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Leaky Petrol Tank Cap Solutions?


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#1 Tornado99

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Posted 17 November 2020 - 06:36 PM

Has anyone found a good way to stop fuel splashing out from the tank cap? Seems to be a common issue with different cap types.
Ive taken my flip type cap off and plugged the vent hole (tank has a vent line near top already) and tried stretching the cap spring to give greater pressure on the seal. No real improvement.

Edited by Tornado99, 17 November 2020 - 06:37 PM.


#2 imack

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Posted 17 November 2020 - 07:26 PM

How does your flip cap attach to the tanks filler neck?

#3 Chris1992

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Posted 17 November 2020 - 07:35 PM

I used to have this problem as the rubber ring that sealed the cap against the filler neck had been squashed over time and offered less resistance. I cut out another one from thicker rubber and pushed that into the cap as well as the original seal. It's a rather crude solution, but so far it's worked a treat! I have one of the fuel caps you twist into place and then lock. 



#4 JCmini

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Posted 17 November 2020 - 07:54 PM

I bought a new seal. Seemed to sort the problem out. 



#5 imack

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Posted 17 November 2020 - 08:15 PM

How does your flip cap attach to the tanks filler neck?

#6 Tornado99

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Posted 17 November 2020 - 08:59 PM

How does your flip cap attach to the tanks filler neck?

It is the one with an outside threaded brass sleeve that is force fit on the filler neck. No original cap inside it like the ornamental cover type flip caps. 

 

Looks to be this one:

 

http://www.minispare...e=350/SP228.jpg

 

http://www.minispare...01.aspx|Back to

 

 

 

In addition to making the spring a bit longer by stretching it, I placed a large rubber washer between the cap and the spring, to give it even more force on the seal. It now needs a fairly strong push to get the cap the latch on the base....so should be making a lot more pressure on the sealing surface...but still have fuel outside the neck under the cap after a fill up. I've tried keeping the fuel level to well below the cap, but still enough sloshing that it escapes.


Edited by Tornado99, 17 November 2020 - 09:03 PM.


#7 sledgehammer

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Posted 17 November 2020 - 09:07 PM

would silicon grease massaged into the rubber seal help ?
 

or would the petrol just wash it off ?



#8 Tornado99

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Posted 17 November 2020 - 09:27 PM

I see two cap seals on MiniSpares. One appears to be a spongy rubber. Anyone know if these work for the flip caps? 



#9 Tornado99

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Posted 17 November 2020 - 09:28 PM

would silicon grease massaged into the rubber seal help ?
 

or would the petrol just wash it off ?

 

 

Worth a try...



#10 imack

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Posted 17 November 2020 - 09:30 PM

How does your flip cap attach to the tanks filler neck?

It is the one with an outside threaded brass sleeve that is force fit on the filler neck. No original cap inside it like the ornamental cover type flip caps. 
 

Ok, so it fits the same as my old Enots caps. Mine used to leak but the problem was the fuel coming from between the tank neck and the brass collar and in later years from between the cap and the collar when the original gasket shrunk.
I fitted a thin butal O rings between the collars and tank filler necks and made new gaskets from gasket paper to replace the original gaskets between the collars and caps. No more leaks, you can open the caps and there'll be a puddle of fuel sitting up against the brass collars but they dont leak. I blocked the cap vents years ago.

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#11 Tornado99

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Posted 17 November 2020 - 09:55 PM

To leak from the brass to neck area would require fuel getting past the seal ring to sealing surface flange. I guess putting some teflon tape or paste on the brass threads might help this. But real fault is at the seal/flange point.

Will explore a few of these tips.

#12 Tornado99

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Posted 17 November 2020 - 10:01 PM

On second look, maybe I've been misundertanding where the rubber seal contacts. Had thought it was the stock cap sealing surface sitting down at the neck opening and those cap notches were making a thin sealing area. Now I see the flip cap should seal on its own collar. Thus leaks from brass ring to neck area are a real potential.

#13 surfblue

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Posted 20 November 2020 - 04:55 PM

 

Has anyone found a good way to stop fuel splashing out from the tank cap? Seems to be a common issue with different cap types

 

Put less petrol in?  ;D



#14 Moke Spider

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Posted 20 November 2020 - 06:01 PM

I haven't tried these type of Flip Lids, but they do look promising for this issue.

 

On the Mokes, I have made my own fuel tanks, mainly for safety, I have put 'leak proof' lids on these. I've fitted a threaded neck to the tanks, and I have a simple screw on Brass Cap, into which I've fitted a rubber seal and a retainer for the seal. It's kinda crude, but it works, even in a roll over, they don't spill a drop.

 

I have fitted vents to the tanks, these have one way valves so they only let air in. The only 'down side' of having these is if you are only doing short runs or parking up for a while is to be sure the tank isn't full but has some air in them, otherwise on a warm day, as the pressure builds in the tank, the fuel will come out the Jet in the Carb and find it's way down the cylinder that has the open Inlet Valve, enough to cause them to hydraulically lock when trying to start them ! I could have fitted an expansion chamber in the tanks, similar to the stock ones, but we need maximum range and as long as one is aware of this issue, it hasn't been a problem.

 

I'm just now going finding a similar solution for a screw on cap for a good friend, that can be retrofitted to a standard tank, it would also work on the standard Mini fuel tanks.

 

I don't know if this might be an option here ?



#15 Tornado99

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Posted 20 November 2020 - 06:37 PM

Motorcycles can also suffer from fuel temperature expansion issues. typically need a vent/overflow tube fitted, even with fuel injector systems. My injected engine Triumph bonneville will dribble fuel if tank filled near top and left sitting on a warm day. Vent tube drops overflow right on the exhaust pipe near where silencer connects!




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