Some of the people I fly with seem to lose a few mufflers every year. If you just slap the muffler on with little thought to the tremendous vibration that a single cylinder engine works in, then it will occasionally fall of. The engine usually quits and if you are in the wrong place you may have a bad crash. You may also experience many engine out conditions because the muffler pressure will not be constant. An added benefit, in my opinion, of using Silicon Automotive Adhesive Sealant (RTV) is that it helps keep thing together and tight to resist the vibrations. I take my mufflers apart and put RTV at every joint, and blue loctite on all threads. At the first sign of a leak anywhere in the exhaust system, I take it apart and do it over. This happens maybe once per year if you alternate flying say 4 planes.

That may be so, but I've been flying my Venus II now for, oh, two years I guess.. and so far, I installed the OS 1.20 AX, tightened the muffler (and I mean tight) and let it go. It has not leaked nor come loose.

Jeech.. now that we are talking about it, Murphy's Law will definitely prevail..[:@] I had better get some hi-temp RTV!!

I always disassemble new engine mufflers for the RTV treatment, before I ever run them. I've lost muffler halfs anyway, and it's never been from a loose bolt. Rather, the thru-bolt in my 46AX muffler would occasionally pop it's head right off (the bolt itself would fail). It wasn't overtightened, and had been on over 2 dozen flights. At that point I leaned the engine a tad more (it being well broken in by then), and the extra heat caused the bolt to stretch and fail. The engine didn't quit, it seems to draw fuel quite well even without pressure, though I avoided throttling up (muffler pressure is more and more important as the throttle opens. Idle has the best fuel draw.

I've taken to drilling a tiny hole in the fin of the p-box style mufflers. Then a piece of tie wire ties the rear half to the front half. Next time the bolt breaks, I won't loose the muffler half. That said, anyone know the hole diameter in the 46ax baffle?

J

The muffler bolt (the through one) on the 1.20 AX on my Excelleron 90 broke in flight. We were lucky enough to find it on the ground after it came apart. When it did, I shut down and did a dead-stick landing. The bolt was snapped right at the beginning of the threads.

OS sent me a new bolt and a pair of ny-lock nuts.

I've lost muffler halves before all well. What I do to prevent losing the back half of the muffler it use safety wire to secure the back half of the muffler. When/if a bolt breaks I will then drill out the hole in the muffler and put a piece of all-thread through the muffler to secure it.

Ken

To be honest, Ken, when mine broke, I headed down to the hardware store and bought a length of all-thread and a pair of nylocks and drilled it out. That's the way it is now, by the way, and I have the "stock" bolt that OS sent me in the spare parts drawer. I also drizzled a drop or two of locktite on the threads. It ain't coming apart any time soon. And, the allthread I got was standard (vs metric) and slightly larger in diameter than the stock bolt, so I presume it's stronger.

Only problem is that the hole in the muffler is no longer threaded (drilled out) so the stock bolt will not work on that particular OS 1.20 AX.. but I have two others, and a spare bolt... just in case.

CGr

CGR,
Yes, I use allthread after the bolts break. But when a stock muffler bolt is in place I use the saftey wire to keep from losing the muffler half if the bolt does break

Ken

I too replaced the bolt with #6 threaded rod. The first time I did that it came apart again on the second flight. I'd overtightend the rod, causing it to not have enough stretch left when it warmed up. It was actually that time that I lost the baffle (the first time the vent line kept the muff on the plane, along with the LE of the wing). Now I have a few split lockwashers under the front nut to act as a very stiff spring to allow some extra stretch, and I've been very careful about tightening the bolt gently, but firmly.

I now wire all muffler rear halves regardless of where the bolt came from. If supertiger's one piece mufflers were'nt so bloody ugly, I could find myself liking them! Guess I really need to talk to a club member who has a TIG setup... I can't see any reason the damnable things ever need to open!

J

What the heck is a "Cigarette Box"?

And why isn't the OP just flying with that spacer he already bought?

Dave Olson
My buddy's tagline says "Just shut up and play that darn guitar!"

Cigarette come in lift-top box and soft-pack. The box is a good quality thin yet stiff paper. The carton paper would likely be even better.

