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Muffler Crack...

Piper J3

Well Known Member
I'm doing Annual Condition Inspection now and found a crack in the muffler where the exit exhaust tube is welded on. Looks like vibration induced metal fatigue from long cantilever exhaust tube. TT=750. Muffler is in back of car and headed for local TIG welding shop...
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Jim,

Thanks for posting. I’m in annual now and will take a close look tomorrow. I’ll post my results (about 1250 hrs total).

Rich
 
In the certified world, some exhaust system manufacturers double their warranty if you have the prop balanced, vibration causes cracking.
 
Crack found

Started my annual today. After reading Jim's posts, the muffler was high on my list. Found a pretty nasty crack, almost 180 degrees around the exhaust tube the exits the muffler and also extends into the muffler body just like Jim's. An experienced welder here thinks it will be an easy fix. If that doesn't work out, I guess I will be looking at the new EX-00044 exhaust system. Airplane has 690 hours, my prop has been dynamically balanced from early on.
 

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Jim, Tony, have either of you had to replace muffler springs, if so how often?

I wonder if the vibrations that are getting to the muffler to cause the cracks are the same that cause spring breakage / wear. I remember reading on here someone had the bell sockets on the muffler wear, another sign things are moving around.
 
Walt
I have never had a broken muffler spring. I did replace all the springs about 300 hours ago, just because.
 
I am at 930 hrs and inspected my muffler because of the cracks you and Jim found. Mine isn’t cracked, yet. I have never broken a spring but 4 were worn 1/2 way through on the spring, the muffler hooks were fine. I replaced all 8 with the stainless ones from Spruce.
 
I am at 930 hrs and inspected my muffler because of the cracks you and Jim found. Mine isn’t cracked, yet. I have never broken a spring but 4 were worn 1/2 way through on the spring, the muffler hooks were fine. I replaced all 8 with the stainless ones from Spruce.

Since you would rather replace springs than muffler hooks, perhaps stainless steel is not the way to go?
 
Since you would rather replace springs than muffler hooks, perhaps stainless steel is not the way to go?

That very thought came to mind, I am not sure which would wear faster. Sometimes the softer material takes on surface grit and wears the harder material. I believe the original springs were high temper steel. They should have been harder than the hooks especially after annealing from the welding. I will watch these to see which side is wearing.
 
Started my annual today. After reading Jim's posts, the muffler was high on my list. Found a pretty nasty crack, almost 180 degrees around the exhaust tube the exits the muffler and also extends into the muffler body just like Jim's. An experienced welder here thinks it will be an easy fix. If that doesn't work out, I guess I will be looking at the new EX-00044 exhaust system. Airplane has 690 hours, my prop has been dynamically balanced from early on.

Tony - When welding a repair on muffler, the inside has to be purged with Argon gas. All muffler openings need to be capped off to contain the Argon. Also, very difficult to clean crack with carbon contamination. The guy that TIG welded my engine mount won't work on mufflers...
 
Not sure of the significance, but it appears the original exhaust springs, # 938 795, have been superseded by part # 938 796. Rotax says the old ones can still be used, but wonder what was changed? Not sure if this might help some of you experiencing issues.
 
Talk to a welder about a weld overlay with filler as opposed to just trying to fuse the crack. That way you’ll add some structure and avoid the issue of contaminants in the crack weakening the weld.
 
Tony - When welding a repair on muffler, the inside has to be purged with Argon gas. All muffler openings need to be capped off to contain the Argon. Also, very difficult to clean crack with carbon contamination. The guy that TIG welded my engine mount won't work on mufflers...

Jim, our welder ran a TIG bead around the exhaust exit pipe. I'm not a weld expert but it doesn't look completely fused to me. I may end up putting on the new exhaust system. Other's have reported lower cockpit CO with the new system compared to old and the additional clearance to oil cooler is a plus.
 

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Tony -

Weld is not the prettiest I've ever seen, but if welder things he had good penetration, I'd say give it try. Might be stronger than when new. I'd inspect fairly often until you have good level of confidence...

Jim
 
I put the new exhaust system on mine and have zero co in the cockpit ad my oil temps are much lower. If you want my old exhaust you can have it for the shipping.
 
I put the new exhaust system on mine and have zero co in the cockpit ad my oil temps are much lower. If you want my old exhaust you can have it for the shipping.

What is making the new muffler give you cooler oil temp. Does it sit farther from the oil cooler? What is the distance difference between the two?
 
As a follow up to my post #12, if anyone is interested in the difference between the new 938 796 and old 938 795 exhaust springs, this was the response I received from Dean Vogel at Lockwood:

“If you look at the attached file… the one on the right is the 938 796. Rotax is attempting to get away from the environmental impacts of doing coatings, so they went with one that is stainless steel. The regular steel tends to take the vibration issues better, but it also has a tendency to corrode more quickly.”
 

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I'm unsure which springs my engine came with.. but I can say after about 250 hours, almost all of them have broken by now. I've been replacing with with silver-colored stainless steel springs from Aircraft Spruce, and have not had one break yet.

The old springs seem to corrode quickly with rust and pitting and I've seen them break mid-spring, or just before the hooks at the ends. Luckily safety wire has caught all but one of the breaks.
 
Those silver stainless springs have a hook-to-hook dimension of 75 mm vs. the 66 mm of the original 938 795/6 springs, so that may be a factor. I’m at 190 hours on the original springs, with no noticeable wear, and no breaks. I do my CI next month so will see how the wear on the spring hooks and muffler and exhaust ears look when I remove them.
 
