Resealing fuel tanks

[N6867N]

I’ve tried other places, but with mixed results. Can someone here provide a list of the materials and parts required to reseal the fuel tanks on a 1968 M20C?

if anyone has photos or videos of their process, I would appreciate that, as well. 
 

BTW, Bladders are not an option for me. 
 

Thank you in advance,

Robby Knox

[N201MKTurbo]

It is all in the service manual. Have you read it?

[Jim Peace]

This is all you need to know:  Wet Wingologists 954-647-0154

https://wetwingologistseast.com

[Fritz1]

Or weep no more in Wilmar MN, tank sealing is the one job you want to stay away from no matter how smart or experience you are

[Jsno]

I am in the process of resealing one of my tanks.  It takes a lot of time and incredible patience to strip the tank.  You will need plastic and nylon scrapers that you can find on aviation supply sites.  Do not use metal scrapers. 

You will also need to use Polygone sealant stripper.  It comes in gel and liquid form.  I used gel.  You have to keep stirring it on the sealant with a nylon brush.  I would initially scrap what I could off and then apply stripper and let it sit overnight.  That usually loosens and splash coat and will start working the sealant loose. Although it is safe to use be sure to wear gloves or your hands will be severely dehydrated. Also use good ventilation. I used alcohol to neutralize the stripper and wipe off dissolved sealant with lint free wipes.

I just kept scraping followed by more stripper until I got the majority off.  I did use picks to dig out the sealant from corners and around rivets.  Be careful to not scratch the aluminum. 

This was followed by wiping down with alcohol, acetone then finally with MEK.  Be careful with the MEK as it is very toxic.

After cleaning then Scotch Brite the areas that were scratched and apply alodine to it to prevent corrosion.  Followed by more cleaning with acetone or MEK.

I also found the removing the fuel outlet tube and screen allows you to reach the inboard aft corner much easier as the screen will either get broken or covered in sealant.  Its four rivets.

For sealant use PRC 1422 B or PPG 870 B for fillet sealing and on each rivet.  Then after it sets up brush a thin coat of 1422 A2, or PPG 870 sealant. There are many sealants out there that are cheaper, but these two are corrosion inhibitive. Your maintenance manual has illustrations and instructions on how this is done.  Tou will use 1428 to seal the fuel panels except for the one under the wing walk.  On that one use 1422 so that it won't leak when you step on it.

You will need a pneumatic sealant gun, tubes and various plastic tips to apply the sealant.  Plastic spatulas and small brushes.   If you buy sealant in the can instead of tubes it is cheaper.  A couple of boxes of latex or rubber gloves. A six inch mirror to lay in the tank and be able to see the blind spots.  There are areas that you cannot see on the inner section on top from the access holes. I also ordered new screws for the panels because the old ones had sealant on them, and I had to drill several out.  Order stainless.

Most of all you will need a lot of time and patience. Good luck.

 

Mine is prepped; I am just waiting for a good uninterrupted weekend to reseal.

 

[N201MKTurbo]

MEK seems like awful stuff, but if you look at the SDS for MEK vs Mineral spirits, mineral spirits seems worse than MEK.

[N201MKTurbo]

I use the SEMkits for the fillet, so I can use the dispenser, and the cans for the brush and panels.

[Huckster79]

Man I’d really consider one of the pros.  Wetwingologist has mine right now.  He is undoing years of bad tank repairs- some set me up for an accident- the holes for water to get through to make its way to the drains some were blocked.  A bad patch around the fuel drains caused moisture to collect under the failing sealant and was causing some corrosion.  My fuel pick up screens had been partially blocked w sealant then picked at to remove it making the holes larger than they should be.

its your fuel system, I’m glad now mine started leaking before the old hack jobs caused me real trouble - I’m very thankful for all that wetwongologist is correcting even though it’s going to be a good sized bill- I’ll know my fuel system is now in top notch order.  

[N201MKTurbo]

I have fixed two tanks that were resealed by the pros. One the sealant was not mixed properly and didn't cure most places. The other wasn't cleaned properly after stripping and was outgassing along all the seams and blowing holes in the sealant along all the seams.

