I'm afraid I just made a huge mistake. I was adjusting my clutch screw on the crankcase and when I tightened the retaining nut I stripped the housing! (not the screw) Is there anything I can do besides replace the entire crankcase? I was almost done with my 2 year restoration project and was going to crank the motor for the first time next week :( Would a helicoil be a possibility?

Maybe a Time-Sert would fix it easier than helicoil.

Well after playing with it for awhile, I found that there are still about 3 good threads left. I was able to get it adjusted. Hopefully it is enough to hold. If not, I ordered a M12 helicoil kit.

Good thing about that system is there's no great pressure on it as only lifts or lowers the arm to bring closer to the pushrod. I'm guessing a bit but if the fixing option was a dismantle i think i'd lift the arm until it strikes the rod. Measure the gap under the arm. Then unhook & swing back to lift out. Then stack washers equal to predetermined gap under the arm--to hold it up there. Then replace the arm & hook cable up. Umm--that'll work, i think. Then bung the unused hole.

Hi Renegade578. I'm not conviced a helicoil would work in this particular application.  Behind the crankcase thread that is damaged is a void that receives the clutch actuator arm. As it is a void there is nothing to stop a helicoil from simply continuing to wind inwards as you thread in your clutch adjuster spigot. The beauty of a time-sert is that it has a shoulder to stop it winding in too far. If the time-sert insert proves to be too long you can simply cut some threads off the non shouldered end. 
Ensuring swarf is contained and fully removed when drilling and tapping the new oversize thread in the crankcase could be your biggest challenge.  Mind you don't let that put you off what sounds like an interesting challenge to overcome. Good luck with it all, Andy

I didn’t realize you could cut the time serts if they were too long. I guess that is probably the best option. I wonder if a helicoil would work if I don’t drill all the way through. That would keep it from going too far in and the tail on the adjustment screw might be long enough to make up the gap. Let’s just hope that the 3 threads left hold….

I personally would use a time-sert and not take a chance you have spent a lot of time and effort on your bike so fix it to last another 50 years 

Locknut won't need to be much more than finger tight so might get lucky. The unused thread may not be locatable but hope it is, or has never been turned as far in as it should or can be which might save your day. With cable unhooked you can go up down up down with the arm untill it's bottomed out in the pin guiding slot in the arm, then back it out half a turn or just enough to get the arm about right angle. Then you're using as much thread as possible--i think.!!

If you have enough threads left to engage the eccentric screw and adjust the clutch, I'd just be gentle on the locknut and leave well enough alone. 

Hopefully you'll be fine. 

The cheapest M12 time sert kit I can find is $125. Is there a place that loans out time sert kits?