Nuts on carbs and fuel servos

[lr172]

Originally Posted by JonJay

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.

Sorry. I didn't mean to imply that it was an aviation standard and that others should use it. I was just throwing out another alternative for others to consider. Clearly, the accepted standard isn't working or being followed as inspectors are seeing this somewhat regularly.

It was my opinion that double nuts would work better than a star washer so I used it. Double nuts as a loosening prevention method goes back over a century, before we had lock washers. I thought I mentioned, but apparently didn't, that their use requires proper technique to be effective so this isn't the fix to the problem out there, which I would agree is an "installation issue."

http://www.boltscience.com/pages/twonuts.htm

[JonJay]

Originally Posted by lr172

Sorry. I didn't mean to imply that it was an aviation standard and that others should use it. I was just throwing out another alternative for others to consider. Clearly, the accepted standard isn't working or being followed as inspectors are seeing this somewhat regularly.

It was my opinion that double nuts would work better than a star washer so I used it. Double nuts as a loosening prevention method goes back over a century, before we had lock washers. I thought I mentioned, but apparently didn't, that their use requires proper technique to be effective so this isn't the fix to the problem out there, which I would agree is an "installation issue."

http://www.boltscience.com/pages/twonuts.htm

Great reference. Thank you.

[jrs14855]

Some certified Pitts models use double nuts on the outboard end of flying wires, Plain nuts are also used as locking devices(jam nuts) on opposite end of flying wires and on various control rod end bearings.
I go back quite a while with both Continental and Lycoming powered aircraft. I have a distinct recollection of pal nuts on Continental but not on Lycoming. The big issue with double nut is whether the stud is long enough to adequately engage the second nut.
Of course none of this is really relevant on EAB, any reasonable locking method is acceptable. For example on the exhaust I use split stainless lock washers with no flat washer.

[8 Builder]

This is very timely. Just yesterday, I called Airflow Performance to see what kind of bolt they prefer a builder to use when attaching my RV-8 snorkel to the throttle body of my FM-150. They didn't use anything that special due to the fact that the FM-150 is tapped for 1/4-20 bolts and the bolt can be torqued to spec without a nut on it. I went one step further and used a drilled-head hex head bolt,
MS20074-04-06. It's a 20 thread per inch "engine" bolt instead of the usual 28 thread per inch found on that size bolt. I was then able to safety wire the bolts.

[jibby212]

I just mounted my carb a few days ago and was not happy with how easily the nuts would come off using the standard star lock washer. I ended up going to Lowes and getting some grade 8 split type lock washers, these give noticeably more resistance when removing and the spring tension remains even after you begin to loosen. If you think there is any negatives from using this type of lock washer, please voice your opinion.

[rocketbob]

I have yet to have anything come loose using split grade 8 washers with a thin backing washer. I buy them by the pound at Tractor Supply. Wouldn't hurt to throw blue loctite on and maybe even a palnut.

[fixnflyguy]

It has been in earlier forums, and at least several RV's I know of, including mine, have had the carburetor attach nuts back off (even with lock washers) due to the engine torque and a very tight FAB snorkel set-up. If your installation is "new", make sure your flex joint at the cowl inlet is not too tight. The engine torque will turn the snorkel assembly into a breaker bar and loosen the carb nuts, resulting in leaning and backfire/idle problems initially, worse if left unchecked. I routinely reach in the inlet and look for play in the FAB. I also ran some safety wire around my carb studs to prevent the nuts from fully backing off in the event they loosen. The carb bowl screws/nuts are equally as vulnerable, even with the bent tab safety's.

[snopercod]

Has anybody tried using Nord-Lock washers in this application?

[OZCleco]

Unless I'm missing something the current Lyc parts catalogue from their website lists a plain washer (STD-35), plain nut (STD-1410) and palnut locknut (STD-1763) for the O-320 B & D.

Our engine had the lock-washer and plain nut configuration which seems to be what all new Lyc's leave the factory with. Do you reckon I could find a reference for that?

Installed a new carb on our O-320 with new lock washers and the original single plain nuts and never felt comfortable. Way too much rattling going on there to suit my liking.

Swapped out the plain nuts for AN363's and immediately felt a sense of ease.

Also, where does it say you can't reuse all metal self locking nuts? I presume the prevailing torques mentioned in AC 43.13.1B, Section 4, Para 7-64, Sub Para F and Table 7-2 relate to all styles of self-locking nuts?

If not, what would the argument be for reusing anchor nuts?

[9GT]

Originally Posted by snopercod

Has anybody tried using Nord-Lock washers in this application?

There is a good comparison and testing video using various methods of nut locking. The Nord-Lock washer is pretty impressive.
https://www.youtube.com/watch?v=IKwWu2w1gGk