The International Cessna 170 Association

Hey everyone,

I just replaced my O300's right hand muffler because the old one had cracks, and most of the internal baffles/piping had broken and fallen out.

Anyway, my mechanic ordered and installed a replacement (Acorn Exhaust P/N 0550157-32), however, the replacement looks slightly different than the new one. The new one does not have the circled flanges.
After I got the plane back from my mechanic, I taxied and did a run-up, and my carbon monoxide detector went off. The new exhaust is leaking somewhere.

Could it be because the new exhaust does not have the flanges? Is it possible the new Acorn Exhaust https://www.acornwelding.com/pub/media/ ... 0_170A.pdf is the wrong one? It's still P/N 0550157-32

Also, I'm needing the following parts:
#40
#41 Anyone have a lead where to get them for cheap?

reecewallace wrote: Also, I'm needing the following parts:
#40
#41

Anyone have a lead where to get them for cheap?

Anyone know where to buy them at ANY cost should be your question. No one seems to make them. They are not seals really but hold the shape of the outside baffle. As they haven't been available for sometime I would suspect quite a few systems don't have them.

There is a tread discussing how they might be or perhaps where made from cutting sections of aluminum pipe.

As for the leaks or quantity of leakage you are experiencing, can't say if the lack of flanges have anything to do with it. But this system has many areas prone to some leakage, nearly impossible to eliminate all of it. The key is to reduce them to a minimum. I'd have your mechanic look it over and see what he can do.

What may not be clear in this thread is the difference between “flanges” and “seal” . The muffler tubing has a flange built onto it to support the heater muffs and to reduce loss-of heated air into the lower cowling. The “seals” (made of soft aluminum pipe and bent to shape) further reduce heated air losses.

GAHorn wrote:What may not be clear in this thread is the difference between “flanges” and “seal” . The muffler tubing has a flange built onto it to support the heater muffs and to reduce loss-of heated air into the lower cowling. The “seals” (made of soft aluminum pipe and bent to shape) further reduce heated air losses.

I'm speaking about two different items—'flanges' which are built into the muffler exhaust fittings, and the aluminum 'seals'

The new muffler I just installed does not have flanges, and I was wondering if this could possibly be causing some of the leaks.

reecewallace wrote:

GAHorn wrote:What may not be clear in this thread is the difference between “flanges” and “seal” . The muffler tubing has a flange built onto it to support the heater muffs and to reduce loss-of heated air into the lower cowling. The “seals” (made of soft aluminum pipe and bent to shape) further reduce heated air losses.

I'm speaking about two different items—'flanges' which are built into the muffler exhaust fittings, and the aluminum 'seals'

The new muffler I just installed does not have flanges, and I was wondering if this could possibly be causing some of the leaks.

OK, thanks for clarifying. I JUST NOW got off the phone with our supporter at AWI (Aerospace Welding) and talking to Charlie Feld who responded thusly:

The “flanges” (referred to as “saddles” at AWI) support the heater-shroud and they provide some “blockage” to air leaks at that point (see further comment by me below.) * Some mfr’s (like Acorn apparently) do not always include them on their PMA’d mufflers…. AWI does.

The “seals” are extremely difficult to find…. but Charlie says they can provide them…and he apologized for the cost (but they are mfr’d by an outside provider under special-order)… our Assoc’n discount is $95 for seals. (Be aware that they are different part numbers and dimensions at each position on the muffler…consult the IPC.)

Charlie agrees that the seals are not critical and if missing do not appear to adversely affect operations.

* ReeceWallace: To answer your specific question about the flanges/saddles: NO! Their absence is not likely what is causing your Carbon Monoxide detection…but their absence may be allowing it to enter your system…..The flanges/saddles provide support for the heater shrouds and improve heater operation by reducing heat-exchanger losses…but they may also reduce the amount of CO….Carbon Monoxide…. that can enter from the exhaust Riser Clamps (PNs 0550157-50) just above. Those clamps are notorious for leaking and the exhaust gases may be squirting down toward the shroud where it meets the riser/entrance to the muffler…allowing gases with CO to enter the system.** This can pollute your cabin heat/ventilation and introduce CO to the cabin, especially I would imagine, on the ground where relative wind is greatly reduced and therefore not pressurizing the air beneath the shroud as it will in-flight.

If your ACORN muffs do not have the flanges/saddles…. I would question them as to “why not?”….because the original Hanlon-Wilsons did as issued by Cessna.

** I solved the leaks at my clamps and discussed it here: viewtopic.php?f=24&t=14367&p=134741&hil ... il#p134741

Those saddle type exhaust clamps cause all sorts of problems and it’s nearly impossible to get a perfect metal to metal seal. We tried sand blasting them before refittment and they still leaked. So our “rule “was use a commercial available muffler putty on the inner sides of the clamps and when fitting use a stainless steel washer under the head of the bolt and another stainless washer under the nut . Use the appropriate heat proof nut /bolt also. All surfaces have to be very clean via sand blasting .

GAHorn wrote:

reecewallace wrote:

GAHorn wrote:What may not be clear in this thread is the difference between “flanges” and “seal” . The muffler tubing has a flange built onto it to support the heater muffs and to reduce loss-of heated air into the lower cowling. The “seals” (made of soft aluminum pipe and bent to shape) further reduce heated air losses.

