Best way to affix new wing fuel sight guage

[Chris K]

So this past weekend one of the wing fuel sight gages decided it no longer liked being affixed to the wing and just departed the aircraft.  Upon inspection, it looks like nothing holds these in place other than plain silicone.  Just ordered a new one to the tune of some 145 dollars.  My question is has anyone figured out a better glue to use other than silicone in order to not lose again?  If silicone is sufficient, how much to put in there to make it both stay and work properly?  It appears that whomever siliconed previously did so while leaving an orifice in the center of the silicone - not sure if that was done for function of the magnetic gage or simply installer preference.  

[Pinecone]

You could probably use a urethane mastic (3M 5200) that would stick down better than silicone.   But, it would make it hard to remove if you needed to do so.

 

You can remove items attached with urethane mastic by running a thin wire through the joint to cut it, but with the fuel capsule recessed, it is hard to do that.

[PT20J]

RTV is actually a pretty good adhesive. I would avoid any voids because if water gets in a void it could freeze and since water expands when it freezes it might break the seal.

[Deb]

Some ideas here: 

 

[N201MKTurbo]

RTV is your best bet. Clean out all the old stuff and sand out the corrosion. They get corroded because people don't use enough RTV. Mask around the hole and the top of the indicator capsule. Fill the hole with a generous amount of RTV. You don't want any voids, that's how you get corrosion. Push the capsule into the RTV until it seats into the hole. Make sure it aligns with the tab and is seated into the tab. DON'T TRY TO CLEAN UP THE EXTRUDED RTV! Just leave it be, go home and let it cure overnight. Come back the next day and peal off the extruded RTV, remove the masking tape, clean up any excess RTV with your fingernail. Enjoy your new capsule.

One reason to use RTV is so you can remove it later if you have to.

[N201MKTurbo]

Holy crap, I wrote almost the exact same thing back in '18.

[N201MKTurbo]

An easy way to mask the wing and the capsule is to just set the capsule in place and then mask over the wing and capsule. then cut the capsule out with an X-acto knife.

[ohdub]

@M20Doc just put a new one on my plane last week. He could tell you what to use.

[Guest]

2 hours ago, N201MKTurbo said:

RTV is your best bet. Clean out all the old stuff and sand out the corrosion. They get corroded because people don't use enough RTV. Mask around the hole and the top of the indicator capsule. Fill the hole with a generous amount of RTV. You don't want any voids, that's how you get corrosion. Push the capsule into the RTV until it seats into the hole. Make sure it aligns with the tab and is seated into the tab. DON'T TRY TO CLEAN UP THE EXTRUDED RTV! Just leave it be, go home and let it cure overnight. Come back the next day and peal off the extruded RTV, remove the masking tape, clean up any excess RTV with your fingernail. Enjoy your new capsule.

One reason to use RTV is so you can remove it later if you have to.

We’re you in my shop last week when I was installing one for @ohdub

[mooniac15u]

15 hours ago, M20Doc said:

We’re you in my shop last week when I was installing one for @ohdub

Where were you able to find one?

[Guest]

7 hours ago, mooniac15u said:

Where were you able to find one?

From Mooney, we’re an MSC

[Shadrach]

2 hours ago, M20Doc said:

From Mooney, we’re an MSC

Did you have them in stock or did Mooney send them to you recently?

[Guest]

9 minutes ago, Shadrach said:

Did you have them in stock or did Mooney send them to you recently?

They took several months to get from Mooney. 

[Chris K]

On 10/4/2022 at 4:16 PM, N201MKTurbo said:

Mask around the hole and the top of the indicator capsule. Fill the hole with a generous amount of RTV. You don't want any voids, that's how you get corrosion. Push the capsule into t

Just realized I never followed up on this topic.  2 years later and followed this procedure - no issues since.  Left no voids which meant cleaning up left over RTV afterward pushing the guage in place.  The cleanup was fairly easy as any excess dry RTV on the wing will just break away from painted surfaces by rolling your finger over. 

[dkkim73]

1 hour ago, Chris K said:

Just realized I never followed up on this topic.  2 years later and followed this procedure - no issues since.  Left no voids which meant cleaning up left over RTV afterward pushing the guage in place.  The cleanup was fairly easy as any excess dry RTV on the wing will just break away from painted surfaces by rolling your finger over. 

Same here a few months ago. Completely filling the space with RTV is the key. I took the additional advice of a piece of 3M clear repair tape over the top. Good insurance.