Fuel Tank Leak

[MCRyder]

A small pool of fuel was on the floor underneath the RT this morning. 

The heat shield padding to the rear half of the tank is soaked with gas which I guessing from there ran down the side of the engine to the ground, I see no active or visible leak with lifting the tank.  I'm spit-balling here.  We had extreme cold a few weeks ago, -6 F at my house in East Texas, temps now well above that (30's-70's).  I'm reasoning something (plastic?) has cracked around the base of the fuel pump mount underneath the tank and is seeping fuel which the heat shield pad soaked up like a sponge and then dripped (?)

I'm trying to remove the tank but having trouble getting the rear fuel hose to release from the tank pipes.  I'm sure the rubber had adhered to the metal pipe.  I'm waiting for it to warm up more and try it then.  If no luck I'll slice the fuel line and replace it.

This schematic is from Bob's BMW.  The part #1 is listed as a fuel filter (?), I'm thinking it's a mount to the fuel pump attaching to the bottom of the tank, maybe the source of the leak?  Any opinions welcome.


Bob BMW.jpg (26.29 kB . 768x537 - viewed 443 times)

[Laitch]

Fuel is delivered and returns to the fuel tank via hoses attached to pipes beneath the front left-side of the tank. The rearmost pipe of those two is the delivery pipe. Is that the one with the stuck hose?

[MCRyder]

Yep.  Got the clamp loosened, but can't get the hose slipped off the fuel pipe no matter how much it's pulled.  The hose rubber cover is cracked, so replacement would good once I get it, and the front one, off.

[MCRyder]

I checked the tank again.  At the base of the fuel tank there's a gold colored plate with 3-4 screw heads, I saw a drip of fuel on a screw head.  Is there an O-ring for a seal?  Bob's doesn't show it.  Maybe a cracked o-ring allowing a leak?

[Laitch]

Heat the hose with a hair dryer then rotate it back and forth with pliers; otherwise, split it then peel it off.

The most likely reason for fuel tank leakage is corrosion along the tank seams along the bottom of the tank (green arrows) or a faulty o-ring at the fuel level sender cover (red arrow). Also, external fuel hoses can rot then leak and their clamps can loosen.

[MCRyder]

Thanks for the reply Laitch.

I've checked the seams, no corrosion or leaks seen.  The drip is directly underneath the fuel sender cover (thanks for the photo).  The heat shielding is soaked where it's around the cover and then to the back of tank.  I'm guessing the o-ring has failed and needs replacement.  From Bob's schematic I'm fairly sure I need part #11


Bob BMW.jpg (44.2 kB . 768x537 - viewed 463 times)

[Laitch]

Break out the visine and coffee there, MC. #8 is a fuel line in your diagram.  #8 is tank insulation in your upper diagram.

It's #11 in this diagram.

[MCRyder]

   Thanks!

[Laitch]

Take it easy withdrawing that assembly so the float wire isn't mangled or sensor banged up.

[The Mighty Gryphon]

You will need to disconnect the fuel pump wires a well.  Someone here didn't, but for some reason I can't remember who it was.

[daveson]

The rubber o ring might be cracked, if not it's probably flattened from the years of compression, enough to result in a leak. You might be lucky if any of the four screws are loose, causing a leak. 

[MIbrick]

FWIW, a couple years back my 86 100RS had the exact same symptoms. The o-ring had indeed gone. I took the opportunity to strip all the original rubber hoses and lines off the bike and replace with OEM parts. Figured if that o-ring had gone, the rest wasn't far behind considering they were all original and how old the bike is. Even switched the brake lines to stainless braided. Was simultaneously a PITA and an educational experience.