Self-locking screws reusable?

Chip Sylverne

Chip Sylverne

Final Approach
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Quit with the negative waves, man.
Can find all manner of guidance about the re-use of self- locking nuts, but can find little about re-using self-locking screws, specifically std-1856 1/4-20 of the type that secure the oil filter housing to a Lycoming accessory case. Since those little suckers aren't cheap, it would be nice to use them again if acceptable to do so.

Lycoming's service letter specifically requires new gaskets and seals, but hardware isn't mentioned.

Any guidance available that I missed?
 
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:needpics:
If it's the kind that has nylon inserted into a slot machined into the screw, I wouldn't reuse it... What's the guidance on a nyloc?
 
Chip Sylverne said:
Any guidance available that I missed?
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Can you post the bulletin or a picture of the screw? The P/N you posted comes up as a roll pin. I don't want to comment until I know specifically what hardware you are talking about. However, Lycoming has in the past allowed alternative "locking" methods.
 
Bell206 said:
Can you post the bulletin or a picture of the screw? The P/N you posted comes up as a roll pin. I don't want to comment until I know specifically what hardware you are talking about. However, Lycoming has in the past allowed alternative "locking" methods.
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Oops, sorry.
STD-1856 SCREW, 1/4-20 x 1.00 long, hex. hd. self-locking. Used to secure the oil filter housing. Everyone seems to reuse them, but that don't make it right. Nothing in AC 41.13 under fasteners about self-locking bolts. Apparently the top few threads are eccentric, which is what makes them lock.

Not hugely expensive, but at $6-$10 each plus shipping, it's worth asking.

www.univair.com

STD-1856 LYCOMING SCREW

At Univair, we’re experts at salvaging and rehabilitating classic planes with our vintage aircraft parts for sale. You can buy classic aircraft parts here!
www.univair.com www.univair.com
 
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Check with Lycoming. An oil filter adapter sounds like a critical installation.

What is keeping the engine oil in the engine worth to you?
 
JAWS said:
Check with Lycoming. An oil filter adapter sounds like a critical installation.

What is keeping the engine oil in the engine worth to you?
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Well, okay, but if Lycoming thought it critical to replace the hardware, wouldn't they have put it in the service instruction?

Not trying to be argumentative, I just find it odd guidance on this type of screw is so sparse.
 
Chip Sylverne said:
Apparently the top few threads are eccentric, which is what makes them lock.
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The self-locking is provided by the preassembled star washer. Its also the reason those screws cost more. So technically based on existing guidance a star washer is a one time use item. However, a simple fix is to cut off the original star washer and install a new washer every disassembly. The replacement standard star washer will be a little looser due to the screw mfg specs but it will still work. Another option is to substitute the screws for use with standard star washers. Or maybe just look for a local source who buys 1856s in bulk and get a better deal?
 
Bell206 said:
The self-locking is provided by the preassembled star washer. Its also the reason those screws cost more. So technically based on existing guidance a star washer is a one time use item. However, a simple fix is to cut off the original star washer and install a new washer every disassembly. The replacement standard star washer will be a little looser due to the screw mfg specs but it will still work. Another option is to substitute the screws for use with standard star washers. Or maybe just look for a local source who buys 1856s in bulk and get a better deal?
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No, sorry, took this from Wilson Garner bolt manufacturing engineering manual.

"A self-locking bolt is a bolt that has a locking mechanism designed to keep the bolt tight without needing a separate lock nut or lock washer."

Has to do with an undercut, head design and an eccentricity in the last few threads. So it's not dependent on the star washer. I guess I'll call them to ask about re-usabilty. Don't know if they manufacture lyc's stuff.
 
From my Lycoming’s IPC-

Nordlocks work better.
 

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Aha! Found it!

Little fun fact. These things are called Place bolts, named after the inventor Charles Place. Using that to search, I found the following:

"What Are Place Bolts?​


Place bolts are self-locking, free-spinning hex head bolts that prevent loosening due to vibration. While other bolts’ locking abilities reside in their threads, Place bolts are unique in that their heads are responsible for the locking action. This is an important quality because it not only produces up to seven times more vibration resistance than conventional hex head cap screws, but it also makes the bolts reusable — giving you the ability to loosen and re-tighten them without any loss of locking."


