Lycoming Lock Washers for Magneto hold downs?

[Gary0747]

I see Lycoming specifies a special lock washer for magneto hold down bolts. Is it really a special part or just a pricey relabel of a standard lock washer? 

STD-475 LYCOMING WASHER, .3125 LOCK INT. TEETH

[Guest]

1 hour ago, Gary0747 said:

I see Lycoming specifies a special lock washer for magneto hold down bolts. Is it really a special part or just a pricey relabel of a standard lock washer? 

STD-475 LYCOMING WASHER, .3125 LOCK INT. TEETH

It’s a standard 5/16” internal tooth lock washer.  MS35333-41

Clarence

[carusoam]

Just remember what makes mags fall off...

Lock washer re-use...

Apparently, they don’t work as well the second time...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Prior owner]

Depending upon which magneto(s) you have, you also may or may not need a flat washer under the internal teeth washer.

[jwarren2]

13 hours ago, carusoam said:

Just remember what makes mags fall off...

Lock washer re-use...

Apparently, they don’t work as well the second time...

PP thoughts only, not a mechanic...

Best regards,

-a-

So, if you go to set your timing and have to re-loosen the mag because the timing moves two degrees on the finial torque does that qualify as using them a second time? Just curious,,,

[N201MKTurbo]

What makes mags fall off is improper torque. The lock washers are a last desperate attempt to keep the nut from un-screwing itself after the torque fails.

[EricJ]

FWIW, my IA and a couple other old, grumpy, experienced IAs that I've asked, say to use split lock washers.    I got some new of the "proper" internal tooth lock washers because I knew we were going to have to adjust timing, and my IA just pointed to the split washer and said, "That one won't come off."   I got the same advice from a couple of other trusted IAs, so I've kept the split washers on.

I'm curious why magneto fasteners aren't safetied (lockwired or cotter-pinned).   I'm sure there's a reason, but I don't know what it is.

 

[kortopates]

26 minutes ago, EricJ said:

FWIW, my IA and a couple other old, grumpy, experienced IAs that I've asked, say to use split lock washers.    I got some new of the "proper" internal tooth lock washers because I knew we were going to have to adjust timing, and my IA just pointed to the split washer and said, "That one won't come off."   I got the same advice from a couple of other trusted IAs, so I've kept the split washers on.

I'm curious why magneto fasteners aren't safetied (lockwired or cotter-pinned).   I'm sure there's a reason, but I don't know what it is.

 

Same here, plus split lock washers continue to function after repeated use - since they don't loose their split. Unlike the internal tooth and star lock washers that after first torquing when you remove them you'll readily see their teeth have been totally flattened and no longer effective - at least not nearly as effective. Iam sure Lycoming picked them because they must have some very small advantage over split ring washers but its bad setup for people that don't realize their not resusable or ignoring that and don't replace them on re-torquing. But after hearing about mags fall off in flight well before I did my A&P training this is one area that's deserves the fullest attention to detail.

As for safety wiring or cotter pins, every engine is different and I am always jealous of my big brother IO-550 which has the mags forward at top of engine - where as mine are buried in the middle of the back of the engine. As it is, I have to remove an alternator for access from the left or the intercooler for access from the right. Then I still need a magnetic pickup tool to get both washer on each stud all the while while I have the mag jury rigged in position to not fall off with some safety wire till I get the nuts on. Safety wiring the nuts would be near impossible.  

[Gary0747]

Why did the engine mfg not specify reusable self locking nuts?

[jetdriven]

5 hours ago, jwarren2 said:

So, if you go to set your timing and have to re-loosen the mag because the timing moves two degrees on the finial torque does that qualify as using them a second time? Just curious,,,

No, they’re ruined after being torqued. I know it is a PITA to pull the magneto mounting nuts off to replace the washers when you torque them to final and the mag moves a degree, but such is life.  This board has a few instances of bendix dual mags Falling off or getting super lose and caught.  Recently a guy landed his F model in a field in the middle of Colorado.  TESTWEST had it happen.  A friend of mine with a G model had it happen.  And many other instances.  I finished an air race and a guy came in with oil all over his cowl.  The right mag was sitting on the wiring harness, fell out of the motor. The hardware was gone too. He adjusted the mag timing that morning. 

[cliffy]

What ever happened to the old stamped PAL nuts?   I would think they would be perfect for the mag nuts situation. Even with the internal lock washers installed   I've got a few of them somewhere on the shelves. 

[Guest]

I’ve never seen an issue with split or internal lock washers allowing the nut to loosen.  I would say that a bigger issue with loosening is not using a torque wrench and re-using lock washers.

On D2000/3000 magnetos use of the new style clamps and new hardware every time is critical, and in these cases I use the Pal nut the Cliffs mentions above.

