Introduction: DIY Self-Locking Nut

Picture of DIY Self-Locking Nut

The humble nut and bolt, they hold the engineering world together but sometimes they won't play ball and the nut wants to spin and fall off.

There are many ways to make sure the nut stays fastened:

  • Nylock nuts
  • Anti-vibe washers
  • Spring washers
  • Thread lock (glue)
  • Double nutting (see picture)

But sometimes you may not have the normal equipment or not have space for a lock nut, this instructable will show a handy hack that will keep a nut in place while leaving the possibility to remove it with a spanner.

Step 1: The Technique

Picture of The Technique

All you need is:

  • Nut and bolt
  • Electrical heat shrink
  • Heat source
  • Spanners

It should be noted that this only really works for bolts larger than M8, any smaller than that and the thread is too fine and the nut won't fit.

The idea is simple, slide heat shrink over the threaded section of the bolt

Heat it until it shrinks into the threads, also shrink the bit sticking off the end (this will act as a guide for the nut)

Push the nut down the tail of the heat shrink and start to thread it on

It will be hard to turn, much like a nylock

The nut will strip the tail and it will fall off

As you thread down, the heat shrink fills up the thread and acts as a thread lock (THIS NUT WILL NOT VIBRATE OPEN!)

If you ever need to remove it, a spanner, some brute force and ignorance will open the nut, which will clean the thread of obstruction as it goes.

Simple, quick and handy

Comments

3366carlos (author)2017-11-25

good idea, I use "plumbers tape" but after watching this video, I will use these washers. What to do for spark plugs?

thardy2 (author)3366carlos2017-11-26

Have you ever had a spark plug come loose? I've worked on cars for 14 years and never seen a spark plug work it's way loose.

UncleEd (author)thardy22017-11-26

Back around 2000, the Ford Triton 5.4 liter truck engine had only four threads for the plug to grip. They were notorious for having the plug come loose and then blow out. My truck did that at about 30 mph (50 kph?) and the plug hitting the hood was a sound I won't forget. I turned into a local repair shop and asked if someone could look at my truck. A fellow just standing there said, "You blew out a plug. I heard it when you drove in."

Fortunately, that day it didn't ruin the engine head or the spark plug, so the mechanic just screwed it back in. It ruined the "coil pack" so I ended up around $100 for screwing the plug back in the hole.

grapenut (author)UncleEd2017-12-10

Thanks; that explains alot. I've never seen (I've only ever looked at MY cars) only 4 threads gripping a plug. That seems to little, especially for something 5.4 liter.

KeithAZ (author)thardy22017-11-26

I've seen plenty of the older aluminum heads from cheaper cars fail... Usually happens when people re-used the old spark plugs that has a hollow collapsing washer.

thardy2 (author)KeithAZ2017-11-26

Fail like how? I've never worked on a car with a cast iron head, I've never seen a spark plug come loose.

KeithAZ (author)thardy22017-11-26

Here is a great read... if anyone is following that cares about the do's and don'ts with sparks plugs https://www.pepboys.com/car_care_corner/do_it_your...

grapenut (author)KeithAZ2017-12-10

Thanks; I read it; very helpful; covered lots of bases.

jwzumwalt (author)KeithAZ2017-11-29

I have been saving tips for personal use and found your link helpful - THANKS!

MillerI (author)KeithAZ2017-11-26

I was taught in auto shop class to not reuse the compressible washers but did it dozens of times without a single failure. I'm not sure if you're talking about someone over-torquing a plug but I've never seen a plug come loose, washer or no. The washer is there for sealing, not for retention. Non-washer plugs are beveled and require a certain amount of torque that is not recommended for the older aluminum heads. I won't even get into dissimilar metal galvanic action.

KeithAZ (author)MillerI2017-11-26

Here is a great read... if anyone is following that cares about the do's and don'ts with sparks plugs https://www.pepboys.com/car_care_corner/do_it_your...

