A few years ago, the SCCA Solo Nationals week started off rather promisingly. A third-place trophy in the CAM Invitational gave us high hopes heading into the SCCA Championship event. But our excitement dropped to the ground when our inattention to a single bolt cost us a strong finish. We want you to learn from our misfortune, so we put together a guide on keeping fasteners fastened.
The jam nuts I've used (bulkhead nuts?) are thinner than the nuts they're jamming.
With safety wire, note the excellent photo in this piece, which shows that there is actually some thought involved; the wire should go in the direction of tightness. (This seems obvious, but I've seen it wound the other way a surprising number of times.)
So us helicopter mechanics may be useful after all. 
Saw the painting method (where you mark the bolt and nut, or bolt and area near where bolt engages the surface) used on a friend's car. Really smart way of making sure fasteners that are supposed to retain tension are in fact, doing just that. If you're gonna mark things in more than one place, for ease of quick viewing, just make sure you don't mark them 180 degrees opposite of each other. if the fastener spins 180 degrees, you'd never know. If the marks are uneven intervals, the only way it can be correct is if the fastener has held its tension, or spun a full circle to the exact same spot, which would be somewhat unlikely.
Most important thing, I've discovered, in regards to bolts and other things in the engine bay, is environmental consideration. Is the fastener you're using made of an appropriate material for the job you're asking it to perform? Consider:
-Temperature
-Vibration resistance
-Pressure
-Tensile strength
Example that most comes to mind in my case have been related to my turbo system. The guy who put my engine together at the machine shop used grade 5 bolts between my head and exhaust manifold, and exhaust manifold and turbo. Had to re-clock the bearing section of the turbo (because it was sitting with the oil drain about 45 to 50 degrees from vertical, which is less than ideal and causing me some nasty issues), when I attempted to remove these grade 5 bolts... disaster.
Ended up breaking a bolt off in the manifold, as the threads had effectively welded themselves to the manifold flange. That was NOT a fun job to fix, and ended up requiring the manifold to be sent off to a machine shop to repair. The solution? Stainless ARP studs in my case. Meets the temperature requirements for such a hot area of the engine bay, plenty of tensile strength, and should prevent any unexpected funkiness from using typical hardware store bolts...
More recently, had the line from the turbo compressor housing to the wastegate develop a hole. It was Parker nylon air line, good for 150psi, which meets the pressure requirement, BUT... a quick look at their spec sheet revealed that it's max operating temperature was only 200 degrees F. The coolant running through my engine, used to cool the other parts down runs nearly that hot... how warm do you suspect the actual components themselves, and the air around them is? Little surprised this one failed.
What's the danger with a blown wastegate line, you ask? Well, in simple terms, if that line blows, it keeps your wastegate from opening. Two things then tend to happen. You have a LOT of fun, briefly, before realizing you're running much more boost than usual, and secondly, things get expensive, because you're running much more boost than usual. Fortunately my ECU has a very fast reacting overboost protection circuit, so no harm was done. Potential for a blown engine though...
Sorry for the really long post, but I'm a big proponent of proper material selection, it makes all the difference! Thanks for posting this article online, was a good read on paper, hopefully this is one of those threads that gets a long life and good exposure. =)
Quite good writeup. I'd never thought that the tabbed washers would be failure prone. Does seem to work to keep some Harleys from falling apart.
Also that dirty/oily bolts, nuts, holes don't benefit much from a thread-locker.
In general, and especially with a race car, you cannot pay enough attention to having the right grade of fastening hardware, proper torque and good techniques. I'm still scratching my head about why I lost a bolt and had a catastrophic failure on the track, totaling my almost new car. Stock, it relies solely on tension. Now they have wedge-lock washers and thread locker.
Scargod said:In general, and especially with a race car, you cannot pay enough attention to having the right grade of fastening hardware, proper torque and good techniques. I'm still scratching my head about why I lost a bolt and had a catastrophic failure on the track, totaling my almost new car. Stock, it relies solely on tension. Now they have wedge-lock washers and thread locker.
Poor engineering, or is this a car that might not be expected to be used on a track? I'm curious for more details, if you're willing to share. Failure analysis is something that's always interested me, and I find it a good way of learning.
you forgot cross threading!
Remember, cross threading is nature's Loc-Tite.
In reply to Appleseed :
I think that deserves to go on a bumper sticker or a t-shirt.
In reply to Satch_Carlson :
^^Satch!!
Something to think about, in cases where you have a rod end, turnbuckle adjuster, etc. The jamb nut serves more than one purpose. You have prevention of turning, so that it doesnt lengthen and eventually separate. But then you also have the preload keeping the threads from lashing back and forth and fretting/eroding themselves and causing a sudden pullout/failure if ignored long enough.
Loose threaded fittings dont only fail by backing out.
You appear to haver a fundamental misunderstanding of the Nord-Lock type washers.
They are used in pairs with the serrations together. They will not mar a surface.
Their anti-loosening theory is the serrations form a more-coarse ramp than the thread pitch so as they rotate counter-clockwise against each other it increases tension on the fastener.
In reply to Honsch :
I was also under the impression that they help prevent slip. So not true?
Honsch said:You appear to haver a fundamental misunderstanding of the Nord-Lock type washers.
They are used in pairs with the serrations together. They will not mar a surface.
Their anti-loosening theory is the serrations form a more-coarse ramp than the thread pitch so as they rotate counter-clockwise against each other it increases tension on the fastener.
Sorry, but that's not correct. They can and do mar surfaces. The ramps face each other, while the teeth face the bolt and what it's bolting down. That is how they work, though.
The full details are here:
https://www.nord-lock.com/shop/private-use/how-it-works/
Excellent article!
