Favorite thread locker?

[Crimson Tim]

What’s your favorite way to lock in a nut or bolt that just won’t stay tight?
But one that you may still have to disassemble some day?
The specific machine in question happens to be a washing machine. I have replaced the seals and bearings on the main drum shaft for the third or fourth time, because the bolt keeps loosening. This lets the seals come apart, lets water into the bearings, and lets the pulley and belt shift enough to burn into the back of the tub.

The plastic pulley on the back is held on by a 3/8” bolt that is threaded into the drum axle. I have torqued it to spec. I have used a split lock washer. I have used a star lock washer. I have used blue permatex thread locker (after thoroughly degreasing). I have used the lock washer with the permatex. I just now sheared the head off the bolt tightening it for the second time TODAY after just replacing the bearings again last weekend using a brand new bolt.

I guess permatex has one level stronger thread locker I could try, but the blue has proven so feeble this time around that I don’t have much hope for the next level, either.

If there is an easy solution, some magic lock washer and/or thread locker that anyone can recommend as a superior combination, I would sure love to hear about it!

I’m not sure why this should be so troublesome. I assume it’s the vibration that is causing this to loosen. But it’s a washer. It’s going to vibrate. The springs and dampers and deadweight all seem to be doing their jobs, and the vibration seems to be typical of other washers, so what gives?

Otherwise, I’m starting to look at more hardcore options:
- Tack weld the bolt to the washer that tabs into the pulley and hope it doesn’t get hot enough to damage the plastic pulley. Knowing I’ll have to grind it off if I have to disassemble in future.
- Braze a stud into the axle and drill it for a castle nut and cotter pin.
- Some other device to physically prevent the nut from moving similar to the washer bent against the flat of the nut in the Cub hydraulic pump.

The castle nut and cotter pin fix seems like the most effective and cleanest, though most involved, option. Just out of curiosity, has anyone done this on the hydraulic pump since those nuts are somewhat prone to coming off?

If anybody else has any great ideas on what to do with this, I would sure appreciate hearing about them!

[outdoors4evr]

Get a longer bolt and add a jam nut. Thread the nut all the way onto the bolt, put the bolt in place and tighten it down. Then thread the nut down against the shaft and tighten it so it "jams" the threads and won't allow the bolt to back out.

[Bob McCarty]

How about inserting a stud (all thread ?) with an epoxy cement like JB Weld and then place a nyloc nut on the outside, or double nut with a jam nut too? See "self-locking hex nut" at McMaster-Carr for other options.

[Urbish]

How about safety wire? Do you have something you can tie the wire off to? Simple solution that is easily removable should you ever have to mess with it again. Or could you bend the washer in 1 or two places against the flat of the bolt to keep it from moving? EDIT: Looks like you already considered my 2nd suggestion.

[Jim Becker]

What grade bolt have you been using? A grade 8 will be slightly larger than a common ungraded hardware bolt. A grade 8 might reduce thread clearance and allow the blue thread locker to actually work.

[Don McCombs]

If I'm reading your description correctly, your bolt is going through one side of the plastic pulley hub and into a threaded blind hole in the shaft. Is this correct?

[Crimson Tim]

If I'm reading your description correctly, your bolt is going through one side of the plastic pulley hub and into a threaded blind hole in the shaft. Is this correct?

Yes, that is correct.

What grade bolt have you been using? A grade 8 will be slightly larger than a common ungraded hardware bolt. A grade 8 might reduce thread clearance and allow the blue thread locker to actually work.

Interesting. I don’t think the original bolts have had any special grade. I figured on replacing with grade 5 or 8 once I drill out the one I snapped off. (Using the left hand drill bit trick that I learned on this site, so thank you for that). So I’ll definitely go 8 then.

How about inserting a stud (all thread ?) with an epoxy cement like JB Weld and then place a nyloc nut on the outside, or double nut with a jam nut too? See "self-locking hex nut" at McMaster-Carr for other options.

JB would be easier than brazing. Not sure which would do better for vibration. Do you think a nyloc nut or one of those distorted thread nuts would hold on better? I guess I can double them up and jamb them, too, for good measure.

Get a longer bolt and add a jam nut. Thread the nut all the way onto the bolt, put the bolt in place and tighten it down. Then thread the nut down against the shaft and tighten it so it "jams" the threads and won't allow the bolt to back out.

