Bill, you're a smart man!

Yamaha manuals and specs do have errors so I checked a 1978 GT80 Service Manual.   Note that going all the way back to the 1964 YJ2, the early 1970's JT's, and the 1973 to 80's GT80 all use the same stud.  

1978 GT80 manual says torque is 7 ft-lb.




 

Thanks for your effort to verify our concern. I learn as I go and this forum has been an unbelievable source of knowledge.

Thanks everyone! You've all shared a lot of good info here. I'll keep you posted with progress or questions.
ZT

I have bought a stud removal tool . It was like a deep socket with three rollers inside .
They were sized to match the stud being removed , 6mm in this case .
Once on a power bar , removal was easy . You look to have enough of the stud proud of the case ,
so you should be able to get some purchase on the stud .

Thanks for your reply Swoop!

"I have bought a stud removal tool . It was like a deep socket with three rollers inside .
They were sized to match the stud being removed , 6mm in this case .
Once on a power bar , removal was easy . You look to have enough of the stud proud of the case ,
so you should be able to get some purchase on the stud."

Ironic that you should mention this. I had never seen or heard of these "no-drill" extractors and I had high hopes when a mechanic friend suggested I try his set before resorting to welding anything. His set had no rollers but rather six spiral flutes to bite into the broken stud.



Unfortunately, the smallest extractor (6mm) was too large and spun freely on the reduced diameter threaded portion of the protruding stud; which measured only 5.52mm.

So I'm on to doing a bit of welding practice today before trying to secure a nut or plate onto the broken stud. I'm planning on trying the de-plated nut first... Thanks @MarkT, the muriatic acid worked great!



If the weld fails and the nut spins, I think it will do less damage to the stud and I will still be able to try the beveled hole plate I've fabricated.



I hope to post on my progress later this afternoon or evening.
I do appreciate all of your help and suggestions!
ZT

I'm pleased to report the broken stud has been removed without any damage to the case mating surface.

The welded nut worked great and a 10mm socket on a short handled ratchet turned the remains of the stud out easily.

Any tips on installing a new stud are appreciated. I couldn't find anything in the GT1/GTMX service manual I have.

Do you just run the stud in with two nuts on the top threads until the stud bottoms out?

Do you ever use any thread-locker or "stud locker" on the bottom threads?

I tend to be cautious and often overthink what I'm doing, so I really appreciate your collective feedback and suggestions. Thanks again to all, who helped me get this done!

That’s a good question and I look forward to the responses. I have currently used blue loctite on mine and threaded them into the cases until they bottomed out. I simply snugged them up using the head nuts which I threaded fully down onto the opposing end of the stud. I can still undo my method since I am still waiting for all my new parts to arrive…..

Congratulations!!!!

The way Schu described is perfect.  
Only caution is be careful how much liquid loctite gets in the blind hole, especially if threads are tight. Hydraulic pressure will actually crack the case when the stud is threaded in if enough liquid gets into the bottom of the hole and can't escape.  Don't ask me how I know.

Also, "snug" is just fine.  I'd thread it in to the same height as the other studs even if it's not bottomed out yet.  It does not need to be tight.  BUT, if it gets tight, stop.   

Thanks again Gents!