Those Nordlock washers look like a good option too, but aren't in the IPC for the O-540 A1D5.
 
Chip Sylverne said:
These things are called Place bolts,
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FYI: the STD-1856 in not a Place bolt. If you call Lycoming they will tell you the 1856s are a one time use due to the star washer providing the locking. Plus I doubt there are any oldtimers left at Lyc that will tell you to simply replace the washer. The undercut under the head on the 1856 is solely to hold the washer which is installed prior to the threads being cut. Regardless, if you want to believe these are Place bolts to justify reusing them rock on. Most people just reinstall them and move on.;)
 
Ok, so, while we're at it... I recently read about internal vs. external tooth lock washers and failed to understand why you would use one over the other. Is there a difference?
 
GeorgeC said:
I recently read about internal vs. external tooth lock washers and failed to understand why you would use one over the other. Is there a difference?
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I never really saw an authoritative explanation on those differences, but with the wide varieties of those lock washers from teeth on both inner and outer edges to cupped and keyed versions, I would think there has to be something, somewhere.

What I do remember on the aviation guidance side, they only show/discuss the external tooth versions and I seem to recall the teeth on the external AN washer variety were more aggressive than the internal tooth washer. And that same guidance shows to use a plain, flat washer with all lock washers to protect the base material.
 
I didn't realize that there was a star lock washer under the head.

As Bell206 mentioned, that screw relies on the locking action of the washer. And those screws hold the oil filter adapter in place.

For less than $50, I would replace them. Cheap insurance.
 

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All our Lyc factory overhauls came with plain bolt, internal star washers and plain washers. The star washers were replaced each time. I also found split lock washers there; they lock more definitely and the plain washer prevents any scratching of the casting. The spring action of the lockwasher discourages loosening.
 
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Nord-lock washers came on my wheels securing the bolts to the brake discs. I didn't trust them in that critical application and replaced them with safety wire.
 
For the rotors? Nylocks. Calipers? Flat washers under the bolt heads. I don't know anyone who safeties caliper bolts. Preflight item.
 
Stewartb said:
For the rotors? Nylocks. Calipers? Flat washers under the bolt heads. I don't know anyone who safeties caliper bolts. Preflight item.
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This is the wheel:
matcoals.com

W50S1.25 - Matco Aircraft Landing Systems

WHL & BRK ASSY 5"
matcoals.com matcoals.com
Item number 26 on this diagram is the nordlock washer:
After disassembly a time or two the nordlock washers seemed to lack much resistance to loosening. I changed back to safety wire bolts (as were used in the earlier version of these wheels) in that application.
 
No reason for lock washers there. Nylocks on the other end do the work. Certainly no need for safety wire, either. The nuts are the critical part. Wiring the bolt heads is useless.
 
Stewartb said:
No reason for lock washers there. Nylocks on the other end do the work. Certainly no need for safety wire, either. The nuts are the critical part. Wiring the bolt heads is useless.
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There are no nylocks on the other end. Not even nuts on thee other end. Those bolts screw directly into the wheel / rim edge.
 
Ahh. Not like Clevelands. I’d still have used Nord-Locks there. Read the tech.
 
In case anyone is skeptical of the need for lock washery, I was witness to an incident where the bolt securing the top of the alternator arm to the engine block was not safety wired. It's easy to forget because it hides under the baffle. Sometime during the first 30 minutes of flight afterwards, that bolt departed the aircraft.

My rebuilt engine came with a mix of integral star washer screws and separate washers. Generally speaking, the standard AN fine thread bolts and screws use separate star washers with internal teeth, while the larger coarse thread screws and bolts that go directly into the case or cylinders used integral star washers with external teeth. Those are all Lycoming p/n. I suspect it could be as simple as Lycoming figured that was the best way to ensure nobody ever forgot to put a lock washer on at the factory.

