Oil tank studs

[a64pilot]

Does anyone know the size / threads?
Are they 1/4x28 on both ends or maybe 1/4x20 on the end that screws into the case?
I need to order longer because I just don’t see how my exhaust bracket can mount on the factory stud, as is it takes a thin washer to give enough length for the cotter pin.
So I’m thinking as was advised to replace it with a longer stud and use an all metal high temp self locking nut, but would like to know what stud size to order, parts manual seems to indicate only that’s it’s a 1/4” x 1 1/16 length but doesn’t mention thread pitch.

Course pitch is real common on Lycoming’s , but don’t know about TCM.

[6643]

I could be wrong, but I think all those studs that go into the (aluminum) case are coarse thread on the case end. Be careful changing that; you may end up buggering the threads in the case.

[a64pilot]

I was expecting that, assumption being that the case side is 1/4 x 20, that being a common number.
I’d prefer not to have to helicoil the case or worse yet, bust a stud off flush.
But it seems I have little choice, the stock stud is very short, unless the bracket is the thickness of a thin washer, it’s not going to be enough stud to have one thread exposed past the nut.

Then to compound my confusion, there is no real rear stud, but two studs are almost parallel, one slightly more rearward than the other, but it’s not centered.

I assume these studs that have been in place for 77 years can be removed by using two nuts and simply unscrewing it?

Sorry for the stupid questions, but I’ve never seen an exhaust brace installed, my 140 knowledge base is from one C-140

[2066]

Here's the current stud:

IMG_1972.JPG (387.85 KiB) Viewed 2582 times

...and, here's a pic of the bracket. It'll fit to the rearmost stud.

EXHAUST BRACKET RESIZE 3.jpg (46.54 KiB) Viewed 2582 times

Jody wrote: "I assume these studs that have been in place for 77 years can be removed by using two nuts and simply unscrewing it?" Yes, but for the ones that screw into the magnesium accessory case, that is some tough stuff. I've heated (heat gun -- no flame!) before removing studs...and, that may or may not help, but I haven't broken one...so far .
Mac

[6643]

I assume these studs that have been in place for 77 years can be removed by using two nuts and simply unscrewing it?

Pardon my French, but I don't think there's a snowball's chance in hell that will work. A little help and a lot of penetrating oil (Kroil) might make it happen. And, come to think of it, it is in the accy case and if yours is original, it is magnesium.

Sorry for the stupid questions, but I’ve never seen an exhaust brace installed, my 140 knowledge base is from one C-140

I have one, and don't recall if the stud is different or not. I am using self locking, reduced flat nuts.

[8424]

John,

Is this the nut you are using?

Aircraft Spruce: Home / Hardware / Nuts / Hex Nuts /Hex Nut - Low Height

https://www.aircraftspruce.com/catalog/ ... exnuts.php

Spruce says they are 9/64 thick.

Steve A H

[6277]

Those are the nuts that I used to mount the oil tank to my accessory case. I also had one stud that was loose in the accessory case and was leaking oil. There are studs available with the coarse threads oversized to prevent leaks. If I recall, they are color coded to indicate the amount that they were oversized. A dab of gas resistant grease also helps with preventing leaks past the studs.

[6643]

I use MS21042-4.

[a64pilot]

John,

Is this the nut you are using?

Aircraft Spruce: Home / Hardware / Nuts / Hex Nuts /Hex Nut - Low Height

https://www.aircraftspruce.com/catalog/ ... exnuts.php

Spruce says they are 9/64 thick.

Steve A H

Those are not very good nuts.
The MS nuts John uses are I believe the high temp nuts you see holding turbine engine hot sections together, their silver color comes from them actually being silver plated for high heat resistance, they are a strong nut and really not expensive, and are pretty corrosion resistant as well.
This is a pic of them, these are only 10/32 and not 1/4” but otherwise pretty much the same.

BB12CF35-A478-4581-9790-9AD8B8B5F934.jpeg (120.86 KiB) Viewed 2507 times

If I can’t get the stud out by screwing two nuts together I’m not going to remove it. That method gives you plenty of torque to bust a stud, and I’ve seen too many busted magnesium cases in my career. Airplane is 77 yrs old, one assume at some time in its life it had the correct exhaust brace on, so there must be a way
I got the Wag Aero brace in yesterday, the tab measures 62 thou thick, a thick washer is 60 thou, so it ought to work. I have cotter pins in my studs now, some studs required a thin washer 30 thou and some a thick, 60 thou, I assume due to being set at different depths and not different stud lengths?

Everything except the nuts should be here before Christmas, but I believe that the MS nuts will work on existing stud, and the castellated ones that are original may. I’d prefer to stay with the Castellated myself as they are drilled studs

[6643]

MS21042.jpg (16.93 KiB) Viewed 2502 times