ezflyr

My Feedback: (32)

Hi all,

The muffler on my OS 91FS recently came loose in flight, and now the internal threads are shot. A replacement muffler is about $60, so I'm going to try a helicoil repair to the damaged threads. Does anyone know the thread size for this muffler?

BTW, this is the 2nd time this has happened to one of my OS 91FS's....... The muffler is made out of really soft aluminum, and the exhaust header is steel, so guess which one wins [:@] ??? If the repair is successful, I might do this to all my OS mufflers.

Thanks,

John

w8ye

My Feedback: (16)

I think they are 11mm X .75mm?

The Heli Coil kit will be expensive

You could put a Magnum 91 muffler on it?

ezflyr

My Feedback: (32)

Hi W8YE,

You are 100% correct. I measured the threads today, and they are indeed 11mm X .75mm. I checked in all the usual tool supply sources, and could only find taps for this thread, but no helicoils ! I could find helicoils for the more common 11mm X 1.5mm thread, but no luck for the finer thread.

No matter, however, because I found an easier, and cheaper, solution! The 'throat' of the muffler is quite long, so I simply turned it down on a lathe until i just got to the 'good' threads that remained. There is still plenty of thread to securely attach the muffler. This time, however, I'm going to give it a good dose of locktite during the re-assembly!

Thanks for your input!

73! (if W8YE is a ham call.....)

John (KA1JMF)

w8ye

My Feedback: (16)

73's, w8ye

rcdude7

My Feedback: (264)

If you are not doing so already, balance your props! and don't use a soft mount, these can cause a muffler to shake loose from your engine.

tande

My Feedback: (48)

You might want to consider "Teflon Plumbers Tape"....For me it works better than "Locktite"...FWIW