85 K100RT Fuel Cap Assy Stuck

[phildo253]

This is my first BMW, but not my first bike.  I just picked up a 1985 K100RT w/ 75K miles from a retired state patrol motorcycle cop.  The bike seems to be well taken care of, but hasn't been registered or ran in about 10 years.  I am going through everything to make sure that everything looks good before I attempt to fire it up.

For whatever reason, I cannot get the fuel cap assembly off of the tank.  I unscrewed the four screws, wiggled, jiggled, pried with a soft wood dowel, covered it with a towel and whacked it a few times with a rubber mallet, watched 1000 videos and searched every forum post that I could find and I cannot figure out why the sap is still stuck the the tank.  The only thing that I can think of is that the guy that i bought it from may have epoxied the assembly to the tank.

Has anyone ran into this before?  Everything I see and read shows that it comes off fairly easily with a little wiggle.  I don't want to ruin the tank.  Despite sitting for a decade and being 39 years old, the tank and paint are pretty much flawless.  The insides of the tank are almost as clean and shiny as the day that it rolled off of the assembly line.

Any help would be greatly appreciated.  i would really like to check out the fuel pump seal and parts and the fuel filter.  And, now that i have been trying to get the cap assembly off, there is a bunch of specks of dirt in the tank, so I have to flush it before i can start it.

[volador]

Here is what the under side of the petrol cap assembly looks like with the flapper valve in place. A flat rubber gasket approx. 8mm wide goes around the outer lip.

Try a mild application of some heat with a heat gun.

[phildo253]

OK.  Thanks for that pic.  I will run a mirror inside to see if that plate might be holding things on from the inside.  Mine doesn't have that flapper.  From the top, when you open the cap, it has a black ring with the four screws and an open funnel slope, but no flapper. 

[volador]

I believe the '85 had 2 versions of the petrol cap assembly. Probably a service bulletin about it somewhere. If you have the older version can upgrade to latest petrol cap version.

You will find the '85 K100 to be a one hit wonder.

Petrol Tank Return Check Valve, thermistor type Petrol Level Sender, Petrol Tank (with rear mounting flange) are specific to the '85 only.

WARNING: The petrol level sender is NLA (NO LONGER AVAILABLE). Be careful with the Sender "Mounting Nut". Age of the plastic requires a light touch.

The hole at 6:30 is the petrol cap water drain. The notch in the petrol tank cap base has to line up to that hole. The indicated tubing end is the internal tank vent.



'85 K100 petrol tank bottom for illustration purpose of tubing nipples. In center tank location forward nipple is tank vent, rear nipple is water/rain drain



'85 Petrol Tank Return Check Valve
pictured valve is clogged





'85 Petrol Level Sender





More petrol tank info

https://www.motobrick.com/index.php/topic,13517.msg120814.html#msg120814

[volador]

'85 Vacuum Pressure Switch can be removed or left as is

https://www.motobrick.com/index.php?topic=8494.0

Good Luck with your new ride

[phildo253]

Holy Smokes!  This is awesome.  Thanks for all of this info.  I knew that the 85 was unique due to being pre-CA compliant, but didn't know that it affected so much.  Based on the VIN, mine was made 07/1984, so I would assume early 85 info is more applicable, but I will verify tonight when I get home.

Well, I wanted a winter project.  I guess that I got one. 

Thanks again for all of the info.

[Chaos]

Removing the flapper was a common mod to top up the tank a little more.  I'm guessing you cap is somehow corroded to the tank, maybe soaking in PBblaster, tapping with a hammer, repeat

[phildo253]

Thanks.  I will give that a shot also.

[Laitch]

If you look at the underside of your Brick's fuel tank, you should see two outlets, each with a hose attached. One of those hoses is likely attached to a port in the forward part of the crankcase. It diverts tank fuel vapor to the crankcase to prevent the raw vapor from entering the atmosphere. The hose has a pressure valve in it and opens when a specific pressure is reached within the tank. It was a pea-brained invention.  If you don't have two ports, maybe your Brick is truly pre-CA.

The CA-compliant emission system was flawed and could effect hot weather performance. Eventually BMW published a service bulletin explaining how the system could be modified in non-California motorcycles.  Yours might have been modified already. Of course, Californians took advantage of those instructions, too.
 

