The Cessna 120-140 Association Forum

I'm looking at purchasing a C-120 that has the C-85 exhaust. How involved is the inspection on the exhaust to comply with the AD? How much time does it typically take to do?
If I wanted to upgrade the exhaust to a C-150 exhaust, what might that cost in terms of parts and labor?

Parts for at the C150 exhaust complete are around $1700 new from MacFarlane. I think there are two vendors making them now. There may be a few ancillary bits as well. If you have the rear-cowl exiting flat-ish exhaust pipes you'll also need to cut holes in the lower cowl.

If you have the straight pipes that exit at the rear lip of the lower cowl then the AD doesn't apply. If you have what's called the "pancake mufflers" then the AD does apply. The C150 exhaust conversion is a good solution; the pancake mufflers will never be fixed permanently. (Hence the AD...)

So I take it the "pancake mufflers" are what the AD refers to as exhaust muffler assemblies that are fabricated by welding exhaust stacks to muffler? I'm still low in my familiarity with 120s and 140s. Is it relatively easy to tell the difference between the two types of exhaust? Is there any correlation between manufacture year or serial number of the airplane?

The straight pipes are exactly that. They exit between the firewall and the lower lip of the cowl. The pancake mufflers are sort of flat and exit through holes in the cowl lower skin. The C150 style mufflers look like round cylinders (Quaker Oats boxes, if you're old enough).

Look at your AD compliance sheet. If it says something like "not installed" then you (probably) don't have them. If it says "Complied with by inspection" then there's a good chance you do have them, unless the inspector forgot to include "found affected parts not installed".