Optional rear heat muff

[smcnutt]

Here's a picture of ours. It has the doublers on both ends. I know that we also had an issue with it having some wiggle in it that was adding to the problem. We found there's a little tab coming off of the outside elbow of the pipe that needed replaced. That tab is a support for the muff and gets sandwiched between the two halves. Ours had partially rusted away and wouldn't catch the muff. Simple fix but made all the difference.

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[Troy Hamon]

We had a new stack with a new tab but the tab as fabricated was too short to actually attach the new shroud when I was installing it. We extended the tab so we could attach the shroud and it has worked great at keeping it totally set in place. My IA also likes having these set in place at the forward end with RTV, so that likely helps as well. In fact, we used RTV to also seal the two halves along the seams.

[walt.buskey]

Yep, Steve, that's about the way I work, too... might take me four times, but I don't give up! LOL

Great suggestions, thanks!

Troy, I like the idea of RTV -- can't help but assist with vibration damping. I'll suggest it to my A&P/IA.

smcnutt, yep, same here, except it was the aluminum of the muff that corroded away - steel tab was still there and OK. I shaped an external bridge strip of 1/16" aluminum on mine that fit over existing side flanges on the muff, went around the curve where the part that attaches to the tab was missing, and continued around a bit more. Drilled through that to attach to the tab and the muff. All fastened with high-temp locknuts & machine screws. That worked as well.

[walt.buskey]

...So I hate to admit it, but I have given up. My former-student-the-DER/DAR came by last week and got me to realize it might well be best to go ahead and get the gold-plated Univair parts, so they're on order. Just too many OTHER (non-airplane) things going on! I'll post a photo when the pieces arrive....

[walt.buskey]

New heat muff parts came yesterday... and yep, they're nice 'n' shiny, just like the Univair pics. Have to admit the weld job on the outlet pipe appears better than what I have, which may in fact be an original 1956 part. I just have a hard time getting over the price, $535, for both upper & lower half. At least shipping (std ground) was included....

So I guess, aside from crying over the price, I'm glad I got new ones; I hadn't realized before how worn my old ones were on the inside of the "small end"! Anyhow, here's how they look:

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[walt.buskey]

Troy, do you recall what type of RTV (brand) your IA used there? I assume it was high-temp... and I'm guessing by "the forward end" you're meaning what I called "the small end"? (That's the end that is smaller diameter, without the squiggly band, and fits over the "can" on the exhaust header, as in the last pic above.)

Thanks -- W

[Glen Geller]

I would not apply RTV to seal the muff to the exhaust pipe, it will be very difficult to remove at next annual and you might bend up those shiny new $500 parts. This muff is only for carb heat and is not used for cabin heat, so no need to make a NASA spaceship seal there.
Maybe just a single wrap of thinnest, softest, aluminum sheet around the steel can area of header, to provide a cushion and take the wear from steel-vs-aluminum. Just secure it with an inch of masking tape, let it wear instead of the fancy new parts.
-
My IA had me install an internal doubler at the forward/small/header end of the muff, to conceal/reinforce the scuffed areas on my very old heat muff parts.
I used the thinnest aluminum sheet I had on hand, I think .025 thick.
I formed it to shape, applied red high temperature RTV to the mating areas and clamped together with a bunch of clothes pins overnight.
Trimmed the excess material, drilled thru holes and installed to the exhaust system.
Oh, and I painted the muffs and rocker covers with Ford Engine Blue high temp rattle juice because I had a can of it in the hangar and it amused me.
It's a real conversation starter with the nerds at the fly-ins.

[Troy Hamon]

Walt, I don't know the brand, just that it was the red hi-temp RTV.

I am no expert on Glen's concerns, but I have removed and reinstalled the shroud. I just cut the RTV with a razor and then it just goes back together cleanly.

[Steve Pierce]

Glen is referencing the exhaust pipe to muffler and Troy and Walt are referring to the heat shroud that goes over the exhaust pipe on the right side. I use the red/high temp RTV at both contact points. I apply a thin film, let it dry and then install. Keeps from the two metals rubbing and wearing through.

[walt.buskey]

Thanks, Steve. Yes, that's it, #16 & #17 in inset illustration.


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