Advice needed - prop governor locking nuts

[Nev]

I’m after some advice.

Regarding the nuts that hold the prop governor onto the studs, what is the preferred way of securing them ? Should they be drilled and lock wired ? Or use a castellated nut ? Or a self locking nut ? A split washer ?

They same question applies to attaching the fuel servo body to the engine studs. This is something I have discussed with my mentor……but for my own reasons I’d also like to see what others are doing.

The usual places….AC43, Lycoming engine manual etc aren’t shedding the light on it that I’d hoped so I’m guessing that it’s probably something so fundamentally obvious that I’m expected to know it.

Thanks in advance.

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[Chris Werner]

I have a 250 Comanche with an O-540. I believe the carburetor and prop governor both have a flat washer, star washer and plain nut. I'll be at the hangar tomorrow and can verify.

[Nev]

Thanks, appreciate that.

[Chris Werner]

Confirmed, the O-540 in my Comanche has a flat washer, star washer with internal teeth and a nut on the carburetor, propeller governor, magnetos, and exhaust flanges. I also looked in my Lycoming parts manual and found they call out for a flat washer, plain nut and a pal nut. In the last 62 years the star washer method hasn't failed on my airplane.

[Mark Dickens]

The way you have it is the standard. When I installed my prop governor on my RV-8, I went a little farther and installed Nordlock washers, but it wasn't necessary. A MS35333 star locking washer against the usual AN washer is standard

[Nev]

Many thanks Mark.

[alaskabearhawk]

Agreed. The Lycoming parts catalog I have for the IO-540 says plain washer, internal star washer, then the nut.

[Battson]

I can't tell, have you got a star crush washer under there? That's all you need. Of course, torqued to the right value.

[Nev]

Thanks guys, exactly what I was after.

[svyolo]

Is there a "convention" for where to use the star washers? All metal lock nuts?

[noema]

I always found the NASA Fastener Design Manual helpful when faces with design decisions. It's a pretty easy read.

https://ntrs.nasa.gov/citations/19900009424

For star lock washers it says. "[...] Although this washer provides some locking action, it damages the mating surfaces. These scratches can cause crack formation in highly stressed fasteners, in mating parts, or both, as well as increased corrosion susceptibility."

In short, this manual includes many things not immediately obvious while giving solid general advise.

[Bcone1381]

The Lycoming parts manual calls for a plane washer under the star washer like Nev did in post #1. The teeth grip the nut and the plane washer avoiding damage to the mating parts.