Warbird Information Exchange

Well, on a British aircraft, probably oak.

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James K

"Switch on the underwater landing lights"
Emilio Largo, Thunderball.

www.VintageAeroWriter.com

IIRC they are a brass alloy. I believe some early Merlins also used a similar alloy on the bottom end. I don't remember if it was on rods or main caps though. Can anybody set me straight? They didn't hold up well so a steel alloy was used.
Rich

They do seem to have a yellow-ish tinge from the pictures.
However, I find it hard to believe that brass or or even bronze could be torqued up to 115 lb/ft without stripping the threads.

OTOH, a metallurgist I'm not.

I believe they are a bronze or brass. Definitely not magnetic.

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The more I learn about aircraft, the more I realize I still have to learn.

Talked with Sparrow today- they are a bronze alloy.
I haven't seen a nut strip, only crack as shown.
I have seen the studs pull out of the case that these nuts screw onto. When that happens you are screwed.
Rich

They may be bronze as a safety issue. If someone accidentaly overtorques a steel nut you could most definitely pull a stud. But a bronze may be designed to strip the thread at some percentage of overtorque to keep from pulling a stud.

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"You cannot invade the mainland United States. There would be a rifle behind each blade of grass..."
Admiral Isoruku Yamamoto

AMS 4631 Bronze.

Rick's got it figured out. The nut is the weak link, as it's a whole lot easier to replace it than repair the crankcase. The bronze also has less friction on the surrounding steel parts so it torques smoother.

Chris,

You might look into what commonly causes them to break. They are talking to you!

Our 25 hour "run the rack" engine inspections are now mostly to re-torque the heads and check the nuts for cracks after installing the Merlin Fingers.

Torque on head nuts on Packard cases is 100Ft Lbs for center 10 and 90 ft lbs for ends as per book. We have always torqued them to 100 straight across, Thorn had us do it that way for years and have just continued on, have not noticed any adverse effects by doing so after 20 years. 600/700 series crankcase head nut toque is 115 ft lbs straight through. I would tend to think that a steel head nut would gall up in the steel saddle, In using strong backs for bank build up, that is what tends to happen. Head nuts tend to crack once in ahwile, just probably cause they're 60 years old. However, if the same engine has a tendency to crack the same nut or nuts continuously, as Glenn says "It's talking to ya." If ya pull and bank stud from the case--just pull the bank and heli-coil it!!

Sparrow

Those nuts were the first two we've found. everything else looked great. We'll monitor it closely though

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The more I learn about aircraft, the more I realize I still have to learn.

Funny stuff.
FAA approval etc. Personally I don't see what drives it all. And I make airplane parts as my daily job. So is this a US built merlin? So now lets look at some Allison nuts.