Ounce of Prevention Vs. Pound of Cure

@not-2-old-for-2-seater PST 592 is a good choice especially on stainless

My activities include greasing some bolts, anti-seize some, Loctite red some and Loctite blue some.  I've never used the PST.  In practice what I use depends on the area and function. Most often I think that bolt has to be easy to remove one day...  When I did my clutch/pressure plate,  I recall being concerned that the SRP bolt lubricant would change the torque specs.  But the instructions called for the use of lubricant and provided the torque values. I was not sure how to address that, I lightly coated the bolts.  The SRP bolts don't stretch (OE bolts added a stretch torque like head bolts if I recall correctly).  Luckily the torque values were reasonably low.  Regardless this reminds me that another part of the equation can be that too much lube/lock might create pressure from taking up space in the bolt hole.  Some cars (German?) have bolts that have a drop of bright blue head marking type lock on the interface between bolt head and surface. That stuff breaks off easily, but it apparently survives until the part needs to be removed. I figure that is a marking function in the build, but perhaps it is also a non-thread lubing lock. Funny anecdote is I did once grab my CRC Disc Brake Quiet to mark the bolt position.  Easy to apply, easy to see and I have no idea if it actually does anything. 

@ispyThat dry blue stuff on OEM bolts is an encapsulated threadlocker that function like a wet loctite

@ispy I wouldn't worry about hydraulic locking in the fastener, just use the the lubricated thread torque spec on lubricated fasteners and dry on clean and dry ones.  Also note that just because the tightening spec calls for an initial torque plus a final tightening angle, soen not mean it is a "stretch" or torque to yield bolt.  It just means that they are specifying a more precise way of tightening the fastener.  Torque values alone do not give as reliable clamping force as does an intitial low torque figure plus an angle.  Fastener engineering is a whole sub-set of Mechanical engineering.  Some folks make a whole career of the engineering of fasteners.

dbloti: as always, your technical expertise and ability to "break concepts down" for us non-engineer types is really appreciated.  Given both the critical nature of the info provided in this thread and its (no doubt) wide applicability, is there a way to have the MODS make this topic a "Sticky" so it is readily avalabile?

Paul

Until tare torque is being factored in, I am not going to start getting uber precise on my torques.

Rob

@helowrench If an OEM nut is self-locking, the Tare torque is accounted for in the torque spec.  We are not talkin about being Uber-precise, we are discussing the very large difference in  the relationship between torque and tension in a fastener, between clean and dry threads and wet threads.

dblotti,

I fully understand exactly what is being discussed here. There is a very valid reason to differentiate between dry/wet torques.

When adding loctite to  a normally dry torque fastener, I usually drop 10-15% below the minimum listed for dry torque. It should yield mid range once wet.

This is based on a chart I saw a long time ago showing a roughly 15-25% higher clamping force wet vs dry.

But, I check the hell out of everything any time I happen to be under the car anyway. One loose bolt causes a retorque of anything associated.

I sincerely doubt that Tare torque is fully captured in the normal torque specs if they never have you check for a minimum drag torque on a self locking nut. That is, unless the total range given is from no drag to max drag.

The ral thing that bother me is the stationary nuts..... Torquing from the bolt head is verboten in most other places.

I just installed a set of new “three amigo” nuts yesterday.  The BGB is so specific on torques that it specifies whether to lubricate threads with sealant or motor oil. Do you suppose they calculated the running torque caused by the deformed thread locking feature on the three amigos?

@helowrench     Are you saying that if the BGB calls out a torque spec on a fastener that has self-locking, you don't follow the spec?

Posted by: @dblotii

@helowrench     Are you saying that if the BGB calls out a torque spec on a fastener that has self-locking, you don't follow the spec?

If I am adding Loctite to a normally dry torque fastener, then I have already deviated from spec

Directly speaking to the self locking nuts, I typically do not reuse self locking nuts, as that is what I am used for my work. On the rare occasions I do, I mark, engrave etc the nut to indicate it was not new, and replace at the next opportunity.

The "deviation from spec" decision does not get made lightly. fortunately I have a good friend who is a ME, so I discuss with him the application, recurring problem, proposed fix, and it gets monitored to see if it worked as intended, or if another type of corrective action is required.

Rob

This is an interesting discussion, although anecdotally I have yet to see much of a difference between torqued to wet spec, dry spec, or Gutentight spec. I would suspect that for all but the most precise of bolts (engine/internal trans) the required torque can be broken down into broad categories of snug, tight, & attempted murder. This isn't to say throw the torque specs out the window, but for the overwhelming majority of applications there is a solid amount of wiggle room. Loctite is a nice go-to but I have found parts that do wiggle free after being torqued down properly may also benefit from new hardware or use of a thread restorer.

FWIW if using Loctite, just make sure you put the correct product for the application. Some genius at the tire shop slathered red loctite on the lug studs of my Saab (And I'm sure zipped them on "attempted murder" tight with air tools)....luckily I found out while using an impact gun intended for the axle nut....each lug stud was harder to break free than the axle nuts were 😑

@forminfunction The engineers that spec torque values aim for an assembly that never strips threads, never vibrates loose, and gives enough clamp load so that the 2 joined surfaces don't move relative to each other under load.  So there are a lot of considerations that go into torque specs including the scatter-band of clamping load you get from an applied torque.

Dave

@cyclehead

your not crazy,

I was merely pointing out the mechanical locking device under the head of the bolt can be destroyed by turning the bolt to loosen.

the manual has a warning about this.