Not sure if due to vibration or due to overtightening the screws, but now I can fully tighten only single motor mounting screw which results in not being able to keep motor in position with proper belt tension. The motor is sk3 6374.
What are my options? Open up the motor and put the nut inside to properly tighten it?
Tap the hole to the next size up thread.
NOOOOO!! There will be metal shavings in the motor if you do that, I suggest just getting a new motor but I have seen someone put nuts inside
Exactly what @SORRENTINO said. They’re probably M4, get an M5 tap and tap it up to an M5, then buy M5 screws… and don’t tighten them so much next time! lol
Take the bell off the motor. There are plenty of creative ways to block the shavings when you tap the new threads. Getting a new motor because you stripped out you threads is not the correct answer yet lol
You can put a small hose on to a vacuum cleaner and suck out any swarf that might be in the motor. If you wanted to do it right, take the can off of the motor and clean any swarf/filings/shavings/bits of metal away that way…
Well, you just have to take off the rotor can first
I had the same problem and i just increased the m4 to m5 screws. The shaving is aluminum so a simple vacuum should be able to remove all shavings.
You already have metal shavings in your motor if you have stripped screws/threads, no biggie. Stick a nice chunky magnet on bit if you have one,itll grab a lot. This is the perfect opportunity to take it apart and clean it out 
Hi,
I know this is an old thread (no pun intended), but for future reference, this is a useful article that explains how to remove a stripped screw https://www.accu.co.uk/en/p/121-how-to-remove-a-stripped-screw
It will need to be cleaned once you have taken it apart.
Zara