ceecrb1

Ok, today I had something unexpected happen...

mid flight my exhaust fell off!!

It landed perfectly with its screws still "in place" (ie loose inside the holes of the exhaust).

It looks like they had just completely rattled loose.


Now I am PRETTY sure I fixed them with a decent "glob" of loctite/ screwfixer but that was over 6 or 8 months ago, and I used a silicon gasket rather than the paper one...


Is loctite a bad choice for engines due to the heat?

Whats a tried and tested way of getting them tightened "forever".

aussiesteve

The method I use (as suggested by others with a lot of experience) is this"

Clean threads are important
FLat flange faces are important - use a file to achieve this, especially on the muffler flange.
No exhaust gasket
High temp silicone on the flange faces (but only a light smear). I use Permatex Ultracopper but the Loctite one works well too.
High strength Loctite (Red) on the bolt threads.



A light smear of silicone on each face, let it "tack off".
Apply a couple of drops of red loctite to the bolt threads and tighten up the bolts.

I have never had an exhaust work loose when I have done this.

Oh - of course if the exhaust doesn't have solid tubes or other support to take the compression from the botls and tranfer it to the flanges, nothing will solve the issue.

daveopam

My Feedback: (9)

One other thing. After you have done the above. Start and warm up the engine. Then retighten.

david

All Day Dan

My Feedback: (5)

Use inside star washers, no gasket and no Loctite. Check for tightness after each days flying. Dan

MTK

We have had a similar problem on new small gas engines before GHoffman suggested Nordlock washers under the bolt heads. If you followed the approach AussieSteve suggested with the UltraCopper hi heat silicone gasket material and also used Nordlock washers with the bolts, you will have a very secure muffler or header.

Get Nordlocks from McMaster Carr

captinjohn

Both internal threads and external threads need to be absolutly clean. You can use carb cleaner and blow dry a couple of times with compressed air. Use new bolts if they look worn from viabration while loose. Capt,n

ceecrb1

The check after EVERY day of flying just isnt an option when its inside a cowel.

But thanks to all who replied... will take this new knowledge and use it as best I can!

yeah the silicon I used is some high temp silicon for gaskets... I had done as described.. just a thin "film" to find and block any tiny holes... rather than create a thick silicon gasket.

All Day Dan

My Feedback: (5)

Use socket head screws and drill some holes in the cowl to give you access to the screws with an allyn wrench screw driver. Dan.

spaceworm

Run a safety wire from the muffler to a secure part of the engine. If it loosens the wire will keep it from getting lost. This just happened today at our field. The plane landed with the muffler hanging, but still with the plane instead of out in the corn.

Tired Old Man

My Feedback: (1)

Used to use that method. Got expensive ($100,000.00+/plane) with mufflers falling off and passing into and through the prop on an aft mounted engine. Went to the Ultracopper/Locktite method about 3,500 engines back and haven't lost a muffler since. Do what works for you though....

For those that do use Locktite or other thread componds, once it's tight, leave it alone unless you want to start all over and replace it. It does not reseal after breaking bond.

STUKA BARRY

I use red (looks more orange than red) RTV #106 high temp on both flanges with the paper gasket in the middle. Tighten the bolts per spec and let the RTV dry for 8hrs. minimum before starting. You will have no loose bolts and no exhaust leak. I've been using this method since 1986 and never have a muffler problem. You can also run a small bead from the muffler over the head of the bolts, if for whatever reason they come loose, you will know if the bead is broken. In the aviation industry, we call this torque striping.

Lnewqban

There is where your problem is.

I completely agree with Post #2 above.

Supporting the muffler with a flexible anchor from somewhere in the fuse, liberates those poor bolts from a lot of stress from vibration and muffler weight.

zacharyR

My Feedback: (5)

I know on 3W the deal is you dont use anythign specil . just start the motor get up to runing temp . the soon as you shut it off tighten those bolts and thats it

but thats just a idea try torqueing the bolts tight witht he motor warm from just being ran in the pits . along with your other methoeds

Tired Old Man

My Feedback: (1)

After a few thousand 3w engines I can assure you that Ultracopper and red Locktite is a very good idea. Jeeze, all the amatuer experts and their manuals....

The suggestion to use a support strap is also one people should pay attention to. Bolts get leveraged by moment arms.

aussiesteve

ceerb1 -I make this post because I am aware you are reasonably new to gassers. - Pay attention to the person I have quoted here - his advice on muffler mounting is absolutley accurate and I can vouch for that as it is he who originally pointed me in the right direction to stop mufflers coming loose.