There is no magic to sealing a tank, just a lot of work.

Is there a lot of people doing improper repairs in the field? Absolutely! I have never seen a field repair that was done according to the service manual. I always thought that was a requirement. It is amazing how many mechanics think they know better than the manual, or they just don't care. A properly done repair should be as good as the original sealant from the factory.

[Paul Thomas]

When I built tanks for my RV7, I found that working with the sealer was no-where as bad as advertised -- as long as you kept your work area and gloves clean. That is the big trick, if not, the mess gets exponentially bigger as you continue working. I found the best use of gloves was the cheap one from Harbor Freight... wear two layers and keep changing the outer layer. Two layers makes it easier to quickly change gloves as you continue working.

The sealant working time was shorter than advertised for me and would cut it in half. It did not flow as well once I got past half working time but my working temp is high 70's.

[Jsno]

4 hours ago, Paul Thomas said:

When I built tanks for my RV7, I found that working with the sealer was no-where as bad as advertised -- as long as you kept your work area and gloves clean. That is the big trick, if not, the mess gets exponentially bigger as you continue working. I found the best use of gloves was the cheap one from Harbor Freight... wear two layers and keep changing the outer layer. Two layers makes it easier to quickly change gloves as you continue working.

The sealant working time was shorter than advertised for me and would cut it in half. It did not flow as well once I got past half working time but my working temp is high 70's.

I like to use the sealant with long working life such a B-2 rather than B 1/2.  That is 1/2 hour vs 2 hours.  Temperature and humidity affect the cure times.  So I do mine in the morning when it is cool.

 

[LANCECASPER]

11 hours ago, Jsno said:

I used alcohol to neutralize the stripper

I'm not sure I'd admit that on an online forum . . . lol

[M20F]

I think many are going with reseal feedback here versus patch.  In most cases a patch suffices and a reseal is not needed.  
 
People treat tanks like cylinders, 1 goes bad and the solution is a TOP.  

IRAN is always the answer. 

[Huckster79]

30 minutes ago, M20F said:

I think many are going with reseal feedback here versus patch.  In most cases a patch suffices and a reseal is not needed.  
 
People treat tanks like cylinders, 1 goes bad and the solution is a TOP.  

IRAN is always the answer. 

Very true… I guess I’m too close to my own current project.  A patch was not an option for me, but if it is then that’s great.  Mine was just shot, we attempted a patch but found the original sealant was very crumbly… so we felt we would be chasing patches over n over.  But if sealants in good shape overall I’d agree.  

[whiskytango]

21 hours ago, Huckster79 said:

Man I’d really consider one of the pros.  Wetwingologist has mine right now.  He is undoing years of bad tank repairs- some set me up for an accident- the holes for water to get through to make its way to the drains some were blocked.  A bad patch around the fuel drains caused moisture to collect under the failing sealant and was causing some corrosion.  My fuel pick up screens had been partially blocked w sealant then picked at to remove it making the holes larger than they should be.

its your fuel system, I’m glad now mine started leaking before the old hack jobs caused me real trouble - I’m very thankful for all that wetwongologist is correcting even though it’s going to be a good sized bill- I’ll know my fuel system is now in top notch order.  

I agree with @Huckster79 and @Jim Peace.  Back in 2005 my previous K model was on the ramp after having its annual performed.  A hail storm rolled through and did major damage to the wing, elevator and fuselage skins.  The insurance company included stripping and resealing of the main and aux fuel tanks in both wings as part of the hail damage repair.  The shop that did the work assured me that they had done other Mooney fuel tank strip and seals and knew what they were doing.  Big mistake.  They took MONTHS tracking down multiple leaks that they created as a result of their strip and seal job.  When I needed to have the tanks in my current K model resealed I used Wetwingologists East.  The job was done perfectly the first time and came with a 7-year transferrable warranty.

[Kelpro999]

I’ve tested many removers, strippers and cleaners. The winner was polygon gel and liquid. The liquid is stronger but drying time is much faster. I found that different strength compounds can be a mix of both. It takes a few days for the gel to uptake liquid but will 100% when kept in a common container.

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