Exhaust Leaks

[GrassStripFlyBoy]

Yesterday did a bunch of PM work, oil change, new carb bowls, plugs, gascolator clean, and general overview of inspecting and tightening up things - all is normal and test flight has it running smooth as silk. 

I needed to tighten cyl #4 header tube nuts again, these seem to slowly loosen up and I retighten every oil change ~ 50 hours, nothing crazy - maybe a 1/4 turn or less on both, just enough looseness that grabbing the header tube allows a tick of a wiggle.  But I wonder why this location loosens and other three never do.  I suspect the studs might be turning and not the nut, but have not confirmed, has anyone seen this and does a new properly installed stud correct it, or maybe these nuts have lost their anti rotation strength, they are rusty looking and probably original?

Second, the socket interfaces of header tubes to the muffler are leaking slightly, springs are holding compression, again these are not gross leaks but would like to tighten up.  When I first bought plane several were zero spring compression being loose, I bent the spring tabs to develop some compression, and after 100 hours they remain holding as I bent them, still not much compression though.  Wondering what other solutions may be possible for this interface.

Thanks, Darrell

 

[Roger Lee]

Typically the studs do not require any sealer or Loctite, but there have been some instances where they have a slight leak or a tad lose and Loctite can be applied to the threads. We talk about this in some of the Heavy Maint. classes.

The knuckles where the exhaust pipe meets the muffler joint can and do leak many times. This is either caused by the knuckle out of alignment which I fix many times by loosening the exhaust stud nuts and pushing the muffler over an inch or so or by tighten the springs some by widening the gap between the springs by bending the loops outward a tad more or I just apply a piece of header wrap around the knuckles if you don't want to wrap the whole exhaust pipe. I prefer wrapping the entire pipe and have probably done that to 75 plus CT. Many other have wrapped their own pipes.

[GrassStripFlyBoy]

Thanks Roger - did a quick search and located your post with pictures, looks like the wrap and clamp would be a good countermeasure for this slight amount I'm dealing with.  One more item on the to do list.

[Roger Lee]

To wrap all 4 exhaust takes about 1 hr. a few clamps and the 2" header wrap from an auto parts place.

[sandpiper]

If Roger says it takes him an hour I know it will take me two. As an aside, never bet him that he can't do something in the time he says he can do it. You'll be paying up. Ask me how I know.

[Roger Lee]

3 hours ago, sandpiper said:

If Roger says it takes him an hour I know it will take me two. As an aside, never bet him that he can't do something in the time he says he can do it. You'll be paying up. Ask me how I know.

And that's while I'm eating a sandwich. LOl

Hi John,

Nice t here from you. Hope all is well. Why don't you come back down to Marysvale, UT in Sept.

[sandpiper]

23 hours ago, Roger Lee said:

And that's while I'm eating a sandwich. LOl

Hi John,

Nice t here from you. Hope all is well. Why don't you come back down to Marysvale, UT in Sept.

We might just do that!

[Roger Lee]

10 hours ago, sandpiper said:

We might just do that!

We'll be in Marysvale, UT from Sept. 6 - 30th. If you do want to come it may have lots of people so better make reservations now. If something comes up you can always cancel. I'm in space 70. 

[ls6pilot]

I just wrapped one pipe due to leak at knuckle. 2 things I learned

1. If in SC in summer do it early morning.

2. Take the damn springs off.

[Roger Lee]

Hi Rich,

Taking springs off can help, but I'm guess I'm too lazy.  Then I have to put them back on and safety wire them.  Some spring gaps between the pipes are certainly wider than others. For the loser ones I just pass the header cloth under the springs. For the tight springs I use a screwdriver  to poke it through to the other side and then pull it the rest of the way through with a pair of needle nose pliers. Then just open the clamp up and pass it between the cloth and spring. So far I haven't had to remove the springs.

 

Look at it this way. It's done.  

[FlyingMonkey]

My exhaust joints leak quite a bit, but I don't think wrapping them is going to stop that, it just leaks under the wrap and since the wrap is not gas-tight the gasses just get out anyway.  If the leak is strong enough the heat and gas pressure will eventually degrade the wrap.

The only way I know of to reduce leaks is to adjust the exhaust system by loosening at the cylinder and adjusting the pipes.  Additional anti-seize at the joints *might* help.  Frankly, I don't really worry about exhaust leaks too much; my pipes have always had dust plumes at the joints indicating leaks to some degree, and I've never gotten a high CO indication in the cockpit. 

