Torque Seal Question
 

During my annual, I am facing the following situation: all critical bolts and nuts fasteners like the bolts securing the engine on the motor mount or the bolts and nuts attaching the landing gear to the U channel have been marked with torque seal at installation. Inspecting these bolts, I do not see any seal broken. In these conditions does it make sense rechecking the torque? I would think that the purpose of the torque seal being to detect a bolt or nut getting loose my inclination toward leaving those that are intact alone (particularly the motor mount ones that are so hard to reach). I further believe that tinkering with well seated bolts and nuts may unlock them and leave them more prone to getting loose in the future.
What says you fellows with experience and/or wisdom (whichever came first ;))?

Put a wrench on everything. Torque seal is just a tool to help the installer double check his work. Indication of torque seal is no guarantee it was torqued.

I teach that torque seal is a good tool to use in keeping track of when a fastener has been torqued (good habit during the build, especially when more than one person is doing work) and whether it has been tampered with afterwords, but not as an indicator that it is still torqued.

Think of the landing gear bolts that were highlighted by the S.B. as an example. Most people probably torqued them properly first time, but parts can settle in in use.

Good point with the landing gear, Scott, I intended to retorque it anyway given the issues highlighted in the SB. For the motor mount however I don't see what could settle as the bolts are threaded straight into the engine block. Is there anything between the bolt head and the motor mount that could settle or shrink?

Any coating (primer, paint, powder coat, etc.) that is on surfaces within a stack-up of parts held together by a threaded fastener has potential to cause a reduction in torque over time.
The coatings aren't as hard as the other materials and can compress slightly over time.
Under high load, even some aluminum alloys can do this.

This is the main reason Van's has not specified using thread locker on the engine mounting bolts. If the engine mount has powder coat at the fastener location which compresses over time, and the bolt is locked in with thread locker, even if you do check with a torque wrench, it might measure as being properly torqued (stretched) but it in fact is not.

I have not used thread locker on my engine mount bolts as I agree with VANs position. Now, the purpose of the fastener is to keep the parts together and I assume the torque specification is aimed at providing the best grip for the fastener. If the torque is not correct, we have the risk of either weakening the fastener by stretching it with too much torque or have it slowly release its grip if not enough torque. As long as my bolt was initially torqued correctly, does it matter if the torque has decreased slightly as long as my torque seal shows that the bolt has not rotated? I understand that if the bolt torque continues to decrease at some point the grip will be lost but as long as the bolt head stays in place I see no harm leaving the bolt alone provided the torque seal is inspected at reasonable intervals like the annual inspection process. Intuitively (and it may be where I am wrong :eek:) I feel that not moving the bolt through an attempt to retorque prevents breaking the existing grip which proved to be effective.

Torquing puts an initial tension in the bolt that is important in maintaining its resistance to fatigue caused by cyclic stress changes when vibration is involved. If the pre-load drops low enough because it has `settled in', the bolt may still be tight and the head may not have moved, but its fatigue resistance may be compromised. The only way to be sure is to re-check the torque.

I find motor mount bolts and many others loose on a regular basis during condition inspections, especially the hard to reach ones, and many still have torque seal on them (which I obviously choose to ignore).

Don't worry about "breaking the grip" on the nut, if its loose tighten it and if not just move on.

You've gotten some good advice from some knowledgable folks in this tread, now its up to you to take that advice or not.

If you have a joint with the potential to relax the preload without backing off the nut (e.g. wear) you should check the torque. Since it's tough to definitively say a joint is not susceptible to loss of preload it it best to check the torque.

From my Navy QAR days, we used "torque seal" as a visual indicator that the QAR has witnessed the proper torque value. Torque seal is only good till the post-maintenance-check-pilot completes his preflight inspection. From then on, it is to be considered suspect.