Runtoeat Posted November 8, 2016 Report Share Posted November 8, 2016 It pays to inspect the springs and muffler on older aircraft. The springs may look OK but are pretty worn where they hook onto the muffler. Also, I know of one 2008 CTLS which had a crack on the face of the muffler near the muffler's outlet pipe. This was hard to see but close examination revealed a small white line running about 2". I note also that there is at least one CTSW has a small brace added by the factory to support the outlet pipe to the muffler body. My CT does not have this nor did the CT which had a crack. I'm assuming it has been installed (for some reason on some CT's but not all) to prevent the unsupported cantilevered outlet pipe from causing a crack as a result of it vibrating and "working" the muffler body. Link to comment Share on other sites More sharing options...
Tom Baker Posted November 8, 2016 Report Share Posted November 8, 2016 I have replaced 2 sets of springs this year. From what I am seeing about 10 years and they need replaced. The Rotax part number is 938-795. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted November 8, 2016 Report Share Posted November 8, 2016 Here's what happened to my exhaust at only around 350 hours, even with good springs and everything appearing to be normal. I think the issue was poor factory welds and vibration over time. I recommend keeping a close eye on the condition of your exhaust every time you remove the cowling. Link to comment Share on other sites More sharing options...
Runtoeat Posted November 8, 2016 Author Report Share Posted November 8, 2016 Tom, this confirms what I suspected about the springs wearing. Andy, I knew your muffler developed a crack but hadn't seen pictures. Believe Roger helped you repair this at last year's Page event? I think there might be a good possibility that cracks will eventually develop on a good number of CT's at the weld joint where the outlet pipe is joined to the body and/or on the end of the muffler body near the joint. Especially on those CT's that don't have the brace. I envision the non-braced outlet pipe being excited by engine firing at a pretty high amplitude because it is not constrained. Link to comment Share on other sites More sharing options...
FredG Posted November 9, 2016 Report Share Posted November 9, 2016 I wonder if dynamic propeller balancing might decrease the tendency for these cracks to occur. Dick, I agree that more planes will show cracks as the fleet ages. Link to comment Share on other sites More sharing options...
Roger Lee Posted November 9, 2016 Report Share Posted November 9, 2016 These cracks occur due to poor stress relief during welding and poor spring tension which allows the exhaust to vibrate in the sockets on top of the muffler. I find way too many springs that have no tension on them. The springs should have 1mm space between coils. Bottom line you should see some light through the coils. Do not fill your springs full of RTV like Vans does. Rotax used to use this 20+ years ago, but found they retained too much heat without the airspace within the spring which cause premature spring failures. They just broke. Just applying the RTV on the outside allows the spring to dump heat. Link to comment Share on other sites More sharing options...
Anticept Posted November 9, 2016 Report Share Posted November 9, 2016 I wonder if dynamic propeller balancing might decrease the tendency for these cracks to occur. Dick, I agree that more planes will show cracks as the fleet ages. Yes it does as it reduces vibration, and so does keeping the knuckles lubricated. Rotax mentions that when these lock up, cracking results. Install manual Ed 2 Rev 1, 78-00-00, page 3. We've had to repair several exhaust cracks before we got the issue under control by making sure the prop is pitched and balanced, and making sure a good antisieze is used. I strongly recommend nickel for the stainless steel exhausts as it lasts quite a long time, and copper is NOT compatible with stainless as it causes inter-granular corrosion! Link to comment Share on other sites More sharing options...
FlyingMonkey Posted November 9, 2016 Report Share Posted November 9, 2016 I wonder if dynamic propeller balancing might decrease the tendency for these cracks to occur. Dick, I agree that more planes will show cracks as the fleet ages. My prop had been dynamically balanced. I'm sure it would help, but it didn't save me from a failure. Link to comment Share on other sites More sharing options...
Andy Posted November 9, 2016 Report Share Posted November 9, 2016 Appreciate the info, guys. Just had to repair a muffler crack noticed after my last oil change. Link to comment Share on other sites More sharing options...
Runtoeat Posted November 10, 2016 Author Report Share Posted November 10, 2016 I brought this up because it appeared to me muffler cracking might be an issue which Rotax users could experience. Looks like this is an area Rotax owners must be aware of and should be looking out for on a frequent basis. I will be replacing some/all of my springs due to the "hooks" being worn as noticed at last conditional inspection. When I replace the springs, I'll also lubricate the joints with nickel based anti-seize. The first thing I did when i bought my CT was to have my prop balanced and pitched correctly. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted November 10, 2016 Report Share Posted November 10, 2016 The first thing I did when i bought my CT was to have my prop balanced and pitched correctly. It does make a huge difference. When I first got my CTSW the prop was poorly balanced, something like 0.6. After a dynamic balance it was 0.05, and the difference in smoothness was startling. I could no longer see the mushroom/binnacle slightly shaking while the engine was running... Link to comment Share on other sites More sharing options...
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