200HP Lycoming Exhaust System


November 2003


This month’s ShopTalk discusses the 200 HP Lycoming IO360 exhaust system installed on the Mooney E, F & J models. Because all non-turbocharged Mooneys have similar exhaust components, the following inspection can apply to models A through J. Inspection of the exhaust system is required, at least, at every annual inspection.


This inspection encompasses the following areas:

  1. Remove muffler shroud and inspect muffler can for bulges, cracks and any signs of exhaust stains or dust. As on any aircraft with a muffler shroud heat exchanger, this inspection item is extremely important to prevent any CO from entering the cockpit through the heater system.

  2. Inspect all four-header pipes at their ball or slip joints where they attach to the muffler. Look for signs of wear, cracks, holes and exhaust stains or dust.

  3. Inspect the four header pipes where they are welded to the exhaust flange for cracks and missing exhaust nuts or blown-out exhaust gaskets.

  4. Remove the tail pipe from the muffler and using a flashlight visually inspect the condition of the flame tubes inside the muffler. This item is important as the flame tubes help to distribute the heat from the exhaust evenly in the muffler can to prevent any hot spots. Hot spots can crack or bulge a muffler can and allow CO to enter into the heater shroud assembly.

  5. Inspect the fresh air hose leading into the muffler and the hot air hose between the muffler and the heater box on the firewall. Any tears in these hoses will allow exhaust gases that may be present in the engine compartment to enter the heater system. CO tainted exhaust gases may exist under the cowl from a leaky exhaust system or even from a slight tailwind during ground operations.

The underlying reason for this inspection is to prevent CO from entering the aircraft cabin and therein the occupants of the cabin. Dr. Achtel’s article in the July MAPA issue emphasized just how dangerous CO poisoning is. If you missed it, please read it.


Most 200 HP Mooney aircraft came with a ribbed can type muffler. Some had ball joints with bolts and springs that held the header pipes to the muffler; others had slip joints for the header pipes. Earlier Mooneys came with a Hamlin and Wilson studded type muffler can that was physically smaller than the ribbed type muffler.

The Hamlin and Wilson system was a very robust system, but these systems are now pushing 40 years old and it is very rare to see a serviceable one anymore. Wall Colmonoy Corporation (http://www.wallcolmonoy.com) rebuilds Mooney exhaust systems under the name Nicrocraft. Unfortunately, after they rebuild a system, it is coated with a product that makes it almost impossible to repair by welding. If you have a Nicrocraft system, you might get Wall Colmonoy to rebuild it one time for you. Very few exhaust rebuilders will rebuild Hamlin and Wilson systems.


The old exhaust system pictured is from a 1968 M20F. This system was rebuilt by Wall Colmonoy in 1986 at 2020hrs TT. It now has 4040hrs TT on it and by studying the photos one can see the flame tubes inside the muffler are coming apart and there is a hole in the #1 header pipe ball socket. Because it is a Nicrocraft rebuild, it is not easily repairable. With over 4000 hours on these components, the metal has become very thin from normal exhaust erosion. So, what are the options?


If you have a Hamlin and Wilson system that is not serviceable, you will require the purchase of a new M20J shroud, which will cost around $630. And then, either…

  • A new complete Mooney exhaust system costs around $2700 (includes the muffler which alone is $1500). Or...

  • In Loomis, California, Knisley Welding, Inc. holds a PMA (parts manufacturing approval) to build a new thick-wall exhaust system that may be installed using the old ribbed style muffler shroud. Knisley Welding can be reached at 800-522-6990 or https://knisleyexhaust.com. Their system is a different design than the Mooney system and tends to hold up better. The Knisley system is not coated so it is completely rebuildable. The Knisley system will set you back $1600.

The labor to replace the entire system is around 3 to 4 hours, so set aside several hundred dollars for your favorite mechanic’s time.


With winter just around the corner, now is the time to get your Mooney exhaust system inspected before you use the heater. There is no reason to risk becoming a victim of CO poisoning. A little preventative maintenance now may save lives later on.


As always, if you have a question about this article, you may contact me at my aircraft repair shop, 307-789-6866 or via e-mail. Until the next ShopTalk, enjoy flying your Mooney.