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Thread: Sonex/Jabiru 3300 Exhaust Question

  1. #1

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    Sonex/Jabiru 3300 Exhaust Question

    I have a Zenith CH750/Jabiru 3300 and the exhaust system is very leaky at the slip joints where the 3 headers on each side meet the muffler's sockets. The slip joints aren't the tightest and due to backpressure, most sealants burn/blow out. Compounding the problem is that there really isn't enough room on the muffler side of the joint to wrap, clamp, band, etc. any sort of overlapping material to attempt to seal the joint.

    Why's a CH750 owner asking a Sonex question?

    I understand that the usual Jabiru 3300 installation in a Sonex utilizes straight exhaust pipes rather than a muffler. Seems like that should provide very minimal back-pressure on the 3-into-1 collector. The muffler on the CH750 installation seems very restrictive and probably produces a lot of back-pressure. Are the Sonex's slip joints very leaky? Just wondering if reducing back-pressure on my 750's exhaust system would help cut down on leaks or help keep sealant in the slip joints!

    John
    N750A

  2. #2

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    I made that switch on my Texas Sport Cub with a Jabiru engine. The original big can-style muffler that came with the engine is a piece of junk. It leaked so badly that I removed the cabin heat valve for fear of killing myself with CO. I complained to Jabiru USA about it and they sent me a new muffler, but it was just as bad as the one I had.

    The Sonex-type collectors -- one on each side -- work much better and have a much better seal where the exhaust pipes enter the collector. It is not perfect by any means, but it is MUCH better. I think the engine makes a bit more power, too, although I have no way to actually verify that.

  3. #3
    sonex293's Avatar
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    Yes, the Sonex exhaust is also "leaky" at those seams. I've got mine wrapped with and it helps control the leak, but doesn't prevent the leak. I have to replace the wrap every year at annual time. Someone on the Yahoo! SonexTalk forum created a custom tool to add a "bead" on one end and he claims it really helped control the leaks. We'll see after he's flown with it for a year!

    ==
    Michael
    Sonex N293SX

  4. #4

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    I, too, am chasing high CO in the cockpit and believe most of it is coming from under the cowl from the leaky slip joints. I'm sealing the firewall as much as possible, but still want to eliminate the source!
    I found that one of my baffles was loose, so I'm having the muffler shell opened up to retrieve it and told the welder while he was at it, to go ahead and remove the other baffle. The 2" o.d. exhaust pipe crosses the interior of the muffler shell and is welded on both sides for support. I "think" it is just perforated with tiny holes as it crosses the interior of the muffler. I told him to cut big holes in the interior exhaust pipe to the point to just leave enough structure for support. This should reduce the backpressure in the muffler quite a bit.
    I'm then going to reinstall it with Wurth's Exhaust Sealant - good for 1300F and OEM to Porsche and apparently used on motorbike header/exhaust slip joints with success. Hard to find and expensive (by car standards, not aviation standards! HA!), but I figure the Wurth is worth (pun intended!) a shot! I'm going to use some "Tiger Patch" resin impregnated glass cloth (good for 1900F) secured with stainless wire ties to butt up against the gap between the header and the muffler inlet socket. Hopefully, this will "dam up" the sealant to help prevent blow-out. Better would be to wrap it around the joint on both sides, but as you know, the muffler sockets are right against each other and you can't get anything around the exterior of them.
    If all else fails, I may very well go the straight pipe route simply to get the lowest possible backpressure and have more exhaust go out the end of the pipe and not the slip-joint! I'd really prefer, however, to retain the muffler shell so as not to have to fabricate new cabin and carb heat systems.
    Last edited by jaustinmd; 03-07-2013 at 05:16 PM.

  5. #5
    Eric Witherspoon's Avatar
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    I have the Sonex/3300 3-into-1 outlets. I wouldn't be surprised if they are using the exact same tubing combination of OD x wall as on the muffler you're having trouble with, because they fit really loose and leak like crazy. I tried wrap, but you know what? If you don't stop the FLOW, wrap just gets blown through and burned up (something about that 1300-1400F exhaust gas). I believe wrap can truly insulate to the SURFACE temp of an exhaust pipe, but when there's flow, wrap is hopeless. It just turns to charred ash and falls away, and you're back where you started. So you have to stop the flow.

    Someone on the Sonex group mentioned chimney cement - not sure how much jaustin's Wurth's stuff is, but chimney cement is about $3 for a little tub at the local airplane supply (hardware) store - enough to do 100 airplanes' worth of exhausts. But the little tub will dry up and turn into a brick-in-a-can before you can re-apply it next year... It's a ceramic product, which means it's crumbly, and will probably just turn to dust and fall out of the joint after a while. But it's cheap, easy to apply, and does seal the pipes.

    Any comments about "reducing the back pressure" - well, that's like putting your thumb in the dam. Say you reduce the back pressure by 2psi, when there's 100 psi coming out, how much flow did you reduce? If there's leaks in the joint, it's gonna leak (big) under the cowling regardless of whether you have 10" or 3 feet of tube between the leak and the outlet. Stop the flow is the name of the game.

