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Hole in muffler


tennesseect

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My 07 CTsw slowly got noisier over the past few months and then got real loud.  When I opened the cowling I found a chunk of metal - about 2" X 6" - missing from the front right of the muffler.  My wife and I flew it 40 miles home.  There were no abnormal instrument readings other than a somewhat lower than normal left cylinder head temp.

Is this normal wear and tear?  Do I just replace the muffler or is there something else I should check?

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You need to fix that as soon as possible, it is a fire hazard. The muffler also drives a certain back pressure into the exhaust of the engine; without it you lose fuel economy and increase wear on the valves. *

 

Also, have someone look at the muffler to make sure there's nothing else wrong with it. I don't know if CTs have internal baffles to help with the back pressure tuning; if they do, it can block the exhaust and exacerbate the problems.

 

* Explaination: Engines are tuned to have a certain amount of "valve overlap," which is the time between the exhaust and intake strokes that both valves are open. The reason is as follows: the exhaust valve is open throughout the exhaust stroke, the intake valve opens right at the end of said stroke. This means there is inertia of the exhaust gasses leaving the exhaust port, and high pressure at the intake. Exhaust ports are also smaller than the intake port, and Bernoulli's principle takes effect. The intake port air is at a higher pressure, and the exhaust port air is at a higher velocity. Coupled with the fact there is already inertia carrying the exhaust gases out, this allows some of the intake air to further purge the combustion chamber of exhaust gasses, and help with cooling. With no back pressure, the cooling effect is amplified, and you lose a lot more intake air (which means more fuel goes out the exhaust too in carb engines). This is where the efficiency part comes from.

 

Valves, without back pressure, can slam into their seat, increasing wear. That's why it's bad for valves to have no back pressure.

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Hi Tom,

 

The muffler itself is Rotax, but FD did the heater shroud. I would be interested in the pictures too when you get them. If you replace the muffler only then the female sockets for the pipes have to be welded on. If you have to get a complete muffler I bet it will be from FD and it probably won't be cheap for the entire piece. The muffler from Rotax alone is $1289. You might be able to rob the FD parts off the muffler and reuse them.

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I haven't seen or even heard of something like this. My best guess is it started to crack around the weld at the pipe and with vibration and exhaust pressure and pulsation took its toll expanding the cracks. Why it broke out as it did is anyone's guess. Regarding the break towards the center, is there anything welded right where it seperated?

 

These guys are right, it should be grounded until fixed.

Sorry, but this won't be cheap.

 

I'm going to send this to Rotax and get their take.

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