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Discussion Starter · #1 ·
Hi All,

I'm at my wit's end trying to get the fuel flange reinstalled on my 916. Yesterday I went and bought a used tank since the mating surface was a bit distorted. Before anyone asks, yes I replaced the o-ring. I've now tried reinstalling the flange 4 times, each time I get a steady drip.

I've tried applying light silicone grease and pushing it in.

I've tried permatex #2 gasket maker directly on the ring, and around the perimeter of the flange.

I've tried permatex gasket dressing (blue, always tacky).

I'm begining to think this is not somthing possible to fix. Has anyone had one of these things not be a nightmare?
 

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Sounds like your main o-ring is twisting on installation.

You're installing the fuel pump plate by slowly and sequentially tightening M6 x 20 bolts (longer than OEM), correct?
 

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Mayor of Simpleton
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Are you sure it isn't the fuel SENDER that's leaking? The originals had a plastic nut. It is prone to cracking, or it could also be the viton o-ring above it.

I have an extra unit, if needed. And I think I also have an aluminum replacement nut. The new assembly versions have switched to the aluminum nut as well.
 

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Are you sure it isn't the fuel SENDER that's leaking? The originals had a plastic nut. It is prone to cracking, or it could also be the viton o-ring above it.

I have an extra unit, if needed. And I think I also have an aluminum replacement nut. The new assembly versions have switched to the aluminum nut as well.
First time I had my 998 back home after buying it, I smelled gas. Sure enough it was that stupid plastic nut. I feel like there is a decent chance this might be it; my experience with the giant o-ring and flange is that it's pretty difficult to nick it if it's lubed up nice and good. And if you're getting the same leak on a second tank (if I read the post right!) I'd lean heavily towards taking the sender nut off and giving it a good look-see.
 

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You could always try to double up the o-rings at the flange. I'm not sure why there's a difference (other than the MV Agusta tank being plastic) but the MV parts and service manuals show an o-ring in the same position as the Ducati, but an additional one at the base of the flange.

MV Brutale pump on the left in my pic, Duc 916 on the right. The other pic is from the net showing both o-rings in place.
 

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Post a picture. Or several.

Tank off with some fuel, photos from the dripping area.
 

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You could always try to double up the o-rings at the flange. I'm not sure why there's a difference (other than the MV Agusta tank being plastic) but the MV parts and service manuals show an o-ring in the same position as the Ducati, but an additional one at the base of the flange.

MV Brutale pump on the left in my pic, Duc 916 on the right. The other pic is from the net showing both o-rings in place.
brutale has 2 due to the plastic tank and paranoia i assume. the f4 only has 1 with the steel tank.
 

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lots of other things to leak - quick release fittings, sender nut, sender wires, breather or cap recess drain outlets.

often, if there's fuel in the tank when it's upside down it gets into the cap vent circuit and then comes out the bottom when it's turned over. sometimes it pisses out all over you.
 

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Discussion Starter · #11 ·
Thanks for the reply all. I'm on my second tank now, youd think if it were the tank that would solve it. I haven't tried doubling up, do the other bikes you mentioned use the same flanges part? Would the second o-ring go above, closer to the flsnge portion of the player or below (deeper in the tank)?
I've check the fuel sender but, and to be sure applied some sealant there (fuel resistant), so I've eliminated that. This is coming after I replaced the quick releases, and I looked at them closely, I dont think the release is there. My dad and I sat and watched fuel drip for about 10 minutes yesterday, I'm really thinking it's coming from the o ring. I tried 4 times now to install, each time with a fresh o ring.
Last night I applied a layer of permatex gasket maker at the base of the flsnge to try and over kill the leak. Next step will be buying a new flange.
I'll try and include pics and a video when I get home.
 

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That was unclear to me. I've never known the flange to be an issue. Pinching the o-ring on the install is something that I am familiar with.

Pictures clarify.
 

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What I’ve done forever to find a oil or fuel leak. Clean what you are checking thoroughly then spray with foot powder. YOU WILL SEE INSTANTLY where the leak is coming from.
 

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Discussion Starter · #18 ·
@Namor sorry for the lack of clarity. The leak looks like it's going past the o-ring, at least best I can tell. I'm usually a fairly competent mechanic, so I'm a bit stumped that after 2 fuel tanks, and 4 rings it's still leaking. Only thing I can think is the baseplate (flange) itself is warped, or the second fuel tank is also slightly warped. I've been using silicon spray to get it in, maybe I should try a different lubricant?
 

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I believe I've got a spare flange somewhere in the attic, it had a broken breather post on the inside tank portion but that got JB welded back together and seems to hold. I don't mind forwarding it on to you to see if it works out. It's missing the quick disconnectors; it was a 748E flange but it's been threaded for the 1/4 NPT threads of the QDs. If you're interested I can probably get it in the mail Wednesday or Thursday (if I still have it, pretty sure I do but I'll need to check in the morning!)
 

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Found it; it's not in the best of shape and has been repaired. It was working when I pulled it out of the bike 4 1/2 years ago and have stored it since. Here are some pictures of it; it's yours if you want it.
 

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