MOTOBRICK.COM

TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: MCRyder on March 20, 2021, 11:00:26 AM

Title: Fuel Tank Leak
Post by: MCRyder on March 20, 2021, 11:00:26 AM

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 444 times)

Title: Re: Fuel Tank Leak
Post by: Laitch on March 20, 2021, 11:14:06 AM

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?

Title: Re: Fuel Tank Leak
Post by: MCRyder on March 20, 2021, 11:31:14 AM

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.

Title: Re: Fuel Tank Leak
Post by: MCRyder on March 20, 2021, 11:44:22 AM

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?

Title: Re: Fuel Tank Leak
Post by: Laitch on March 20, 2021, 11:48:12 AM

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.

(http://www.motobrick.com/gallery/3/1601-200321114003.png)

Title: Re: Fuel Tank Leak
Post by: MCRyder on March 20, 2021, 12:06:38 PM

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)

Title: Re: Fuel Tank Leak
Post by: Laitch on March 20, 2021, 12:15:38 PM

Break out the visine and coffee there, MC. #8 is a fuel line in your diagram.  :laughing4-giggles: #8 is tank insulation in your upper diagram.

It's #11 in this diagram.

Title: Re: Fuel Tank Leak
Post by: MCRyder on March 20, 2021, 12:20:13 PM

 :1thumbup  Thanks!

Title: Re: Fuel Tank Leak
Post by: Laitch on March 20, 2021, 12:25:15 PM

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

Title: Re: Fuel Tank Leak
Post by: The Mighty Gryphon on March 20, 2021, 05:48:29 PM

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.

Title: Re: Fuel Tank Leak
Post by: daveson on March 20, 2021, 07:13:17 PM

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. 

Title: Re: Fuel Tank Leak
Post by: MIbrick on March 22, 2021, 09:13:24 PM

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.