Muffler bolts
 

Hey guys need some help. Iam back into-rc planes and have a 46 os fx motor. I put a new muffler on it and it comes lose . Can i use loc-tite on the threaded bolts ? If so what kind.

Thanks Brian

RE: Muffler bolts
 

Use blue locktite or a little of the high-temp RTV silicone (usually orange) on the threads. Also try re-torquing with the engine hot.

RE: Muffler bolts
 

Thanks i will try that. I have it on a test stand. I will get the motor hot and back the bolts out and then put the loc- on the bolts.

Brian

RE: Muffler bolts
 

You might try just tightening the bolts when hot. They lengthen when hot. Tightened then, at their operating temperature length, usually is adequate.

LocTite works for sure. When you don't have any and want to avoid the expense, or just want to fly the next day..............

RE: Muffler bolts
 

Below is a quote from another RCU forum by Bill Baxter reqarding torque values for OS engines:

"O.S. does not specify torque values. They really aren't needed. We've only used torque wrenches on certain gasoline-fueled engines, and then only on specific parts of those engines where the manufacturer states that tightening to a specific torque value is absolutely required.

_____________________________

Bill Baxter, Manager Hobby Services/Futaba Service/North America
3002 N. Apollo Dr. Ste. 1 Champaign, IL 61822 USA
Service Phone: 217 398-0007
Email: [email protected]"

I would think that tighening the muffler bolts when the engine is hot would be my last choice. Use the Blue Loctite when the engine is at room temperature. As the the engine heats after start, the aluminum will expand to a greater degree than the steel bolt causing a more snug fit between the cylinder/muffler and the steel bolt.

RE: Muffler bolts
 

I'm guessing that the reason it works so well would be due to two things.

You do the tightening after stopping the engine and aluminum cools quite a bit faster than steel. A bolt that's almost completely encased with no contact with the air certainly won't be cooling very fast. Second reason is like everything in our hobby, there is a technique to be learned/used. Gotta learn how strongly we need to tighten the suckers without stripping them.

About technique.......... The through bolt on lots of mufflers are often a problem. The technique with them is most certainly something many have to learn. Many guys don't realize the bolt threads through the endcap. It's very important to tighten that adequately before tightening the nut that's present. The nut is actually a lock nut, yet many think it's the primary holder. Just another detail to be learned by some in our hobby. (It seems appropriate to mention the muffler bolt because it's quite often the problem newbies have with loose bolts.)

RE: Muffler bolts
 

The muffler is at minimum torque when cold. It will tighten with heat as the aluminum expands as previously mentioned. If you go just a litle past snug when cold, that will leave enough stretch in the bolt to allow for expansion when hot. Locktite is handy to keep the bolt in place, because the oil from the fuel along with the muffler's vibration is bad about rattling it out.

RE: Muffler bolts
 

I think you might have misunderstood me or I wasn't very clear. I didn't say to use a specific torque value. All I am saying is to take a screwdriver, allen wrench or whatever it happens to be and cinch it down when hot. Re-torquing or re-tightening the bolts when hot on certain assemblies is pretty common and often effective. I've worked on everything from small engines to automotive engines to industrial stuff since the late 80's. One way I learned to prevent exhaust leaks and loose bolts on exhaust manifolds was to get the engine hot, and re-tighten the bolts. Why does it work? I can theorize all day but the bottom line is that it does generally work and that's what matters most. I've found that it works well on RC engines too.

Another thing I've done is put the assembly through several heat/cool cycles then re-torque it. I'm guessing this allows everything to do all it's moving and slight shape tweaking then that final tightening locks it all in place but who knows. Again, it just seems to work.

RE: Muffler bolts
 

Yep, they expand, contract and distort very differently and at different temperatures. I've also found that what a material does when heated is often a little different than you might expect. Sure, it will expand but it might grow in one direction or another depending on its shape, how its assembled, etc.

RE: Muffler bolts
 

I fly the plane, land and tighten my mufflers or headers while at operating temperature. I have never lost a muffler or use lock tite, something must be working?

RE: Muffler bolts
 

The bolt also grows in length when heated so I don't think it is necessarily tightest when hot on every example. Plus the hard steel of the bolts and aluminum of the engine & muffler behave very differently.