Shock Cooling and Muffler Damage

TedR3

TedR3

Pre-takeoff checklist
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Ted
I recently received the following information from our club maintenance officer regarding our '79 Archer II:

"When the Archer was in the shop, the shop also noticed that the mufflers were cracked and had to be replaced. The shop indicated this was partially due to shock cooling the engine and excessive leaning."

Does this make sense? I've always associated shock cooling with turbos.
 
That shop doesn't know what they're talking about. Suggest they stop giving advice, or you find another shop.
 
Or another mx officer...who may be twisting things to support his own wive's tales.
 
Are there any operating procedures/issues that would affect the lifespan of mufflers?
 
TedR3 said:
Are there any operating procedures/issues that would affect the lifespan of mufflers?
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I'd think that routinely starting the engine and then not flying the plane would. Also just sitting for extended periods would probably affect the lifespan.

The main enemy of exhaust systems is corrosion. Regular flying keeps the moisture out.
 
You might want to have your club check the invoice -- the shop might have gouged you on a propwash top-off and unnecessary spools of flight line, as well.
 
TedR3 said:
I recently received the following information from our club maintenance officer regarding our '79 Archer II:

"When the Archer was in the shop, the shop also noticed that the mufflers were cracked and had to be replaced. The shop indicated this was partially due to shock cooling the engine and excessive leaning."

Does this make sense? I've always associated shock cooling with turbos.
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:popcorn::popcorn::popcorn::popcorn:;)
 
TedR3 said:
Are there any operating procedures/issues that would affect the lifespan of mufflers?
Click to expand...

Vibration and high EGTs will shorten its span.

However the likely reason it failed?

It was a muffler on a Cherokee.
 
Ted DuPuis said:
That shop doesn't know what they're talking about. Suggest they stop giving advice, or you find another shop.
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Agreed.

timwinters said:
Or another mx officer...who may be twisting things to support his own wive's tales.
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Also agreed.
TedR3 said:
Are there any operating procedures/issues that would affect the lifespan of mufflers?
Click to expand...
General use if going to wear them out. They take a fair amount of abuse in there. I will say this. The Caravans we fly crack way more exhaust than the caravans that are not used in skydiving ops. I know its from the rapid cycles it sees. That being said; you are not going to see that in the normal archer flying.
 
When I first bought the Aztec, my mechanics told me LOP would cause all sorts of problems, including my exhausts failing. When 100 hours into ownership the right exhaust failed, they blamed LOP ops and ignored the fact that it was really old and had been repaired multiple times. New exhaust right side, no other problems.

Morals: a number of mechanics tell you thinks that aren't necessarily true. We are lucky to have good ones on here.
 
TedR3 said:
I recently received the following information from our club maintenance officer regarding our '79 Archer II:

"When the Archer was in the shop, the shop also noticed that the mufflers were cracked and had to be replaced. The shop indicated this was partially due to shock cooling the engine and excessive leaning."

Does this make sense? I've always associated shock cooling with turbos.
Click to expand...

If you lean your engine until it starts popping and leave it there, then yes it can damage your muffler. If you go from a nice hot exhaust in cruise, pull the throttle out and shove the mixture in as you enter the pattern, then yes it can also damage your muffler. Maybe the non pilot mechanic needed to further explain himself. Be gentle with power and mixture changes and your fwf will appreciate it.
 
Most mufflers can be damaged when the pilot is checking the mags during a runup and inadvertently switches to Off and then back on again when at runup RPM. The raw fuel accumulates in the muffler and fires once the flame starts coming out of the exhaust ports again. The concussion will easily crack mufflers.

The problem often arises when the pilot pinches the mag switch key by its edges instead of by its flats. He switches to L or R and then his fingers slip off the edge of the key and turns it too far.

We used to tell our students that if the engine dies when they were checking the mags, let it stop and then restart it.

