John Young
Member
I’m having exhaust issues that I wanted to put in front of the group for comments…it’s a bit puzzling. I’ve read through several threads about the standard exhaust, no flame tubes, Power Flow, etc. and am trying to decide which direction to go here. Apologize for the longer post…but this has been quite the dilemma and I wanted to share what I‘ve found with the group.
I had a very strange exhaust noise that was very rhythmic and consistent…first thought it might be an exhaust leak…but when I uncowled it and ran it I confirmed it was coming through the exhaust system. Since I verified it wasn’t a gasket leak I went further with an IA…I’m an A&P myself…but just do maintenance on my aircraft.
We verified the following:
- Backflow checked the gaskets…no leaks
- Boroscoped the exhaust…couldn’t get a good picture with a lower end boroscope.
- Boroscoped the cylinders…all looks good.
- Compression Checks…all good normal leakage around the rings…none from the exhaust or intake valves.
- Checked valve backlash…all within limits.
- Removed, cleaned and checked the lifters…all in good shape.
- Checked the travel on the pushrods to see if the cam was going…all in good shape with consistent measurements.
- Borescoped the exhaust with a higher end more flexible borescope…found deteriorizaiton of the baffles.
This is where it gets interesting:
I touched base with AWI in Minneapolis…great conversation and what seemed like sound advice. As a note, most if not all of the other exhaust overhaul/welding companies, Acorn and others, have been bought up by AWI. They recommended I pull the entire exhaust (muffler, shroud, tube) and send it to them…they said that most exhaust overhauls come in at about $1,900…and I’d basically be getting back a new exhaust as they also manufacture the exhausts for Aviat...they would also incorporate any upgrades. My IA and I inspected/consulted and came to the conclusion that the shroud and down tubes were all in good shape. So I pulled the exhaust stack to send it in for inspection/overhaul to AWI.
What I found when I removed the exhaust was surprising. I found a round disk lodged in my #2 exhaust tube coming from the muffler blocking off about 90% of the exhaust flow. It was most likely the sound I heard from the engine. Keep in mind that doing a normal annual the exhaust would have passed had it not been for the noise and the deteriorated baffles wouldn’t have even been discovered. Here’s what I discovered and what happened next
- I went back in the records and discovered the #2 down tube had been replace and the exhaust fully overhauled by AWI just prior to my purchase…a little over 500 hours ago.
- AWI came back and said the round disk was most likely from the end of one of the exhaust baffles and that it is common for them to come loose and just fall out of the exhaust tube. I’m kind of scratching my head on this one…not sure how it would work its way into an exhaust tube opposite of exhaust flow. They also asked that I send the shroud and downtubes in and they would do the complete overhaul.
- Going off of what I was told earlier concerning cost I decided to follow that advice.
- I did ask if they would rebuild it without the baffles and they declined to do that. I understand the logic in this if it’s not covered by TC or STC...but based on some of the comments in here I wanted to ask anyway.
I just received the estimate back on Friday. They now say most of the system needs overhaul/replacement including down tubes, slip joints, and rebuild of the exhaust. Also, they are insisting on doing an Aviat design modification for rubbing problems that moves the muffler back 1/2”. As far as I can tell…I have no rubbing issues.
New rebuild estimate: $3,500!
As you can imagine I’m not very happy right now and considering my options. I’m not keen on spending near that kind of money for an exhaust overhaul that won’t even last 500 hours. I feel like I was lead down a path that wasn’t represented well at all. I see the Power Flow debate with varying opinions, results and concerns. I also feel like this is a direct result of all the other welding houses being bought up by one entity. BTW…AWI is owned by Hartzel that’s now owned by an investment firm.
Thoughts on this?
I had a very strange exhaust noise that was very rhythmic and consistent…first thought it might be an exhaust leak…but when I uncowled it and ran it I confirmed it was coming through the exhaust system. Since I verified it wasn’t a gasket leak I went further with an IA…I’m an A&P myself…but just do maintenance on my aircraft.
We verified the following:
- Backflow checked the gaskets…no leaks
- Boroscoped the exhaust…couldn’t get a good picture with a lower end boroscope.
- Boroscoped the cylinders…all looks good.
- Compression Checks…all good normal leakage around the rings…none from the exhaust or intake valves.
- Checked valve backlash…all within limits.
- Removed, cleaned and checked the lifters…all in good shape.
- Checked the travel on the pushrods to see if the cam was going…all in good shape with consistent measurements.
- Borescoped the exhaust with a higher end more flexible borescope…found deteriorizaiton of the baffles.
This is where it gets interesting:
I touched base with AWI in Minneapolis…great conversation and what seemed like sound advice. As a note, most if not all of the other exhaust overhaul/welding companies, Acorn and others, have been bought up by AWI. They recommended I pull the entire exhaust (muffler, shroud, tube) and send it to them…they said that most exhaust overhauls come in at about $1,900…and I’d basically be getting back a new exhaust as they also manufacture the exhausts for Aviat...they would also incorporate any upgrades. My IA and I inspected/consulted and came to the conclusion that the shroud and down tubes were all in good shape. So I pulled the exhaust stack to send it in for inspection/overhaul to AWI.
What I found when I removed the exhaust was surprising. I found a round disk lodged in my #2 exhaust tube coming from the muffler blocking off about 90% of the exhaust flow. It was most likely the sound I heard from the engine. Keep in mind that doing a normal annual the exhaust would have passed had it not been for the noise and the deteriorated baffles wouldn’t have even been discovered. Here’s what I discovered and what happened next
- I went back in the records and discovered the #2 down tube had been replace and the exhaust fully overhauled by AWI just prior to my purchase…a little over 500 hours ago.
- AWI came back and said the round disk was most likely from the end of one of the exhaust baffles and that it is common for them to come loose and just fall out of the exhaust tube. I’m kind of scratching my head on this one…not sure how it would work its way into an exhaust tube opposite of exhaust flow. They also asked that I send the shroud and downtubes in and they would do the complete overhaul.
- Going off of what I was told earlier concerning cost I decided to follow that advice.
- I did ask if they would rebuild it without the baffles and they declined to do that. I understand the logic in this if it’s not covered by TC or STC...but based on some of the comments in here I wanted to ask anyway.
I just received the estimate back on Friday. They now say most of the system needs overhaul/replacement including down tubes, slip joints, and rebuild of the exhaust. Also, they are insisting on doing an Aviat design modification for rubbing problems that moves the muffler back 1/2”. As far as I can tell…I have no rubbing issues.
New rebuild estimate: $3,500!
As you can imagine I’m not very happy right now and considering my options. I’m not keen on spending near that kind of money for an exhaust overhaul that won’t even last 500 hours. I feel like I was lead down a path that wasn’t represented well at all. I see the Power Flow debate with varying opinions, results and concerns. I also feel like this is a direct result of all the other welding houses being bought up by one entity. BTW…AWI is owned by Hartzel that’s now owned by an investment firm.
Thoughts on this?
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