Daniel-EL

My Feedback: (9)

My OS FS91 II will not hold it's muffler on in flight. I have three flights on my RV-4 which each time have been cut short due to the muffler shaking off. First it was the muffler-to-engine pipe that unscrewed, so I cinched it up tight using thread locker. Then the muffler body unscrewed, so I cinched it up tight too.....too tight it seems. The thing came off again, this time inspection revealed the threads were stripped out of the silencer body. With a fly-in coming up next Sat., I need a quick fix. I was thinking I could drill a hole through the diameter of the muffler end and connector pipe, then install a 4-40 bolt through the whole thing with a lock nut. Would this jury rig work, at least through next week's fly-in? Is there a better way?

SansHeli

Hi Daniel-EL

I had a very similar thing happen to me on my CAP-232 using the same OS motor - the exhaust/silencer were fine for the first 20 flights but I had to remove them after a minor crash. When I put the plane back together again all I used was high temp silicon gasket sealer again - I believe there is no point using thread locker because of the temps on the exhaust/silencer - the thread locker just melts.

I obviously didn't tighten the lock nut enough on the manifold to head and on the first flight that came loose - no problem because the cowling prevented it from going anywhere. I tightened that up again and in the second flight the silencer came off the end of the manifold - the engine flamed out (no pressure to the tank) and lucky I was close to the strip and got her down OK. The problem is that because of the soft aluminium silencer rattling away on the end of the manifold as it unscrewed, the threads were severely damaged. I managed to saw off the stripped end of the silencer leaving enough undamaged thread to screw it back on the manifold. I screwed it as far on the manifold as I could using all the available thread

I have put another 10 flights on the plane since the last repair and it has been fine (touch wood!!)

I have to admit that I found it really difficult tightening up - you don't want to over tighten and strip anything but at the same time if it is not tight enough the vibration (and don't those motors vibrate!!) will loosen things in a flash!!

I don’t know about the bolt to secure the silencer on the manifold – perhaps someone else has tried that and can comment.

SansHeli

Bax

My Feedback: (11)

Your idea would work, but you'd also be restricting the exhaust flow a bit. Just use a short screw on both sides. Make sure you use a good-quality, high-temperature thread locker, and that the surfaces are clean and oil-free.

When you install a new muffler, make sure you have the locking nut tight and that the muffler is supported. Just having it hang off of the engine isn't really enough support. You'll need to add support to the muffler to help it stay onto the engine.

Daniel-EL

My Feedback: (9)

Thanx, Bax. I have "supported" the exhaust as best I can (using clothes hanger wire wrapped around the exhaust screwed into the firewall) and tightened it on with high temp silicon. Hope this works. Will let you know.