I can't keep a Bisson/pitts muffler on a YS-110. The nut that holds the adaptor to the engine exhaust port keeps comming loose, red loctite isn't enough, any ideas on what works.

Try teflon thread tape - it works well on my problem Saitos. - just make sure that you place it neatly so as not to get any inside the engine.

Red loctite is designed for much smaller fasteners ,like rifle scope screws. I use the blue loctite on my St and it works fine. Makes sure to clean the threads before appling.

G'day Mate,
Vibration is the major problem, in keeping mufflers from coming loose, balance props, blades & hubs, & spinners.
In the case of the YS, a small out of balance in the hub, blades or spinner, will cause huge vibration, because of the large diameter prop.

Add a 2nd nut.

You could always safety-wire it