Hi all,
I am looking for some methods/options for fixing a stripped engine case hole... . I fixed the clutch slipping issue on my CTC-1. I was almost done re-installing the cover,...the bottom-center bolt started to not get tight anymore..I got that sick feeling and my worse fears came true. I had trouble sleeping last night..It doesn't leak..yet.. but I just hate having a bad fastener in a critical area..ARRG. At least the clutch works better now..Runs awesome with new springs..
Any thoughts or past experience others have had with similar issues I would love to hear about them.
I uses a new gasket, clean mounting area, Yamaha bond #5.
Thanks in advance..

Not for the purist, but could you tap a new 7mm (M7) thread into the hole? If yes, might also have to ream out the crankcase hole a smidge as well.

Edit.

Maybe a 0.25 inch screw would fit in nice and snug?

Thanks. I was thinking about a standard vs metric also. I replaced the cover bolts with what looks like hardened steel hex bolts. They are very heavy duty and need to be careful when tightening them. Good thought, thanks.

This is why I don't torque my side cover bolts, and only use a standard allen wrench. I also just used grease on the gasket, which worked out well because I had to remove the cover several times after I rebuilt the clutch. It weeps oil very slightly, but I can live with that. I hope the 1'4" bolt works for you!

Helicoil, or better yet a time sert insert.

If it’s not leaking oil, then leave it alone.
Sometimes’ you can run a tap through the threads and install a slightly longer M6 bolt.

Blue Lock-Tite or Black RTV might help for a while.

I have seen some pretty tight outside case bolts and removed many unharmed. Those threads do not strip that easily. It would be nice to know that you have at least a 1/4” - 3/8” of threads sticking out past the outside case.

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I would use a Timesert next time you remove the cover
www.timesert.com

Considering you'd rather not touch the case seeing as its good now, i'd fix it properly next time, but for now i'd pull the screw straight out which will bring the damaged alloy out on the screw--in a perfect world-- then measure how much hole is left past the screw length then go find a longer screw. Could even get a longer than necessary screw with thread all the way then cut the head off & somehow screw it fully to the end of the hole just to be sure ya using all the thread left. Then put a nut on it. Or if the length is cut right just put a nice looking dome nut on.
Sorry long story about a simple operation. Just things i do in desperation.

A time sert I don’t think would work because the end would stick out to far or be real close to not letting it seal completely I just looked at a spare CT1c case I have don’t get me wrong I use time sert MarkT has recommended I think is a loctite thread repair kit maybe he will chime in 

I agree with ASCO, remove the bolt screw and use a very small drill bit by hand to get the smegma out of the bottom of the hole. Spray with brake clean and compressed air. Then measure the depth with a paperclip or the drill bit and see if you can use a longer bolt  screw. Bolt Depot sells 6mm in many lengths but shipping sucks for a one off. Better to get a running list of bolts screws to change to make it more cost effective. Good luck