× PA-30/39 Twin Comanche

Question pa-30 exhaust cracks

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01 Dec 2023 11:43 #4155 by Kristin Winter
Replied by Kristin Winter on topic pa-30 exhaust cracks
I would get rid of that cross-brace. I have never seen that before on a Twin Comanche and it is likely to introduce additional stresses. As the engine heats up, the cylinder get longer. That is why there is the slip joints in the crossover. That cross-brace keeps the end of the exhaust from moving away from each other than the engine heats up. That will put a torsional stress on the #3 and #4 riser.

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01 Dec 2023 11:11 #4154 by Masa Hirvonen
Replied by Masa Hirvonen on topic pa-30 exhaust cracks
Hi Kristin,
I made a reminder to myself to apply anti-seize to the expansion joints periodically (my friend has a Mooney with an upgraded engine and he has to do that at every annual, but I think it's a good thing). I have attached another picture of the rear of the original stacks - there was a lot of hardware down there that was not per the Piper design. I am sure someone had all the good intentions, but with the front expansion joint completely frozen and the rear clamped down like that, I can see why the #4 cylinder stack failed and no, the original (how I bought the plane)/failed stack did not have any ball/slip joints on the riser for #4. We (my mechanic and I) ended up removing the extra hardware at the rear but made sure that the vertical support was still there (per the Piper design). The rebuilt stack had this ball joint on the #4 riser.

I can't remember the exact sequence but I think I ended up buying one rebuilt set of stacks first and then, when I removed the broken one - I sent that set for an overhaul/rebuild, and when I got that back, I ended up with all rebuilt stacks. That gives me peace of mind.

-Masa
 
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01 Dec 2023 09:19 #4153 by Kristin Winter
Replied by Kristin Winter on topic pa-30 exhaust cracks
Now that I can look at the pictures, does that stack that separated have an expansion ball/joint? Was that a component that AWI worked on?

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01 Dec 2023 09:16 #4152 by Kristin Winter
Replied by Kristin Winter on topic pa-30 exhaust cracks
Hi Masa!

I do have the expansion balls/joints, whatever, on the riser. Two observations I have about the exhaust on the PA-30. If the hangers at the tailpipe end are not providing some support, larger stresses are put on other parts of the system. Also, the slip joints are key. Whenever I separate or otherwise install the, I liberally apply C-5 copper anti-seize. With an already installed unit, a little Mousemilk wouldn't hurt, though how much it might help I can't say.

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01 Dec 2023 08:43 #4151 by Masa Hirvonen
Replied by Masa Hirvonen on topic pa-30 exhaust cracks
OK, let me try those photos in a different way (it seems like my original captures did not come through).
-Masa
 
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01 Dec 2023 08:40 #4150 by Masa Hirvonen
Replied by Masa Hirvonen on topic pa-30 exhaust cracks
Hi Kristin,
This is the first time using this forum, so I apologize if something looks goofy with my photos, etc.

The first pictures are after my own ferry flight literally across the whole country - from Oregon to North Carolina. This must have happened towards the end because you can't see much exhaust gas traces anywhere near that hole. After that spooked me enough - I gradually replaced all my stacks on both of my engines with rebuilt ones. I got them from a couple of sources, AWI was one of them. One of my expansion joints up front was like welded together - it took all my strength and a couple of tricks to get them loose.

To answer your question: I don't have a sliding expansion joint on #4, but I have that "ball joint" to give it some degree of freedom (you can see that in the last picture). And to answer your other question: it cracked near where this new "ball joint" is located (I like to think there is a good reason for that joint).

Everything has worked fine since I replaced everything.

-Masa


[img]blob:https://piperflyer.com/cc66c85e-7f05-45fd-8f2b-4805334a980e[/img]

[img]blob:https://piperflyer.com/ba4f09f6-8352-4220-af85-a6b7ce65835e[/img]

[img]blob:https://piperflyer.com/f1cf9350-2007-416b-a977-775f87e09bff[/img]
 

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