Clarence

Edited May 16, 2020 by M20Doc

[EricJ]

Here are a couple vids that show some basic fastener performance under transverse vibration.   Not every fastener experiences transverse vibration, but it's often considered the worst case as it apparently is the most likely type of vibration to undo a fastener.
 

This one compares split washers and star-toothed lock wshers and shows they're basically the same in these conditions.
 

 

[MB65E]

Awesome Videos!

-Matt

[jetdriven]

I’ve used nord-lock washers on my BMW exhaust. They really are cool. However, not sure how compatible they are with aluminum. 

[PT20J]

On 5/15/2020 at 10:37 AM, kortopates said:

Same here, plus split lock washers continue to function after repeated use - since they don't loose their split. 

Paul, this seems intuitive, but...as the videos show, it doesn’t work that way. What really happens is that the split washer flattens when torqued and essentially becomes a flat washer with no holding ability. See page 9.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900009424.pdf

Skip

[kortopates]

1 hour ago, PT20J said:

Paul, this seems intuitive, but...as the videos show, it doesn’t work that way. What really happens is that the split washer flattens when torqued and essentially becomes a flat washer with no holding ability. See page 9.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900009424.pdf

Skip

Indeed Skip, it wasn't too positive on the star washers either. I read somewhere, which I'll try to find, that Star washers did have the edge on locking (which seems to be in agreement with your citation) while split washers where superior in slowing or resisting loosening once torque was lost. 

[PT20J]

Most of the Junker machine tests on Youtube are posted buy the makers of Nord-Lock showing how much better their product is compared to split lock washers. And, it does seem to be an impressive product. But, I cannot find a video of a test showing how well internal tooth or external tooth star washers perform. Since Nord-Lock didn't compare their product to these, it makes me wonder if the star washers are not pretty good -- and cheap.

Skip

[carusoam]

What is the purpose of a split washer?

It doesn’t seem that locking is in its description...

 

From the fastener design manual, Skip linked above...

“The lockwasher 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 Iockwasher of this type is useless for locking.”

 

The design document points out a bunch of various failure points of each type of locking device...

Making it seem like there can be elevated risk of it not working as designed... just by changing the environment it is in....

temperature, torque, vibration strength and frequency, materials of construction of everything from the bolt to the parts being held in place...

So... what works on various other machines in tough environments.... may not be better for the magneto’s environment...

 

Some lock nuts, like the castellated ones also lose their locking abilities with re-use....  use caution, because they look like real locking nuts... but they can have lost their locking ability.... 

 

Kind of leaves us in the position of using exactly what the procedure calls for..... specific hardware, torque and methodologies... or become a ‘test mechanic’ similar to being a test pilot....

The fastener design manual is a really interesting short story of everything needed to know about fasteners...

Something that comes to mind when One MSer (aka Turbine Tom) found a wing bolt to be slightly undersized in his (non-Mooney) rocket ship... The in spec, but slightly undersized diameter, caused the bolt and hole to move around....

So much to know...

PP thoughts only,

Best regards,

-a-

[Gary0747]

Spring type washers serve a valuable purpose and in some applications are preferred over locking washers with teeth that grab the nut.  Especially in applications where you have large temperature cycles that will change the length of the bolt and reduce the preload torque. The Belleville cup spring washer is used extensively in the Chemical Process Industry on equipment such as heat exchangers and reactors.  If specified properly it will maintain preload through a variety of temperature and pressure situations.   Our Magneto studs see some of these temperature changes but whether it is enough to cause a problem is debatable.  It does seem like we have seen a lot of magnetos coming lose and we tend to blame them all on maintenance error.  Perhaps loss of preload could be a contributing factor in some?
https://en.wikipedia.org/wiki/Belleville_washer

[EricJ]

2 hours ago, PT20J said:

Most of the Junker machine tests on Youtube are posted buy the makers of Nord-Lock showing how much better their product is compared to split lock washers. And, it does seem to be an impressive product. But, I cannot find a video of a test showing how well internal tooth or external tooth star washers perform. Since Nord-Lock didn't compare their product to these, it makes me wonder if the star washers are not pretty good -- and cheap.

Skip

Internal toothed lock washers are the second test in the second vid.    

Edited May 17, 2020 by EricJ

[PT20J]

51 minutes ago, EricJ said:

Internal toothed lock washers are the second test in the second vid.    

Thanks, Eric. I didn’t watch these because I thought I’d seen them all when I went searching for these videos for another thread recently. Apparently I missed that one. Thanks for pointing it out. According to the test results, the star washer isn’t really any better than the split.
Skip

[Guest]

Has anyone ever mounted their Go Pro in their cowl aimed at the magneto studs?  I doubt that the studs and nuts vibrate anything like the  video posted above.

Clarence

[Shiny moose]

 just change the coorect lock washers evry time you loosen them. They are inexpensive

.02

[cliffy]

I buy them by the 100 lot.