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Securing the Muffler

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Securing the Muffler

Old 04-18-2010, 09:38 AM
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timcat26
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Default Securing the Muffler

Hello all,

I've got a .46 sized Phoenix Extra 300S with a Tower .46 2 stroke installed. The plane runs and flies great...for about 2 flights, after which the muffler vibrates loose no matter what I've done to secure it. The engine is mounted90 degrees to the right. I've got a muffler spacer on it to allow the space to clear the firewall. Standard mounting bolts with lock washers have resulted in the muffler vibrating loose on the bench if run for a few minutes at various RPMs. I've taken the further step of using Red Loctite and letting it set for 24 hours before running the engine. This helps and I can get 2-3 flights in before losing the muffler. I've found that I needto be pretty careful in itghtening the muffler or Iwind up stripping the threadson the muffler.I've hesitated to use JB Weld so far but would be willing to try it if this would finally do the trick. Any other ideas/suggestions? Thanks in advance.
Old 04-18-2010, 09:55 AM
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delman
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Default RE: Securing the Muffler

Try tightening the muffler bolts right after shutting off the engine while hot. Also check the balance of the prop to try to remove the excess viration.
Old 04-18-2010, 10:07 AM
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timcat26
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Default RE: Securing the Muffler


ORIGINAL: delman

Try tightening the muffler bolts right after shutting off the engine while hot. Also check the balance of the prop to try to remove the excess viration.
Thanks for the reply Delman. The engine is not vibrating excessively, I'd put it in the normal range. When tightening the bolts while the engine/muffler manifoldis hot I tend to strip mout the threading in the manifold, without much pressure/torque applied.
Old 04-18-2010, 12:43 PM
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jay2000dakota
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Default RE: Securing the Muffler

I'll bet JB weld will work, As you said it would be a last resort. I used it as thread locker on a pitts muffler to hold a stud in place and I hasnt let go after 2 yrs
Old 04-18-2010, 01:02 PM
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ChuckW
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Default RE: Securing the Muffler

How deep are the threads going into the muffler. If they are easily stripping, maybe the screws aren't long enough. These guys have metric and standard socket head screws in various lengths that work great for muffler mounting: http://www.microfasteners.com/

Are you running gaskets between all the mating surfaces? If so, they may be burning out and allowing everything to loosen up. I prefer to use no gasket.

I've also had good luck with a little high temp RTV on the threads and under the screw head. This provides a little bit of thread locking and resists the heat. Some regular thread lockers will soften at the high muffler temperatures; it says right on the bottle that you need to heat them to remove.

I also re-torque the screws with the engine hot and rarely have a problem.
Old 04-18-2010, 08:36 PM
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LargeScale88
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Default RE: Securing the Muffler

I had the same problem. I just put lock washers on the bolts. Otherwise, I used removable locktite, which worked, didn't like the heat though. So I would go with lock washers. My muffler came loose, i lost pressure for fuel, and that airplane crashed. BECAREFUL with this situation, can save a crash.
good luck!
Old 04-18-2010, 08:40 PM
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jester_s1
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Default RE: Securing the Muffler

If you've already started to damage the threads in the muffler it's never going to stay on. I haven't had one of these before, so I'll ask can you drill the holes all the way through and use a nut on the other side? In order for any fastener to stay on, there has to be some stretch in the bolt. If you can't tighten it down enough to stretch it, then it'll always vibrate loose.
Old 04-18-2010, 09:21 PM
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huck1199
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Default RE: Securing the Muffler

This won't keep the muffler on but you won't lose it. I put a mini zip tie arround the muffler flange and another zip tie through that one and arround the throtle push rod.  This way if the muffler losens it will not drop off.
Old 04-18-2010, 09:25 PM
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Default RE: Securing the Muffler

I agree with Jester's post above.

These are M3x40, with about 20 mm of thread, which should be more than enough for a strong torque assembly.

http://www3.towerhobbies.com/cgi-bin...&I=LXJB22&P=RF

If the aluminum thread is fully damaged, the repair is difficult, but no impossible, if you cannot find a replacement muffler:

Drill and tap a bigger diameter thread, insert a brass bolt, cut it flush, drilll and tap the bolt for M3.

Best luck!

Old 04-19-2010, 08:53 AM
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JohnBuckner
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Default RE: Securing the Muffler

Through drilling is not an option on the Tower muffler. The header extension and its length is a contributing facrtor as well as exactly how it is designed.

As one of the gentlemen already noted if you are using any kind of gasket on the two mating surfaces then you need to loose those, not needed and they definaately can contribute to loosening especially when two separate gasketed surfaces are involved.

John
Old 04-19-2010, 09:26 AM
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timcat26
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Default RE: Securing the Muffler

Thanks for all of the responses. I bought this plane used with a Pitts style huffler already installed. I couldn't get the engine tuned, even with plugging one port of the Pitts, to save my life. I then installed an O.S. .46 muffler I had with an extension so it would clear the firewall.I used bolts with lock washers and Red LocTite in this initial install. This is the one that eventuallygot stripped while tryingto tighten it with the manifold hot. I'm now going to go to a Magnum .46 Muffler with the spacer and new bolts to give it a try again. I'll run it on the bench until hot and then gently tighten it to see if I can get this setup to work.
Old 04-19-2010, 11:00 PM
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jester_s1
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Default RE: Securing the Muffler

Again, if the threads in the muffler are stripped, you'll never get it to stay. The solution posted above is the best, but many setups can just be drilled to the next bigger size and retapped just fine.
Old 04-20-2010, 02:05 AM
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Sandmann_AU
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Default RE: Securing the Muffler

Jester's solution's the right one - replace the damaged thread or you'll never get it tight enough to stay. If you don't feel capable of drilling & tapping brass bolts you can also get helicoils to replace the damaged threads - though you'll till need to drill & tap the original thread to take the helicoils.

I've had a similar problem getting mufflers to stay on small Super Tigre 2 strokes and I've had some success using red RTV silicon as a thread locker. This is designed as an automotive exhaust sealant so it'll handle the heat where locktite won't.
Old 04-20-2010, 10:24 AM
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JRFisher
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Default RE: Securing the Muffler

Another solution would be to JB Weld studs into the muffler and then double nut and lockwasher them against the engine
Old 04-20-2010, 04:54 PM
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Default RE: Securing the Muffler

Try a couple of wraps of teflon pipe thread tape on the bolt threads. Tighten the bolts down as usual, and as mentioned above re- tighten after the engine and muffler are hot. I've found that loctite seems to allow things to vibrate loose and then seems to wear the threads out even faster. The teflon tape seems to work the best for me. Also don't use a gasket.

bhady

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