Spark plugs I've seen blown out of the cylinder are due to the forces of the combustion chamber overcoming the retention of what the threads should hold... or well, any of those "Don'ts" are done. It's hard to say " not causing the problem myself" what exactly happens to the cars I've had to "heli-coi"l or re-sleeve but most times I've seen more than half the threads just ripped right out and the spark plug is dangling by the wire boot or somewhere on road.

clark5113 (author)thardy22017-12-10

Yes I have seen plugs come loose to the point of blowing out on the freeway. We had to keep a length of rubber hose in the glove box to replace it as it was recessed into the head. But it was a volkswagen so........

johnny3h (author)thardy22017-11-29

At 75, I've done small engine maintenance since12, motorcycles from 14, and cars and trucks up to today, AND I have NEVER seen a properly installed sparkplug "back out!!!"

thardy2 (author)thardy22017-11-26

You can't put something between the threads on a spark plug because the screw shell of the plug grounds the ground electrode to the engine. You also risk adding pressure to the head which could crack the head over time.

LloydF1 (author)thardy22017-11-26

You're 100% correct that you can't insulate the threads of a spark plug from the engine 'head' or you will have no ground connection. However, I have to somewhat disagree about the part of cracking the head. They would have to be either some *really* over-sized spark plug threads -or- some really, really crappy heads (like the GM 333882 casting 76cc heads from the 70's.. LOL). Of coarse, I'm talking about iron heads. I generally *hate* aluminum heads and try to forget they exist. =P

thardy2 (author)LloydF12017-11-26

If you take any metal and stuff something in between some bolts in some threads, then heat and cool it over and over, it will crack. You're putting way more stress on those threaded holes than they were designed for.

AndrewA167 (author)thardy22017-11-26

3366carlos probably owns a Ford 5.4L Triton...

thardy2 (author)AndrewA1672017-11-26

They have the opposite problem, they won't come out.

grapenut (author)3366carlos2017-11-26

I am suspicious that Carlos may have meant to comment on a different thread? clue 1- plumbers tape? is an anti-seize product, not a nut locking product. clue 2- spark-plugs? As many commenters have pointed out, they don't have a problem vibrating out. Carlos must be wondering how to keep the plugs from getting stuck. I had this problem years ago and used a spray can anti-seize grease with copper in it. I later switched to spray anti-seize with graphite; but they both worked well and that engine nissan 4 cyl. ran great with little to no oil burn at 187,000 miles before I finally moved on to another vehicle. I like the spray can because the anti-seize goes directly from the can to the threads keeping things cleaner (grit free) for the inside of the engine. Does anyone know if it is necessary to gap new replacement plugs? (for newer cars) or are new plug gaps better off left alone?

3366carlos (author)grapenut2017-12-10

thanks for all responses. I should have used a torque wrench last time I replaced my plugs, im gonna have to go and retighten, I did use antiseize spray thought. I did not have to gap my plugs.

geraldpaxton (author)grapenut2017-12-03

on plug gap, check specs for gap and always check...

jwzumwalt (author)grapenut2017-11-29

I am a aircraft mechanic and also use a copper based bearing grease product as anti-seize for spark plugs - works great!

Champion makes a supposed anti-seize that looks very thin and black for aviation. my experience and all mechanics I have talked to believe it doesn't work.

Oh you'd want something designed for that kind of heat and chemical environment. Not too sure about spark plugs

jimvandamme (author)3366carlos2017-11-26

Follow the manufacturer's instructions. Nowadays they tell you not to use antiseize goop, just tighten according to the specs. I've never had one fall out.

thardy2 (author)jimvandamme2017-11-26

I always use anti-seize on spark plugs. I broke one in a head once. Never again will I install a plug without anti-seize.

JerryL1206 (author)3366carlos2017-11-26

"heli-coil"

PhilipH88 (author)2017-11-27

and yet another variation is to mash the threads of the bolt with a chisel peen hammer or center punch, just in the area where the nut will engage when tightnened. Like many things, its all a matter of degree and not overdoing a good thing. If you believe you will never have to remove the nut in the future, then you can rivet the end of the bolt over the nut with a ball peen hammer, but I wouldn't, because my ability to accurately predict the future has proven to be defective.

ash304 (author)PhilipH882017-11-30

i rarely do it, but another solution is to throw the bolt in a vice to ever so slightly deform the thread.


Nasty.

clark5113 (author)ash3042017-12-10

I like it nasty. I have (if space permits) left about 1/2" of thread past the nut, split it with a cutoff wheel and spread it. You can still get it off and if you bevel the end of the bolt, it will rethread :)

PhilipH88 (author)ash3042017-11-30

Indeed, seems as though it ought to work in much the same way as the version that I suggested. I would really like to see what would happen to these techniques when the bolt is subjected to that vibration machine of which there a video accompanying this discussion.