    Practically, though, for how short the Sonex 3-to-1 outlets are, I wonder why they are separate parts, other than to make the engine easier to fit into their shipping crate. Anybody just weld it all up and be done with it? The old "log" style headers used to be that way - just 1 all-welded collection of tubes per side. Here's some photos I took of the factory Sonex/3300 back in 2000. Exhaust = 1 piece per side, so it can and has been done.
    sonexe3.jpg
    sonexe2.jpg

    sonexe1.jpg
    Murphy's 13th: Every solution breeds new problems...

    http://www.spoonworld.com

  6. #6

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    Eric - Stopping flow through the slip joint is exactly what I'm trying to do! The Wurth's is to seal the joint (stop flow or blow back) - the wrap is merely to help hold the sealant in place, not to seal off the flow. We're talking the same ideas, just different materials.

    HOWEVER, I think you're underestimating how much backpressure reduction is possible. I've found one guy with a 3300's headers just jammed into a single collector (no slip joints) that tapers to a straight pipe. He really has less blow-back than a stock system through slip joints into a restrictive muffler. That's why I'm gutting the muffler to reduce back pressure on the slip joints.

    By the way, the Wurth's sealant is about $17 for 140 gms - enough to do several systems. The catch is that it's mostly available at foreign car aftermarket sources such as Pelican Parts - so you have to pay a few bucks shipping. Supposedly, it's superior to the chimney cement, Permatex, etc., but maybe that's because one paid so much for it!
    Last edited by jaustinmd; 03-09-2013 at 07:23 AM.

  7. #7

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    I've not had issues yet, but am getting a CO meter to check the situation. I did just notice that I've got a lot of rust on the bottom of my muffler? I'm thinking that the weather here in northern Illinois has been so humid and cold that the problem is greater than norm? Anyone else have the problem?

  8. #8

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    I'm a sonex builder but am using the aerovee so my comments may or may not apply. If it is just a matter of the two muffler pipes not fitting tightly together they make a tool called a tail pipe expander that you can use to make the inside pipe a little bigger for a snugger fit. Harbor freight sells a few different sizes for under $20 or you can usually rent one from your local autozone or Napa. An impact gun with a socket works best to make these tools effective although you can get away with a long breaker bar if you don't have one.

    http://www.harborfreight.com/medium-...der-37353.html


    Keith

  9. #9

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    Keith - The Jab 3300's headers are approximately 1 1/8" i.d., but a 1 1/8" tail pipe expander will NOT fit! Probably doesn't matter anyway, as I've been told that the expanders will simply round-out pipes and push out dents, but not actually expand something as tough as the .050 stainless header. Apparently, it takes a commercial-quality hydraulic expander to stretch the pipe, but most muffler shops don't have anything as small as 1 1/8".
    Another elegant solution is to bead the header, but the only one I've seen was done by a custom-made bead roller. Of course, you have to remove the headers and do a lot of beading and individually fitting to get it "just right."

    I wound up using the Wurth's Assembly Paste with a couple of Tiger Patch wraps arouind the header adjacent to the end of the slip joint to help hold the sealant in place. The Tiger Patch was so thin and slightly tacky that a couple of wraps is all I could manage before it starting gumming up and getting uneven. So, I abandoned any more attemps at more than two wraps each header and butted-up stainless hose clamps against the end of the slip joints to further obstruct it and retain the sealant. I preheated with a heat gun, idled the engine for a few minutes to cure everything, and then flew for about an hour. So far, no leaks, but of course, the problem with all these fixes is the duration of the "fix." So, that's to be determined!
    Quote Originally Posted by kmacht View Post
    I'm a sonex builder but am using the aerovee so my comments may or may not apply. If it is just a matter of the two muffler pipes not fitting tightly together they make a tool called a tail pipe expander that you can use to make the inside pipe a little bigger for a snugger fit. Harbor freight sells a few different sizes for under $20 or you can usually rent one from your local autozone or Napa. An impact gun with a socket works best to make these tools effective although you can get away with a long breaker bar if you don't have one.

    http://www.harborfreight.com/medium-...der-37353.html


    Keith

  10. #10

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    Hi Ed! - My muffler is stainless and although it will discolor to a brownish color, I've seen zero rust/corrosion. I'm in mid-east Tennesse, and we have rather mild winters, but plenty of rain and humidity. My 750 is hangared and I have a preheater (very low output electric heater with fan) on a timer that blows warm, dry air up into the cowl each a.m., so everything stays dry, the oil and battery are warm, and it cranks instantly on the worst winter day! I suppose that would keep any corrosion down, too.
    Quote Originally Posted by Ed Olds View Post
    I've not had issues yet, but am getting a CO meter to check the situation. I did just notice that I've got a lot of rust on the bottom of my muffler? I'm thinking that the weather here in northern Illinois has been so humid and cold that the problem is greater than norm? Anyone else have the problem?

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