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Discussion Starter · #1 ·
Here's my situation: Boat is powered by the mighty Atomic 4 which, of course, runs on gas not diesel. Said gas is in an aluminum tank under the settee. There is an approx. 3" hole in the top of the tank for the sender of the fuel gauge; the plate holding the sender is shown in the attached image. To orient you, you are looking down onto the top of the aluminum tank and the round plate has the +-contact for the sender (marked S) and the ground (marked -). As you can see, there is a black rubber gasket between the top of the tank and the sender plate which is held by 5 screws.

Now this is where the problem is. At some point I noticed that there was a smell of gasoline when I lifted the settee cushion. All kinds of alarm bells went off, I surely don't want to have a gasoline leak into the boat. First I thought that the gasket was probably old so I replaced it (to my pleasant surprise, this is a standard part, a "fuel sender gasket" that sells for a few dollars).

This may have helped a little (not sure) but it did not cure the problem, it still smells like gasoline, in particular on a boisterous sail on starboard tack with a full tank (when the liquid presses against this side of the tank). The problem is that the 5 screws that press the gasket against the top of the tank are just sheet-metal screws into the aluminum. Given the softness of the aluminum and the thin wall of the tank, there is only very little force one can exert without stripping the threads. The keen observer will notice that two of the screws don't match the others; this is because exactly that happened and I had to replace the originals with a slightly larger screw. So I cannot apply any more force on these screws to tighten up the gasket.

So what is a sailor to do? Is there a trick that will allow me to exert more pressure on the rubber gasket?

Or should I smear some sealant onto the gasket? This is something I prefer to avoid since I doubt that a rubber gasket is meant to be used with a sealant.

Am I overlooking something?

Thanks for any insights
 

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Tap the screw holes for bigger machine screws. Change the hoses to the newer less gas permeable hose. It could also be leaking at the S and - wire posts.
 

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S/V Caper Nonsuch 36
'86 Hinterhoeller Nonsuch 36, major refit '14-'15, Yanmar 4JH4AE 54 hp.
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Try to use a hex head screw w/ lock washer, up from the tank into the rubber gasket. If the gasket is a tight fit it will hold the screw and lock washer, it not upsize the screw. Place the cover back on, put on new nuts and tighten. If that doesn't work try to epoxy or similar the screws in place up through the tank. Good luck.
 

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I've used Permatex, and similar sealers, since I was a kid, and always had good results...if I used the right product/formula...and did proper prep (no lazy short cuts).
In your case, also think about lathering it on the screws.

Cheap fix...just your time.
 

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You can get a weld-on boss for the sender. Welding it might be more than you want to get into, but it may be possible to epoxy it to the tank instead.

The boss will have good machine screw threads in it with a flat face, so the sender gasket will be true and tight.

Mark
 

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Discussion Starter · #9 ·
Permatex fuel resistance sealer. used on aircraft tanks with the same type fuel sender. you could install rivnuts in the tank which would use machine screws instead of sheet metal screws
I suppose the Permatex would go together with the rubber gasket, not instead of it, right?

I had thought of rivnuts but I have never used them. Having machine screws instead of sheet metal screws would, indeed, so much better!

However, the concern I have is that the rivet heads will protrude over the surface, and thus indent the rubber gasket from below. Won't that be leaking? Am I visualizing this wrong?
 

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Discussion Starter · #10 ·
It might work to remove the screws, fill the holes with JBWeld or similar, rotate the piece a bit, bore suitable holes in fresh aluminum.
Yes, this may be a possibility. But it does not address the basic design problem, that the aluminum is just too thin and too soft for hold the self-tapping screws. So, I think I will continue looking for another solution
 

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Discussion Starter · #11 ·
Tap the screw holes for bigger machine screws. Change the hoses to the newer less gas permeable hose. It could also be leaking at the S and - wire posts.
Bigger machine screws: Not sure that would do much. I haven't measured the thickness of the aluminum (perhaps I should) but it may well be less than 1/8". There will be very few threads in the material, whether I use a self-tapping screw (like now) or a machine screw.

I don't think the hoses are the problem, the smell is only right at the sender. But you are right, I should take a closer look at the wire posts. Thanks for the suggestion.
 

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Discussion Starter · #12 ·
Try to use a hex head screw w/ lock washer, up from the tank into the rubber gasket. If the gasket is a tight fit it will hold the screw and lock washer, it not upsize the screw. Place the cover back on, put on new nuts and tighten. If that doesn't work try to epoxy or similar the screws in place up through the tank. Good luck.
I would be concerned about the first solution, relying only on the friction of the rubber to prevent the bolt dropping into the tank which would really suck.

The second may be a possibility, though. I am still considering option and will keep this in mind. Thanks!
 

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Discussion Starter · #13 ·

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Discussion Starter · #14 ·
You can get a weld-on boss for the sender. Welding it might be more than you want to get into, but it may be possible to epoxy it to the tank instead.

The boss will have good machine screw threads in it with a flat face, so the sender gasket will be true and tight.

Mark
I did not know such a thing existed (I now found it as 'flange'), so that is good to know. As you suspected, welding (on a gas tank :eek) will be WAY down on my list of options.

But epoxy-ing it on the tank may be a possibility. Thanks!
 

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I think colemj has sent you in the right direction. A "cheap" fix could cost you your life, so please consider doing it the right, gas tight way. If it was diesel I might try any other method, but with gasoline, no way.
 

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Discussion Starter · #16 ·
If your hole pattern is "Standard SAE 5 hole pattern" you could use the "Stainless Steel Underring" here Mounting Adapters for SHS, S3U, SSS and SSL Sensors by WEMA USA, Inc.

If not you can make your own by "stealing" this design
Huh! What a clever design! The person who put the cut-out in there must be a genius!

I will measure the exact dimensions but this may be the best solution, if it fits. I will even overlook the fact that the S/H is more than the item itself )

Thanks a lot!
 

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Discussion Starter · #17 ·
I think colemj has sent you in the right direction. A "cheap" fix could cost you your life, so please consider doing it the right, gas tight way. If it was diesel I might try any other method, but with gasoline, no way.
You are absolutely right, I am taking this very seriously!

Yes, Colemj's solution is a good one. I have to say that at this point I am even more swayed by the 'underring' solution from Knuterikt. No chemicals (epoxy) whatsoever involved.

Only thing with this solution is to not forget that this thing is under there. To avoid that at some point in the future I loosen all screws simultaneously :eek
 

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Bigger machine screws: Not sure that would do much. I haven't measured the thickness of the aluminum (perhaps I should) but it may well be less than 1/8". There will be very few threads in the material, whether I use a self-tapping screw (like now) or a machine screw.

I don't think the hoses are the problem, the smell is only right at the sender. But you are right, I should take a closer look at the wire posts. Thanks for the suggestion.
If it's 1/8" aluminum a 10-32 machine screw would have 4 threads engaged and that would be really strong. Even thinner aluminum would work. Get a piece of aluminum the thickness of your tank and drill and tap it and test for yourself. Make sure the tank vent isn't clogged causing pressure in the tank.
 

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......Only thing with this solution is to not forget that this thing is under there. To avoid that at some point in the future I loosen all screws simultaneously :eek
Tack it on, with some fuel resistant glue or even the permatex sealant suggested above.
 
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