Exhaust leak

[Warmi]

When changing oil today I discover what looks like an exhaust leak. I haven't noticed anything different about the plane recently and my CO detector has been pretty quiet.

I don't see any cracks and it looks like it is coming from the joint ( at the yellow arrow on the second picture ). How would you go about addressing it ? Wrap it ?

Thanks

Symptom:

OilTank.jpg (113.09 KiB) Viewed 1782 times

Cause:

OilTank2.jpg (129.31 KiB) Viewed 1782 times

[drseti]

Yes, Warmi, it certainly looks like a leak at the sliding joint. Typically, that's caused by stretched muffler springs. I'd replace all 8 just as a precaution - if one sags, the others are about to. Don't wrap those joints, because if they're not free to move somewhat, you'll probably end up with exhaust cracks. And, in addition to running safety wire through the springs, I recommend squeezing a heavy bead of high-temp RTV along the length of each one.

[ShawnM]

I suspect that with the vibrations of the engine and exhaust it may only be leaking during start up or a certain rpm when the vibrations are bad enough that the springs can't hold the pipes together properly. Once running smooth it doesn't leak and that's why your CO sensor hasn't picked up anything.

What strikes me as odd is how close the oil canister is to your exhaust. Seems like being that close would heat the oil prematurely for no reason. I'm surprised there's no heat shield between the two components.

Here's a pic of my springs with the high heat RTV on them like Paul suggested. This helps dampen the vibration in the springs and they last longer. The safety wire is an added precaution to retain the parts if/when they break. Not really that important in a tractor configuration but for pusher aircraft this is a must. If the spring breaks it could very easily go into the prop and cause more damage or worse.

exhaust springs (Small).JPEG (37.57 KiB) Viewed 1747 times

[drseti]

Warmi and Shawn, I'm putting together a webinar on common Rotax problems and issues. Given my ongoing legal battle over educational fair use of copyrighted material, I'm not taking any chances. May I have permission from each of you to use in my PPT slides the photos you've posted on this thread?

[Wm.Ince]

. . . . I'm putting together a webinar on common Rotax problems and issues.

Excellent Doctor!
I am looking forward to that. Enjoy all your Webinars immensely.
That particular one should draw a big croud.

[3Dreaming]

Just a thought on the safety wire. I have seen cases where it was installed, but with to much tension. The wire needs to be tight enough to hold the joint some what in place if the spring fails, but loose enough that that the spring is holding the tension on the joint. In Shawn's picture they look too tight to me, but I would need to see it in person to know for sure. I do mine a little different, but it also take longer. I loop the wire through the bail and twist the wire. The length of the twist is down the the other bail plus 1/8" or a little more. I then stick both ends of the free wire through the spring and one end goes through the bail and the other outside of the bail, then twist the free ends. This way the wire secures the spring, provides a fail safe for the connection, but places no pressure on the joint unless the spring fails. Looping through like Shawn shows is okay, but you need to make sure that he wire stays a little loose, so the spring can do its job.

[Warmi]

Warmi and Shawn, I'm putting together a webinar on common Rotax problems and issues. Given my ongoing legal battle over educational fair use of copyrighted material, I'm not taking any chances. May I have permission from each of you to use in my PPT slides the photos you've posted on this thread?

Sure. No problem.

[3Dreaming]

Something else about these exhaust joints are that they need cleaned and lubricated with an appropriate anti seize compound. I do this anytime the exhaust is removed, and absolutely during the 5 year rubber replacement at a minimum.

[Warmi]

Thanks Guys.
I am gonna replace these 2 springs right now and see if it fixes the problem and then have the rest replaced ( including lubrication ) during my next annual.

Shawn...
Yeah, as far as the oil tank it does seem close but it is not specific to my particular plane - there are close to 1000 various Stings and Sirius planes out there with that very oil tank/exhaust design so I guess it is not a big deal - I don't have any issues with oil overheating or anything along these lines ( unless I forget to take the aluminum foil tape off of the oil radiator when it gets above 40F but that's another story ... )

[ShawnM]

Warmi and Shawn, I'm putting together a webinar on common Rotax problems and issues. Given my ongoing legal battle over educational fair use of copyrighted material, I'm not taking any chances. May I have permission from each of you to use in my PPT slides the photos you've posted on this thread?

Sure, no problem here either Paul. If you need the original higher res image let me know, I resize my pics before I upload them.

These springs and RTV in my photo are now 7 years old (I changed them and added the RTV when I bought the plane) and they haven't caused any issues whatsoever. I feel the safety wire is loose enough as you can wiggle is and squeeze the runs together. That is hard to tell from a photo. I think they have enough play to be effective but also understand Tom's point as well.

Warmi...
I assumed it wasn't an issue I just thought it was od to have the two so close to each other. Heat being the enemy of oil.

[Warmi]

Another question ...

Last week after changing the oil, filter etc .. I did my usual 20 prop pulls until the burp sound and then went out there to start the engine.
As I remember , normally it takes maybe 3 or so seconds for oil pressure to come up after a typical oil change but this time it took about 6 , maybe even 7 seconds. I was about to shut down the engine cause frankly I started to panic a bit that something went wrong but then it shoot up right away to 67 PSI ( it was about 50 degrees outside ) and kept steady at that slowly decreasing as the engine was getting warmer.

Now , we did disconnect the oil tank since we cannot really drain the oil without taking the tank out on my Sting but we kept the lines closed and up in the air so no oil was leaking out of them - there is no other way to do it on this plane since ( as you can see on the picture ) the oil plug is completely inaccessible when the tank is mounted - if we wanted to follow Rotax procedure exactly as written, we would have to do the full oil purge every time we change the oil.

Now , not having any indicated oil pressure for that long freaked me out a bit so I am wondering is it really advisable to do what I am doing ( reading on the rotax-owner site posts from our own Roger Lee and others indicates that it is ok as long as we don't drain the oil from the lines) - but I am still wondering .. what do you guys think ?

[drseti]

I personally pull the tank out for cleaning and desludging at every 100 hour condition inspection, and always do a purge afterward.

[3Dreaming]

I personally pull the tank out for cleaning and desludging at every 100 hour condition inspection, and always do a purge afterward.

Do you do a purge if you just drain the tank to change oil?

[drseti]

No, Tom, just when I remove and clean the tank.

[ShawnM]

I learned that anytime you "open" the oil system by removing lines to remove the tank you have to purge the oil system BEFORE you start the engine. Rotax states in their latest maintenance manual in chapter 12-20-00 section 11.6:

Purging the oil system is necessary:
-before each first start up (e.g. after overhaul)
-after maintenance work during which the lubrication system was opened and voided.
-when engine was cranked with open oil lines (e.g. during oil change).
-when oil system or oil lines were blown through with compressed air.

Removing the tank "opens" the oil system and this means it's necessary to purge the oil system. This procedure is spelled out in SI-912-018 and must be followed "meticulously" according to the manual. Starting an engine without purging it may cause damage. This is what I was taught by my old LSRMA.