1948 C-170 muffler / exhaust cracks

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1948 C-170 muffler / exhaust cracks

Postby tshort » Fri May 22, 2020 1:34 am

The ragwing is in for annual. Unfortunately I am not participating as I normally do due to the damn virus.

In any case, my friend the A&P found cracks in both mufflers. C-145-2H:

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He called Aerospace welding, who he usually uses, and they won't touch them. Is there anyone who repairs these anymore? Is it worth repairing them? If not, where is the best place to source a new exhaust system? It is prime flying season and I hate to keep the plane down longer than I have to...

Thanks in advance for any advice / options.
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Re: 1948 C-170 muffler / exhaust cracks

Postby brian.olson » Fri May 22, 2020 9:46 am

Thomas - my A&P discovered a crack in one of my mufflers last fall, and after calling around to all of the larger and small companies we couldn't find anyone who would touch them. He successfully welded the crack (near the connecting point of one of the flanges) himself. During a thorough "smoke test" of the exhaust and intake systems we found a crack on the other muffler, and I'm currently using a borrowed muffler until I can get a new set of Hanlon mufflers ordered for the plane. I'm letting the "aircraft repair fund" get back in the black again before I do that.
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Re: 1948 C-170 muffler / exhaust cracks

Postby gahorn » Fri May 22, 2020 1:36 pm

AWI (Aerospace Welding Inc) is one of our supporters and Charlie Felds up there works with us price-wise also. He is familiar with the conversion to Hanlon Wilson types (which basically use two left-mufflers on both sides) per the approved service letter. (See the Mx Library) viewtopic.php?f=36&t=6919&p=61077&hilit=Hanlon+wilson#p61077

DO NOT MIX the two systems. DO NOT USE the 172 system on a 170 or 170-A. (Ignore the website RH muffler setup unless you have a 170-B)

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Re: 1948 C-170 muffler / exhaust cracks

Postby Bruce Fenstermacher » Fri May 22, 2020 8:52 pm

That IS NOT a crack in the muffler. It is a crack in the air heat baffle that surrounds the muffler to create hot air for carb heat and cabin heat.
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Re: 1948 C-170 muffler / exhaust cracks

Postby sfarringer » Sat May 23, 2020 2:33 pm

Bruce Fenstermacher wrote:That IS NOT a crack in the muffler. It is a crack in the air heat baffle that surrounds the muffler to create hot air for carb heat and cabin heat.


Not so sure, Bruce.

Looks to me like the outside half of the heat baffle is removed, and we are looking at the muffler.
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Re: 1948 C-170 muffler / exhaust cracks

Postby edbooth » Sat May 23, 2020 2:41 pm

Bruce Fenstermacher wrote:That IS NOT a crack in the muffler. It is a crack in the air heat baffle that surrounds the muffler to create hot air for carb heat and cabin heat.


I don't know a lot about the old pancake mufflers, but it looks like some blind rivets are going through the heat baffle into the exhaust pipes....??? If so, that is not good. :?
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Re: 1948 C-170 muffler / exhaust cracks

Postby tshort » Sat May 23, 2020 2:58 pm

The outer part of the heat muff has been removed. This is the inside part.

Does anyone have pics of the inside of this, or an exploded diagram? It is welded around the edges, and riveted to the exhaust pipes. you can see some blow-by where the riveted area is.

Depending on what the inside is like (how the exhaust is “isolated” from the outer material), I would think those cracks could allow exhaust to leak into the heat muff. I am not sure how easy or practical it would be to disassemble this and attempt repair.

I think the plan is going to be swapping this out for the new system mentioned above.
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Re: 1948 C-170 muffler / exhaust cracks

Postby n2582d » Sat May 23, 2020 6:12 pm

Thomas,
I'd agree with the plan to swap them out for the Hanlon Wilson mufflers. It's amazing to me that those pancake mufflers have lasted for over 70 years (assuming they haven't been replaced since 1950). Can't let this topic die without an additional CAA-approved SNL. :) Does anybody know how Cessna could determine that it was the length of the tailpipe that was causing the resonance leading to loose rivets? By the way, I like the way you added a heat shield to your engine mount adjacent to the muffler.
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Re: 1948 C-170 muffler / exhaust cracks

Postby tshort » Wed May 27, 2020 2:55 pm

So I am communicating with Charlie Feld at AWI; based on the pics of my system, he is not 100% sure the exhaust pipes will exit without cowl modifications. He suggested checking with the Association for input.

Can anyone who has done this on a ragwing comment? Do the pics above provide any reference - I have no idea if the exhaust pipes are as they were from the factory or not. The plane is as it was when I purchased it...
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Re: 1948 C-170 muffler / exhaust cracks

Postby sfarringer » Wed May 27, 2020 5:57 pm

On my Ragwing, the outlet pipe on one side had to be adjusted to line up with the cowling exit opening. Otherwise it fit fine. I forget which side needed the adjustment.
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Re: 1948 C-170 muffler / exhaust cracks

Postby tshort » Wed May 27, 2020 6:01 pm

Thanks for the info; how did you make the adjustment? Did it have to be sent back to AWI?

I was thinking we might have to mod the cowling (cut holes / patch stuff), but if a small mod to the pipe is acceptable that would be easier (and cosmetically better).
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Re: 1948 C-170 muffler / exhaust cracks

Postby sfarringer » Wed May 27, 2020 6:28 pm

My mechanic cut a wedge shaped sliver out of the pipe to allow the necessary slight bend, and welded the pipe back together. It wasn't a big task.
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Re: 1948 C-170 muffler / exhaust cracks

Postby Bruce Fenstermacher » Wed May 27, 2020 9:35 pm

Your pancake muffler exit pipes look typical.

When these aircraft where new, if you had swapped in a '52 B model Hanlon Wilson system for the pancakes, which is the replacement, the exit holes would have worked. As these cowls are now 70 years old, I'd expect a little trimming out of the exit holes might be in order.
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Re: 1948 C-170 muffler / exhaust cracks

Postby gahorn » Wed May 27, 2020 10:44 pm

It’s my opinion the better action is to adjust the cowling tailpipe exits. In that fashion, if future exhaust work is required the standard tailpipes will fit. If you change the tailpipes then future work will be required on replacements.

And on a slightly different note... if I planned to alter the standard tailpipes.... I’d first consider saving that money ordinarily spent on standard pipes and applying it toward the “Bartone” tailpipes.
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Re: 1948 C-170 muffler / exhaust cracks

Postby tshort » Sat Jun 06, 2020 3:39 am

So, the new mufflers have been received and fit up nicely. No issues with the cowl exit.

One issue. The diagram for the Hanlon-Wilson modification references a support bracket. This is #5 in the diagram.

I did not have any bracket / support on the old pancake mufflers. I discussed with Charlie Feld, this is not something they include / fabricate. He thought it might be p/n 0450340-1, which is used on the C-150 system and the C120/140 modification.

What is the correct part here?

Thanks in advance for all the help thus far. I am ready to get flying again!
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