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Dennis Kirby
Joined: 05 Dec 2013
Posts: 35
Location: Albuquerque, NM
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 Posted: Mon Apr 25, 2016 10:43 am Post subject: Securing Muffler Springs |
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Kolb Friends -
I'm sharing with you a tip that may prevent you some grief that I encountered recently on my Mark-3. One of my muffler springs broke on a recent flight and departed the engine. Went thru my Powerfin prop and it took a bite-sized chunk out of the leading edge of one prop blade. Damage was beyond repair - cost of a new blade was $250.
All 8 springs on my Rotax-912 muffler are safety-wired, per common practice intended at securing the spring when (not if) they break. I always check the safety wire on each muffler spring as part of my preflight. Apparently on this day, one of these safety wires was worn partially through and still appeared secure when I checked it. When the spring broke in flight, the instantaneous energy must have been sufficient to break the already-weakened safety wire, resulting in the spring's departure from the engine. Double failure.
So, here's the tip: I will no longer rely on ordinary safety wire to secure my Rotax muffler springs. I've upgraded to 1/16" braided cable to secure these springs. This is bicycle brake cable, available at any bike shop. I use one piece (about 10 inches long) for each pair of springs. The cable ends are joined and secured using a swaged ferrule. Cheap, easy to install, and most of all, WAY more secure than a single strand of .032 safety wire! Constant engine vibration will not wear thru it, as it does on safety wire.
Fly safely ...
Dennis Kirby
Mark-3 / 912ul
Sandia Park, NM
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stuart(at)harnerfarm.net
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| Posted: Mon Apr 25, 2016 11:20 am Post subject: Securing Muffler Springs |
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Dennis,
Very interesting. Thanks for sharing. Makes me want to use the flange/bolt
method.
Did you use RTV to keep the safety wire from bouncing around and wearing
out? I have always done this, but don't like not being able to see the wire
and judge its condition.
Do you have any pictures of your new method?
Question for the group.
Do you think the stainless steel springs are better, and would it be a good
idea to just replace the springs at say spark plug replacement intervals?
Thanks,
Stuart
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Mon Apr 25, 2016 12:19 pm Post subject: Securing Muffler Springs |
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Dennis K/Kolbers:
Until I went the expensive SS spring route, I had problems with breaking
springs. They didn't go through the prop because I use a lot of silicone
seal to encapsulate the entire spring from one end to the other, including
the hooks. No need for safety wire.
I bought a set of SS springs to go with my new Titan exhaust system, some
800 hours ago. The springs are pricey, but they work. Well worth the
money.
As far as props go. The reason I use WARP Drive props is because I can't
find a better one for performance and for durability/reliability. You could
have put that spring through a WARP Drive blade and kept on flying.
Probably take a little cosmetic work, but not a new blade.
Here is the url for the springs:
http://jbmindustries.com/SOCKET.html
john h
mkIII
Titus, Alabama
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_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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| Posted: Mon Apr 25, 2016 5:31 pm Post subject: Re: Securing Muffler Springs |
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Silicon? Safety wire? Um - no. How about some 5/16" bolts and springs from Ace hardware? The lugs that the bolts go through are cut off the ends of some big muffler clamps and welded to the pipes. Drill a hole in the end of the bolts and put a cotter pin through them. Replace them every year during condition inspection.
Don't know how a 912 exhaust is configured, so it might not work for that application.
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Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. |
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Watkinsdw
Joined: 15 Mar 2009
Posts: 138
Location: Deerfield Beach, FL
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| Posted: Tue Apr 26, 2016 4:43 am Post subject: Re: Securing Muffler Springs |
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I, too switched to SS springs on my 912 ULS with its Titan exhaust. Stainless Steel springs cured the problem of periodic breakage, although I only flew it about 50 hours after the installation before it was sold. It was always a pain when doing pre-flight and noticing that I needed to replace a spring, assuming I missed it on the post-flight inspection.
Here's another twist- at one point, I noticed that the tangs on the exhaust system that the springs hooked to showed considerable wear from the vibration, and I had two of them tig welded to build them up as soon as I noticed it. It's worth checking, because that would be another way to lose a spring and the safety wire connection as well. If you use high temp goop on both ends of the spring where it connects to the tang, any wear could go unnoticed.
Dave Watkins
Pompano Beach, Fl
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zeprep251(at)aol.com
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| Posted: Tue Apr 26, 2016 1:05 pm Post subject: Securing Muffler Springs |
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stainless steel springs give an added margin of saftey.From JBM.
| Quote: | On Apr 25, 2016, at 2:38 PM, KIRBY, DENNIS T GS-13 USAF AFMC AFNWC/EZS <dennis.kirby.3(at)us.af.mil> wrote:
Kolb Friends -
I'm sharing with you a tip that may prevent you some grief that I encountered recently on my Mark-3. One of my muffler springs broke on a recent flight and departed the engine. Went thru my Powerfin prop and it took a bite-sized chunk out of the leading edge of one prop blade. Damage was beyond repair - cost of a new blade was $250.
All 8 springs on my Rotax-912 muffler are safety-wired, per common practice intended at securing the spring when (not if) they break. I always check the safety wire on each muffler spring as part of my preflight. Apparently on this day, one of these safety wires was worn partially through and still appeared secure when I checked it. When the spring broke in flight, the instantaneous energy must have been sufficient to break the already-weakened safety wire, resulting in the spring's departure from the engine. Double failure.
So, here's the tip: I will no longer rely on ordinary safety wire to secure my Rotax muffler springs. I've upgraded to 1/16" braided cable to secure these springs. This is bicycle brake cable, available at any bike shop. I use one piece (about 10 inches long) for each pair of springs. The cable ends are joined and secured using a swaged ferrule. Cheap, easy to install, and most of all, WAY more secure than a single strand of .032 safety wire! Constant engine vibration will not wear thru it, as it does on safety wire.
Fly safely ...
Dennis Kirby
Mark-3 / 912ul
Sandia Park, NM
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Dennis Kirby
Joined: 05 Dec 2013
Posts: 35
Location: Albuquerque, NM
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| Posted: Mon May 02, 2016 5:25 am Post subject: Securing Muffler Springs |
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Kolb Friends -
After sharing my broken spring (and subsequent broken prop blade) experience
with the List, a few of you asked to see a picture of my fix. Here it is.
On my 912 muffler setup, one piece of braded bike cable easily secures two
springs. You can see the swaged ferrule that secures the cable ends just
above the carburetor dome.
Dennis Kirby
New Mexico
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