Which tank do I have? Which one do I need?
by Anton Largiader and Brian Curry
There are two main versions of the K-bike fuel tank. We can call them the K75 and the K100 versions, although that's not definitive as the K75RT and the K100RT used the same tank. Low/tall, wide/narrow, call them what you want but here they are.
You can see that the shape is different at the lowest part, and the K100 tank has a sharper and taller hump. The K75 tank has a flatter curve to the left and right, as well.
The K75 tank does not have the grommets for mounting the side covers, but rather a more pronounced seam that the side cover can clip onto. It has prongs in the front for mounting the radiator cover on some models.
The K100/K1100 has side tabs at the rear for mounting side covers, although not all bikes use them.
The first K100 tanks (before 5/85) had:
- a ball-type check valve in the return line. The resulting rattle annoyed many owners and it was removed
- a rear mount that bolted on (which was prone to cracking)
- strip-based level sensor which didn't work well
- No provision for a screen on the fuel pump
- a small vent chamber directly behind the filler opening.
In 1985 the tank was changed to add two mounting posts for the rear of the tank, replacing the flat plate and single bolt that was prone to causing tank cracks. An opening was made to allow a vent hose to run down from the vent chamber to the filter basket on the pump. This apparently helped when the fuel got very hot, which was a big issue with the early K100s.
In mid-1986 when the K75S was introduced (according to Clymer's) the fitting for the check valve was removed from the tank. From that point onward, all of the tanks had regular pipe stubs for the inlet and outlet. This indicates that the first year (1986 models) K75T and K75C may have had the threaded return fitting.
At the same time, or possibly as late as the early '90s, the small vent chamber was replaced by a flat plate bolted to the roof of the tank, which created a baffled space in the upper half inch or so of the tank.
In 5/91 the rear mounting brackets in the frame changed. The previous ones had 13mm holes and used grommet 16 11 1 455 167, while the later brackets had a 17mm hole and used grommet 16 11 2 309 163 that was less likely to push through when installing the tank. The posts on the tanks changed over time, as well. Early tanks had a 9mm post with a an 11.5mm head on it, without a circlip groove. Later tanks had an 8.25mm shank, 10.5mm head with 8~9mm groove and used the 10mm clip 07 12 9 934 330. The latest tanks THese used The early system uses the 16 11 1 455 167 grommet and 12mm clip 07 12 9 906 727, while the later system used the flanged grommet 16 11 2 309 163 and 10mm clip 07 12 9 934 330.
In January of 1993 the tank was redesigned. The width of the forward mount was increased from 90mm to 130mm (20mm extensions 46 51 2 320 960 and pins 962 were used to lengthen the frame posts). The "false roof" baffle was replaced by a cylinder in front of the filler opening. The bottom was flattened, removing the narrow tunnel. Also at this time the 52mm Bosch pump was replaced with the 43mm VDO pump, although the only effect this had on the tank was to eliminate the rubber hose from the vent to the filter basket. The return fuel discharge was aimed into the right side of the tank, prompting a Service Bulletin which added a hose to re-route that to the left side again.
| Description | Part # | Width | Notes |
|---|---|---|---|
| K100 police to 5/85 5/85-on |
16 11 2 300 298 16 11 2 303 101 |
Discontinued before 1993 | |
| K100 California to 5/85 5/85-on |
16 11 1 453 420 16 11 1 455 101 |
Possibly the '93 tanks had the emissions improvements so there was no '93-on California tank |
|
| All K100 to 5/85 K100 and K75RT 5/85 to 1/93 K11 to 1/93 K11 and K75RT from 1/93 |
16 11 1 450 631 16 11 1 455 011 16 11 0 026 150 16 11 2 307 468 |
90 90 90 130 |
Single-bolt rear mount Flat bottom and 90mm? Cylindrical baffle? |
| K75 police K75, C and S to 1/93 K75 and S after 1/93 |
16 11 2 303 282 |
90? 90 130 |
Possibly never updated to '93 design |
http://www.motobrick.com/index.php?topic=10105.0
https://bmwk100k75.weebly.com/fuel-tank.html
Also we need to define the VIN breakpoints in the fuel level sensors for the K100.