He has also been very much a mentor to countless numbers of us in the selection and use of good gas engines and good gas engine practices for our hobby. I personally consider him to be one of about 4 to 6 people whom I truly look toward for honest advice.

iflyg450

The best way to keeps the screws in place is find ones that have a hole drilled through the head. Then safety wire the bolts together, this methode has been used is aviation for ever. Do a youtube search for aircraft safety wire or lock wire installation. When done correctly the wire will pull the bolts together in a tightening direction. The wire used is stainless steel and come in a few Dia. Something in the .020 range should work. You might be able to find the wire a motorcycle or any kind of race shop. Or just swing by your local airport and ask an A&P tech for some trust me he won't mind the stuff comes in huge rolls. If that doesn't work give me you address and I'll send you some. Oh it also works great on engine mount bolts.

RCFlyerDan

My Feedback: (54)

I use Green High Temp Lock Tite, and lock washers.

spaceworm

Do you have a source for SAE and metric thread socket head screws with the cross drilled head for the safety wire? Thanks

Kostas1

Guys,

what can be done with my muffler ? Can i use some white tefflon ?

Saito FA-80 - aftermarket muffler


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GreatPlanes Cherokee 40 ARF /w Saito FA-80 !!!

[youtube]http://www.youtube.com/watch?v=jOrKvF4xNqE[/youtube]

Tired Old Man

My Feedback: (1)

Ahhh yes, the dreaded Saito muffler condition. Teflon will not save the day since it's intended use is as a lubricant to prevent thread galling with an unintended byproduct of becoming a sealant.

Pre-drilled screws and bolts for use with safety wire can be found, and this should not come as a surprise, at McMaster Carr. Aircraft Spruce and Specialty is another location, along with MSC Direct. Not all sizes and pitches are available but there are many more than you might anticipate. I've even found cross drilled 4-40 stuff there. The previous call to use .020 wire was good advice. .020 stainless wire can be kind of scarce but Chief's Aircraft sells a 1 pound roll for about $10.00.

Safety wire by itself will not save the day if used incorrectly. It must be installed in a manner where movement of the screw after installation causes the opposing screw to make the wire become tighter. So the wrap around a scrww has to oppose the loosening rotation of each screw. If you are a person that used muffler gaskets you can still lose a muffler with wired screws. Once the gasket blows out, and it will, the muffler will bang against the cylinder until that movement finally pulls the screws through the threads. Been there, done that, and why I tell people not to use muffler gaskets. It's also why I tell people to use a muffler support strap, especially on wrap around mufflers.

spaceworm

Monel safety wire is also available at marine supply stores and is used to safety wire turnbuckles and clevis screws.



Sincerely, Richard.

iflyg450

If you have socket head screws you can drill a hole thru the head. If you don't feel like doing that hit the yellow pages for a fastner supply shop such as fastenal or even grainger. You might also try microfasteners.com. The lock wire works best thread lock will work but what happens when you want to remove the muffler?? You don't need a pair of safety wire pliers it can be done by hand. If you have any questions stop by your local aircraft mx shop the mechs will be more than happy to help.

Lnewqban

Completely agree.

Kostas,

Your muffler is too heavy and far from the seal; hence, forces of flight and ground handling put a lot of stress and torque on that seal and locking mechanism.
Remember that bolts and nuts work only on the principle of friction force apposing "unbolting" forces and torques.

There is only so much friction that these bolts and nuts can develop (for which bolting torque values are specified).
However, the intensity and frequency of the "unbolting" forces can grow very high with unsupported layouts.
Once a bolt rotates a tiny bit, the friction force on the threads decreases greatly.

Another method used in industry to prevent bolts and nuts loosening up due to vibration is deformable washers.
Those are made of steel sheet metal and anchored to a fixed point.

Kostas1

Guys,

i don't understand what you are saying.....i apologise, but my english is not so good.

Do you have a diagram or picture ;

Tired Old Man

My Feedback: (1)

From the beginning, just about all of the 4 stroke glow mufflers have been a problem. Because of their length and angle away from the engine it's difficult to provide a useful support.

Safety wire is pretty much over the top, though. There really is no need for it if you do most everything else right. Clean threads, Locktite, Ultracopper, eliminate any fiber gaskets, and use a support strap. Without the support strap and using a fiber gasket, safety wire only keeps both screws together when the muffler pulls off the engine. This I KNOW to be true.