One thing Lycoming did not use was metal lock nuts. The AN4 bolts securing the oil sump to the case are fastened with plain hex nuts and secured with internal tooth star washers under both the bolt head and nut.
 
Ed Haywood said:
In case anyone is skeptical of the need for lock washery, I was witness to an incident where the bolt securing the top of the alternator arm to the engine block was not safety wired. It's easy to forget because it hides under the baffle. Sometime during the first 30 minutes of flight afterwards, that bolt departed the aircraft.
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After my top overhaul and prior to first flight I inspected the re-installation work done by the A&P. I noticed the alternator was loose. That bolt, hidden behind the flywheel, was out.
 
I don't know anyone who safeties caliper bolts.
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I do, as required. If the bolt call out has a wire hole in the head, it gets safetied. Cheap and easy to preflight.
 
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Stewartb said:
I don't know anyone who safeties caliper bolts. Preflight item.
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From the Cleveland wheel and brake maintenance manual:

1701712358722.png

I encountered many brake calipers with AN4H drilled-head bolts. I lockwired them. OEM equipment for many years.

https://www.parker.com/content/dam/...iterature/AWBCMM0001.pdf#page=21&zoom=100,0,0

If the airplane is wearing wheelpants with the brake fairings, preflighting the caliper bolts is pretty much impossible.

From the Cleveland parts catalog:

1701713120312.png
1701713208411.png
https://www.parker.com/literature/Aircraft Wheel & Brake Division/AWB Static Files for Literature/AWBPC0001.pdf

I have also used blue Loctite. It works well.

One thing: The torques on those bolts vary, depending on the caliper part number, from 60 to 90 inch-pounds. 70 or 75 is common, and that is not much torque. If one does it up "until it feels right," it will likely be overtorqued. I have found those bolts necked and ready to fail from that, and had one actually fail in service.
 
FORANE said:
Nord-lock washers came on my wheels securing the bolts to the brake discs. I didn't trust them in that critical application and replaced them with safety wire.
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One thing to note with nord washers and similar tension locking devices is they call out for a higher torque value to ensure 100% engagement. However that 100% torque value can exceed the maximum standard torque value of the fastener especially on aircraft.
 
Ed Haywood said:
Generally speaking, the standard AN fine thread bolts and screws use separate star washers with internal teeth, while the larger coarse thread screws and bolts that go directly into the case or cylinders used integral star washers with external teeth. Those are all Lycoming p/n. I suspect it could be as simple as Lycoming figured that was the best way to ensure nobody ever forgot to put a lock washer on at the factory.
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Then I wish they would just call them "screws with lockwashers" in the IPC, rather than "self-locking screws". They really are two different types of fastener.
 
Chip Sylverne said:
Then I wish they would just call them "screws with lockwashers" in the IPC, rather than "self-locking screws". They really are two different types of fastener.
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Not necessarily. There are many variations to self-locking hardware. The Lycoming bolts, which are actually called "pre-assembled screws" or SEMS, is one type and been around for decades. Others will have a machined groove in the threads filled with plastic or nylon material as the locking mechanism. Or some fasteners even come with pre-applied lock-tite or similar material. While I have seen the distorted thread type you mentioned above, I dont recall any while working on aircraft as the screw or bolt was usually standard but the nut or nutplate had the distorted feature to lock the fastener. Really boils down to what reference or industry is used when it comes to defining hardware, etc. For example, there is no MIL-SPEC for a SEMS screw but they are still used on aircraft like a number of other off-the-shelf fasteners.
 
When I was building race cars I had 2 friends who worked for GE jet engines in Evendale Ohio, suburb of Cincinnati.
They brought me jet engine fasteners that they said were thrown away new. Our cars were loaded with titanium and other rare light weigh hardware. Not all of it came from GE, some of the titanium came from racing sources. I learned several ways that fasteners locked and they were most all one time use.
And not one of them have found there way onto my cessna, not a one. Not all of these came from GE and that nylon locking nut was not used on our race cars because they were not strong enough being grade 2 most likely. The 7/16' nut in the lower left is a hard anodized aluminum nut and holds on a screw supercharger on aluminum studs designed to break in a back fire.

