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1001001 12-08-2020 06:01 AM


Originally Posted by lr172 (Post 1483559)
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, are you using the Robbins on your RV-10?

bkervaski 12-08-2020 06:31 AM

Same here, both become loose again after about 50 hours of flying.

bmarvel 12-08-2020 07:20 AM

Part number
As an FYI until I get some pix today, the part number involved is EX-00013C and in my plans is shown on page 48-04, figure 2.

On this drawing you can see what I call "tabs" on both the O.D. and the I.D. of the part. The outer tabs lie against the heat muff skin and the inner tabs lie against the exhaust pipe.

The only way to secure the entire assembly to the exhaust pipe is by bending the tabs on the I.D. so that they press firmly against the pipe. From what I saw yesterday, and will photograph and post later today, is that some of these inner tabs apparently wore away, allowing the sharp edge remaining to cut into the exhaust pipe. As others have pointed out, this is very thin material and is easily distorted. I suspect this situation is ripe for a solution, either by Van's or some aftermarket source. Will know much more when I disassembly mine, take photos and post them. Stand by...

lr172 12-08-2020 08:46 AM


Originally Posted by 1001001 (Post 1483583)
Larry, are you using the Robbins on your RV-10?

No, I have them on my 6A. One came from Vetterman iwth the exhaust and the other I purchased from Robbins and he gave me custom clocking of the tube flanges to help with the scat routing. I have the vetterman exhaust on my 10 and they used to source muffs from Robbins and I believe they still do. The vetterman muffs on the 10 are also very high quality, though unsure if they come from Robbins. The Robbins muffs use a machined hole (close tolereance) in substantial end plates (no tabs or anything like that). The also use long threaded rods to add rigidity to both end plates. I think I only paid $70 for mine from Robbins and that included an extra $10 for custom clocking. These muffs have a very good service history and will last a long time.

Last I checked, he offered them for 1.5 and 1.75" exhaust pipes. Given the potential market to replace what appears to be a less than optimal design, I am sure he would tool up to make them for whatever size pipe is used on the 390's.


JHartline 12-08-2020 01:46 PM

FYI - I have a Vetterman exhaust (IO-390] which I believe I ordered in 2018. The exhaust muffs are from Robbins Wings. The ports on the muffs are set up for the RV-14. The flange that rests against the exhaust pipe is one piece versus the tab design.

Bill, thanks for this post. You’re helping us non-mechanics do a better job maintaining our planes.

bmarvel 12-08-2020 06:02 PM

Heat muff photos
Today I removed both of the heat muffs from the airplane. I have new end plates on order from Van's but they alone will not solve the problem seen in the photos below.

I may use the replacement parts along with some modification to them but will also look at whatever aftermarket muffs are available. Based on what I saw, I do not believe the existing components will last long term due to both the thin material used on the end plates and the friction mechanism for holding them in place on the exhaust pipe.

Vibration causes the friction tabs on the I.D. of the end plates to erode against the exhaust. This causes even more erosion with the result that the end plates become guillotines that cut into the exhaust pipe.

This is what I first saw in a routine inspection of the aft muff. Nothing appeared out of the ordinary.

Looking at a different angle showed some erosion of the forward end plate.

After removing the muffs, this is what appeared under the plate in the above photo. You can see two different cuts into the exhaust pipe. The lower one is not quite as visible in the photo.

Note the two arrows. They show areas where the friction tabs on the I.D. of the end plates have worn off, leaving a razor sharp stainless steel cutting knife that was working its way into the exhaust pipe. Also note the two broken off parts where the end plate halves bolt together. Three of my four end plates were broken like this.

The areas of the exhaust under the other three end plates did have wear but not cuts like shown in the photo above. In all three of those cases, the friction tabs on the I.D. of the end plate were still intact. To me, this is a problem area that needs to be solved. Sure, you can take off the muffs and inspect under them but the real solution is a design that does not have the capability of cutting into an exhaust pipe in the first place.

JDA_BTR 12-08-2020 06:26 PM

What size pipe is the standard Vans exhaust?
For the two muffs, what are the angles for the connections?
I could take them off my plane and measure them but maybe someone else already has it apart..... Mine is in flying condition today!

I suppose you could put a pair of hose clamps on the exhaust pipe, and have the muff ride on between the clamps, with some material clamped between the muff and the pipe. That would reduce a fret of the pipe itself. Not sure how to execute that.

JDA_BTR 12-08-2020 06:52 PM

I looked at some of the Robbins' muffs on the Internet. Perhaps we don't need the muff part entirely. Would the end-pieces of the Robbins muff match our existing "shroud" part? So all we get to improve things is the Robbin's ends?

GOFT 12-08-2020 07:20 PM

Exhaust RV 14 Vans stock
1.75" OD.
Scott come in, Scott come in. :)

bmarvel 12-08-2020 08:05 PM


Originally Posted by JDA_BTR (Post 1483536)

FYI I helped an RV-6A owner install one of those on his airplane. It is an excellent unit, very durable, and the best part is that it is in two halves that clamp together over the exhaust pipe. There is no interior skeleton followed by an external skin like in our 14s. As I recall, the end plates were about 1/4 inch thick so they were well supported by the exhaust pipe.

Downside is the higher cost but the larger problem is that we would have to get two different ones manufactured with the correct inlet/outlet locations and angles.

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