'Cause I just bought it online last night

I called Tower today, and they said ther IS a side note with the Nexstar that a spacer is required due to the new shape of the .46AX muffler. I feel a lot better about things now.

I am new to this R/C bizz....sooo....I HAVE to read everything thoroughly...(several times)......I have alot more questions than answers at this point.....but glad I could assist.
A pointer taken from a veteran club member......make it a habit to check bolts/nuts/screws/GLOW PLUGS....for tight after 5-6 flights.......give things a snug test during pre flight check.....suprise/scare yourself.In the short time I have been invloved I have witnessed main gear coming off in flight and engine mount coming loose(that was pretty).

I've lost many muffuler halves over the years.
The problem is..i can't get a decent torque from a miniture screwdriver( front) so i can tighten the rear nut good.

Luckily I've been able to get lock nuts with inserted star washers on them, this way it'll bite into the muffuler a bit.
I still double up on the nuts.

I've put JB weld, CA, expoxy on the threads behind the nuts to prevent the nuts from spining out.

The manufacture can resolve it easily by drilling a little hole into the bolt. This way you can loop a little
wire through to prevent the nuts from ever spining completely loose from the bolt.

It's the samething that's keeping the front wheels for your car from flying away.lol
You can turn that nut by hand even
Your lives are dependent on a little pin.lmao

If they can drill little air breed holes and other smaller holes, they can do this , if they wish to.

But they're arnt going to do that... becuase someone invested a lot of stocks on replacement muffulers parts.

I can't remember (or find) if I posted this but I called Tower, and there is a 'side note' that people seem to be overlooking that says that a muffler extension is recommended. I also called Hobbico and they verified that the 46AX probably wouldn't clear the cowl without an extension. Whew!

Thanks for the input on the silicone sealant and thread lock; I can't say I would have used either, but they both make so much sense.

I have been flying R/C since 1972. This means nothing but does give a frame of reference. It is my opinion that when the muffler center bolt breaks in flight, it is because the muffler halves and center bolt, and maybe the muffler and the engine, have been rattling around beating each other up, generating greater stresses than if everything was tight and held together. This is why I RTV every joint and loctite the bolts, and do the job over whenever I see a sign of a leak. I would not be surprised to learn that the muffler center bolt is made of an alloy steel with a tensile strength well over 120,00 PSI and the replacement all thread rods are made of low carbon steel with a tensile strength of around 60,00 PSI. If you lightly hammer that center bolt at 12,000 blows per minute, is it a surprise to see it fail? If things are kept tight the bolt will works like a spring and absorbs the 12,000 blows per minute because the stresses will be within the bolt elastic limit. I almost lost a muffler about 10 years ago. Then I started to use the RTV and loctite.

In my experience, the centre bolt was tight. The muffler joints were RTV'd. It had not loosened in 20+ flights, and in fact, the nut and the bulk of the bolt were still in the back half of the muffler, still tight. The head itself had popped off, a tensile failure.

Aluminum expands at about 2x the rate of steel with heat. I think I probably had slightly over-tightened that centre bolt, and when the muffler came up to heat, there wasn't enough stretch left in the bolt. There was no sign of necking down or other plastic failure modes, just a sharp, right angle brittle fracture. Either I over-tightened the bolt, or it was improperly heat treated. It should not have failed at that location, there's even a fillet under the head to prevent this stress rizer. It should have failed in the threaded portion.

I've wondered if I should thread the ends of a piece of music wire, then bend a little zig-zag in it's middle, harden and temper it (I have that technology), and use that for the thru bolt. Music wire is fine high carbon steel, huge tensile strength, and a little zig-zag would give it muchos stretch, while still holding the muff together. And glow engines exhaust doesn't get hot enough to ruin the temper...

Maybe I'll try that if the current arrangement fails again....

J

Well, in my case, this was the third or forth flight on that particular engine after break-in. And it was not loose. If anything, it was probably to tight and snapped... or it was a defect on the bolt itself. It snapped cleanly right at the base of the threads on one side of the bolt.

I don't know. All I know is that the all-thread bolt is in there and it's been working fine now for about three years.

CGr.