IMG_87921.jpg
 
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Gary Ward said:
When I was building race cars I had 2 friends who worked for GE jet engines in Evendale Ohio, suburb of Cincinnati.
They brought me buckets loads of jet engine fasteners that they said were thrown away new. Our cars were loaded with titanium and other rare light weigh hardware. Not all of it came from GE, some of the titanium came from racing sources. I learned several ways that fasteners locked and they were all one time use.
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I also had a friend that worked in the aerospace industry when I raced karts. He was part of the team rebuilding B-707's for the Northrup-Grumman Joint STARS program at Chenault airfield. He had buckets of different fasteners that were lightweight and of different profiles that worked well in racing applications. I used a bunch of little stamped metal nuts with upset threaded diameters that were self locking. Neat bit of kit for certain.
 
Gary Ward said:
When I was building race cars I had 2 friends who worked for GE jet engines in Evendale Ohio, suburb of Cincinnati.
They brought me jet engine fasteners that they said were thrown away new. Our cars were loaded with titanium and other rare light weigh hardware. Not all of it came from GE, some of the titanium came from racing sources. I learned several ways that fasteners locked and they were all one time use.
And not one of them have found there way onto my cessna, not a one. Not all of these came from GE and that nylon locking nut was not used on our race cars because they were not strong enough being grade 2 most likely.

IMG_87921.jpg
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The large nuts look like the NAS fasteners for my gear leg bolts. Finding a 12 point crows foot extension for the torque wrench was entertaining. But turns out Amazon does indeed have everything.
PXL_20210306_162353288.jpg
 
Ed Haywood said:
The large nuts look like the NAS fasteners for my gear leg bolts. Finding a 12 point crows foot extension for the torque wrench was entertaining. But turns out Amazon does indeed have everything.
View attachment 123009
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I believe it.
Those large 1/2" 12 points are head stud nuts among other uses. Some of our head studs are 9/16" We did reuse those about 5 times before we replaced them. The face would wear out and not give consistent torq/clamping. We removed the heads often so we did buy a fair bit of premium hardware in a race season.
 
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Chip Sylverne said:
Oops, sorry.
STD-1856 SCREW, 1/4-20 x 1.00 long, hex. hd. self-locking. Used to secure the oil filter housing. Everyone seems to reuse them, but that don't make it right. Nothing in AC 41.13 under fasteners about self-locking bolts. Apparently the top few threads are eccentric, which is what makes them lock.

Not hugely expensive, but at $6-$10 each plus shipping, it's worth asking.

www.univair.com

STD-1856 LYCOMING SCREW

At Univair, we’re experts at salvaging and rehabilitating classic planes with our vintage aircraft parts for sale. You can buy classic aircraft parts here!
www.univair.com www.univair.com
Click to expand...
I would replace these every time.
 
Checkout_my_Six said:
I can’t believe no one knows this…..:D
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It's not as simple as question as it appears. Some self-locking fasteners that lock by virtue of an angular or pitch change in the ramp of the threads are indeed re-usable many times. Fasteners that lock by virtue of patches, adhesives or inserts aren't. Fasteners that lock by virtue of lock washers such as internal or external star may be re- used, but the locking washers are one-time use. Nordlock being the exception, but as was pointed out, those too have their drawbacks.

The problem I had with Lycomings IPC is that it called these fasteners self-locking, but come to find out they aren't, they lock by virtue of a captive washer. As expensive as they are, I assumed they would lock by the threads and actually fall into the reusable category. Turns out that was wrong by a long shot. I'm a bit OCD when it comes to nomenclature, I guess.

Pursued this more out of curiosity than anything else. Glad I did, I learned a bunch.

BTW, think I found that oil leak we were chasing ;).
 
I wouldn’t trust the threads in the case to hold the same self-locking screw twice. That’s a stupid system. Probably why it isn’t used these days.
 
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