Your fuel tank cap gasket has degraded during neglected maintenance and turned into adhesive. If all other methods fail, [. . .  Previous text within brackets expurgated as faulty mental product. . . ..]

[phildo253]

Thanks.  Man, this is all great info specific to the 1985 model year.  I messed with pb blaster and some plastic wedges to try to get the cap to rock a bit.  After a couple of hours of soaking and tapping, I think that it is starting to move.  I am trying to be careful because the paint on the tank is nearly flawless.  I am going to let it soak overnight and will check it in the morning.  Once I have it off, I will check the things that you mentioned to see if it is truly a pre-CA model. 

I did learn that the vent tube is cracked and I have penetrating oil all over the right side of the case and floor now.  Fun!

[Laitch]

After a couple of hours of soaking and tapping, I think that it is starting to move.  I am trying to be careful because the paint on the tank is nearly flawless. 

I'm suggesting that the blade be manipulated between the gasket and flange within the perimeter inside, not from the outside perimeter. It seems you're making progress. Keep it up!

[phildo253]

Ok.  Yeah, that makes sense.  It will give that a shot.  Plus PB Blaster acts like kind of a lubricant for a blade.

[Laitch]

I'm suggesting that the blade be manipulated between the gasket and flange within the perimeter inside . . .

This is an unqualified loser of an idea if your old cap is anything like my newer cap. Stick with the Blaster/jiggling technique if  it seems to be working. Be persistent and you'll eventually loosen it.

[phildo253]

Haha!  Thanks.  I let it sit overnight and it doesn't seem any looser.  I sprayed it again before I left for work.  I will just keep at it.  It will come off eventually.

[Laitch]

You can use a hair dryer to warm up the gasket: Plug the tank opening or drain the gas from the tank and rinse it; you don't want to inadvertently ignite fuel vapor.
Here's another fun thing you can try while you're Blasting. Get a length of 10lb test monofilament fishing line or some thin picture hanging wire. Cut a two foot length. Put on some gloves. Wrap the line around each hand. Insert the wire or line under the outside edge of the cap flange and start sawing back and forth through the hardened gasket goo between the cap flange and the gasket toward the funnel wall, moving around the flange.
Record it on video. When you're successful post it on YouTube and wait for the ad revenue to come rolling in after it becomes viral.

[alabrew]

The tag under the seat will tell if it is 49 state or 50 state compliant.

[phildo253]

I will look again, but I dont think that there was a tag.

[Laitch]

The tag under the seat will tell if it is 49 state or 50 state compliant.

I will look again, but I dont think that there was a tag.

It doesn't matter, does it? You're going to ride it regardless, if you can get the damned fuel tank cap off.  Right? Otherwise you'll need to drill another hole in the tank so you can add fuel coming from an IV bottle on a rack bolted to the handlebar and hope for the best.

[phildo253]

You're right Laitch.  It doesn't matter.  I would ride a teal Honda spree if that was what was avaliable.   I just kind of geek out in the history of stuff like that.

At last, success!  I soaked it again before I went to work today.  Came home and it wouldn't budge.  I took a soft wood paint stick handle and pried just a tad and it popped right off.  So excited. 

[Laitch]

 

[Chaos]

Soft wood paint stick handle???  Big F***ing hammer would have been faster

[volador]

^^
Malnourished Strumpet prolly couldn't wield a feckin hammer in Professor Laitch shop class

[volador]

one more honorable mention concerning the '85 FYK (Finest Year K)

The seat is specific to the '85. Seat pan has the molded handles. 1986 & onward the molded handles are part of the rear tail cowling.

Caveat: If the rear tail cowling is upgraded to newer type then the newer version of the seat will be installed

'85 Seat with molded handles



OE Fehrer Newer version seat, sans handles

[phildo253]

Based on the VIN, all of the info here and the K100-forum, and a bunch of pics, after pulling the tank today, I think that I did luck out on a true FYK in decent shape for only $750.  Here are a couple of pics of the seat and the tank.

[phildo253]

More.. BTW, the tank isn't scuffed.  It's just dirty from a couple of hours of me wrestling with it to get the pump and filter out.