Exhaust Flange Cylinder #3

[Amadeus]

Two flights ago my carbon monoxide in the cabin rose to 40 ppm on takeoff. I attributed this to outside air vents closed and heat on both sides fully open and climbing at full throttle. However a few days ago I had the opportunity to fly and the carbon monoxide went up to 60 ppm on takeoff. Being just a couple hours from an oil change I opted to perform it early and inspect the heat muff.

What I discovered was the number 3 cylinder exhaust flange was loose on the studs and had been flopping around long enough to wear the threads off the stud and also wear down the lock nuts. The cowling was off 47 flight hours ago and it did not look loose on that engine inspection.



In this next photo you can see how soot has covered the surfaces. Just six months and 47 flight hours ago these surfaces were pristine clean. The engine has NEVER been dirty like this.



Lockwood has the stud and locknuts available and in stock ready to send. Has anyone had to remove one of these exhaust studs? I have given it a couple sprays of Kroil over the past week or so.....should this screw out fairly easily or is there a risk of cracking the cylinder head?

 

[sansoneservices]

Kroil and heat from a propane torch should remove it. The kroil will burn off so spray it again. Be patient, locking two nuts together or use a stud remover. You may need to heat, spray, repeat. Patience

 

[seagull]

When using heat try to heat the aluminum not the stud. Heat will expand the metal, you don’t want to grow the stud.

 

[Darin Watson]

When using heat try to heat the aluminum not the stud. Heat will expand the metal, you don’t want to grow the stud.

2nd that ….and Al has a much greater thermal expansion coefficient than Fe Alloy….whatever you do, DO NOT USE INDUCTIVE HEATING!!!

 

[Amadeus]

Fortunately I was able to fix this rather easily and relatively cheaply. Lockwood has the studs and nuts (studs are #10 and nuts #11) in stock and ready to ship. I sprayed Kroil the studs at the cylinder head (it really doesn't take much as Kroil follows the surface area inside the head) then waited three days before spraying again. After waiting a couple more days for the Kroil to do its thing I used two of the new nuts onto the stud threads and locked against each other and was able to slowly back the stud out of the head. Luckily there were enough remaining threads to make this possible. If the threads had been completely worn off then maybe I could've filed down flat opposing sides of the stud and tried a vice grip. I did not apply heat to the studs or the head as others suggested; my fear was cracking the head and looking at another $2,600. I worked the stud out slowly and steadily to try saving the head.

While I had the cowling off waiting for the parts and the Kroil to do its work I checked the rest of the flange nuts (all loose) and exhaust pipes. The #2 exhaust pipe has a doubler welded on the top bend but #1 does not and I found upon inspection that it was cracked at the seam. It is a $744 pipe but I found a certified welder that would fix it and added a doubler at the bend for $175.

Two flights since the repairs and the highest readin on the CO has been 2ppm.