andrew wisc.

My Feedback: (4)

HELLO ALL!
I WAS WONDERING IF ANY OF YOU HAVE USED JB WELD FOR EXHAUST REPAIR. I HAVE A MAGNUM 120 FS THAT WAS IN A
PLANE THAT CRASHED. THE MUFFLER HIT AND RIPPED THE THREADS OUT OF HEAD DAMAGING AND CRACKING THE EXHAUST
BOSS ON HEAD. CRACK DOES NOT EXTEND INTO HEAD JUST RUINED THE MOUNTING BOSS. ANY ONE WITH EXPERIENCE WITH
JB WELDS ABALITY TO WITHSTAND VIBRATION ,HEAT,OIL PLEASE LET ME KNOW AS I WOULD LIKE TO TRY THIS BBEFORE SPENMDING MONEY ON NEW HEAD.
THANKS ANDREWWISC.

Campy

My Feedback: (1)

JB Weld will work fine on the engine. Over the years, I have made a couple of repairs using it .

Make sure that the surfaces you intend to put the JB Weld on ARE CLEAN.

I suggest cleaning the area AT LEAST twice using denatured alcohol (or acetone) and CLEAN cloths each time.

Use the regular JB Weld, not the quick JB Weld and let it dry/set up for a MINIMUM of 12 hours before doing any trimming or drilling in it.

If you can properly support the bolt, put a THIN coat of Vasoline over the threads of the bolt to prevent gluing the bolt in place and build the JB Weld up around the bolt.

Another option would be to use a "strap on" muffler.

jetmech05

I have an OS 1.60 pits style muffler that the nipple only had a 1/2 thread do to a break. I put "Metal Set" same thing as J B Weld on the threads and on the hexs on the outside of the nipple.. worked so well I've forgot about it until I read your post

Dr1Driver

JB Weld will work good in that situation. BE SURE the area is clean of grease or oil. After applying the JB, DO NOT move it until it's completely set. After that, you can drill, grind, or otherwise machine as you need.

Dr.1

hrrcflyer

A friend of mine and I used JB Weld to try to put the exhaust tubes back on his pitts muffler after a very hard landing broke them off. We cleaned the area very well and let it set up for over 48 hours before we moved it. The problem is that they still fell off the next time he flew the plane. I'v been told that JB Weld will not work in high heat applications. Where did we go wrong? Any suggestions are welcome.

Fly safe and have fun!!
David

NCIS

David,

If your engine is running that hot you need to richen up the mixture. This will allow the engine to run fine but also make it run cooler. 2-strokes run leaner than 4 strokes and on a 4-stroke the muffler and head should run very warm but not real hot as to cause the oil residue to burn and stain the muffler. 4-strokes run much cooler than 2-strokes but require a much richer setting. I have used JB weld on other muffler situations on cars but never on a RC engine. Everything that I used it on worked very well.

Barry

Insanemoondoggie

Like others have mentioned, cleaning , is the key to getting a good bond . Also the longer you let it set the better.

tnd

I rebuilt the boss on a TT 46 with JB Weld. Working great so far. I used a wax coated wooden dowel the same size as the bolt and built the boss around it. I rubbed a candle on it to coat it.

da Rock

Actually, this is not exactly the case. FLY R/C MAGAZINE does engine reviews and they are quite detailed. The author, Andrew Coholic, almost always includes temperature readings. They are eyeopeners. I just pulled a couple of issues out to get some numbers for us.

What are we interested in here? Whether or not JBWeld holds in heat. And some have posted that it did for them, and some have said it didn't. I'm betting both are telling the truth. So............

Turns out that it depends on where the temp is taken, and where the epoxy is used. The magazine guy reads head temperatures and exhaust temperatures and lists them in his articles. And we can use those two different to see what's what.

Turns out the 4stroke article shows that engine running head temps from around 225-260F when burning 15% fuel. The 2stroke article shows that one running head temps from 270-290F. Not much difference but the 4stroker is some bit cooler. What is interesting is the exhaust temps. And since the muffler sees those up close and personal, these might matter to this discussion a bit more than engine temps.

The EGTs for the 2stroke ran from 168-201F. The exhaust is cooler than the head. Not surprising, a 2stroke blows a lot of unburned liquid out on purpose. The idea is to take heat out that way, but unfortunately, unburned fuel hasn't absorbed much. They still do it, eventhough it isn't really super effective.

The EGTs for the 4stroke ran from 250F to over 300F.

Which muffler is going to hit the JBWeld with almost half again more heat?

Truth is, the failure point of some epoxies to heat just might be in those ranges. So it probably depends on where the patch is on the muffler, and what heat the muffler is seeing.

