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Fuel filler cap assembly. Removal. 4 screw 38mm.


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Hi,

I am thinking of fitting a fuel filler lock like the one on Midland Chandlers. See photo.

My filler is a 38mm flush screw cap and the outer containing body sits about 5 to 10mm high above

the hull surface and has 4 screw holes to fix it in place.

Can anyone tell me how this part is removed / replaced please?

Taking the filler cap out it looks like it presses down on a rubber seal although this may be for the cap.

If it does then surely fitting the lock under the cap assembly will hold it higher than before and it may not seal?

The body is 'painted in place' and I am very wary of trying to remove things when I'm not sure what is holding them

in place.

In the engine bay the Deisel tank appears to fit flush with the underside of the hull so there is no internal access to

the filler assembly. In fact I think it is part of the hull as I can see seam welds around it.

Fuel_Lock.jpg

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Undo the 4 screws in the outer ring and the whole thing should come upwards.

There should be a (probably rubber) gasket seal under the outer ring. You will need to fit that below the MC lock widget and obtain another seal to go between the lock ring and the filler outer ring.  You might be able to get away with Marine Flex or other sealant, but because any leak will end in your diesel tank (promoting diesel bug) you need to be sure you have a seal.

You may need longer retaining screws to allow for the thickness of the lock and the extra gasket.

 

N

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Ahh ok so the Deisel seal is the filler body to the hull surface?

I assumed a separate tube from the tank which the filler body sealed to further down

because filler bodies I have seen for sale have a metal pipe below the cap.

Makes sense if the fuel tank is welded to the hull surface.

Looking at that photo the lock is in two parts which means it could never be sealed with circular

gaskets.

I may have to shelve this idea.

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19 minutes ago, Cruiser_Boy said:

Ahh ok so the Deisel seal is the filler body to the hull surface?

I assumed a separate tube from the tank which the filler body sealed to further down

because filler bodies I have seen for sale have a metal pipe below the cap.

Makes sense if the fuel tank is welded to the hull surface.

Looking at that photo the lock is in two parts which means it could never be sealed with circular

gaskets.

I may have to shelve this idea.

 

What is the fuel tank on your boat? Is it a separate tank under the rear deck with a pipe, or hose between the filler and tank, or is it built in to the shell, so the rear deck is the top of the tank? This has implications for how the lock is assembled and sealed. Your wording suggests the former.

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48 minutes ago, Cruiser_Boy said:

Ahh ok so the Deisel seal is the filler body to the hull surface?

I assumed a separate tube from the tank which the filler body sealed to further down

because filler bodies I have seen for sale have a metal pipe below the cap.

Makes sense if the fuel tank is welded to the hull surface.

Looking at that photo the lock is in two parts which means it could never be sealed with circular

gaskets.

I may have to shelve this idea.

On Narrowboats the top of the diesel tank is also the stern deck so they just cut a hole in it and then seal the top ring to the deck with 4 screws drilled and tapped into the deck. The neck just hangs inside the tank.image.png.c9eee9684ea1f68b42af60440cd173af.png

 

 

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1 hour ago, Cruiser_Boy said:

 

Looking at that photo the lock is in two parts which means it could never be sealed with circular

gaskets.

I think the idea is that the two semi circles butt up against each other to give you a flat surface above and below for the gaskets.  I would want a smear of Hylomar or similar between the two halves to make sure that in driving rain or a leaky gate there was no leak path into the tank.

 

Alternatively get a staple welded either side of the filler and put a bar through with a padlock one end and a bend the other.

 

N

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47 minutes ago, ditchcrawler said:

On Narrowboats the top of the diesel tank is also the stern deck so they just cut a hole in it and then seal the top ring to the deck with 4 screws drilled and tapped into the deck. The neck just hangs inside the tank.

Not all narrowboats. Some have separate tanks, hence my question earlier to the OP. It makes a difference how the filler is sealed.

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1 hour ago, Jen-in-Wellies said:

 

What is the fuel tank on your boat? Is it a separate tank under the rear deck with a pipe, or hose between the filler and tank, or is it built in to the shell, so the rear deck is the top of the tank? This has implications for how the lock is assembled and sealed. Your wording suggests the former.

No I think it is built in I was assuming again which is always dangerous :-)

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1 hour ago, ditchcrawler said:

On Narrowboats the top of the diesel tank is also the stern deck so they just cut a hole in it and then seal the top ring to the deck with 4 screws drilled and tapped into the deck. The neck just hangs inside the tank.image.png.c9eee9684ea1f68b42af60440cd173af.png

 

 

Yes that sounds like mine. I can see no gap between top of tank and underside of hull. So the pipe can raise up without affecting the seal. I just need to find a way to seal the two part frame. I have to wonder why it isn’t all one part.

42 minutes ago, BEngo said:

I think the idea is that the two semi circles butt up against each other to give you a flat surface above and below for the gaskets.  I would want a smear of Hylomar or similar between the two halves to make sure that in driving rain or a leaky gate there was no leak path into the tank.

 

Alternatively get a staple welded either side of the filler and put a bar through with a padlock one end and a bend the other.

 

N

Yes I was thinking of a welded part when I found this online. I know someone who can weld it but I’m worried about all the hassle of preventing the boat catching fire :-)

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7 minutes ago, Cruiser_Boy said:

I have to wonder why it isn’t all one part.

So that you can fit it around a fuel filler which is connected to a pipe leading to a separate tank, without disconnecting the pipework.

  • Greenie 1
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