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INSTRUMENT ACCESS PANEL


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During my first annual inspection, my A&P pointed out that someone sealed our instrument access panel with tar.   What a mess!   I'd seen this nasty, black goo oozing out at the seams, and figured it was the appropriate sealant from back in the early sixties when the plane was built,  and it was just something our certified aircraft had to continue to use for a seal on this piece of cowling.  My A&P says someone probably got frustrated from having water leaks in the cabin and use this, and this wasn't the appropriate sort of seal for the access panel.

On inspection of the tar covered mating surfaces of the panel, it appear there is a half-round groove formed into the skin and also the mating surface of the panel, as if a round, rubber cord fit into this groove.  I'm wondering what Mooney intended for this seal, how effective it was and what other guys on C models are using to get a nice water-tight seal on this access panel.

I'm thinking of cleaning all this tar off the mating surfaces, getting a round rubber cord of the appropriate cross-sectional size and then trying a silicone gasket seal in addition to it.  Any thoughts?  I'd like to fix this before she done with her repairs and all buttoned up, but I guess I could do this back at our hangar if worse comes to worse.

If anyone has the appropriate seal done here, is the rubber for this solid or tubular?  Is it simply a rubber cord, or is there a specific gasket/seal for the job--something like a flat, 1" wide piece of rubber with a raised semi-circular bead on it, to fit into the grooves.  I'm thinking a two part, non-adhesive silicone gasket compound might work well too.  Knowing I'll need to remove this panel again without damaging it, I want to avoid adhesive silicone.   Any help or guidance is greatly appreciated.  I don't want tar--but I don't want leaks!

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Yeah, that seems like a good solution, I was just worried about adhesive silicone.  Prying that thing off with any sort of force can deform that thin aluminum, but something that's non-adhesive might be the way to go.

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The 3M product listed above is what I've seen and used on my and other Moonies. It is messy but if carefull it's not bad, RTV is too permanent and hard to remove the panel if needed with out bending it. As for the grove, that is there for the water to travel down, there should be a weep hole in the cover on the side for drainage

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4 minutes ago, Toothdok50 said:

Thanks Mike...that looks like a good product for the job.  I suppose it wouldn't hurt to embed a rubber cord seal in those grooves as well.

keep the grooves free, notice they should act as a rain gutter and let any moisture exit at the lowest elevation of the panel down the side of the plane. 

I think you can get the 3m caulk at (N)atiional (A)ero (P)arts (A) or Aerozone, if not, get it Here

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@orionflt turned me on to 3M Fire Barrier moldable putty to seal that up with. Previous owner had used silicone and cling film to do it, and that was a messy PITA.

The putty is great. It's re-enterable and doesn't grab on with so much force that it could damage the panel. Really sticky to get on your hands, but super easy to work with and makes a great seal.

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Ah, I see, those groove are now full of tar.  I'll get them cleaned out and just put the 3M Calk on either side of the channels.  Seeing one on each of the mating surfaces had me thinking this was for a bead seal...

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My A&P who does a lot of Mooney work says its tar.  Smells like a tar-based roofing sealant too.  Whatever is on the plane, its a mess.  It oozes out and when you try to wipe it off it leaves brown streaks...like tar would.  You got to work at cleaning it without dissolving anymore of the oozing material.  Getting that channel cleaned out seems like a necessary goal in this too.  Thanks for all the input and suggestions.

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Roll it out to about 3/16", it goes to the inside of the grove and around the screw holes, sealing the outside edge doesn't work and will block the grove from doing its job. Place it on the plane not the panel, I keep mine in the refrigerator in the hangar as it's easier/cleaner to work with when cold. I tape the edges of the opening and the panel, any that gets squeezed out is on the tape. Remove excess with a dull safety razor blade, wiping will smear it all over the place

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ShuRugal's suggestion seems promising too.  Hmmm...  

I may just get both of these 3M products and see what's easiest to handle and clean-up.  Not sure which way to go.  Here I was thinking there'd be a called out, approved sealer or preformed seal for this since its a certified aircraft...  

3M Fire Barrier Moldable Putty Stix MP+, Red, 1.45 in x 6 in_ Paint_ Amazon.com_ Industrial & Scientific.html

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Just now, Toothdok50 said:

Thanks RLCarter...appreciate the tips on applying the seal.  Lots of good info...  This makes sense to keep the black calk from oozing out at the seam, like mine is now.  Its quite unsightly.

Sounds like the last guy put way too much, there is only so much room when everything gets tightened down so all the extra has to go somewhere. Take your time and be careful and the mess will be minimal

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DOK,

That area has been sealed with everything over the years...

3M is a supplier of choice when it comes to sealant materials... they live in the automotive space...

It is possible that Mooney didn’t use anything originally... that just doesn’t work very well...

My C used a gray 3M putty material...  easy to get out every year... easy to put back...

It is good to have access back there... the heater controls and other things need to get lubed... and the brake fluid is up there as well...

Best regards,

-a-

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17 hours ago, Toothdok50 said:

I may just get both of these 3M products and see what's easiest to handle and clean-up.

Looks like you just signed up to do a followup comparison write-up. ;-)

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