What is making the new muffler give you cooler oil temp. Does it sit farther from the oil cooler? What is the distance difference between the two?

Yes the exhaust sits much further aft, lower and away from the oil cooler. I did not have to modify the cowling either. it fit like a glove.
 
Yes the exhaust sits much further aft, lower and away from the oil cooler. I did not have to modify the cowling either. it fit like a glove.

I am curious how much room you have between the muffler and the oil cooler. My cowl has been modified to move the cooler forward, I have 3/4” space to the original muffler. I wonder if that is enough space to get the improved cooling you are seeing.
 
Seagull -

What Oil Temperatures are you seeing with 3/4" spacing?

There are so many variables, OAT, rate of climb, cruise speed, altitude, RPM, gross weight, etc. I have charted it over 2 years with most variables. Tell me a few parameters an I will look it up.
 
I have documented OAT, Oil Temp, and Oil Press in stabilized cruise flight at near gross weight and 3000’ MSL. Rotax states 260F Max Allowed Oil Temp with 190-230F Normal Range. I have been using Full Synthetic Mobil1 4T 10W40 for last 650 hours.

Note items #1 and #4 in section 6 of Rotax Service Instruction below:

Rotax Service Instruction Titled: Selection of Suitable Operating Fluids for ROTAX® Engine Type 916 i (Series), 915 i (Series), 912 i (Series), 912 and 914 (Series). The publication is dated May 28, 2021. pdf file is d06902.pdf in the Technical Documentation Section of https://www.flyrotax.com.

Section 6 states:

6) General Engine Operation Requirements and Operating Tips

1. Keep the engine oil temperature below 120 °C (250 °F) over most of the operating period.
2. Always ensure that the oil type used is adequate for climatic conditions and peak engine operating temperatures. If operational oil temperatures exceed 120 °C (250 °F), use of a mineral or petroleum based oil is not recommended.
3. For turbocharged engines ensure an adequate running cool-down period to prevent deposits by coking of oil.
4. When operating with unleaded fuels or MOGAS and when engine oil temperatures often exceed 120 °C (250 °F) use of a high quality full synthetic oil is recommended.
5. To avoid formation of condensation water in the engine oil, the oil temperature must rise at least once every operational day to at least 100 °C (212 °F).
6. Avoid extended use of carburetor air pre-heating when safe and reasonable.
7. Automotive fuels have seasonal blends and MUST be used in the correct season. Failure to do so can cause hard starting or serious issues like vapor lock.
8. Depending on the type of fuel used, operating conditions, and the demands of the engine mission profile it may be necessary to increase the frequency of oil changes to avoid the excessive build- up of lead and other residues in the engine oil. Always adjust the engine oil change intervals to avoid excessive build-up of sludge in the engine oil.
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Seagull -

What Oil Temperatures are you seeing with 3/4" spacing?

I pulled this data from the Dynon. This data spans a 2 year period to current. I used a point in the flight that had at minimum of 5 minutes level flight in cruise.

oil temps.jpg
 
Also, in thread for "High Oil Temp", MMiller mentions ground path problem with D180 that causes indicated oil temp to be higher than actual. I verified this using his suggested test method, and I read 5F higher than actual at 200F. So, my guess is maybe 8F higher at 230ish…
 
Jim, it is strange that as your oil temp increased your oil pressure also increased. I would expect the pressure to remain the same or decrease as the oil thins with temperature.
 
Oil is 10W40 multigrade.... It is 10 weight when cold and 40 weight when hot. Best explanation I can give....
 
I use Aeroshell Sport Plus 4, it is also 10W-40, I’m not seeing that pressure changing. Do these engines have an oil pressure regulator?
 
Yes the exhaust sits much further aft, lower and away from the oil cooler. I did not have to modify the cowling either. it fit like a glove.

I pulled the cowling and measured the distance from the Exhaust to the oil cooler with the new EX-00044 and it is a whopping 2 1/2 inches. The exhaust is also lower so it sits below the oil line fitting on the bottom of the crankcase by about a 1/2 inch. As I recall the original exhaust nearly touched that fitting.
 
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I pulled the cowling and measured the distance from the Exhaust to the oil cooler with the new EX-00044 and it is a whopping 2 1/2 inches. The exhaust is also lower so it sits below the oil line fitting on the bottom of the crankcase by about a 1/2 inch. As I recall the original exhaust nearly touched that fitting.

Thank you, good information.
 
Extra clearances everywhere

The EX-00044 system installed:
 

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I had the crack in my muffler welded by a certified welder. I think it looks good. The muffler will be kept as a spare. I was able to purchase early SN exhaust systems with only 70TT, but that is system that is giving higher oil temps...
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Wow.!!! I just checked mine and i have signs of developing crack . Maybe I can find an older one that was removed for the new system like Jim did My original lasted 1200 hours . If not I guess I will be welding.

Anybody have one out there !!!

Brad Stiefvater
Salem SD
 
Welding is an acceptable repair if done correctly. I think what causes the crack is the long cantilevered exhaust stack vibrates and stresses the end bell of the muffler. I have been told that Argon shielding gas should be used to purge the inside of the muffler when welding, however, the certified weld shop that just welded my muffler said it isn’t necessary. In any event, welding mufflers is tricky. You might even consider sending the muffler to a FAA repair station that specializes in exhaust systems...
 
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