Loctite, where to use or avoid

[ArlyA]

Thread locking chemicals have there place. Even when some machine was properly designed assembled.

 

[3930dave]

What he said. Twice

I mostly don't disagree about proper torque, but, there are some other factors....

A) sealing against corrosion, esp. in salt-country.

B) While those of us who are disciplined and focused on working on our own stuff may execute torque consistently, with commercial work (paid staff) YMMV.

A buddy who owned and ran his own big light-duty service garage found that it was much more practical to get apprentices to consistently use Blue Loctite on brake caliper bolts, than take the time to hunt down a proper torque wrench. (It never happened when my buddy worked on a car/truck himself, but the policy came about after bolts fell out on other customer's vehicles). The blue Ltight solved that human-factor problem..... leading to me to conclude that blue loctite is a pretty good idea on caliper bolts, esp. for people who don't do brakes often or/and refuse to buy/use a low capacity torque wrench.

C) You'll find some OEMs instructing - "replace these bolts with New ones, when doing _________ service". That policy could be because:

C1) Those fasteners are torque-to-yield.
or
C2) They come with factory bolt-retaining goop baked onto them.

If there ever is a failure or accident relating to those ^ bolts, then the OEMs first response may be "Show us the invoice for the replacement bolts". Which, could be just another way to transfer liability, even if there is no technical reason to replace the bolt....

Rgds, D.

 

[GeneV]

I worked briefly for NASA in 1963 doing this for critical assemblies that went onto the tower next to the rocket to keep the tanks topped off until the moment of launch. They told me it was called "torque painting" and they used specially formulated paints that had an odd mix of many obscure ingredients, the purpose of which was to make it practically impossible to imitate the paint. This torque painting was done to make Soviet sabotage less likely and more easy to detect after the fact if it did happen. The paint was very special, yes, but it was put in ordinary nail polish bottles.
The reason I was hired to do this was that I was only 6 years old at the time, and could fit into small places. These assemblies were too big to reach into and too compact to crawl into for adults. I crawled in with a mirror and a paint bottle. Engineers outside had me position the mirror and point to fasteners as they guided me, and when I was pointing to a fastener that needed torque paint, they'd say "Yes, paint that one", and we worked our way through the whole thing. I got some kind of paper certificate from NASA (which was a pretty young agency at the time) and we kept it posted in the kitchen for years.

My contribution to the Loctite discussion: I had a hard time keeping the urethane bucket edge tight every winter. I tried fine threads on stainless nuts and bolts, which are less likely to come loose, but one of them seized during disassembly one spring and it took a lot of work with a grinder to get it disassembled. In retrospect, fine threaded stainless is particularly prone to this and was a bad idea. So I went back to coarse threads on zinc plated steel, but with purple Loctite. That worked great! Just a bit more effort to break loose, no problem. And all of them stayed put until I put the wrench to them.

Wait, that's a crazy story man, NASA employed you when you were 6 y/o, or am I reading this wrong?

 

[jigs_n_fixtures]

I knew a guy named Bobby Takewaa, who worked for FMC building APVs he was small enough to go into the metal ousting which held the fuel bladder, and grind the welds smooth.

 

[SmallChange]

Wait, that's a crazy story man, NASA employed you when you were 6 y/o, or am I reading this wrong?

They sure did. My father had set something up with them. He had a small mechanical engineering company that specialized in pneumatic and hydraulic controls, especially valves. He was a subcontractor to NASA. But he got me something direct with NASA, not as his employee. I don't know the exact nature of it, but given that employment law (especially regarding 6 year olds) was a lot less formal nearly 60 years ago, it probably wasn't hard. Thus the special certificate from NASA, I'm sure.

I've been mechanically inclined for some time....

 

[SmallChange]

Did you keep the certificate?

I regret I have no idea what became of it. Sure wish I still had it.

 

[caver]

My Case backhoe manual specifies blue Loctite on the first 6 threads of the piston rod in all the hydraulic cylinders. Then the nut is torqued to some really high number depending on location. We used red and blue all the time in my days at the power plant.