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Comment by spike021 | Hacker News Reader

I know of a pretty famous car tuner in the US (I won't get too specific for various reasons) and despite most people in my community going to him for service over the years, multiple people have come out and proved he rarely if ever torques anything to spec. For the longest time he even allowed customers to watch in the shop space as he worked on their cars and he'd hand-torque many things that the car manual was very clear needed to be specifically torqued for safety and operational reasons.

The fact that people would share this and it didn't curb the amount of business and referrals he got just proved to me what you've said for the longest time.

People don't like to be troubled with details and they'd rather be ignorant of them.

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It is even worse than that: those that don’t care will make life intolerable for those that do until they give up trying to help and go away.

You would definitely hope aerospace assembly would be immune to this widespread phenomenon though.

I imagine at least part of this is that specs (and documentation generally) just suck now. It's nigh impossible to sort out which bits are CYA legalese, and which bits are "no, actually, do this or else <terrible outcome>".

That obviously isn't the problem with airplane manufacturing, and maybe not for car mechanics either. But it's totally endemic in the consumer world.

"Do not operate while driving" on car HUDs. "Do not consume if pregnant" on perfectly safe OTC medications. "Do not continue to ride after a crash" on bike frames.

It's not surprising most of this is just ignored now -- there's no information content. The documentation is nothing more than a list of things for which the manufacturer would like not to be liable, and the marginal cost of adding to that list is ~0. It will grow until we run out of room in the manual / space on the packaging.

"Store between 68 and 75 F." Or what? Is that a "must follow or else death", or a "it may reduce efficacy 0.5%" or a "we've never run a sufficiently powerful study under any other conditions, but there's no theoretical reason it should matter"? It matters quite a bit to me which!

I don't see how we can hope to have good-faith communication under such a heavy threat of litigation. I would not be surprised if /that/ turns out to be relevant to the Boeing issue, even if the rest is unrelated.

My beef is that torque specs are for factory assembly. If you’re using new parts, sure, but once they’re old/re-used parts with some corrosion due to dissimilar metals, age or salt belt, you’re flying blind and probably undertorquing if going by the book.

Given the amount of (soft) aluminum on aircraft, (737 is 80% aluminum), it would be insane to not precisely consider torque.

Steel on steel is more forgiving.

Why would the softness matter for torque, if there has been some shift or compression since original install the torque should still ensure the correct pressure between the fitting, no?

That’s assuming then original install torque spec was correct.

Much easier to strip aluminum threading if you over torque. Steel tends to just bend (and bend back better).

Aluminum also fractures while steel bends/stretch back and forth better.

(This is mainly from my experience working on bicycles, and a little auto)

A major concern is presumably over-torquing a screw and causing partial failure of threads in the material. This could be subtle and difficult to detect, but present as a problem over time.

Soft materials develop wear more easily.

e.g. any slight boogering of the threads of a used fastener could translate into rotational torque that doesn't end up being converted to a clamping force.

(or in more extreme instances, some fasteners are torque to yield, and change shape after their first use, and must be replaced. But I'll presume that's not what they were talking about here)

Aluminum has no fatigue limit, so you really need to do things by the book.

> If you’re using new parts, sure, but once they’re old/re-used parts

Most service manuals require new bolts, fasteners and washers for torque-critical parts.

Skipping that part is even more ubiquitous than failure to properly torque. It takes a lot of effort to buy the correct bolts, only specialists have them to hand for a given make. Even dealers might not have every bolt. So it means you need to procure many more parts you would otherwise (the part you're replacing, plus 20 specific bolts with part numbers).. Most mechanics don't bother unless it's something really big like cylinder head bolts or an axle nut.

That is probably valid reasoning when talking about a neighbourhood mechanic dealing with all brands but it does not hold for an aircraft maintenance shop. Skipping this step makes them liable for any problems caused by failure of related parts so I assume [1] they keep to the book in this respect. Anyone here who has experience with one of these shops want to chime in? When I work on machinery I tend to follow the rules when dealing with stretch bolts since these do tend to fail far more often when re-torqued but for normal (non-stretch) bolts I do often reuse them if they're in good enough shape. I work mostly on farming/forestry equipment and our personal vehicles though, not on airplanes.

[1] which makes an ass (out of) u (and) me

German torque specs: "gutentight!"

Nach fest kommt ab.

Probably one of those guys that says "click!" whenever they tighten a bolt.

How many times are the torque specs available to me when working on my car? I have no idea what random bolts are supposed to be so they get the good n tight click.

Workshop manuals are your friend.

Buy a service manual for your vehicle? I have yet to see an important fastener without a specification (torque and pattern).

If you are a professional mechanic, it's your responsibility to obtain the specifications and follow them. This is especially true when it comes to a licensed and certified A&P mechanic and not your neighborhood shadetree mechanic.

To be fair, manufacturers are trying to discontinue the ability to 'buy' a service manual and make you pay for x amount of time of access. And IIRC they don't format the page into something that's offline friendly.

It's still doable to get the full manual off, just not easy anymore.

If you don't know what you are doing then better stay away from anything critical. There are 'stretch' bolts, bolts that are definitely not to be overstressed or they'll weaken and bolts that will cause damage to whatever they're bolted into if over torqued. Every workshop manual and every workshop process has specs for all fasteners.

It gets worse when bolts and part are of different materials (say: steel bolt in aluminum part), that's a very nice recipe for trouble (also in the long run, not just during assembly because oxidization will almost certainly occur on the interface and oxidized metal takes up more room than clean metal so unless you very explicitly protect against it the fasteners won't come out without massive damage to the part).

The vast majority of fasteners on your car do not depend on being torqued precisely. Basically anywhere you need to worry about clearance (e.g. bearings). If it's a matter of ensuring nothing comes loose you'll have things like threadlocker or a cotter (split) pin.

Exactly this, old school mechanics work by feel and only need a torque wrench for things like head studs

When I was in high school I helped a lot of my friends fix issues caused by quick tire and lube shops. Lots of snapped, stripped, and rounded fasteners.

I've noticed the same with electrical work. How many use torque screwdrivers, even when dealing with high load appliances (eg, a 50 amp EVSE)?

I've worked in stage lighting and general construction at different parts of my career, and I never saw these being used by anyone despite them being very much required for a proper job.

WAGO clamp terminals are a godsend here - no need to take care about wire nuts going loose, screw terminals being too loose or too tight (leading to fracture), ferrules being properly crimped... just insert the cable, lower the lever, and off you go. Unfortunately, standard DIN fuses still come with only screw terminals.

Sounds like Hennessey.

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