Cracking on rear engine cowling.....
 

Hey Ernie (or anyone else),

Do you ever have any issues with cracks on your rear engine cowling of your 73 G model? I have been battling this ever since I purchased the airplane almost 10 years ago. Countless repairs have not held up and my IA thinks it's time to find an entire replacement assembly of the upper and lower.


1552200-200 Upper Tail Cap Assembly

1552123-9 Lower Tail Cap Assembly

The names are slightly misleading. These are the top and bottom of the engine cowl for the rear engine. See page 188 in the parts catalog, Figure 72 for the diagram. I need item number 26 (lower) as seen in the diagram and item number 36 (upper) as seen in the diagram.

I am on the hunt but curious if you have had any of these issues.

Thanks,

Ed

Just a shot in the dark here, but how are your rear motor mounts? If they are getting worn it is possible that your rear exhaust pipes are vibrating against the cowl where they exit, and or just excess vibration.

Thanks Roger,

Several of the engine mounts have been replaced over the years. In fact I have one on the front that will be replaced this annual. The cracks keep occurring on the lower "ring" portion of the cowling underneath the prop spinner. It has been repaired several times but the underlying issue seems to be that the entire assembly cannot be reassembled after the repair without having that piece under some stress. The repairs last about 100 hours and then the cracks reappear. The entire cowling has many patches on it so my IA's thought is to attempt to just replace the entire two assemblies hopefully from the same airplane.

We'll see!

Ed

Roger,

I'm assuming you have not had this issue with your airplane??? I believe our airplanes are identical back there.

Ed

Yes my motor mounts were soft and it allowed the engine to drop enough that the exhausts had actually slightly deformed the bottom of the holes where they exit the cowl. I didn't have any cracks but I did have a bunch of loose rivets which I think were caused by the issue

Interesting. I have not experienced that sort of issue with my airplane.

Also as I think back about 15 years ago I hare a 70 skymaster that had a screen on the top half and disc on the bottom and the bottom kept cracking. My 80 h doesn't have the screen on top and I haven't had the cracks, just the vibrated out rivets.

No screen on my 73 G either. I'm searching as we speak for the two assemblies. Sending emails to every salvage yard Ernie has listed on his web-site. Hopefully I get lucky. The thought of wasting more time and money trying to repair my existing one again does not sound too appealing.

Have you tried doing a propeller balance? It might be worth looking into.

I was thinking prop balance too. I had some cracking around these areas in the past but since I installed the MT props no issues. I will take a photo of the cracks and we can compare.

Thanks Herb,

I have had my props balanced twice in the past. Each time after they come back from the prop shop after reseal. It has been about 3 years now. The props go out every 5 years for reseal.

http://www.ebay.com/itm/Cessna-337-S...f#ht_539wt_689


http://www.ebay.com/itm/Cessna-337-S...f#ht_500wt_689

My '73 has had some cracks in the upper tailcap, which required some metal work with doubler and has held up well, but nothing on the lower tailcap. One of the rings (either 35 or 48 in the figure) broke and I replaced it with a carbon-fiber STC unit from Owen Bell at Aviation Enterprises, which has held up well.

Ernie

Thanks Herb for the eBay link. I did see that one but the part numbers do not match. Not sure if it would work or not but I will look into it. Ernie, that carbon fiber sounds interesting. I will look into that.

Thanks everyone. I will keep you posted.

Ed

Ernie, one more question for you.

It is number 35 in the drawing (the lower ring, part number 1552127-2) that keeps cracking. The entire assembly has other patches on it that seem to be OK but it is the lower ring that keeps failing. Anyway, reference the carbon fiber option, is it the ring that is actually made of carbon fiber? How does it get attached to the rest of the assembly? Is it riveted? Can carbon fiber be riveted to aluminum? I have sent an email to Owen asking if he had the entire assembly but I have not heard back yet but this sounds like a potential option to me.

Thanks,

Ed