090 starter cup nut won't stay tight

[Nothinghead]

Howdy! I have two 090's I picked up. The one runs but in chasing down air leaks, I suddenly can't get the nUT that holds the starter cup to stay on. I can snug it down as tight as a 12" ratchet will let me with string in the cylinder as a stop, and it still comes loose when the engine fires up.

I've put the washer on both ways. I see this one is kinda cupped. Maybe I need a new washer and nut? Locktite?

Thanks for the help. Here's a picture of them when I brought them home.

 

[homemade]

Picture doesn’t show.

I looked at the ipl and it only showed a standard washer. Blue loctite won’t hurt anything. If your putting full torque of a 12in ratchet, you probably stretched the threads of the nut. The crank being harder probably is ok. Try a new nut and loctite.

 

[Nothinghead]

Easy enough. I should get a torque wrench.