Our hobby usually isn't as simple as our sound byte wisdom suggests.

da Rock

Also, epoxy's failure mode may have something to do with why some JBWeld fixes failed and others didn't.

Heat can defeat it. No argument. But what happens when it fails?

If the heat isn't enough to cause it to burn, it usually melts. But if the fix is hot on one side and is being cooled on the other, is it a given that the epoxy melts completely? And if the outside stays cool enough to not melt, will it hold the melted stuff where it is....... I'm betting that happens when the temperatures encountered are marginal for failure. And the mufflers see cooling airflow.

Simple as a sound byte? maybe so, maybe not

NCIS

da Rock,

What publications did you get those temps from? It seems to me that when I run my Saito 4-stroke engines at a high rich setting that the muffler is much cooler than my OS 2-stroke mufflers which usually need a leaner setting. I will have to determine what is correct but he is fixing the head not the muffler. So the 4-stroke would have a cooler head as I stated.

JMHO,

Gibbs

da Rock

Where did I get the temps from? Here's the answer:
Yeah, I knew he was fixing the head, but since this thread has covered everything I figured I would too. And mentioned head temps to back up your post. You don't like corroboration?

As for what leaner or richer does......... That's the needle setting and that's what's going into the combustion chamber, not out of it. And the muffler sees entirely different exhaust cycles 4C to 2C. The 4s almost completely burn their charges and have lots less cooling content in the exhaust. The why isn't really as important when you have actual observed readings. But how are you reading the temps? Surely you're not touching the suckers.

rcuman

I had acquired a .60 OS engine with a pitts muffler on it. I wanted to install it into a H9 Corsair. I had used a brass pipe that would fit the outside circumference of the stack and made a piece that fit across the two pipes turning it into one exhaust stack. I used JB weld the first time and it fell apart after two flights. I friend of mine suggested that I use what they call Silver Solder which can be purchased at a welding shop. You have to use a mini torch to get it to melt and adhere to the metal. I am not sure how it would work on aluminum though but mine has not come apart since and it has about 10 flights on it so far.

Campy

My Feedback: (1)

Aluminum is TRICKY to weld or solder to. It has a very narrow heat range - too cold and the weld is no good, too hot and the aluminum melts. If the JB Weld (for what ever reason ) doesn't work and a strap on muffler is not available/feasable, the only options left are to replace the engine or take it to a welding shop and have them weld it.

Gringo Flyer

My Feedback: (18)

I think the reason that most JB weld fixes on engines dont hold has nothing to do with the heat... its the vibration. For example, the stacks on a pitt muffler have to hold up to a lot of vibration and thats why they generally come loose with JB weld. However, I have seen posts here on RCU with JB welded stacks that hold. Its seems that if the JB weld is pretty thick it can withstand the vibration.

Since pitt muffler stacks are so prone to break off in a nose over landing I think its easier just to cut the stacks short to start with and then use exhaust deflectors on them. With the stacks short they are a lot more resistant to less than perfect landings.

andrew wisc.

My Feedback: (4)

hello again!
i finally got digital camera to work. here are some pics of crack in exhaust boss. thanks for all your responses. i think
i am going to go ahead and try the jb-weld. will post some more pics when done.
thanks andrewwisc.

Jazzy

Andrew and all,
That crack doesn't look too bad at all! It does however look like a crack is extending inward - not so good.
The keys to using JB are:
1. Area must be clean.
2. JB must have something to hold onto.
3. The higher the stress (vibration or other) the more JB must be used.

Pitts mufflers are easy to fix with JB. The trick is no. 2 above. Lightly grind or scuff the intended area with coarse sandpaper to remove the "factory" finish on the metal. JB WILL adhere nicely to raw AL.

What I would do for this particular fix is remove the head, clean exhaust header and head thoroughly with denatured alcohol, obtain a raw metal area surrounding the crack/break, clean again and put it back together and snugly as possible. Make sure to position the header in the intended direction. Take a toothpick or very fine paint brush (a trimmed one will work) and apply a coat of oil to the threads of the header and the face of the lock nut. Mix and apply a layer of JB to the area. JB can be carefully worked with until it starts to cure. Leave at least 1/8" of JB on the area. Let sit for 12-14hrs.
Should work just fine.

This is an in-cowl muff I put together using JB. Notice the shiny raw AL in places.

TimC

Since nobody has mentioned it, having Clarance Lee install a brass sleeve is also an option. Here is a photo of his fix on my Enya 1.20. Andrew, in your case though, there might be too much damage for a sleeve.