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We have on our 2004 V-Fun Skyranger what I believe, from looking at diagrams on the Rotax parts vendors sites,
http://www.cps-parts.com/catalog/rtxpages/912914muffler.php
is a standard Rotax 912 exhaust system.
So first I’d like to confirm that this is a Rotax part, not a Skyranger (BestOff, the maker of Skyranger kits) part?

On a flight yesterday we heard a slight change in engine sound and got a little smell of exhaust fumes in the cockpit. Was pretty sure we’d developed an exhaust leak.
Opened the vents, and since all gauges were behaving, no other dangerous sounds, and it wasn’t getting worse (and since nearby landing options all had some undesirable features) proceeded the hour to our home field without incident… if with a little nervousness looking for emergency landing sites.
On landing we discovered a small crack about 1 millimeter wide and 10 millimeters long in the muffler right at the base of collar that fits to one of the four incoming header tubes.
Since then the crack widened to the point where the collar that the header inserts into the muffler has completely separated from the muffler by about 2 millimeter. See pictures.

If the muffler is a standard Rotax part we can of course order the part and replace it.
On discovering (a) the whole exhaust system is stainless steel, and with at least a bit of shock that (b) the stock muffler at CPS (and presumably other Rotax parts sellers) is about $1000 US, want to explore what alternatives for repair or replacement might exist.
#We could remove the muffler and take it to someone qualified to weld stainless and repair it.
# As perhaps a temporary repair we could repair/plug it with JB high heat putty which they specifically recommend (in areas where the continuous temperature is less than 450º F) for exhaust systems?
-------------
http://www.jbweld.com/product/j-b-highheat/
Temperature Resistant Epoxy Putty
Strength 800 PSI at Room Temp. 600 PSI at 400ºF
Set Time 1 Hour, Functional Cure 8 Hours, Dries Machine Grey
Great For: Exhaust Manifolds, Tail Pipes, Mufflers
-------------
Seem like that one option might be in the category of “worth a try” especially if testing in local air flights (as contrasted to trying to fly the Atlantic). My concern with even trying it includes the possibility that if we got that stuff on the crack it could interfere with latter doing a real proper weld repair (I sent an email to JB to hear their answer to that.) But if we decide to get a new muffler, might not hurt to try while waiting for the parts to arrive?

# I see at
http://www.rotax912exhaust.com/index.html
a Czech company making a complete stainless steel exhaust system for 912. Emailed them. Price is a fraction of the Rotax part -- the complete system is about $550 US including shipping. Anyone know anything about that as an alternative? According to their site it appears that their exhaust is used on at least some CT’s.
(“Airplanes with our Rotax 912 exhaust system:
SOVA, PEGASS, EUROSTAR, SAMBA, LAMBADA, KOYOTE, SWING, TEXAN, ZEPHYR, CT 2, CH 601, CH 701, TL 2000 – STING, ALEGRO, SAVAGE”)

# Thought I’d seen discussed here a cabin heater system based on a shroud around the muffler. Maybe even some here using it already. IIRR it involved replacing the whole muffler, or maybe the whole exhaust system, so at the time I first heard of it I ruled it out as I couldn’t see my way to replacing a whole “perfectly good” (or so I thought) exhaust or muffler to add a cockpit heat source. But if we’re looking at replacing the muffler might a an opportunity to do that. Anybody direct me to THAT product? Any experience using it?
 
Finally, I’m curious if anyone has seen or heard of a similar mode of muffler failure?
The engine is a 1999 Rotax 912UL with approximately 800 hours on it.
This SEEMS to me a premature failure. Something that IMO should be rare and/or perhaps even reflect, as they say, “product manufacture defect.“ Any speculation of possible causes (if only so we don’t put a new one on and in 800 hours duplicate the failure?) Given that in the pictures (which I’ll try to attach) you’ll see that after the attachment tube fully separated from the muffler it offset itself a bit out of line with the header entering, it appears that the header was tweaked a bit to force it to fit…. putting sideways pressure on the fitting.

Al

P.S., I see I double posted this. Will delete the other if I can.

Also:
Found this:
CKT Engineering manufacture a stainless steel exhaust and heater muffler for 912's




Here is the link:

www.cktengineering.com

Any feedback on THAT company's system?
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  • Re: Cracked Muffler 912. Suggestions?

    by » 8 years ago


    This is a stainless steel muffler. What most likely led to this failure was vibration that you may or may not feel. Having any stress on the joint would add to this problem. It can be welded by the right person good at stainless welding. I would find the cause. It wasn't just the metal separation. I would get a dynamic prop balance and change my engine mounts if they are over 5 years old. When was the last time you pulled the muffler and lubed the sockets with ant seize?
    Pull the muffler and inspect the other joints.


    "# As perhaps a temporary repair we could repair/plug it with JB high heat putty which they specifically recommend (in areas where the continuous temperature is less than 450º F) for exhaust systems?"


    No putties. Vibration broke this putty will be worthless.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Cracked Muffler 912. Suggestions?

    by » 8 years ago


    Thanks Roger for reply.

    Never have pulled the part and applied antiseize
    Never heard of this as part of routine maintenance. :ohmy:

    Engine mounts were replaced only about 50 hours ago, but the old fairly chewed up ones were in there about 500 hours. Could be contributory cause. Before recent carb rebuild engine ran a bit rough (with more vibration than presently) as certain RPMs. Also possible contributary cause. If those were the cause(s) they've already been remedied.

    We do have acess to an experience skill stainless steel welder guy who has done several jobs for out local A&P and is recommeneded and trusted.

    If we are unhappy with the weld job and decide to replace the muffler do you have any opinion on the alternate sources for muffler I mentioned?

    Al

  • Re: Cracked Muffler 912. Suggestions?

    by » 8 years ago


    Hi Al,

    If that is a stock Rotax muffler I only know of the dealers that carry them. I think the welding will work okay. Your muffler sockets should be lubed with copper anti seize occasionally. This keeps down the exhaust pulsation chafing in the sockets. I have seen a number of the sockets worn right through and break from this. It's in the manuals.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


    Thank you said by: Bob Jones

  • Re: Cracked Muffler 912. Suggestions?

    by » 5 years ago


    I am doing my first annual after the first 60 hours (NOT 600!) on my Kitfox and discovered similar cracks in the muffler (the tailpipe support bracket) and a hairline crack in in another part. Stainless steel part supplied with the engine but it could be a non - Rotax product.
    Any new discoveries fixing it?

  • Re: Cracked Muffler 912. Suggestions?

    by » 5 years ago


    Rotax doesn't supply completely welded mufflers and exhaust pipe setups because so many aircraft are different. They do supply some fittings and pipe, but the finished product is up to you or the aircraft Mfg.

    Most I know just get someone with a TIG welder to do the stainless welding to fix breaks.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


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