I'm speaking about two different items—'flanges' which are built into the muffler exhaust fittings, and the aluminum 'seals'

The new muffler I just installed does not have flanges, and I was wondering if this could possibly be causing some of the leaks.

OK, thanks for clarifying. I JUST NOW got off the phone with our supporter at AWI (Aerospace Welding) and talking to Charlie Feld who responded thusly:

The “flanges” (referred to as “saddles” at AWI) support the heater-shroud and they provide some “blockage” to air leaks at that point (see further comment by me below.) * Some mfr’s (like Acorn apparently) do not always include them on their PMA’d mufflers…. AWI does.

The “seals” are extremely difficult to find…. but Charlie says they can provide them…and he apologized for the cost (but they are mfr’d by an outside provider under special-order)… our Assoc’n discount is $95 for seals. (Be aware that they are different part numbers and dimensions at each position on the muffler…consult the IPC.)

Charlie agrees that the seals are not critical and if missing do not appear to adversely affect operations.

* ReeceWallace: To answer your specific question about the flanges/saddles: NO! Their absence is not likely what is causing your Carbon Monoxide detection…but their absence may be allowing it to enter your system…..The flanges/saddles provide support for the heater shrouds and improve heater operation by reducing heat-exchanger losses…but they may also reduce the amount of CO….Carbon Monoxide…. that can enter from the exhaust Riser Clamps (PNs 0550157-50) just above. Those clamps are notorious for leaking and the exhaust gases may be squirting down toward the shroud where it meets the riser/entrance to the muffler…allowing gases with CO to enter the system.** This can pollute your cabin heat/ventilation and introduce CO to the cabin, especially I would imagine, on the ground where relative wind is greatly reduced and therefore not pressurizing the air beneath the shroud as it will in-flight.

If your ACORN muffs do not have the flanges/saddles…. I would question them as to “why not?”….because the original Hanlon-Wilsons did as issued by Cessna.

** I solved the leaks at my clamps and discussed it here: viewtopic.php?f=24&t=14367&p=134741&hil ... il#p134741

Thanks for all the info.

We did a leak down test today, and the majority of the leakage was where the exhaust pipe is clamped onto the bottom of the muffler. It was quite a loose fit and carbon monoxide was traveling upwards into the shroud then blowing into the cabin. I wrapped the top of the exhaust pipe with adhesive aluminum tape, then inserted the muffler inside this. It created a tight seal, albeit maybe only a temporary fix. I did a run-up and flight, and there was ZERO CO in the cabin.

After reading your response though, it sounds aluminum is not the right material to use. I'll find some stainless steel foil, and redo it with this. The correct seals from Acorn Welding are almost $400 for the 3 of them!

Because of a general perception that the exhaust doesn’t do much for flight …and because the parts are expensive….Exhaust systems are often neglected.
Even experienced aircraft inspectors are prone to neglecting the exhaust. (I bought a 172 with a recently-overhauled engine, fresh paint/interior, and a Very-recent annual inspection (less than 30 hrs since annual) which had Both Mufflers eaten-out at the ends and leaking so much exhaust it could be smelled in-flight. (Discovered during climb-out in weather, a quick return was not appropriate as I was departing to beat a thunderstorm moving onto the field. Fortunately the “Cabin Air” shut-off worked. CHECK YOURS anytime the cowling is removed, i.e., oil changes etc. Opening wing-root vents and bringing-in fresh air was also helpful to increase cabin pressure to keep exhaust fumes out.)

If the tailpipe is loose upon the muffler lower exit then it has likely “thinned” out from vibration, which makes for a loose fit. A new tailpipe might be in-order. Tight-fitment is important for all exhaust fittings.

I recently did some minor exhaust repairs involving a small amount of stainless steel foil. I located some through Grainger Industrial Supply. It was not cheap-about $50 for the roll but it should last me and everyone I know a few lifetimes of exhaust repairs. I notice you are Canada so it would probably take too long for me to send you some. Another friend of mine used stainless steel foil from the local hobby shop. It is a much smaller roll but no less effective (and way cheaper). Knife makers use stainless steel foil as well, under the name of Heat Treating Foil.

darhymes wrote:I recently did some minor exhaust repairs involving a small amount of stainless steel foil. I located some through Grainger Industrial Supply. It was not cheap-about $50 for the roll but it should last me and everyone I know a few lifetimes of exhaust repairs. I notice you are Canada so it would probably take too long for me to send you some. Another friend of mine used stainless steel foil from the local hobby shop. It is a much smaller roll but no less effective (and way cheaper). Knife makers use stainless steel foil as well, under the name of Heat Treating Foil.

Thanks for the tip. I looked all over Vancouver, BC today (city of 3-million), and couldn't find stainless steel foil anywhere. I'll take a look at Grainger.

Very pricey, especially when you only need a little bit of it. If you want to mail me some, I'll cover the shipping

This might work

https://www.amazon.ca/Silver-Temperatur ... B00L48YL0W

Maybe HVAC suppliers?

If you’re still stuck in the big smoke this weekend PM me and we could meet YPK, might have some stuff in the hangar.

daedaluscan wrote:This might work

https://www.amazon.ca/Silver-Temperatur ... B00L48YL0W

Maybe HVAC suppliers?

Good thinking, Charlie! But I’d avoid anything with adhesive such as tape. Also available is plain stainless steel foil: https://www.amazon.ca/DSFHKUYB-Thicknes ... r=1-3&th=1