The International Cessna^® 170 Association

I recently experienced a pretty seriousl exhaust leak in my plane while climbing out of a long high canyon. It was rather long climb about 20 minutes at about 70mph indicated. Other than that I haven't really had any indications that I'm getting exhaust in the cabin while using the heater. No, I haven't turned the heater on since then, but did use it frequently this last winter and spring.

Has anybody else had problems with exhaust in the cabin, while using the heat during an extended climb?

My plane is a 52 B model with the early A(?) style cowling, and is using the Hanlon Wilson mufflers. I just got finished pressure testing my muffler. I discovered that the muffler itself appears to be fine, and shows no bubbles while being submerged. The exhaust pipe however (which is in good shape) has a huge leak where it is pinned to the muffler along with the hanger clamp. It also leaks a little at one edge. The pipe itself appears aviation quality, could be origional, looks like stainless steel, and was expanded slightly to slip over the exhaust exit pipe coming down out of the muffler itself, and it also has four short slits (about 1/2" vertically) in it to aid in slipping it onto the male pipe. This leak is about 3/4" below the heater shroud. Has anybody else out there run into this?

Also I have found that there is obviously some exhaust leaking out under the clamps that join the muffler to the headpipes. There is no sealant, or gaskets at these joints, is that typical?

The "headpipes" (your term) I believe are more properly termed "risers". The clamps which attach them to the mufflers are a topic discussed several times in these forums, ...you might make a search for the topics. The bottom line is that I discovered a couple of years ago that a well-known engine shop (in Waco, TX) uses common muffler tape wrapped around the joints prior to clamping them, and I've personally done the same with excellent results. Approval basis... zip.
The CO found at the lower joint you mention is not likely the source of your cabin CO. The most likely source during protracted climb is:
1. The left, lower wing strut seal allowing engine exhaust to enter below the cabin floor on the left side of the cockpit. Inspect and correct the seal at that area.
2. Air flow in the aft fuselage typically is in a forward direction at speeds below 85 kts and exhaust will be "sucked" into the fuselage at the tailcone/spinner/elevator torque-tube areas and flow forward. It enters the cabin via the rear cockp,it bulkhead area, which is typically not "walled" off above the hat-shelf. Many owners have added a sheetmetal "wall" behind the uphostery above the hatshelf. (This has an added benefit of reducing cabin noise, expecially when taxiing, noticeable to rear-seat passengers as the tailcone makes an excellent sound-box and magnifies cable-slap, tailwheel noise (as it passes over pavement-joints, and surface irregularities, etc.)
3. Lower anti-collision beacon installations divert exhaust into the lower fuselage as relative wind presents exhaust gases to the beacon protruding into the slipstream. Seal the lower beacon installation.

Finally, it has recently been brought to my attention that many Hanlon-Wilson exhaust system installations are missing the "seals" which are depicted at items 27. 28, 29, 39, 40, 41, 13, 12, 8, in the B-model IPC, Fig. 51. These are PN's 0550157-29 , -30, -31, -30. A complete system will require four -29 upper seals, and two -31 lower seals (prior to aircraft serial number 25373) and one -30 and one -31 after that serial number. This info ONLY applies to the Hanlon Wilson exhaust systems.
These seals help prevent exhaust gases from entering the cabin heat ventilation system due to exhaust gases that might be present within the cowl.
These seals are getting hard to find. They are not hard to make however from ordinary 1/4" thick aluminum tubing with a tubing cutter or hole saw, and bent to accomodate the muffler shape.
Hope this helps.

George, thankyou, that does help. I've misplaced my parts catalogue but those seals...............I realized what they were after reading your post. I assumed they were just spacers, when I took the system apart. I think I may have several small leaks that are adding up to the total problem.

I would like to see a picture of those seals!