Case thru stud broken

[JPerkins]

Found this today while working on the plane. Little unnerving at first as there was evidence of the engine running with the nut rattling around against the baffle.
Anyone have any ideas what could have caused it? Looks like a clean break.
Haven't chatted with my IA yet. Hoping I don't have to split the case. Got some ideas on getting the old one out, but worried of the possibility of the crank bearing spinning without the clamping force of that stud.
It's lycoming part #75154

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[Steve Pierce]

I have seen this before. Only thing we could attribute it to was lack of torque. If you can get it out without splitting the case I would retorque everything and not turn the prop.

[dgapilot]

Low cycle fatigue. You can see some beaching marks. Most likely low torque or over torque. I would suspect if you split the case you will have some pretty good fretting on the mating surfaces.


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[efrench]

DANG! Sorry to hear about this. I am about to reassemble my engine, but not before sending the thru bolts out for NDT!

[rocket]

Jason,
I have seen a handful of these and always attributed it to miss torquing. Three of them the other studs were under torqued and I am assuming the tightest of them took all the load and failed. One of these had a fancy paint job and was the paint was under the nuts rather then being masked off as required.


Had a wrench been on these nuts recently?


Best to check them all.


If you wanted to be extra cautious get a spring scale and find a place about midway down your prop and make a reference pull that is repeatable. Then retorque in 5 ft lb increments wheel checking the rotational drag of the crank. I always did this building up VW engines in another life. What you are trying to determine is how much wear has happened wile things were loose. As fresh as your stud break looks I am guessing it hadn't been broken long and shouldn't be an issue. You will want to keep an eye on your oil temp during the first flight after getting her all back together as well as inspecting your screen/filter after an hour and say five hours or so.


I have never seen a thru stud fail on the lycoming but a couple on the 520 conti. loose a stud on the 985 and required to change both adjacent studs, loose more then two and required to change all of them. Fun times!


Steve, ever change the thru stud on a small lyc?


Rocket

[Gilbert Pierce]

I know someone who used RTV on his O-320 cylinder bases at rebuild. A whole bunch of them broke.

[JPerkins]

The cylinder base nuts have never been touched since I owned it.
Thanks for all the insight everyone. Rocket I'm going to use your technique when I install the new stud, which I might have a line on a good used one locally.

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[JPerkins]

UPDATE. Stud part number is actually 69377. The one I listed previously is for the newer model wide deck O-320-A2B.

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[Steve Pierce]

Steve, ever change the thru stud on a small lyc?

Helped on two, one was a free floating thru stud and the other was screwed into the opposite case half.

[Steve Pierce]

I know someone who used RTV on his O-320 cylinder bases at rebuild. A whole bunch of them broke.

Our favorite person.