Exhaust break

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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drdehave
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Re: Exhaust break

Postby drdehave » Fri Sep 29, 2017 11:58 am

1. Dave: I've had exactly that same break (plus one break at a weld to the plate) on one of my "arms." Mine was caused by the bolt loosening, despite the thread-lock. Since then, I always paint those three bolt-heads with torque-seal and check them every few hours. The only question now is: Was this the source of your vibration or just another symptom of some other source? If that "better than new" weld (I heard that one a few times) is going to let go, you'll likely know within 50 hours. When they start to crack and let go you can hear a definite change in the engine tone (plus vibration in the rudder pedals)--a good reason to start up before putting your noise-cancelling headset on, if you use one.

2. Roger: Yes, the misplaced temp sensor on that pipe was TL's doing--that's where the original was, despite Rotax's guidance. The latest and greatest new pipes from TL aren't pre-drilled anymore, so presumably one can get it closer to spec location, given clearance issues. I do see a wider range of the four EGTs than most folks and this is no-doubt why.
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Wm.Ince
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Re: Exhaust break

Postby Wm.Ince » Fri Sep 29, 2017 12:38 pm

roger lee wrote:In the picture above on the welded coupled weld it shows the EGT about 1" - 1.25"" away from the head exhaust port. These should be 3.9" (4" works) or 100mm away from the exhaust port.

Okay.
So what's the fix?
Bill Ince
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Retired Heavy Equipment Operator

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drseti
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Re: Exhaust break

Postby drseti » Fri Sep 29, 2017 5:45 pm

MrMorden wrote:
What “cold tin” do you mean? The exhaust pipes are many hundreds of degrees, especially close to the cylinders.


Cold is a relative term, Andy. Yes, the pipe is at several hundred degrees, but the combustion chamber (where the lead gets vaporized) is several thousand. So, when the lead vapors come out of the exhaust port and hit the (relatively cooler) pipes, they condense, and coat the insides of the pipe (even somewhat near to the exhaust port) with lead.
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Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS/PPC, iRMT
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roger lee
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Re: Exhaust break

Postby roger lee » Mon Oct 02, 2017 12:15 am

Wm.Ince wrote:
roger lee wrote:In the picture above on the welded coupled weld it shows the EGT about 1" - 1.25"" away from the head exhaust port. These should be 3.9" (4" works) or 100mm away from the exhaust port.

Okay.
So what's the fix?



Plug that hole and drill another in the right place.
Roger Lee
Tucson, Az.
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(520) 574-1080 (Home) Try Home First.
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drdehave
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Re: Exhaust break

Postby drdehave » Mon Oct 02, 2017 12:50 pm

roger lee wrote:
Wm.Ince wrote:
roger lee wrote:In the picture above on the welded coupled weld it shows the EGT about 1" - 1.25"" away from the head exhaust port. These should be 3.9" (4" works) or 100mm away from the exhaust port.

Okay.
So what's the fix?



Plug that hole and drill another in the right place.


Roger, all four of the exhausts are of TL manufacture. The distance they are using (as shown in the picture below--except for the far right example, which is another ready-to-go "sleeved repair" in case I ever need it) is about 1.50-1.75 inches, from the port to the temperature sensor. The sensor is also elevated by a raised "bung" so that only the tip of the probe extends into the pipe, thereby disturbing "flow." That is evidently where & how TL engineers wanted the probes placed in their pipes. It seems to me, I'd need a LOA from TL to move it to the 4.0-inch position, with or without the probe extending fully into the pipe, and that in our case (Stings) the "right place" is what TL uses. No?--Rich
tubes 001 (747 x 1328) (560 x 996).jpg
tubes 001 (747 x 1328) (560 x 996).jpg (203.84 KiB) Viewed 291 times
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roger lee
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Re: Exhaust break

