Author Topic: Need help with a fuel tank issue update  (Read 1605 times)

Offline Johncolleary

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Need help with a fuel tank issue update
« on: February 18, 2018, 01:48:10 PM »
I have a 2001 Aprilia Falco that has been sitting for quite a while with "good" california fuel in the tank.  I want to sell it as I don't ride it any longer. about 6 months ago it began to leak fuel so I drained it and figured I'd deal with it at some time, now is the time.  Have a new o ring for the full pump assembly so today I pulled it apart and installed the new o ring. still leaks. pulled it apart again and put a straight edge in the sealing area and found the plastic dips down between each threaded insert enough so that the o ring won't seal any ideas on a resolution my thought is that the fuel distorted the plastic causing the low spots in between the inserts.  is there a gas resistant sealer I could use?  or a source for a custom O ring that would be of greater diameter?  Help I really want this thing to go to a good home without leaking.  see photos  Looks like the largest gap with a straight edge is .018 in.




« Last Edit: March 04, 2018, 03:20:16 PM by Johncolleary »
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Online RinkRat II

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Re: Need help with a fuel tank issue
« Reply #1 on: February 18, 2018, 02:24:59 PM »

 A local bearing house should have o-ring material to make one but I would see if they have Square-ring material. They make it in different dimensions that are not square as the name implies, for example 1/8 X 3/16" Something a little taller  than your O-ring should make up the gap.

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Offline rodekyll

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Re: Need help with a fuel tank issue
« Reply #2 on: February 18, 2018, 02:56:21 PM »
I don't know the bike or the tank.

That said, it looks to me like the o-ring seals in a "circle" inside the "circle" of screws.  As the screws are carefully not overtightened, the two surfaces should be drawn together and the depression between screw holes should flatten out.

Since I don't know the tank, please tell me if the threaded inserts are open to the inside or blind.  Also, how tall (proud) does the o-ring set in its groove?  0.018 isn't a lot of gap.  I would expect the o-ring to crush into that amount of space.

Possible generic thoughts on sealing:

There's a product called "SEAL ALL" that I've used successfully to seal gas tank leaks.  I even used it to pot an LED bulb in place at the end of a sight glass (to light up the sight glass).  No leaks if used correctly, and I've been able to pry parts loose (very carefully) without distorting either part.

You might be able to "boost" the o-ring in its groove by pre-packing the groove with waxed string (like candle wick).  The string doesn't make the seal, but it makes the o-ring "bigger".

You might make a flat gasket from fuel-proof gasket material (available by the sheet at the auto parts store and a lot of hardware stores) to take up the surface irregularities.  Dress it with a little sealer on the tank side and a LIGHT torque on the gasket to produce a flat surface.  Then do the plate install against the newly-flat tank.

Of course none of this will fix anything if the threaded inserts are leaking or if there's a leak somewhere else pretending to come from the plate.  So after sealing as well as you can, seal the known openings of the tank, inject a little air (a couple # should do it) and immerse the tank in water.  Any leaks will reveal themselves as bubbles.

Offline guzzisteve

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Re: Need help with a fuel tank issue
« Reply #3 on: February 18, 2018, 03:21:28 PM »
I've done a few Ape tanks and you need the sealer for fuel, just like the service manual says, won't work w/o it. The new o-ring is right size, needs to be coated. Tank bottoms are like that even new ones.
It's Loctite #518, I also use it on Stelvio tanks for the tank fill rubber on earlier models so fumes don't get on paint.
« Last Edit: February 18, 2018, 03:25:19 PM by guzzisteve »
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Re: Need help with a fuel tank issue
« Reply #3 on: February 18, 2018, 03:21:28 PM »

Offline Johncolleary

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Re: Need help with a fuel tank issue
« Reply #4 on: February 18, 2018, 04:20:12 PM »
I don't know the bike or the tank.

That said, it looks to me like the o-ring seals in a "circle" inside the "circle" of screws.  As the screws are carefully not overtightened, the two surfaces should be drawn together and the depression between screw holes should flatten out.

