da Rock

Best technique for model mufflers........

what GrayBeard said.

Tighten the bolts right after running while the bolt is hottest. It's longest then. The muffler will have cooled more then and will be shorter than at operating temps.

It's worked for me for 50+ years. I think for GrayBeard probably 80+

MTK

The simplest for me has been Permatex Ultra Copper high temp gas resistant silicone sealant. I haven't lost any bolts since going to this stuff 3 years ago and will use it until something better comes along. Easy removal too

dasintex

My Feedback: (10)

Appreciate all the input, I think this is what I will do, Use Anti Sieze Compound, Run Engine, Retighten Bolts and Secure with Lock Wire; may be over kill, but this will be on a Cowled Engined Plane and I don't want to have to take the Cowl Off to fix a loose Muffler after a couple of flights; the other area I am considering since this a 'Wrap Around Pitts Muffler', is to use a 'Support Strap', I have read that Cracks can develop on this style of Exhaust from Vibration, my plan was to use a 1/2 to 3/4 inch wide Aluminum Strap with one end Secured/Screwed to the Muffler End Plate/Disc and the other end mounted underneath the Engine Mounting/Standoff Bolt; seems to me that the Muffler has to move with the engine, so I wouldn't think Mounting the Strap to the firewall would be as good as mounting it to the engine.

Again any feedback is appreciated.

jester_s1

I'll toss this out there too: mufflers going loose may not always be a case of the bolts vibrating loose. If the bolts weren't torqued right to begin with, loctite or anything else isn't going to help. Bolts have a certain amount of stretch built into them. You can feel it as you tighten. As you turn the bolt, you feel the initial snug, then you are able to keep turning for a while until a point when it gets a lot harder to turn. The initial snug is when the stretching starts, and the second big increase in torque is when it reaches its limit. If you keep going you'll permanently stretch it and then a turn or two later you'll break the head off of the bolt. If you overtighten the bolt and go all the way to that upper limit, you may get that permanent stretch in the first couple of hot engine runs as the aluminum expands. That will give you a loose bolt fairly soon even though the head hasn't turned the tiniest little bit. It's better tighten the bolts just past the snug point so that you have some stretch left to expand into. A new bolt will permanently stretch a little after being installed regardless of what you do, which explains the need to re-torque them after a couple of engine runs. Once that's happened though, the friction on the head and threads is pretty strong, so it shouldn't take much to hold it in place.

ovationdave

My Feedback: (16)

There is also an option of using a lock plate. I cut a strip of sheet steel and drilled two holes in it (same with as the mouting holes on the muffler), sandwich the plate between the bolt heads and the muffler when you tighten it up, then bend the steel sheet up so it locks across one or more of the flats on each of the bolts. This has worked well for me with my G-38 when I had re-occuring muffler issues.

(Obviously though, this doesn't work if you have recessed holes in the muffler and using Socket-Head Cap screws, my Bennit Built muffler was flush on the outside)

~Dave

unclecrash

A friend and I use permatex copperplus or the stuff above. Use it just like the directions say. Use it on the bolts and with no gasket on the exhaust

joebob

My Feedback: (14)

+1000

Started using this on my DLE55 when I couldn't keep the bolts tight. I was having to snug them down after every flight. Started using this stuff and have not had one come loose since. It also makes a great gasket between the muffler and engine. Throw the paper one away and spread a thin even coat of Ultra Copper on the flange, dab some on the bolts, and tighten it down.

airraptor

My Feedback: (66)

Just tighten the bolts when the engine is hot and never have to worry again. i have been doing this for a awhile and no more loose mufflers.

PHall

+1

Tony Iannucelli

My Feedback: (193)

Tighten hot bolts, use Permatex high temp gasket maker, both work great. I don't fly a lot of YS, but those mufflers should be wired on.