Two things here:- Your third picture down, unless an optical illusion, appears to show distortion of the tank fixing flange face*, This alone would cause a fuel leak under some circumstances certainly with temperature fluctuating. Secondly, did you cure the pressurising problem? This certainly won't help and could be the main cause of persistent leaking despite pump flange face being distorted*.
Chris, thanks for the reply. I think it's an optical illusion; I've got both a level and a machinist's flat so I'll put those on there and see if it's distorted or not. I haven't. To be honest, I'm not sure what I can do to fix it? I've checked that the breather hose flows freely, and I think the breather valve operates properly, but outside of that I'm not sure what I can do.
if it were me, I would get a matchstick or similar (something soft) and see if you can slip it into the gap while clamped down because it could well appear to be flat when you remove the pump assy. If this is the case, make sure you don't overtighten the fixings as this can be another factor. There is a common design of fuel pump used on many cars through the 50's right into the 80's where the two fixings are far enough apart to cause a similar problem as time goes by. If persistent I used to dress and shape the face of the pump to exert slightly more pressure on mating face between fixings. Re: breather - if you are no longer getting a big pressure equalisation when you open the cap then all should be fine as far as that contribution to the problem is concerned.
Had a leak on mine recently, sanded the face & found the brass inserts & surrounding areas were proud, doing this & replacing the o ring solved the leak. The face still had a slump along the long sides but the o ring seems to tolerate this.
That sounds like a good idea, I'll give it a try. Thanks! @Chris per your previous post I pulled the pump yesterday and checked the bottom of the tank with a ruler.. it looks very straight: I checked it front to back (with a license plate!) and it looked straight that way too. It's been a while but I think I'm still getting the pressure equalization issue. To be honest I'm not sure what else I can do.. I've replaced the breather, and the hose from the breather isn't blocked. If the tank is building too much positive pressure and the breather isn't working, I think you're right - it's going to continue to leak. (The tank wouldn't build vacuum, would it?) The o-ring I got is aftermarket; I'm going to replace it with a factory part (the post-recall part). That's a good idea about sanding: which grit did you use?
It was quite course, 240 maybe, the important thing is to use a good flat plate behind the paper so you do get the high spots around the inserts, actually a file may be better as it wont distort.
I'll give that a try. What did you use for a sanding block? I still think the core of my issue must be related to fuel tank pressurization. I can fill the tank to the brim and, if I don't run the motor, it will never leak fuel. Or I can put a gallon of fuel in the tank from empty, run the motor, wait 10-15 minutes and all of a sudden it's pissing gasoline out the bottom.
I can't remember exactly what was said earlier in thread, but I or someone must have suggested opening cap to confirm pressurisation? This is an easy test to do, but obviously do it with care, as fuel could spray out but either leave the key in cap ready to open during running or open immediately you shut engine off.. Just a further thought - I would think long and hard before sand-papering any surface where an "O" ring is involved. This relies on an ultra-smooth surface, and this is easily breached. As you have said, the "O" ring is designed to accomodate some distortion but if this is down to too much distortion then best find it definitively before doing anything drastic.
Those were all good suggestions -- but I never got to try them due to moving, the weather, and (of course) COVID. But spring is here and maybe I can try this weekend? That's a fair point. I think my main goal is to check the threaded bosses for the screws to make sure they're not sitting proud. There's also some gunk that I need to clean off the bottom of the tank, but some Simple Green should take that off.
yes, I was trying to study hard the "footprint" showing on the tank flange! This sometimes makes it easy to find. i can see one of the tapped inserts is quite wet but it's possibly nothing - are all inserts soundly housed or do you detect any might spin on doing up? if this is the case then it could be the culprit. Obviously go careful on checking as they are not the best design and you could disturb their attachment. I think you could reach two fingers inside the open flange and carefully test each one to see if any react differently. EDIT Also have to say number 9, I wasn't going to comment, but your steel rule picture does nothing to demonstrate the flatness of that flange for me.. it could be an optical illusion but it seems to show massive (inboard of tapped fixings) gaps to me. Also:- unless the lines are in previously applied resin, it looks as though someone might have used something abrasive on the face already.
I removed them yesterday and re-installed them, and none of them felt like they were spinning. Do you know how the breather valve is supposed to work? As far as I can tell it can only be assembled one way, which is the way that I've assembled it. I can blow air through it, but I'm not sure if air is supposed to flow both ways or not.
that's a very good question because when i've tested mine air will go both ways, but both under duress, so I guess it is designed to cater for depression as well as compression. Either it's correct or the valve has worn a little, our bikes are "old" now! - never tried it out on a new valve - this might be answered somewhere on the dedicated Multistrada Forum.
Just reading through this thread the first thing I would do is ditch the breather valve and just run a rubber hose in its place to temporarily bypass it if possible, sounds like it could be the cause of the problem to me.
I tried that today. See below for what happened... Although this is a factory tank, I took a chance and reached out to Chris at CA Cycleworks given he's done a lot with HyperMotard tanks. He suggested I cover the o-ring in grease and re-install it, then look at the "shadow" left by the grease to get an idea of how well it was sealing. It's a little hard to tell because I foolishly used grey grease, but you can see that the grease at the top of the flange doesn't show a great seal. I cleaned off the grease and re-installed the tank. This is what it looked like: The lighting makes it look slightly worse, but as we saw in previous pics there's still a gap at the top of the flange. I removed the breather, put half a gallon of gas in the tank, and started the bike. This time, it started leaking almost straight away. Previously it would only leak after the engine had been running (and the tank pressurized), but now it's leaking at idle or even with the motor off. And it's leaking from the top of the flange, where we can see the gap between the tank and the plate. A friend has an OEM tank that I can try, and I'll get a new o-ring from Ducati. I guess I could try and find a gasoline-safe silicone sealant, but I don't really think it's worth the risk.
Make a template of the fuel pump hole in the tank. Do this using the grease you have used to transfer the outline onto a piece of card or paper. I would incorporate the bolt holes as well. Use nitrile rubber to make a gasket. Fit this gasket between the tank and the pump/O ring. See if that takes up the gap.
In your last (top) picture you can clearly see the two areas that are compromised both of them between the fixings. IHDKWIFB
I can get a used tank for $150 locally; I'll check it out and see what condition is. If it's in decent shape, I think I would rather spend the money than try and bodge up the current tank. I just don't think it's worth risking a temporary fix. Funnily enough, my name is also Chris W I don't know what that acronym means?! I had googled "gasoline safe silicone sealant" 5 minutes after it leaked yesterday.. but I'm not sure that I want to risk it. If the choice was between that and a new $800 tank, I'd consider it, but if this used tank checks out I'll just go that route. Speaking of which: how difficult is it to replace the tank?
I picked up a used OEM tank this morning. And something else to go along with it... A set of non-S forks with the Ohlins cartridge kit installed and already sprung to my weight.
