Dry Torque vs. Wet Torque

[tdub13]

Hello All,

I've been building engines for 20 years (motorcycle engines, mostly 2T race bikes). I've always known about the difference between wet and dry torque. But in all my service manuals there's a range given for torqueing fasteners, but never a mention of whether this is wet or dry.

Can anyone enlighten me as to what the Clymer, Chilton, and factory manuals expect?

Could it be that the torque range given by the manuals are meant to be deciphered as lower end of the range for wet and the high end of the range for dry torque?

Thanks! Todd

 

[Lou Scannon]

Well, it's kind of important to know the boundary conditions that are assumed for specified torque values. I'm surprised that the manuals you are referring to don't make the boundary conditions clear.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[MikeHalloran]

It's almost never stated _with_ the torque specs, but the typical factory manual states in the general section that the torque values given are for clean, new, oiled fasteners.

... because that's all they have at the factory.



I usually aim for the low end when using thread lubricant.




Mike Halloran
Pembroke Pines, FL, USA

 

[tdub13]

clean, new, oiled fasteners.

... because that's all they have at the factory.


Makes sense to me. Thanks for helping me clear that up!

 

[Deividas]

Is this statement right: "Thread lube, including thread locker (wet torque), reduces friction and allows a given torque value to apply more tension to a bolt than dry torque"?

 

[tdub13]

Yes. That is the main difference.

 

[anyoldname]

Thread lube, including thread locker (wet torque), reduces friction

Loctite's literature states that their thread lock products act as a lubricant but I did a training course on bolted joints 2 years ago and the very knowledgeable instructor was adamant that this is not the case, based on my own experience (more feel than scientific based), I agree with him.

 

[Tmoose]

ARP is a respected aftermarket supplier of high performance automotive engine fasteners.

They offer a fastener lube and make a few claims, among them consistent preload for a given torque from the very first torque cycle.

http://arp-bolts.com/i/t/PreloadGraph.gif

What I find most interesting about their spiel is -
** With almost any lube after several torque cycles the preload (and resulting bolt stress) approach the same value. ***


So, if, when I use something slippery to assemble fasteners I back off the torque a bit hoping to avoid overstressing the fastener, I ought to also lower the assembly torque if I'm re-assembling an engine for the 6th time with lightly oiled fasteners.

Actually, I sometimes will loosen and tighten fasteners a few times to create a smooth luxurious "feel"

 

[Lou Scannon]

...the first time that you torque a fastener past the yield point it won't necessarily fail, but it might fail on the nth time...!

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[desertfox]

Hi dtub13

I have always understood if there is no mention of a lubricant then the torque figure is considered dry.

 

[FennLane]

I would agree with the above comment - If there is not statement about oiling a fastener then assume it is a dry torque figure.

I build Porsche 911 Engines on a regular basis and the factory manual tells you if the fastener should be lubricated.

I am not sure about aftermarket manual.

Thread lockers are interesting and Loctite do say that they act as a lubricant but provide no data of the effect on 'nut factor'.

If you read Permatex data sheets they tell you that the thread locker acts as a lube in terms of consistency but to torque to the standard dry torque figure.

What do you do about brand new fasteners? the surface roughness of the thread when first used can cause errors in preload.

All new fasteners need to be tightened a couple of times to burnish the threads and eliminate variability.

The modern trend of using lower measured torque and then tightening through a specified angle removes many of these issues and gives much more consistent preload results.

 

[gruntguru]

Angle is also required if the fastener is to be tensioned significantly past the yield point. The slope of the stress/strain curve reduces as tightening proceeds - the limiting case being a fastener tensioned to the UTS. This is impossible using a torque (stress) reading but can be approached using an angle (strain) reading.

je suis charlie

 

[Panther140]

Bolt head flange and washer are also relevant variables. Based on my experience with 2t race bikes on motocross tracks, you want to get it right!! I once had the upper subframe mount bolt rattle out of my YZ250 in the middle of a race. The subframe tilted back pretty far when I landed from an 80' table top :/ I learned a lot that day

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin