fbpx

 

I am sharing this story for the interest of all.

I was having an ongoing problem with the exhaust system on my engine (912is).
On at least a half dozen occasions one or more exhust pipes would jump out of the muffer sockets as the engine started.
Rotax engines are not noted for their gentle starting or stopping qualities.
They tend to go from zero to 2000 rpm in an instant when startiing, and come to a screeching halt when stopping.
There is no winding up or spinning down involved.

After resetting the pipes in the muffler and checking the springs a half dozen times, I said to myself,  "What is different from everyone elses installation, and why do I not hear of anyone else complaining?"

My kit supplier supplied the exhaust system partially assembled in the form of the all the springs and pipes were installed on the muffer and then a small Safety Cable was looped through the springs and brackets on the muffler and pipes.
The springs were then unhooked and the pipes were folded down for shipping, with the cables keeping all the springs and pipes together as a package.
All that was needed for installtion on the motor was to position all the components, Bolt it on, and Reattach the Springs.  Easy, Peasy!
The cables, already in place, served as the safety wire to capture any wayward/broken spring parts from departing the engine compartment.

This is where the problem lay.
Most normal installations have the springs safety wired with a wire looped between the spring mounting brackets and passing down the center of the spring to corral any broken springs.
This wire loop also serves an in un-intended but very important function.
It limits the spring from stretching more than ~1/8 inch and allowing the exhaust pipe ends from detaching from the muffler body during the severe motion of the engine as it starts.

I installed the traditional loop (actually a double loop for good measure) of safety wire through each spring and the problem disappeared.
No more Self-disassembly!!!

Sometimes it's the smallest details are what will cause you the biggest problem.
- - -

And Yes, I know that Silicon still needs to be applied to the springs to dampen the vibrations.

 

8284_1_ExhaustSprings.jpg (You do not have access to download this file.)

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Bill.Hertzel@Yahoo.com
Clicking the "Thank You" is Always Appreciated.

  • Re: It's all in the fine details.

    by » 5 weeks ago


    "And Yes, I know that Silicon still needs to be applied to the springs to dampen the vibrations."

    Oh shucks. I wanted to give you a hard time. LOL :) 

     

    I think a good solid layer of silicone would help this too.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

  • Re: It's all in the fine details.

    by » 5 weeks ago


    Bill, that photo shows that your muffler sockets are very shallow. On my 912uls the sockets are at least 3/4" maybe 1" deep. Its no wonder yours jumped out.


  • Re: It's all in the fine details.

    by » 5 weeks ago


    Good observation!
    I don't think the pipes even insert 1/4" into the sockets.
    If I put my body weight on the muffler, it wasn't all that difficult to stretch the springs enough for them to unplug.
    A very rough calculation shows it would now take 500 to 800 lbs to break the 4 strands of safety wire retaining each spring.
    I could hang the plane upside down by the muffler!!!


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


  • Re: It's all in the fine details.

    by » 5 weeks ago


    Interesting approach to store away a plane, Bill!

    Don't forget to post some pics..., sharing that experience is very much appreciated.

    ;-)


You do not have permissions to reply to this topic.