JustH1 (author)2017-11-30

I find this method to be interesting, but double nutting and even crimping a nut in a vice works better with less setup than the plastic melting method

I would normally double nut but this technique is for when there's not enough exposed thread for a double nut or even a nyloc

In which case you can grind down, weld, or combine options with bradding the end with a hammer

I'm only presenting this as one way it can be done. Welding, adding, peening went options for me here.

jumbleview (author)2017-11-28

I myself made inscrutable about non-traditional usage of heat-shrink. But I did not know about usage provided here. Nice and useful idea. I will include it into my toolbox for sure.

can you post the link

https://www.instructables.com/id/Not-for-Insulation-Only/

Here it is

sundug (author)2017-11-26

A technique I have used for decades as an auto tech and motor head is to use a center punch to distort a thread on the bolt where the nut will rest. As long as the bolt is long enuf to allow the nut to start without encountering the distorted thread, this technique will guarantee the nut will not work loose, but will come off with a wrench.

itsmescotty (author)sundug2017-11-26

it's called 'staking'. Usually done after torquing and useing a centerpunch at an angle and contacting both nut and bolt. Industry uses something similar where they impact the nut on the side or top hard enough to marginally deform the nut into the threads.

johnny3h (author)itsmescotty2017-11-29

Right, and if that technique is used, an observer will be able to see a small, rectangular indentation on 3 of the flats of a hex-nut.

That would do it alright thanks for the comment

jwzumwalt (author)2017-11-29

When I was a teenager we would put a dab of silicone caulk on the
threads of model airplane engines to keep them from vibrating off. I
still use this technique occasionally. It holds the bolt but can still
be removed. It is much faster and cheaper than heat shrink.

Never thought of silicone!

meanblackbike (author)2017-11-27

Well here is my solution that is the most cheap and the most hard locking:

Get Locktite glue it is cyanoacrylate glue so if you buy other brand (with name

cyanoacrylate in the description) it is the same.

Do not glue anything, but get the bolt and mark the place where the nut should be and the end of the nut also . In that place on the thread put some drops of the glue and rotate so the drops be in the marks - (use a marker for that).

Then leave the bolt in vertical position to dry and try after the glue is really dry - it looks like glass on the thread.

If it is not locked repeat the drops of glue procedure.

I see you use huge bolts so several drops might work better.

The idea is that it is like thread-locker (the one mentioned above) but in reality it is much locking then the thread-locker :) - I used it on 8mm threads and lower to a 0.5mm on glasses - all work.

For huge bolts like the pictures it might be best to use Locktite gel glue it is sold as a thicker version and is like yogurt of sort, do not spills so much.

To keep it for the next use put it's tap and in the fridge so not drying so fast.

Do not use it on spark plugs.

I have for 3-4 years 2 chainsaws and 20-30 spark plugs - do not ruin your engine for being cheap and ALWAYS use a new spark plug from a good brand. This glue will not help in spark plug just because is is not heat resistant DO NOT DO IT.

Do not glue your nuts and bolts - It will come off I tried.

Eventually the glue can be stripped off if several times you unscrew it but that is like thread-locker no surprise.

About spark plugs - the thread is having special stepping in the end and that seems to block the unscrewing it , so perhaps a quality plug is ALL you need to have - well maybe a new engine as well if all the plugs do not help. But I'm not an expert. Also spark plug that is not screwed to the max is no use for me I have seen to loose pressure on my chainsaws.

elpayo (author)2017-11-27

;)

RonGarza (author)2017-11-26

Teflon tape?

Teflon tape is PTFE plumbers tape

Thanks, I had never heard that name, which apparently is short for PolyTetraFluoroEthylene. I had read that it was made of 2 Flouride atoms bonded to a single carbon atom, that triad then linked to other identical triads carbon-to-carbon two at a time, hence tetra Fs. I just now wrapped two windings on a bolt and screwed the nut over the tape. While I experienced a lesser resistance when removing the nut afterwards, I doubt that the nut is going to vibrate off but I have not actually tested that.

MichaelW311 (author)2017-11-26

Voted twice. Metal Work & Hack.

Great idea!

Thanks!

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Bio: I am an automation engineer but I will give anything a go. I don't know if you call if pessimism or just being an ... More »
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