If you want to wrap your pipes to reduce under-cowl temps that's cool, but if you are doing it to stop or reduce leaks, IMO you're barking up the wrong tree.

[ls6pilot]

Well I agree about the co in the cockpit. I have seen no indications on my monitor. This will be a test as the springs on the front of the 1/3 side didn’t last a year due to the Heat from the  blow by. Will let you know in a year. 

[FlyingMonkey]

7 minutes ago, ls6pilot said:

Well I agree about the co in the cockpit. I have seen no indications on my monitor. This will be a test as the springs on the front of the 1/3 side didn’t last a year due to the Heat from the  blow by. Will let you know in a year. 

Did you use RTV on the springs?  My springs are dusty and discolored from blow-by, but I have not lost one in a couple of years.  If you are breaking multiples in a 12 month period I'd say something is going on, maybe the pipes are adjusted in a way that leaves the springs stretched too much, or inadequate silicone to cushion vibration?

[ls6pilot]

I did use rtv. I did get that pipe adjusted better this year so that may also help.  Will see.

[Tom Baker]

There are 2 different lengths of springs too. I have found that if the spring is over stretched it will tend to break. Also the actual black Rotax spring that they changed to is junk. I use one of these depending on the length from Leading Edge Airfoils.

https://www.leadingedgeairfoils.com/exh-2s-stainless-steel-exhaust-springs.html

https://www.leadingedgeairfoils.com/exh-4s-stainless-steel-exhaust-springs.html

Also on the subject of leaks. Anytime you have the exhaust off remove the pipes and clean the joints with some Scotchbrite, then coat them with anti seize.

[FlyingMonkey]

1 minute ago, Tom Baker said:

There are 2 different lengths of springs too. I have found that if the spring is over stretched it will tend to break. Also the actual black Rotax spring that they changed to is junk. I use one of these depending on the length from Leading Edge Airfoils.

https://www.leadingedgeairfoils.com/exh-2s-stainless-steel-exhaust-springs.html

https://www.leadingedgeairfoils.com/exh-4s-stainless-steel-exhaust-springs.html

I had noticed the two different spring types, one metal colored and one black.  Good to know there is a quality difference.  I have used both and don't think I've had a problem, but I could just be lucky.

Are the Leading Edge springs two different lengths?  It looks like a single part number.

[ls6pilot]

Looks like 

H4452 And H4451. Thanks guys. 

[FlyingMonkey]

4 minutes ago, ls6pilot said:

Looks like 

H4452 And H4451. Thanks guys. 

4452 is for a 9mm longer hook distance, but it's also listed as a 582 spring.  Not sure that's what you want.

[Tom Baker]

I've had some that long spring wasn't even quite long enough. 

[Roger Lee]

There are the two types and either can work. The heavier stainless spring and the black metal spring.

There should be no more than a 1mm space between coils. That's roughly a fingernail thickness.  Over stretching can lead to early spring failure. Too little tension allows the muffler joint to pulsate while the engine is running and can crack and break the joints. You really need to apply the high temp silicone  on the springs too. Not a little tiny pencil bead, but make it 1/2' wide and about 1/8" thick and force it between the coils. Do not fill the spring with the silicone . This cause too much heat retention and early failure of the spring. The spring does far better with the air gap within itself. Safety wire should go down inside the spring and it should not be pulled super tight in the thinking the safety wire is to help hold the joint together. It should be a tad loose. I don't recommend wrapping the wire through the middle and around the pipe. This put the muffler heat directly onto the spring coil and if the spring breaks in many places other than the hook then that half can fall out of the aircraft. Down through the middle retains the spring no matter where it breaks.

[FlyingMonkey]

4 hours ago, Tom Baker said:

I've had some that long spring wasn't even quite long enough. 

So would you order half of the 4451 and half the 4452 springs?

[Roger Lee]

Either of these will work just fine. I have used them both. I tend to use the 938-795. Both are for the 912ULS or UL. Maybe in your wet climate the stainless would be better. It is a stiffer spring.

 

https://www.cps-parts.com/catalog/rtxpages/rotaxspring.php?clickkey=3013536

https://www.cps-parts.com/catalog/eppages/gplssexhaustspring.php?clickkey=3013536

 

 

[FlyingMonkey]

Thanks Roger.