Nuts on carbs and fuel servos

[vic syracuse]

While doing a prebuy on Friday on an RV-8 I noticed a nut missing from the aft fuel servo mounting stud. This is not the first one of these I have discovered missing on an airplane. I know standard practice has been to use a nut, a lock washer, and washer, but for many years now I have been using AN363 all metal stop nuts with a washer in these locations and I have never seen one come loose. You might consider it on your airplane.





Vic

[RV6_flyer]

There was an RV-6A that had engine stop running a number of years back just short of KEMT airport. There were no injuries but the airplane was totaled.

The FI servo was loose.

[az_gila]

Would some blue Loctite be applicable here?

[vic syracuse]

Originally Posted by az_gila

Would some blue Loctite be applicable here?

Sure, that could be a solution, too.

Vic

[boom3]

Mine are installed "standard practice" but I've always kind of wondered about them and check them regularly. Nothing loose so far...

If you have a flat washer, a lock washer, and a nut aren't you essentially just locking the nut to the flat washer? I'm guessing this is why you brought it up. I wonder why this method is "standard practice" here.

[SuperDave]

Originally Posted by boom3

Mine are installed "standard practice" but I've always kind of wondered about them and check them regularly. Nothing loose so far...

If you have a flat washer, a lock washer, and a nut aren't you essentially just locking the nut to the flat washer? I'm guessing this is why you brought it up. I wonder why this method is "standard practice" here.

I've always thought the same thing about the lockwasher on a flat washer...didn't make any sense. Also, it seemed silly that the airbox is safetied to the carb or servo but the carb or servo is not safetied to the engine. Always seemed bassackwards if anything.

[longline]

act as springs, so to speak. That is why we throw away the internally toothed lock washers after one use. There is not enough "spring" left in them to allow the plain nut to maintain torque if they are used again.
I agree with Vic that a metal self locking nut is probably better practice. I will admit to being concerned that a really tight self locker will unscrew the stud when you take it off... but that is why blue locktite was invented for the studs.

[vic syracuse]

I know, we've always heard that the lock nuts will pull the stud out, but I've never seen that happen yet (I know I haven't seen everything yet) and I decided a long time ago that the stud could be taken out of the nut in a vise if the stud came out and then reinserted back into the engine. Haven't had to do that yet.

You are absolutely correct on the internal tooth lock washers. Always throw them out when you remove them and use a new one.

Vic

[moosepileit]

Stud length seems perfect for double nuts.

[rvbuilder2002]

Though I have never found any loose if they have been torqued properly with new new lock washers at installation, piggybacking with a Palnut (google it) is another option for safetying critical course thread nuts.