Castle nut and pin vs nylon locknuts?

[Johnbo]

In preparing for my mechanic to do the annual on my 182 and as a generally good idea I have tried to purchase an assortment of hardware that may need to be replaced so that all the parts are on hand. I have 1962 182E and I have the parts manual which I have been using to determine the correct parts.

my question is with what many mechanics are saying and some of what I read online about when you should use a drilled bolt, castle nut and cotter pin vs using a nylon lock nut on an in drilled bolt. It seems that rotating pints should have a cotter pin which makes sense but a property torqued rod end bearing should not rotate.

More specifically, the service manual for my plane shows AN3-7a & MS21044N3 hardware to be used to connect the rod ends at the aileron bell crank and the control bracket. That listed hardware is not drilled and uses a nylon lock nut.

since it is in the service manual I assume that it was correct at least in 1962 but it is still the correct way to do it?

thx.

 

[AKBill]

I would say if it aint broke don't fix it... Seriously you could search service bulletins from Cessna, for any revisions in hardware. Search AC43.13 or maybe look at a newer 182 manual for the same application

 

[Bell206]

since it is in the service manual I assume that it was correct at least in 1962 but it is still the correct way to do it?

Yes. Hardware selection by the OEM can be based on a number of things to include hardware availability in later revisions of parts manuals. However, I usually stick to OEM recommendations when performing mx. Have you discussed any of these hardware purchases with your mechanic yet? If not you may want to as not all removed hardware requires replacement. Also the cost of hardware drops considerably when ordered in volume. So if your mechanic has a decent stock of hardware may want to check with him what his cost to you will if an item needs replacement. For reference, I would usually flat rate for all consumables (hardware, grease, etc) for an inspection.

 

[kgruber]

One would use the original service manual unless there is an AD.

 

[NordicDave]

One would use the original service manual unless there is an AD.

Or service bulletin or STC modification.

Yes. Hardware selection by the OEM can be based on a number of things to include hardware availability in later revisions of parts manuals. However, I usually stick to OEM recommendations when performing mx. Have you discussed any of these hardware purchases with your mechanic yet? If not you may want to as not all removed hardware requires replacement. Also the cost of hardware drops considerably when ordered in volume. So if your mechanic has a decent stock of hardware may want to check with him what his cost to you will if an item needs replacement. For reference, I would usually flat rate for all consumables (hardware, grease, etc) for an inspection.

Torque putty maybe called for when nylon lock nuts are specified with a visual inspection interval like annual or 100hr.

 

[Dan Thomas]

One would use the original service manual unless there is an AD.

Use the parts catalog. It gives the part numbers; service manuals generally don't. There are plenty of parts catalogs online if one just looks for them. Be aware that they will likely be older versions that are fine, or older versions that have since been updated to correct some deficiencies.

Here's an example of a 172 parts catalog, 1963-1974: http://www.aeroelectric.com/Reference_Docs/Cessna/cessna-maintenance-manuals/Cessna 172 Parts Catalog (1963-1974).pdf

The index begins on page 48 of the .pdf.

 

[Dana]

Use what the manufacturer specifies. That said, it's almost always OK to replace a nylock nut with a castle nut and cotter pin, but the converse is often not the case.

 

[Johnbo]

Thx folks.

 

[pfarber]

Use what the manufacturer specifies. That said, it's almost always OK to replace a nylock nut with a castle nut and cotter pin, but the converse is often not the case.

Citation please?

From my understanding if the parts manual says self locking nut, by part number, and the 43-13-1B gives other guidance, you still have to use the self locking nut. The manual is an authoritative, the 43-13-1B is only acceptable when no other documentation is available.

 

[Domenick]

Be careful--nylon melts. Not all self-locking nuts are nylocks.

 

[pfarber]

That's why you follow the manual. Anything within 6 inches of 250F need metal, not nylon, lock nuts.

 

[Bell206]

The manual is an authoritative, the 43-13-1B is only acceptable

FYI: both the OEM manual and the AC are considered acceptable data per the FAA (except the ALS). And while the OEM manuals are preferred, Part 43.13(a) gives a person performing the work the option of using the OEM manuals or ICAs, "or other methods, techniques, and practices acceptable to the Administrator..." There are also a couple LOIs on this and other guidance as I recall.

 

[Let'sgoflying!]

Not sure this deserves its own thread or not, I can start one if recommended;

I am replacing all the control surface hinge/actuator hardware on my airplane.
I notice that all nuts in the parts manual are AN320 (the boxey, squared off top).

Except for one. The middle flap hinge, which for all appearances is very similar in function and configuration and clearance from other parts of the structure, uses an AN310 (the rounded top castle nut).

Why?
What was the original reason for the design of either rounded- top nuts or the square top nuts?

 

[Checkout_my_Six]

Can it catch during the travel?

 

[Bell206]

Why? What was the original reason for the design of either rounded- top nuts or the square top nuts?

