Urgent Heater Muff/Exhaust Heads Up!

bmarvel · #1 12-07-2020, 05:27 PM

I discovered a problem with one of the heat muffs on my -14A today. Actually, the heat muff was only part of the problem, which also involved the exhaust system. As a data point, the airplane has 700 hours on it.

I thought that both muffs fit tightly enough on the exhaust pipe when I installed them. They are held in place by bendable tabs. Today I noticed that the tabs on the inside diameter of one of the end plates on a muff had worn off. The resulting sharp edge had cut a groove into the exhaust pipe around a portion of its circumference.

I did not measure the depth of the cut but it is very definitely noticeable. I just ordered replacement end plates for both muffs and will pull the assembly apart tomorrow to have a better look at it. There may be damage to the exhaust pipe under the other three end plates but I only noticed this one in the limited time I had.

This is an area you may want to pay attention to as it is not very noticeable and could create some exhaust pipe damage before you see it. And clearly, an exhaust pipe leak into a heater muff is not a good situation.

I don't now how tightly the end plates are supposed to grasp the exhaust pipe, but certainly I intend to bend the tabs sufficiently to tighten up that joint when I install the new parts. It would be be an improvement if the end plates were designed such that they could be attached rigidly to the exhaust pipe with a hose clamp instead of via a friction fit based on how you bend the tabs.

jeffw@sc47 · #2 12-07-2020, 05:46 PM

Good catch.

I'm looking at my exhaust pipe heat muffs and trying to correlate your description of exactly what failed. i think that I see the area that may be the part that failed.

Can you post pictures of the portion that wore off of the bendable tabs on the inside circumference of the end plates after you get into it some more?

bmarvel · #3 12-07-2020, 06:03 PM

Yes, I'll take and post a couple photos tomorrow when I get it apart.

Walt · #4 12-07-2020, 07:25 PM

I just removed a 'front' heat muff from a 14 that had failed, some of the parts had broken off and others were deformed.

azflyer21 · #5 12-07-2020, 07:37 PM

At only 78 hours the outer most muff on the right side did the same thing.

GOFT · #6 12-07-2020, 07:46 PM

Timely!
I found that the heat muffs keeps loosening after a few hours of flying. Tightening the "hose" clamps deformed the very flimsy/fragile endplates.

Just replacing the endplates are not an option. Did so and it failed a second time.

One solution might be to install two endplates (back to back) on each end of the muffler to beef up the surface area and strengthen the endplates so that the clamp force can be increased.

Are thicker/heavier end plates available or any other solutions out there?

Thanking a solution in advance :-)

czechsix · #7 12-07-2020, 08:54 PM

Wonder which supplier is making the heat muffs for Vans these days, or if the design has changed. I think I had a Robbins heat muff on my RV-8A and it's got over 1000 hours on it with no issues.

JDA_BTR · #8 12-07-2020, 09:11 PM

Mine has 140 hours and hasn’t quite failed but isn’t very sturdy either. It’s the forward one that is the worst. I can’t tighten it because of the deformation when the clamp is secured. I’m looking forward to anyone having this problem solved.

Maybe this is better?
https://www.aircraftspruce.com/catal...at05-15249.php

lr172 · #9 12-07-2020, 10:43 PM

Quote:

Originally Posted by czechsix

Wonder which supplier is making the heat muffs for Vans these days, or if the design has changed. I think I had a Robbins heat muff on my RV-8A and it's got over 1000 hours on it with no issues.

I doubt these are Robbins, as mine are very sturdy and well designed. They do not become loose or create wear if installed properly (700 hours for 2 of them on my 6A). The posters here may want to check out Robbins wings to see if they make a muff that will fit the 390 exhaust. Probably a good upgrade idea if the posts here are indicative of the part quality.

Larry

rv8ch · #10 12-07-2020, 11:26 PM

Quote:

Originally Posted by JDA_BTR

Mine has 140 hours and hasn’t quite failed but isn’t very sturdy either. It’s the forward one that is the worst. I can’t tighten it because of the deformation when the clamp is secured. I’m looking forward to anyone having this problem solved.

Maybe this is better?
https://www.aircraftspruce.com/catal...at05-15249.php

Same with mine - it took quite a bit of fiddling with it to make it tight. The muff you linked to looks far better.