Dan
 
How often are you greasing the muffler bearings? It is very hot and cooks the grease out, they need frequent attention. You might want to mention to your mx guru that this is not something to let slide until annual time.
 
JHW said:
How often are you greasing the muffler bearings? It is very hot and cooks the grease out, they need frequent attention. You might want to mention to your mx guru that this is not something to let slide until annual time.
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Those bearings last a lot longer once the piston rings wear out and let lots of oil go through the exhaust.

Dan
 
Skylane81E said:
Vibration and high EGTs will shorten its span.

However the likely reason it failed?

It was a muffler on a Cherokee.
Click to expand...

Not just Cherokees. Aircraft engine mufflers are a joke, and need to be replaced every 350 hours or so simply because they are built too lightly.

I would gladly trade ten pounds of useful load for a muffler that didn't rot out so easily.
 
Dear Club Maintenance Officer,

You have just proven yourself unfit for duty. Please let us find someone that knows how airplane engines work.

Sincerely,
Anyone with half a brain.
 
JHW said:
How often are you greasing the muffler bearings? It is very hot and cooks the grease out, they need frequent attention. You might want to mention to your mx guru that this is not something to let slide until annual time.
Click to expand...

Don't forget your blinker fluid top-offs every 50 hours. That's important to keep the beacon and strobes. On a Cirrus, blinker fluid should be checked every 10 hours.
 
Jay Honeck said:
Not just Cherokees. Aircraft engine mufflers are a joke, and need to be replaced every 350 hours or so simply because they are built too lightly.

I would gladly trade ten pounds of useful load for a muffler that didn't rot out so easily.
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Not just Cherokees but they do seem to be among the worst offenders. As an example it is a rare day when a Cessna muffler doesn't go 1000hrs+ around here and I'm a flame tube nazi.
 
JHW said:
How often are you greasing the muffler bearings? It is very hot and cooks the grease out, they need frequent attention. You might want to mention to your mx guru that this is not something to let slide until annual time.
Click to expand...

My first boss took his Mercedes into the shop years ago as it seemed down on power. He thought they were pulling his leg when the said it had bad muffler bushings but it turned out there was an active baffle that was supposed to move allowing more flow at high power. It was stuck restricting the exhaust flow.


Whatdayaknow
 
Too many click...click..click...BANG mag checks?
 
Cherokee mufflers are supposed to be replaced on a 500 hour schedule. I thought I was going to have to do mine, but during the inspection I really couldn't find anything wrong with it.
 
steingar said:
Cherokee mufflers are supposed to be replaced on a 500 hour schedule. I thought I was going to have to do mine, but during the inspection I really couldn't find anything wrong with it.
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There are many, many items that should be handled that way, and the muffler is one of them. But they do just crack without any signs...
 
bnt83 said:
There are many, many items that should be handled that way, and the muffler is one of them. But they do just crack without any signs...
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True, but the thing seemed in really good shape. Mechanic agreed, and stayed it did.
 
steingar said:
True, but the thing seemed in really good shape. Mechanic agreed, and stayed it did.
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Sorry... My post wasn't very clear. I agree 100% with the "on condition" replacement schedule for most things and the muffler included. ;)
 
KaleCo is my favorite source of elbow grease.
 
steingar said:
Cherokee mufflers are supposed to be replaced on a 500 hour schedule. I thought I was going to have to do mine, but during the inspection I really couldn't find anything wrong with it.
Click to expand...

Once again we are tripped up by the common usage of "Cherokee" when we actually mean several different types of aircraft. Damn Piper, for creating a 50-year problem! lol

Mufflers on the O-320-powered Cherokees seem to last a long time.

Mufflers on the higher powered (O-360, O-540) Cherokees seem to last less time.
 
Location is a big thing on the 28-140 the muffler is a long way from the exhaust port.

BUT it has little support so the exhaust stacks can crack.

On the rest of the line the muffler is so close to the engine that is sees extra hot gasses, but the stacks aren't as much of a problem.
 
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