In general, the 320s are called shear nuts as they should only be used in shear load applications and are strength rated below the 310s which can be used in tension and shear loads. Hence the thickness difference.

 

[Stewartb]

I don’t know what hardware an owner would anticipate being changed on an average Cessna. Mine has never needed any except when a repair was required.

 

[Let'sgoflying!]

Can it catch during the travel?

I suppose it could catch on low hanging branches if one were to do nap of the earth flying, however it is pretty much the same as the others in snag-ability. I'll try to get a photo to show ya.

 

[Let'sgoflying!]

In general, the 320s are called shear nuts as they should only be used in shear load applications and are strength rated below the 310s which can be used in tension and shear loads. Hence the thickness difference.

If that's the case I honestly think this could be a typo in the parts manual.

 

[JAWS]

AN 320 is used in straight shear applications.
AN 310 is used in shear and tension. Used most often.
Each one has different torque specs. Refer to AC43.13.
There are nylon locking caslated nuts that are great for control surfaces. Belt and suspenders and more suspenders!
Engine and airframe controls are (ideally) supposed to have two independent locking devices, which is why castle nuts are preferred: torque and pin. There are exceptions. Rodends get tightened up so that the ball rotates and takes the load. Best to follow the IPC.
Lots of manufacturers are now putting their IPC's online for free. Beechcraft (Textron) is one I am most familiar with. Just need to register, no fees.

 

[Bell206]

If that's the case I honestly think this could be a typo in the parts manual.

Perhaps look in a later revision of the IPC (if one exists) and see if the same "typo" is there. While substituting a 310 for a 320 is acceptable in most cases, the reverse may not be especially if there are any tension loads with that "very similar in function and configuration" part.

 

[pfarber]

FYI: both the OEM manual and the AC are considered acceptable data per the FAA (except the ALS). And while the OEM manuals are preferred, Part 43.13(a) gives a person performing the work the option of using the OEM manuals or ICAs, "or other methods, techniques, and practices acceptable to the Administrator..." There are also a couple LOIs on this and other guidance as I recall.

I would disagree. The manufacturer is authoritative, the 43-13 is acceptable, but only as a last resort.

The first paragraph in AC 43-13-1B:

PURPOSE. This advisory circular (AC) contains methods, techniques, and practices acceptable to the Administrator for the inspection and repair of nonpressurized areas of civil aircraft, only when there are no manufacturer repair or maintenance instructions.

While FAR 43.13(a) seems to allow 'acceptable' methods, the courts are pretty clear that the manufacturers information take precedence:


http://aea.net/AvionicsNews/ANArchives/LegalEaseMar10.pdf

The FAA Office of the Chief Counsel has recommended the limitations in the AC be changed to make it clear that the procedures in the AC are considered “acceptable to the FAA for performing inspections and minor repairs of non-pressurized areas of civil aircraft unless the repair at issue is recommended against in the applicable manufacturer’s maintenance or repair instructions.”

 

[Bell206]

I would disagree. The manufacturer is authoritative, the 43-13 is acceptable, but only as a last resort.

I believe we need to keep this in context. Nowhere in Part 43.13(a) are the OEM methods given priority over “other methods, techniques, and practices.” If anything the FAA has interpreted quite the opposite in various topics when Part 43.13(a) is the principal reference. But we can start with the actual LOI vs the paraphrased version in the article link you posted above.


https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/Data/interps/2010/Inter AC 43-13-1B - (2010) Legal Interpretation.pdf

As you can see, there is no authoritative priority given to OEM data. So on face value per Part 43.13(a) the OEM manuals and ICAs are on the same level as the “other methods, techniques, and practices acceptable to the Administrator.” In addition, it also states it would fall to the FAA to prove my use of AC43.13-1B for hardware substitution is unacceptable in a case by case manner vs OEM data being the authoritative data.

Regardless, the “other methods, techniques, and practices”are not inclusive to ACs only. There are specifications, standards, and other guidance documents that address hardware substitutions which are also acceptable data and would not be covered under this LOI. But as I mentioned in my previous post there are additional LOIs and guidance that show the performance rules in Part 43.13 are not bound to the OEM instructions. If you’d like to see those I can post those as well.

While FAR 43.13(a) seems to allow 'acceptable' methods, the courts are pretty clear that the manufacturers information take precedence:

Courts? If referring to the “court” reference in your article it specifically stated “repair stations” which is completely different as a CRS is required to follow Part 145 which is much more restrictive than Part 43.13. Basically apples and oranges in the context of this thread.

