muffler problems
 

hey guys,
so have the da 50... bison Pitts muffler. every time i fly the muffler comes loose. i use blue loctight and use locking washers. any ideas to keep the muffler on there solid? i was thinking about using the red loctight.... idk any ideas??

RE: muffler problems
 

Most of the time when quality mufflers come loose, it is the result of vibration, the use of a gasket or engine overheating. Is your DA solidly mounted? If it is soft mounted it can shake the muffler loose in one run. Are you using a gasket? If so, get rid of it and just make sure the mating surfaces on the muffler and the cylinder are clean and flat. Just use a light smear of Permatex UltraCopper sealer on one of the surfaces. You don't need much ... if you can see it on the surface, you have enough. Attach the muffler using clean bolts (no lock washers) into clean holes using a bit of red or green LocTite. Green will take more heat than red but red will hold just fine unless the engine is overheated. Don't retighten after running or you will just break the LocTite bond loose. Now if you overheat the engine, the muffler will expand more than the bolts and they will loosen. Good luck!

RE: muffler problems
 

I drill my muffler bolts and safety wire them. Its easier to get them back off if you need to.

RE: muffler problems
 

Most of th time? What else?

RE: muffler problems
 

The other time is when the surfaces are warped and allow tthe muffler to shake loose.

Check that the mating surfaces are flat.
Apply a thin smear of High Temp silicone to one side.
Get a little on the bolt threads too.
Use good socket head screws grade 8 and if you can find them grade 8 "Flat" washers. (Take apart old weed eaters to get screws and washers you will never find in a store)

RE: muffler problems
 

And never use locking washers on aluminum. They will expand into the aluminum because the aluminum is too soft. Locking washers will fail in any exhaust manifold to engine head application.

RE: muffler problems
 

Sometimes the bolts don't engage enough threads in the cylinder. Also, I often use a bottoming tap in the threads in the cylinder so that I have good threads to the bottom of the hole then use longer bolts to engage as many threads as possible. I have seen cases where bolts as supplied were tightened into tapered threads in the cylinder giving the feeling of the bolts being tight when there were not. Check for good thread engagement without the bolts bottoming out in the cylinder threads.

I guess I've been lucky .... never had a muffler come loose but I've sure seen others that did. The reason was usually quite visible upon inspection.

RE: muffler problems
 

I use a much modified Bisson muffler on a Sachs-Dolmar 4.2 cu-in engine. I had a lot of trouble with the screws backing out no matter what type of Loctite I used. These photos show the way that I fixed the problem. I do use Permatex Ultra Copper between the muffler and the engine. No more problems with this setup.

RE: muffler problems
 

Now those are some serious bolts!

RE: muffler problems
 

yep, big bird i moded my muffler just like yours... hopefully she will hold
thanks

RE: muffler problems
 

Good luck with it.