I have two YS .91AC engines and they have all shed their mufflers due to vibration. I tied them onto the plane so they just dangled in the breeze. Now the lower cap has fallen off of them. My plan is to have a friend machine new caps. Does some one know the thread size? otherwise I will just tap the sides and hold them in place with set screws.
Also would some one measure the ID of the exhaust Outlet so I will know what size to make mine?
Thanks
Sparky
And if you a have one that you are not using I would buy the one from you to copy/use.

I've HEARD you can mount them to the fuse and soft connect them with a length of silicone tubing (lexhaust deflector type); this removes some of the mass from the engine vibration and completely isolates the muffler from the engine. Good in theory; I haven't tried it yet because I haven't flown my .91 AC in 3 years...

Gary,
While I guess your suggestion might work. the horses are already out of the barn. What I would like is to either buy your muffler from you or could you measure the ID of the exhaust hole for me?
Sparky

Try your post in the YS engine Forum. I'm sure Dave Shadel will answer your question about exhaust ID.