Bellanca 8KCAB lower cowl exhaust issues

B

BarneyRubble

New member
I have been having some trouble with the exhaust running too close to the lower cowl inside on the right hand side at the front. It has started to bubble the fiberglass with all the heat.

Anyone had any issues or successful repairs/remedies for this problem?

New mounts have been fitted to engine and heat tape is already on header pipe.
 
Is the cowl sagging at all? The attach holes can get larger with age.

Lastly, you can grind the opening in the cowling out for clearance.
 
Cheers Jerry,
The cowl is sitting correctly, the clearance issue is where the header pipe comes out of the front right cylinder into the muffler. It is nearly touching the cowl.
I have a mate with the same model decathlon but he has the later model cowl with the louvre in the side. It seems to be completely redesigned with much more clearance.
I was just wondering if anyone has had any issues with the original design cowls and any successful remedies? I am going down the road of Kevlar heat mat as a possible solution.
 
The placement of the #1 exhaust is still an issue to this day. We have to be very careful when fitting the cowl.

You can add some heat shield inside the cowl. Like the metallic reflective type.
You could glass in something like this stuff: https://www.heatshieldproducts.com/thermaflect-cloth
Home-built market has lots of products too.
 
Thanks Jerry,
Great idea, im glad its not just me with this issue then. Ive just finished a 3 year restoration and dont really want to damage the lower cowls again. Ive just repaired them from the previous damage.
 
Check you rubber engine mounts or Load Mounts whichever you have, they sag over time, especially if you fly aerobatics.
Look at how your spinner lines up with the front of the cowling, if it looks low, replace the mounts and it will give you the clearance it should have, and as Jerry says install stick on heat shield in that area.
Bill B
 
I am having a similar issue with my 1977 8KCAB-150. I have fitted a brand-new Dawley muffler (they have the PMA for new-build mufflers) and it is physically touching the lower cowling in the middle of the bend radius exiting cyl. #1. The engine mounts are fairly new (less than 1 year and 35 hrs.), but, even with the old muffler and old, sagging engine mounts, I did not have any issues with the muffler actually touching the cowling..

As you know, there is quite a bit of "adjustment" available in the positioning of the cowling before tightening the screws, but, tightening it in its "lowest" position yields only about 1/4" clearance and results in the flywheel gear teeth contacting the upper cowling under even the slightest load. I have contacted Dawley about this and they can offer no explanation (there are a few other a/c types using this identical muffler and they said they have never had a complaint like this). Has anybody had a similar issue with a new Dawley Aviation muffler?

I am stuck with an 800 dollar paperweight at this time and am wondering if anybody has made any modifications to the bend radius of the #1 cylinder exhaust pipe as it enters the muffler to provide a little more clearance?
 
Hi Zlin526,

This was the exact issue i had with my aircraft which is what started this post. The heat tape header wrap was useless don't waste your time. I lined the cowl area around the header pipe with a kevlar heat mat and attached with RTV red sealant. I doubled the layer directly under the pipe. http://www.thermotec.com/products/kevlar-heat-barrier.html

Secondly, i had to modify the header pipe. We drilled and tapped a steel bench and bolted the exhaust to it. We then cut the header pipe near the collector weld joint for number 1 cyl. There was enough slack in the sleeve joint to remove some material from the pipe and re tig weld, pulling in the pipe towards the muffler. We also heated up and bent the riser pipe towards the pipe centreline to close the gap.

A word of caution, the exhaust pipe is VERY hard to bend even when heated up to a nice cherry red but it will move enough for the modification.

This modification and careful cowl placement gives you more than enough room to prevent the cowl from burning.

I have a friend with the later model ACA lower cowl on his 77 8KCAB, with the louvre in the left side. This cowl is much deeper in the front near the airfilter mount, allowing much greater header pipe clearance. Very noticeable when the two are parked next to each other. This is where the problem lies for the older, original cowl as I believe the exhaust manufacturers don't recognise the difference in design.

I have had mine on for 300+ hrs now and works perfectly.

Hope this helps.
 
Barneyrubble,

Thanks for the reply. I was just at a local exhaust fabricators asking about doing the same thing (changing the radius of the #1 cylinder exhaust tube as it enters the muffler) - the consensus seems to be shortening each of the 4 - 5" risers by about 1/2" would be their recommendation. It appears there would be adequate clearance between the muffler/engine/components, but, I don't know the legality of such a change, as minimal as it may be...I just spoke to ACA about the new style cowling you mentioned and they stated it is only approved for the 180hp Decathlon, not the 150hp that I have. At this point, Dawley Aviation can't offer any real suggestions, either...
 
I just wanted to post a follow-up on my exhaust issue- albeit a few months late (spent many weeks cleaning up hurricane damage at my house - plane was fine). I eventually spoke to the owner at Dawley Aviation and they gladly modified the #1 cylinder exhaust radius at no charge (I paid shipping back to the factory) and they sent it back to me with a 48-hour turnaround. Much improved clearance now (I did have to install 1/8” fiberfrax heat shielding on that area of the cowl,as well),but, now the area near the bend radius is actually the coolest area on the entire cowl...

Overall, I’m very happy with Dawley’s response and resolution regarding this issue and will definitely use them in the future.
 
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