Postby roger lee » Tue Oct 10, 2017 9:08 am

There have been several aircraft Mfg's that don't follow Rotax specs for whatever reason. Some of these companies have had issues because of it especially with the 912iS engine. The 100mm (4") comes right out of the Rotax installation manual. It would have been just as easy to put the probe where it was supposed to go as it was in the wrong place. I don't understand why some Mfg's think they know better or more than Rotax who's been building engines since 1920 and the 912 series for the last 27 years and has done all the testing.
I see owners get LOA's and sometimes I see them just fixing the issue without an LOA. Have you called TL and ask why they mounted it there and why they went against the installation manual? If you want to fix it you have two choices. Call them and see if they will give an LOA or just do it. You're not removing or adding it just moving back a couple inches.
Roger Lee
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drdehave
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Re: Exhaust break

Postby drdehave » Mon Dec 11, 2017 7:50 pm

A few days ago, the Hobbs on my 2007 Sting ticked through 2,270 hours. And whilst flying, I thought I noticed a change in "tone" of the engine, especially during start-up & whilst taxiing. Right then, I should have pulled the cowlings off for a look-see, but I didn't. :shock:

Then, today, after flying again, I did pull the cowlings--to remove the air filters (to take home) for service. I was greeted by this broken #1 exhaust (sorry, unable to upload the picture, today). No problem, I thought. That's why I keep all those spare parts. I'll just go grab a replacement. That's when I found the bad news: I have TWO #2s, but NO #1s on the shelf! :oops:

Now, I am once again at the mercy of SportairUSA and/or TL Ultralight. I don't like being in this place. I do hope they have one on the shelf tomorrow, when I call :roll: We'll see.

Also, I am now nearly 3 months into going without my whole-plane parachute, which was removed and sent to the Czech Republic for service back in September. That's a whole other sordid story that I will report on when it comes to a conclusion... :oops: Stand by.
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drdehave
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Re: Exhaust break

Postby drdehave » Wed Dec 13, 2017 12:19 pm

Update on that exhaust break I reported 2 days ago: The break was where one end of the flex tubing enters one "hard" section of exhaust tubing (Sorry, I would post a picture, but my photo privileges here were apparently revoked, for excessively gaming the system and contributing too heavily to filling up the Chief's private server. Frankly, I'd be quite happy to pony up a $100 or so a year to get them back, if that would help the situation.)

Anyway, back to the story. Because that "flex" stuff is rather thin and flimsy, my welder and I had very little hope of welding it back to the hard tubing, but I asked him to give it a shot anyway. He did. It looks good and seems to be holding. I flew it successfully (no break/crack) for 0.6-hr yesterday and will be testing it some more the rest of this week.

But here's the rub. After talking to the parts guy, Greg, at Sportair, I discovered that just the flex portion CAN be replaced! It's a "rub" because for 7 years, I've been buying the whole assemblies from Sportair and TL when they have broken--at a total cost of many hundreds, if not thousands, of dollars. The roughly 5-inch pieces of replacement "flex" should be comparatively inexpensive; I ordered two pieces.

What I don't know yet is just how the old flex is removed and the new piece is installed. It is NOT welded (You'd see why, if I could post a picture), I know that. But as soon as I get details--and do it once--I'll report back here. My guess is we heat up the hard part of the tube and press the flex piece into it.

Smooth flying until later...
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FastEddieB
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Re: Exhaust break

Postby FastEddieB » Wed Dec 13, 2017 12:26 pm

If it’s not gaming the system, email me the photos and I’ll post them. FastEddieB@mac.com

I’m curious to see what you’re talking about.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
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drdehave
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Re: Exhaust break

Postby drdehave » Wed Dec 13, 2017 1:19 pm

Actually, Eddie, you can see it in the earlier picture I WAS able to post prior to getting axed, up above in this thread. See that photo of all the exhaust tubes? See the shinny one? That flex section appears to be pressed into the two hard ends of tubing. I see residue of some paste--either an adhesive or something used as a lubricant. The whole shinny tubes--i.e.,assemblies, are what I've been buying, until now. For the temporary repair we just made (until I get new pieces of flex), we just welded the flex (where it failed) directly to the outside of the tube.

And by the way, all this discussion of multiple exhaust tubes failing on my 2007 Sting airplane are in no way an indication of its Achilles heal. Most of the trouble I've had in this area (broken/cracked exhausts) relate back to TWO successive bad Woodcomp SR200 propellers that I had, in which ONE blade became warped AFTER use, causing excessive vibration throughout the airplane. :lol:
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