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Thread: How to prevent cracked muffler on 912uls

  1. #1

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    Default How to prevent cracked muffler on 912uls

    200 hours on my engine and my muffler got a huge crack, clearly this is not ordinary wear. Talked to John McBean and his first guess was that the stinger was banging against the engine cowl on startup. I looked and sure enough, saw evidence on the stinger that it had been hitting the cowl. The distance from my stinger to the cowl is 3/8" which would seem like plenty but in a rough cold morning start, clearly that is not enough. Rather than buy another $995 muffler every 200 hours, I think I will increase the distance to 5/8" clearance And while I am at it, going to replace my engine mount vibration isolaters too in case those are shot and causing excess movement.

    cracked-muffler.jpgevidence-of-hitting.jpgclearance.jpg

  2. #2
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    Default Re: How to prevent cracked muffler on 912uls

    Have you balanced your prop?
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  3. #3

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    Default Re: How to prevent cracked muffler on 912uls

    No, I have not. After reading your comment I headed to the Whirlwind RW-3B installation manual in a panic wondering if I missed something. It appears the prop is statically balanced at the factory because that is not even mentioned in the installation instructions but when it comes to dynamic balancing they say that it is recommended but not required.

    I am fairly confident that the stinger hitting the cowl was my issue because the crack showed up after a particularly rough cold morning start. Agree that its definitely worth checking the dynamic prop balance because that could also be part of my problem but its hard to justify a $4000 prop balancer for one test. I just found this awesome thread where a TeamKitfox member is renting theirs out. I will have to contact them.

  4. #4
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    Default Re: How to prevent cracked muffler on 912uls

    Yes highly recommend getting the dynavibe and balancing your prop. Static balancing of your prop helps but when its spinning with a spinner is another story.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  5. #5
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    Default Re: How to prevent cracked muffler on 912uls

    Last summer, I got a 912 muffler that was cracked up pretty good in the same place. Interestingly all the exhaust pipes were stuck in the muffler and wouldn't come out for anything. I ended up making a cut up the length of each nipple and was able to spread/expand the nipples that way and got the exhaust pipes out. Had it all welded back together, and I think it will last a good while in the next project. I ended up with the exhaust pipes being looser in the muffler than they probably were from the factory, but that will likely help things move around more and maybe not as likely to crack. Could be something to take a look at as well. A looser connection may leak a bit of exhaust, but not as much as a cracked muffler I'm thinking. Especially if the entire pipe breaks off. JImChuk

  6. #6

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    Default Re: How to prevent cracked muffler on 912uls

    Interesting, my four pipes came out of the muffler very easily and also came off the block easily. When I installed my muffler I used loctite LB 8150 anti-seize on the muffler end of each pipe as well as the engine block end of each pipe. It makes sense that if they became stuck that it could lead to cracking just from the thermal contraction and expansion.

  7. #7
    Senior Member Dave S's Avatar
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    Default Re: How to prevent cracked muffler on 912uls

    Interesting discussion - my experience mimics Dan's. The original installation involved a generous application of the silver/aluminum paste antisieze compound. In replacing the engine this winter (after a mere 500 hours) the muffler and pipes came apart with hand bumps. Also, the muffler has a brace going between the stinger and the muffler. Inspection after disassembly revealed no cracks.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  8. #8
    Senior Member Delta Whisky's Avatar
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    Default Re: How to prevent cracked muffler on 912uls

    If this is a contest, then I win! The shame of it all, I read this thread a couple of weeks ago but failed to look as closely as I should have before its last flight. You can see from the picture, I should have bent down and looked really close - it appears that there should have been some evidence of the impending doom. (Its there now!)

    And, the last contact the vagrant exhaust pipe made as it left its welded home was one of the new fairings on the good ol Monster Shock.

    Empty exhaust hole.jpgMissing exhaust pipe.jpg

    Now I need two things: the ability to rotate these pictures and a new exhaust muffler.

  9. #9
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    Default Re: How to prevent cracked muffler on 912uls

    Oh dang that stinks! Did you get to fly before it broke and test the new fairings out?
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  10. #10
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    Default Re: How to prevent cracked muffler on 912uls

    Wonder if you would dare to weld in another elbow? Add a patch on the end of the muffler with the correct size hole in it, weld in the new elbow, and then add the braces from edge of muffler to new elbow. I wish now I had put braces in mine when I had it at the welder. JImChuk

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