Extrnal Fuel Filter Modification - Rob Lentini - BMW R850 Maintenance Manual

External Fuel Filter Modification - Rob Lentini
After I bought my '87 K75S I soon found it interesting (and strange) that the fuel
filter was installed inside the fuel tank! Most fuel-injected cars that I've worked on
have external filters, so I wondered about the theory and reasoning for designing
the filter location this way, but it wasn't a big deal on that K. One can quite easily
access the filter by removing the fuel filler cap assembly and then reach into the
tank with tools and a hand to remove and replace the filter per BMW service
intervals. Mind you, one still has to run the tank mostly dry and then contend with
modern fuel carcinogens on his or her skin (use surgical gloves!). But, filter
replacement isn't a big deal on K bikes.
Type 259 Boxers (Oilheads) are a completely different story, however. Sure, the
filter is (for some reason) still mounted in the tank like the K bikes, but the big
difference is you can't see the filter from the filler opening regardless of whether
the filler assembly is removed or not. You can't even reach the dang thing with
your hands. Besides, you don't even want to attempt to blindly remove and
replace the filter this way or your hand or tools would likely damage the fuel level
float rheostat assembly ($$$)!
On my RS, with close similarities to RTs, GSs, Rs, Cs and I suspect the S, the
fuel filter is part of one main assembly that holds the fuel pump, fuel level
float/rheostat and filter all together as one unit. This unit is, in turn, mounted to
the right/inside flat surface of the fuel tank using a circular flange fastened by six
Allen head machine screws. A large "O" ring seals the interface to prevent leaks.
To replace the fuel filter, one must remove the fuel tank and them remove the
above assembly to gain access to the fuel filter. Even careful removal of the
assembly from the tank risks damage to the fragile fuel level float mechanism
since the darn thing is a tight squeeze in the fuel tank and needs some
"maneuvering" to get it free and clear.
BMW recommends that the fuel filter be replaced every 24,000 miles, or 12,000
miles if fuel is of poor quality. I can vouch from experience that only one bad load
of water-contaminated fuel is enough to clog these filters and bring the motor
(and your ride!) to a halt. I therefore decided early on with my K to replace this
filter more often. I wanted to do the same on my R1100RS but soon discovered
the process was a hassle. Was there a better way?
There is a better way! I've found a sanitary and safe method of installing either
the OEM BMW filter or a less expensive aftermarket variety conveniently outside
of the tank where it may be easily serviced in minutes. Here's how:
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