Nuts on carbs and fuel servos

[YellowJacket RV9]

I wonder if some of these loose nuts are due to torqueing them dry as opposed to with a lubricant as specified by Lycoming. I installed mine on the carb per plans but also keep an eye on them. So far they have remained properly torqued.

Chris

[jrs14855]

I think this is mostly either under torqueing and/or re using lock washers. Remember the connecting rod bolts on Lycoming's are not safetied.

[Bernie RV7]

I use p/n STD 1763 palnuts to lock the plain nuts as per the Lycoming O-360 parts manual.. Got mine from Spruce. Hope that helps

[vic syracuse]

Originally Posted by jrs14855

I think this is mostly either under torqueing and/or re using lock washers. Remember the connecting rod bolts on Lycoming's are not safetied.

I think you are correct. Don't forget we have many first-time builders that are now first-time airplane mechanics once they get their airplanes flying. Most are very careful to reassemble something exactly the way it came apart, not realizing that some parts such as internal tooth lock washers, are not supposed to be reused.

Sometimes it is good to take a look at something and see if it can be made "maintenance proof." In this case, there have been a lot of great suggestions (locktite, palnuts, double nuts, AN 363 metal locking nuts, etc). About the only ones that are "reusable" would be the double nuts, AN 363's, and perhaps a palnut.
First timers in the field don't always have loctite and new lock washers available.
Those who work in shops or on a lot of airplanes certainly do, but for the majority of the new owners the carb may come off once to change a jet, and it is here I think that the reuse of the lockwasher sets the table for a future loose/lost nut.

Just a suggestion.

Vic

[az_gila]

Originally Posted by vic syracuse

.....

Sometimes it is good to take a look at something and see if it can be made "maintenance proof." In this case, there have been a lot of great suggestions (locktite, palnuts, double nuts, AN 363 metal locking nuts, etc). About the only ones that are "reusable" would be the double nuts, AN 363's, and perhaps a palnut.
.....
Vic

I had to look that one up since I haven't used many palnuts...

According to the FAA bible AC43.13 they are not reusable.

https://tinyurl.com/l3gsxl6

So if you are using them, buy a bunch extra as spares.

[vic syracuse]

Thanks, Gil. That's why I said PERHAPS. I should have looked it up.

Vic

[az_gila]

Originally Posted by vic syracuse

Thanks, Gil. That's why I said PERHAPS. I should have looked it up.

Vic

It was an interesting question, and the answer was not obvious...

[lr172]

Originally Posted by moosepileit

Stud length seems perfect for double nuts.

That's what I did. Double nut acts as a lock nut

Larry

[JonJay]

Originally Posted by lr172

That's what I did. Double nut acts as a lock nut

Larry

I have never seen anything documented in the FARS, AC43, hardware manuals, or airframe manuals that state this. Not saying it doesn't make sense, but a "safety" device, devices, or techniques are well covered and this isn't one of them, or at least one that I can find.
If someone can dig up a reference please share.

Certainly not trying to be argumentative, but every time I think there is a logical solution to a perceived problem, there is something that I was not aware of that dashes it on the rocks.

A nut and lock washer has been the standard for eon's in this application for every type of carb, throttle body, injector, etc....
I believe, per Vic's original post, the problem isn't the hardware. It is the hardware not being properly installed and checked.

[az_gila]

Originally Posted by JonJay

....

A nut and lock washer has been the standard for eon's in this application for every type of carb, throttle body, injector, etc....
....

That's what I thought too, but a check of my O-360 (ND and WD) manuals show palnuts called out not lock washers, with the older ND manual calling out a STD-36 rather than the STD-1763 mentioned. The Lycoming superseding parts list says a STD-36 => STD-475.

I guess there are several Lycoming 5/16 palnut versions around.

Update, the Lycoming supersede list has STD-1763 => STD-475, so STD-475 is the current part number for all.

They are also pretty cheap -

http://www.aircraft-specialties.com/...th-sl-std-475/


SECOND UPDATE

My mistake, I didn't look at the STD-475 picture - it's a star washer - so Lycoming seems to have removed the palnuts from their updated use for carb attachment.

My mistake, lock washers are the correct part, but haven't been used for eons...