One thing not mentioned about split pins is that if split pins are used in an application where there is significant vibration, particularly if the ones used are slightly off spec and are bit too small for the hole, they can vibrate and eventually 'lose leg' when one of the bent ends snaps off.
The rest of the pin will probably hold fine, but in some environments the now peripatetic tag end can cause trouble. We tore down a 1950s Jaguar engine once (which used split pins on the con rod big end nuts) where one of the legs on a too small pin had gone walkabout and ended up somehow getting through the screen on the oil pump and causing all sorts of damage once inside the pump.
The Jag specialists can correct me if I am wrong, but IIRC, the Jaguar pins were a slightly odd size and it was pretty common for rebuilds to be done using whatever pins were at hand and a reasonably close fit. I am sure that failing to properly trim the bent ends would also exacerbate the problem (get then short enough that they don't vibrate enough to wear).
I can confirm the 50s Jag engines used castellated nuts and that one of the legs of the cotter pin can break off, be ingested by the oil pump, which wreaks havoc with the pump. I had exactly that happen to my 58 XK150S, and it wasn't pretty. I could have just fixed the pump and replaced the cotter pins, but worry about if I had found all of the pieces of the leg lead to a full teardown and rebuild, which of course lead to balancing and tweaking. Balancing those old long stroke motors made a world of difference - the reciprocating masses didn't bear thinking about. I don't remember about the pins being an odd size, but that was long, long pre-internet, so I doubt I was aware of it.
In reply to Tom Suddard :
Hmm. The ones I ran into years ago were smooth on the non-serrated sides.
I would assume the knurling on the mating surfaces would help increase the probability that the washer halves don't slip on the fastener and clamping surface.
Two points.
1. Tab washers are not any squishier than any other washer. They do not bend because they are "soft" in the squishy sense, they bend because they are thin and they stay bent because they have a low yield strength. Being thin actually makes them less squishy just luck cutting coils on a spring raises the spring rate. It is odd, but pretty much every type of steel in every hardness has the same squishiness (Modulus of Elasticity). The washer is not any easier to crush than the nut, and if you are bolting up aluminum, the aluminum is almost three times squishier (in the same thickness) than any steel washer. If the tab is easy to bend over, then it is also easy for vibration to bend it back. You can gauge locking ability based on the difficulty of fully bending the tab.
2. If using stainless in high heat situations, make sure the CTE (Coefficient of Thermal Expansion) of the materials are compatible or you can have a bolt that loses preload (essentially getting looser) as your system heats up. Or, the other way, you can have a bolt that gets tighter and is broken by the system heating up. Stainless bolts holding stainless headers can be fine, carbon on carbon of course, but not all stainless steels have the same CTE, so check materials and be careful.
Mechanical engineer here, with more fastener training than I could type out in a day. ;-)
Most of the information here is generally correct. I have a personal hatred of split washers and prefer a bolt and nut arrangement torqued properly with NO locking device whatsoever, over a split washer. The only time I'll use a split washer is on something like a deck where a) the materials (i.e. wood) are much softer than the fasteners, and b) nothing is moving or vibrating.
Torquing fasteners properly is the single biggest thing you can do to prevent them from loosening.
Nylocks- not any better at torque retention than a regular nut. The only thing the nylon insert is good for is, as you said, preventing the nut from coming off completely. BUT- this only works if there's sufficient thread penetration past the end of the nut- I typically like to see 2-3 threads. Anything less than that and the nylock is essentially no better than a regular nut. Also, they say nylocks can be reused up to 5 times, but does anyone actually count? My general policy on them is to toss them after every use.
I see tab washers used frequently on suspensions and brake components. IMO they generally work well, although after one or two removals the tabs get fatigued and need to be replaced.
Nord-locks are my personal favorite for when it Absolutely, Positively, Must Retain Torque.
One final thought- use either locking compound, or lubrication on threads. This sounds counter-intuitive and contradictory, but there's a reason. A properly torqued bolted joint will resist loosening- and the best way to obtain proper torque is with lubricated threads. Loctite will "lock" a fastener, but it also helps lubricate it on installation, so that correct torque can be applied. If you're not using a thread locking compound, always use antiseize or similar to help make sure the threads engage fully and you get a "true" torque on the fasteners.
Appleseed said:Remember, SAND is nature's Loc-Tite.
There FTFY
What do you call an ovaled nut? Does that still fall under prevailing torque?
They are common and cheap, although usually designed for a specific application.
Sometimes I make my own by crushing a nut in my vise.
clshore said:Appleseed said:Remember, SAND is nature's Loc-Tite.
There FTFY
Rust.
ProDarwin said:What do you call an ovaled nut? Does that still fall under prevailing torque?
They are common and cheap, although usually designed for a specific application.
Sometimes I make my own by crushing a nut in my vise.
Yes, a deformed nut falls under the prevailing torque umbrella. Sometimes they're ovaled with two crimp points, sometimes three. Like nylocks, they are less effective from more uses, but not as quickly as nylock nuts.
Satch_Carlson said:The jam nuts I've used (bulkhead nuts?) are thinner than the nuts they're jamming.
With safety wire, note the excellent photo in this piece, which shows that there is actually some thought involved; the wire should go in the direction of tightness. (This seems obvious, but I've seen it wound the other way a surprising number of times.)
If you're using the thinner jam nuts, these should go on first and the full size nut applied afterwards. The outermost nut will take most of the load, and it's better that you have the larger nut available for that duty.
In reply to volvoclearinghouse (Forum Supporter) :
If you're not using a thread locking compound, always use antiseize or similar to help make sure the threads engage fully and you get a "true" torque on the fasteners.
I believe I have in the past asked about using anti-seize on Lugnuts. I believe that the consensus was that they should be torqued dry. Could we address that question?
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