Exhaust spring wear

[Roger Lee]

Hi All,

 

While I was doing another rubber hose replacement on a relatively higher time plane I noticed the springs are worn almost half way through where they connect over the loop on the exhaust pipe and muffler. I have seen this many times before and had forgot to mention something before. They do not need to be worn all the way through before they just break off and you will never know when it will fail. On may last plane one did break before I caught it. All the Rotax 912's have spring wear. When your plane gets to approximately 800 hrs. you need to toss the 8 exhaust springs and replace them. The vibration can and will eat right through the spring hook. You don't have to take anything else off, just pull the springs. Safety wire them and then re-apply the high temp silicone on the spring. There are two ways to apply silicone. The first way is to actually fill the inside of the spring with silicone. The second way and the one I use is to apply the silicone on the outside of the spring from top to bottom. Make it at least 3/8" wide and 1/4" tall. You need to give it some strength anbody by making it wide and tall enough to work. I thin little bead is worthless. Work it in between the spring coils. This is to dampen the vibration to the spring and help prevent premature spring breakage and help with the wear I just mentioned above.

 

I have 720 hrs on my plane and they are worn half way through on 3 springs and a quarter the way through on the others.

 

 

p.s.

You can have faster exhaust spring wear so these should always be checked as the engine builds time, but I usually see the problem right around 700-800 hrs. Just keep an eye on yours.

[207WF]

I replace a couple at each 100 hour as a matter of course, and I a carry a couple of spares. Some of them get weakened by exhaust blow by. They are cheap and easy to replace. WF