 

[pfarber]

I believe we need to keep this in context. Nowhere in Part 43.13(a) are the OEM methods given priority over “other methods, techniques, and practices.” If anything the FAA has interpreted quite the opposite in various topics when Part 43.13(a) is the principal reference. But we can start with the actual LOI vs the paraphrased version in the article link you posted above.
View attachment 97511
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https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/Data/interps/2010/Inter AC 43-13-1B - (2010) Legal Interpretation.pdf

As you can see, there is no authoritative priority given to OEM data. So on face value per Part 43.13(a) the OEM manuals and ICAs are on the same level as the “other methods, techniques, and practices acceptable to the Administrator.” In addition, it also states it would fall to the FAA to prove my use of AC43.13-1B for hardware substitution is unacceptable in a case by case manner vs OEM data being the authoritative data.

Regardless, the “other methods, techniques, and practices”are not inclusive to ACs only. There are specifications, standards, and other guidance documents that address hardware substitutions which are also acceptable data and would not be covered under this LOI. But as I mentioned in my previous post there are additional LOIs and guidance that show the performance rules in Part 43.13 are not bound to the OEM instructions. If you’d like to see those I can post those as well.

Courts? If referring to the “court” reference in your article it specifically stated “repair stations” which is completely different as a CRS is required to follow Part 145 which is much more restrictive than Part 43.13. Basically apples and oranges in the context of this thread.

Actually I found the answer I was looking for (parts substitution) is AC 23-27.

I never meant repair or alteration, just parts substitution... sorry if I was unclear on that point.

 

[BoButt]

A rare glimpse of the FAA Office of Reasonableness at work!

 

[Joe Pilot]

Use what the manufacturer specifies. That said, it's almost always OK to replace a nylock nut with a castle nut and cotter pin, but the converse is often not the case.

I agree with this assessment. Thou shalt add but don't take away . . . .

 

[AlphaPilotFlyer]

For what it’s worth….I came across same issue with FAA on a STC project. Your plane is a CAR 3 cert basis which allows for “friction bolts” in many applications but does not specifically give definition, so A&P could likely justify use of a nylon nut….FAA guidance does say the part listed in approved parts manual part is required but makes alternatives substitutes for issues like that part no longer being available, ect…

my experience with nylon lock nuts is never use then in engine compartment where heat deforms the material, and don’t use in places where they get overused such as inspection plates as the friction decreases after several uses.

 

[pfarber]

my experience with nylon lock nuts is never use then in engine compartment where heat deforms the material

Let me introduce you to my little friend: MS21042

250f or withing 6 inches of a heat source is the rule IIRC

 

[Let'sgoflying!]

nylon lock nuts is never use then in engine compartment

I was taught the same.
Funny how the brain will detect variances from what you are taught!
There are likely mitigating circs, but much later after learning this (which I believe to be a good idea), I was working on an O-200. The 1977 parts manual I had listed 25-27 or so elastic stop nuts attached to the engine (some are duplicates so maybe only half that). Oil sump, tach drive, oil filler tube, generator.

Regarding the 250F limitation; how do you find those measurements? Most engine compartments and some of their components' temps don't soar until after landing when the cooling air stops. You'd need remote sensors to know what is 250 and what is below.
Probably best to stick with manufacturer's hardware -and the rule of thumb where none specified.
Great info, thanks all.

 

[AlphaPilotFlyer]

Let’s go flying…….My background is mostly transport category part 25 where temps anywhere near the engine if discouraged. but During my piston development experience we used remote temperature sensors, some wired some Bluetooth, and placed them throughout the engine compartment, as well as heat images and simple infrared temp guns. There’s also single use temp strips you can stick on surfaces that indicate the highest temp reached. From that you get a good idea of the hot spots and where heat shielding is needed or to increase air flow.

You are right about after shut down temp rise, it was over 60F on our C172 with the V8 engine depending on a few factors. Modern cars ECMs will turn on fans and fuel pumps after engine is turned off when temps reach about 130F. To compound the problem, ethanol gas has a lower vapor point then non-ethanol gas which causes vapor lock at lower temps. So, we redesigned the stock Cessna nose cone a bit (you can see the different inlets, including a small slot on top on the corsairv8.com website) to better vent after shutdown as well as more efficiently feed 2 small radiators mounted each side of the engine. We realized early on we needed to decrease post shutdown temps for a number of reasons. Moving the intakes to the side also required a wider spinner to better direct oncoming airflow into the intakes in flight, but most of this air passes through the radiators so it warmed by time it enters engine compartment…. So that small top slot really decreased compartment temps by flowing cold air over top of engine and out rear of cowl.

There’s also best practices for critical components mounted near potential fire sources: so again no nylon nuts there even though it’s normally cool. We did have a few nylon nuts compromised over time, mostly from getting too hot and multiple heat cycles….I noticed nylon component slightly bulging from top of nut as it likely got soft and expanded. But, when I backed out the screw there was still tension on threads. We changed to other type of lock nuts where needed. However, we do use nylon nuts still in the engine compartment for components in cooler area we routinely remove for inspections during flight testing and have not seen any issues.

so to answer your question, that’s how we, at least, find the hot temps and how we mitigate using heat shielding, moving component from heat source, and redirecting airflow.