Another good idea. At first I didn’t see how this would be better than just tightening the nut against the pulley, but no. It’s much better. It removes the torque stress from the bolt and puts it in almost pure tension. Steel likes to fail in shear, so removing the torque from the equation should allow quite a lot more tensile load to be generated against the threads.



McMaster-Carr is a great resource, simply as a research source to see what is out there. They have nyloc bolts, too. Never seen those before. Interesting, but probably not up to this task.
Several heavy duty locking nut options, up to $4 per nut. It’ll be worth it if I never have to mess with this again.
The wire-locking bolt would be the simplest. I guess vibration shouldn’t result in too much unscrewing torque, but if it busts the wire, I can step it up to the threaded rod (or a long, decapitated grade 8 bolt) and one of those fancy extreme vibration lock nuts from MC. I saw one type of nut that is not reusable. I guess if they don’t mention that limitation, then it would be?

I knew you all here would have some better ideas!

[Don McCombs]

Tim, I'm guessing that the repeated failures and vibration have degraded the threads in the tub shaft, accelerating the loosening. How about drilling entirely through the hub and shaft, eliminating the threads and adding a through bolt with a nut and jam nut on the far side?

[Jim Becker]

. . . How about drilling entirely through the hub and shaft, eliminating the threads and adding a through bolt with a nut and jam nut on the far side?

The other end of the shaft probably is inside the tub (water against it). Going that way calls for sealing the bolt/hole against leakage and using stainless hardware.

[Crimson Tim]

. . . How about drilling entirely through the hub and shaft, eliminating the threads and adding a through bolt with a nut and jam nut on the far side?

The other end of the shaft probably is inside the tub (water against it). Going that way calls for sealing the bolt/hole against leakage and using stainless hardware.

Yes. That would be in the tub, and also would be drilling at least 6” if not 8” in length, which is beyond my facilities for doing here with any accuracy. I’d have to take it to someone.
I could, however, just drill and tap the hole 1 1/2” or so deeper for a longer bolt.

I didn’t notice any extra play when starting the bolt, but that *would* explain why it fails faster each time.
The splines on the pulley are probably a bit boogered up, too, which could make for an unstable surface for the bolt to snug up against. I replaced it once already for that reason during one of the previous episodes.
It got pretty sloppy that time, though, and the new pulley really didn’t make much difference in the repair longevity. Maybe as long as the bolt is tight, it stabilizes any unauthorized movement.

Epoxying the threaded rod in and then using either one of those extreme vibration lock nuts or the castle nut/cotter pin is sounding like the best scenario. If the shaft threads are loose, the epoxy will firm them right up.

[Don McCombs]

OK. I understand how it goes together, now. I was thinking that the bolt was perpendicular to the shaft. Never mind.

[Crimson Tim]

The bolt is tapped right down the axis of the shaft. I still have to drill out the broken bolt.
When I took this apart the first time, I was surprised that the bolt just snugs up against the plastic pulley. I don’t remember the actual torque specs, but it was high. And then I was reefing on it even harder than that this last time. The plastic is holding up to that just fine.

There’s a little play in the splines, but I do not see any deformation, so I am pretty sure it’s just a looser fit than might be expected. The plastic splines hang 1/4” off the end of the steel shaft, so an obvious transition point shows up if they get damaged.

[Don McCombs]

I wonder whether the direction of rotation of the shaft tends to loosen the bolt as opposed to tightening it. You wouldn't think that it would because of the splines. But, if there is any play at all, it may be a factor.

[coppersmythe]

one small aspect , make sure the blue "locktight" type thread locker is a fairly fresh tube , and shake before using . i use them on my electric lamps . i had an old tube (6-7 years old ) and almost empty . the lamp i used it on unscrewed in the wind and fell to the ground at my clients house . fortunately it fell on an azalea bush . didnt even break the glass .coppersmythe...........................................

[Urbish]

I wonder whether the direction of rotation of the shaft tends to loosen the bolt as opposed to tightening it. You wouldn't think that it would because of the splines. But, if there is any play at all, it may be a factor.

Agreed. Any play whatsoever in the splines will translate to loosening of the fastener as the drum agitates back and forth. Loctite makes a product (I believe it's their bearing mount stuff - comes in several flavors) that is made to take up play in mating parts. I'd try some of that between the splines and the pulley to remove any backlash. I don't know how good it will work since the pulley is plastic, but might be worth a try.