the Ford suggestion scheme for his discovery.

Most wheel bolts appear to be chromed these days to match alloy wheels. I still put copper slip on them (and on the hub locator).

Old fashioned exhaust manifold nuts I still use these (Ford Escort design, of course), and with copper slip. I guess you Zetec types use ARP bolts?

As I said, I'm now out of date as to the current situation. Up to 5 years ago I was active in the search for and alternative to zinc+passivation without the use of banned chrome 6 & chrome 3. Not long before I retired the ban on chrome3 had been rescinded as no suitable alternatives had been found. I guess things have moved on since then - but have only passing interest in finding out what they are.

[RichardHawkins]

Thanks gentlemen, very helpful. I was thinking of measuring the stretch while tightening the connecting rod bolts. I think there is just enough room for a micrometer. All advice/comments is welcome.

I have a copy of Carol Smith's book on order from the library.

[ardee_selby]

FWIW, been reading this site on the general subject:

http://www.boltscience.com/

Some interesting stuff on it.

Cheers - rd

[bcmc33]

Thanks gentlemen, very helpful. I was thinking of measuring the stretch while tightening the connecting rod bolts. I think there is just enough room for a micrometer. All advice/comments is welcome.

I have a copy of Carol Smith's book on order from the library.

I forgot to mention the ARP catalog which is full of useful information that I particularly like because it imparts so much of the teachings I received as a young engineer. Learning from those teachings is a different matter, and I see great benefit in reminding myself of the details of what I should know by reading the ARP catalog.
The catalog can be downloaded in pdf format from this link: http://www.arp-bolts.com/

[gerrym]

I remember many years ago, fitting a nut to a gearbox output shaft, for a trial fit of the output flange.

I had previously degreased the shaft male thread and the inside of the nut with the recommended Loctite cleaner, because I was going to locktite the nut in place on final assembly.

For the trial fit I was too lazy to re-lubricate and then degrease again. After all, it was only a trial fit and I wasn't even going to tighten to the full torque.

Well, I ran the thread on to its mating thread and quickly ran into trouble and so reached for the socket and the big ratchet. Well when I finally stopped tightening the nut and got the thing off, I had sure learned my lesson on galling.

Morale, call it a coating or lubricant or wax or trace oil, but any thread assembly without some sort of interface can/will seize pretty readily.

Regards
Gerry

[rgh0]

Thanks gentlemen, very helpful. I was thinking of measuring the stretch while tightening the connecting rod bolts. I think there is just enough room for a micrometer. All advice/comments is welcome.

I have a copy of Carol Smith's book on order from the library.

Using a stretch guage which is a specialised dial indicator measuring device to fit the space is highly recommended, i think you may find a micrometer hard to fit in. - I always use one now since the piston you see next to my name destroyed an engine through a rod bolt failure.

Refer to the ARB web site for more details

cheers
Rohan