AN Numbers for Bendix Magnets hardware

[M20F-1968]

I am not near the plane, and even if I were, it is a bit difficult to use a thread gauge where the mags are mounted.  

What ate the AN numbers for the nuts which both the mags onto a Lycoming IO-360 ANA, and what locking nuts should be used?  My mags are single mags, left and right.

John Breda

[M20F-1968]

That should be Bendix Magneto Hardware..............

[N201MKTurbo]

STD-1410 NUT, 5/16-18 plain

STD-475 WASHER, 5/16 lock, internal teeth

17 ft.­lbs. (204 in.­lbs.) (23 Nm).

[Guest]

The nuts are not standard AN numbers on Lycoming engines, they are 5/16-18 NC threads with the part numbers Rich shows above.  If you had a Continental engine it would use AN315-5R nuts which have 5/16-24NF threads.
 

Clarence

[ShuRugal]

That should be Bendix Magneto Hardware..............

Well, magnetos do contain permanent magnets. I don't know if they are affixed with threaded farstners, though.

[M20F-1968]

11 hours ago, N201MKTurbo said:

STD-1410 NUT, 5/16-18 plain

STD-475 WASHER, 5/16 lock, internal teeth

17 ft.­lbs. (204 in.­lbs.) (23 Nm).

Thanks for the info.  I did eventually find a Lycoming manual and that is what they showed as well.

Any reason why then prefer internal teeth lock washers as opposed to split.  I was under the impression the split hold better.  Or perhaps,  the internal teeth hold better but are single use only.

John Breda

[jetdriven]

The internal tooth lock washer holds better, but yes one time only.  

[ShuRugal]

Thanks for the info.  I did eventually find a Lycoming manual and that is what they showed as well.
Any reason why then prefer internal teeth lock washers as opposed to split.  I was under the impression the split hold better.  Or perhaps,  the internal teeth hold better but are single use only.
John Breda

http://hillcountryengineering.com/wp-content/uploads/2011/10/Split-Lockwashers-Separating-Myth-from-Truth.pdf

NASA Reference Publication 1228 (1990) “Fastener Design Manual” addresses
fastener material selection, platings, lubricants, corrosion, locking methods,
washers, inserts, thread types and classes, fatigue loading, and fastener torque.
• The section on lockwashers states:
“The typical helical spring washer … serves as a spring while the bolt is being tightened.
However, the washer is normally flat by the time the bolt is fully torqued. At this time it is
equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a
lockwasher of this type is useless for locking.”

[carusoam]

Nice reference Shu!

Why is the split washer called a lock washer then?

Best regards,

-a-

[ShuRugal]

Nice reference Shu!
Why is the split washer called a lock washer then?
Best regards,
-a-

Because when it was designed, it was believed to do that job.

[Ross Taylor]

1 hour ago, ShuRugal said:

Because when it was designed, it was believed to do that job.

Exactly this!  I spent a recent decade doing technical work on wind turbines around the world...and learned that split washers, once compressed, are no better than a flat washer.  And if you torque to the values required for proper bolt tension/stretch, on larger bolts anyway, it would actually spread the split washer open.  If the aircraft and component designers had Nord-Lock wedge-locking washers back then, I'm sure that's what we'd be using.  Those things are impressive - they're made up of two layers, which interlock.  When I had to remove a bolt with a Nord-Lock, the layers would separate and the loosening torque actually had to overcome the increased thickness created by the internal ridges (sort of like shallow saw teeth or waves).  Damn...I'm not explaining this well...let's say the washer was 1mm thick when installed and torqued...when loosening the fastener, the washer would actually increase in thickness slightly which meant we had to overcome some additional bolt tension (and resulting torque) before it popped free.  This was on fasteners tightened to 700 foot-pounds, using a torque multiplier, so they may not work as well on our smaller bolts and nuts.  But, circling back, split washers are indeed useless crap. 

[MB65E]

Just bought a 25qt of -3, -4, and-5 Nord washers from Aircraft spruce. It would be interesting if they hold torque on the rocker gaskets and baffleing corse thread hardware. Another area could be the brake calipers. Seems like common areas to really improve operation. IPC aside of course. ;-).
-Matt

[EricJ]

Funny how some topics keep coming up, like which washer to use.   In other threads there are links to videos showing how well the various washers work under vibration, and the internal- or external-tooth star washers are not superior to split lock washers.    I think many of the grumpy IAs know this, which is why they often insist on the split washers.   There is, however, a specific internal-tooth single-use washer indicated in some of the documentation.

 

[Guest]

If split lock washers are of no value, would anything care to explain to me why most of the reports of magnetos coming loose or falling off are on Lycoming engines using internal star type lock washers.

I’ve also seen plenty of internal star lock washers ooze out under the edge of the nut at rated torque.

Clarence

Edited June 8, 2020 by M20Doc

[Ross Taylor]

Let me clarify that I know nothing about aircraft hardware!  So, please don't take my wind turbine comments above to imply any recommendation for changing the hardware on a Mooney. 

[jetdriven]

1 hour ago, M20Doc said:

If split lock washers are of no value, would anything care to explain to me why most of the reports of magnetos coming loose or falling off are on Lycoming engines using internal star type lock washers.

I’ve also seen plenty of internal star lock washers ooze out under the edge of the nut at rated torque.

Clarence

Because they reuse them.  

[Guest]

Just now, jetdriven said:

Because they reuse them.  

More so than maintainers would reuse split washers on a Continental?

Clarence

[jetdriven]

I think there’s less reused split lockwashers coming loose than reused internal tooth lockwashers.  

[ShuRugal]

If split lock washers are of no value, would anything care to explain to me why most of the reports of magnetos coming loose or falling off are on Lycoming engines using internal star type lock washers.
I’ve also seen plenty of internal star lock washers ooze out under the edge of the nut at rated torque.
Clarence

Difference torque specs being referenced? Confirmation bias?

[201Steve]

I’ve never fully grasped why some things require safety wire and others do not. Case in point, mag clamps. Why would this not be something that is saftied? Any feedback here?

[carusoam]

Great question Steve!

Somewhere at the factory.... engine and plane...

they must have executed a risk analysis exercise...

for each fastener, its importance, the chance of it getting loose, and what would happen if it fell off...

When it comes to mag Fasteners... the star washers and their re-use must have been skipped during the exercise...

The lawyers couldn’t see it coming...

It would take a flying lawyer like we have around MS to know the difference between a new star washer and a used one...

There is also a lot of standards for the industry regarding fastener selection...

PP thoughts only, not a legal expert...

Best regards,

-a-

[N201MKTurbo]

^^^ what he said,

It is hard enough to torque them, lock wiring them would be crazy!

 

[kortopates]

11 minutes ago, 201Steve said:

I’ve never fully grasped why some things require safety wire and others do not. Case in point, mag clamps. Why would this not be something that is saftied? Any feedback here?

It is interesting that its only really been an issue with the dual mags - since when they do come loose you loose both mags and a lot of oil. 

[N201MKTurbo]

1 minute ago, kortopates said:

It is interesting that its only really been an issue with the dual mags - since when they do come loose you loose both mags and a lot of oil. 

The nuts on the dual mags are harder to get to than the single mags. I think it is just laziness.

[kortopates]

Just now, N201MKTurbo said:

The nuts on the dual mags are harder to get to than the single mags. I think it is just laziness.

makes sense. Mine are near impossible to get at as it is. I use a magnet to drop the washer and mag holders into position. Liuckily the nuts can be put on with an extension. Safety wire would be impossible for sure.