Since I don't know the tank, please tell me if the threaded inserts are open to the inside or blind.  Also, how tall (proud) does the o-ring set in its groove?  0.018 isn't a lot of gap.  I would expect the o-ring to crush into that amount of space.

Possible generic thoughts on sealing:

There's a product called "SEAL ALL" that I've used successfully to seal gas tank leaks.  I even used it to pot an LED bulb in place at the end of a sight glass (to light up the sight glass).  No leaks if used correctly, and I've been able to pry parts loose (very carefully) without distorting either part.

You might be able to "boost" the o-ring in its groove by pre-packing the groove with waxed string (like candle wick).  The string doesn't make the seal, but it makes the o-ring "bigger".

You might make a flat gasket from fuel-proof gasket material (available by the sheet at the auto parts store and a lot of hardware stores) to take up the surface irregularities.  Dress it with a little sealer on the tank side and a LIGHT torque on the gasket to produce a flat surface.  Then do the plate install against the newly-flat tank.

Of course none of this will fix anything if the threaded inserts are leaking or if there's a leak somewhere else pretending to come from the plate.  So after sealing as well as you can, seal the known openings of the tank, inject a little air (a couple # should do it) and immerse the tank in water.  Any leaks will reveal themselves as bubbles.


The inserts are blind the tank is a rotary moulded tank .
the o ring is .05 above the face of the plate.
one thing I was just noticing is that the tank tilts in towards the inside of the tank from the outside edge of the tank that gap is .045



so I would think it would seal but the variations combined must be enough to screw it up Ill try the additional material under the oring and see how that works
I alos ordered Aerolife fuel tank sealer and will try that.
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Offline rodekyll

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Re: Need help with a fuel tank issue
« Reply #5 on: February 18, 2018, 04:24:50 PM »
Pay more attention to GuzziSteve than me.  I gave generic ideas.  He's been hands-on with the actual tank.  If he says to dress the o-ring with a particular sealer, he's probably speaking from experience. 

Offline guzzisteve

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Re: Need help with a fuel tank issue
« Reply #6 on: February 18, 2018, 05:11:03 PM »
The red Loctite stuff is pretty good, the 1st one was w/none and it leaked, had a tube of 518 after that and they sealed. Pretty common problem.
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Offline Motormike

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Re: Need help with a fuel tank issue
« Reply #7 on: February 18, 2018, 06:23:55 PM »
This was (is) a common problem with the plastic "roto-mold" tanks Ducati used on many of their bikes.  Ducati had a recall on the first gen. Multistrada to replace the round o-ring under the fuel pump flange with a square "quad-ring" to prevent fuel leaking.  So going to that type of seal may be the easiest fix.  The root of the problem is the ethanol in the gas causing the nylon material of the tank to distort.  I have seen a couple of posts on various Ducati web sites where the owner goes as far as filling in the low spots on the tank flange with JB weld and then sanding it to a flat surface.  A lot of work, but it seemed to fix the fuel leak once and for all.  Good luck, and let us know what you end up doing, as a lot of Moto Guzzis have nylon fuel tanks too!

Offline Johncolleary

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Re: Need help with a fuel tank issue
« Reply #8 on: February 19, 2018, 06:54:13 AM »
I like the idea of filling it with JB weld seams like a good long term solution might be a couple of weeks before I can get back to it but will update all when I'm done
Thanks
"The secret of life is honesty and fair dealing. If you can fake that, you've got it made." �Groucho Marx
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Offline Johncolleary

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Re: Need help with a fuel tank issue
« Reply #9 on: March 04, 2018, 03:19:51 PM »
Up Date:
Ok so I tried an aircraft fuel tank sealent, 



I applied a small bead in the ring groove of the fuel pump housing and then a larger bead on the seating area of the gas tank itself.  I let it cure for 5 days and reinstalled the tank on the bike and filled with gas.  so far a couple of days all is holding well.
Bike is going up for sale.
thanks all
« Last Edit: March 04, 2018, 03:21:04 PM by Johncolleary »
"The secret of life is honesty and fair dealing. If you can fake that, you've got it made." �Groucho Marx
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