So...I've had my 1985 K100 for exactly one week.  I've noticed the following items:

It has twice as many cylinders as my '63 R60.
It has twice as many volts as well.
It has brakes.

These items are intimidating to be sure, but I can read a manual as well as the next neanderthal, and I haven't found a decent description of how to clean out the fuel tank.

Have you looked in one of these things???  It's not just a curvacious bucket with a threaded thingy at the lowest bit...there's all kinds of plumbing, tubing and what not in there!  Not only that, but I found (since the bike had been sitting since 1996) the most atrocious mung in the crevices and corners of the damn thing.  This stuff is as black, gritty and gummy as the stuff that lives in the hearts of investment bankers (sorry if you're an investment banker, but...c'mon, you know what I'm sayin;).

My question for you that have gone before me is this; How can you effectively clean a K-bike tank without defiling the environment, setting yourself on fire, or having your sweetheart insist that you strip down on the front stoop because you stink of gas gone bad?

Hairball

Hairball wrote: This stuff is as black, gritty and gummy as the stuff that lives in the hearts of investment bankers

Check your financial advisor rubber mounting for the fuel pump, I'll guess you need a new one.
And while you're down there, also check the prefilter underneath the pump.

It's two plastic white tabs on the side of the pump, press these against the pump
and lift the pump straight up.........easy, old plastic is brittle.

Hairball wrote:My question for you that have gone before me is this; How can you effectively clean a K-bike tank

Depending on how very bad it is but what I did was put a few liters of metholated spirits in overnight with the cap on, in the morning give it a damned good shake up over and over round and round and let it sit for another day, then flush it using either meths or fuel.

Most, if not all the gunk fell away and I was left with a pretty much squeaky clean tank

The reason I used meths was because it displaces water (moisture) and still burns off as residue

Outstanding advice!  I'll put something in the beer fund in your honor.

Thank you.

I had my tank off and noticed that I had a leak coming from the Petrol Gage. I found one in N Carolina ($154.00) but in the mean time I tried to repair the old one with form a gadget the hard setting one. Has any one had a problem with this and what did you do?

paulespo wrote:I had my tank off and noticed that I had a leak coming from the Petrol Gage. I found one in N Carolina ($154.00) but in the mean time I tried to repair the old one with form a gadget the hard setting one. Has any one had a problem with this and what did you do?

Yep I had a problem like that.

My solution was to forget the repair.

Bite the bullet and purchase new. Far too critical a component to leave anything to chance

paulespo wrote:I had my tank off and noticed that I had a leak coming from the Petrol Gage. I found one in N Carolina ($154.00) but in the mean time I tried to repair the old one with form a gadget the hard setting one. Has any one had a problem with this and what did you do?

I have a small leak on the left hand side on the seam and will have a go at repairing. 
Do a search from the search tab for 'tank repair' and you'll find lots of threads with info about how to and products etc.
Pretty sure you'll need to use a product thats specifically designed for fuel tanks.

This is the good stuff and it IS permanent http://www.permatex.com/products/product-categories/specialized-maintenance-repair/professional-repair-systems/permatex-fuel-tank-repair-kit-detail

I'm very happy to be able to say my fuel tank is sound.  However, since they are aluminum, can't they be soldered?  There has been on the market for a number of years material that can be used to solder alu.  I've never tried it personally, by the videos make it look simple enough.

Be made wrote:

paulespo wrote:I had my tank off and noticed that I had a leak coming from the Petrol Gage. I found one in N Carolina ($154.00) but in the mean time I tried to repair the old one with form a gadget the hard setting one. Has any one had a problem with this and what did you do?

Yep I had a problem like that.

My solution was to forget the repair.

Bite the bullet and purchase new. Far too critical a component to leave anything to chance

For three weeks now and Had no notice that it is on the way. I called the supplier and they said that they have ordered from BMW. It's October 15 and the weather is getting colder. I hope I get it before the snows fall.

paulespo wrote:I had my tank off and noticed that I had a leak coming from the Petrol Gage. I found one in N Carolina ($154.00) but in the mean time I tried to repair the old one with form a gadget the hard setting one. Has any one had a problem with this and what did you do?

Repaired my tank last weekend using Locktite Radiator & Fuel Tank Repair Kit.  There were two areas with 7 holes in all on the left side. The photos below show the largest corroded area. It was fairly easy to do.


1. Clean off the area to the bare metal.





2. Remove corroded metal and indent the holes. I used a centre punch. Only need to knock it in so there is an indentation about 1-2mm.



3. Mix tank repair as per instructions and apply to holes. Flatten out as much as possible.



4. Cut back repair material as much as possible. I used a fine flat file



5. Fill with two-pack body filler



6. Sand back.


My tank will be getting a resparay next year so I just left it at that and covered it over with some black duct tape for the time being.
I'm also considering getting the tank cleaned, treated and coated on the inside or maybe another tank depending on whether any new holes show up.
Interestingly, I found about 40-50ml of water in ther tank when I cleaned it out.

Kaptain Holister wrote:Repaired my tank last weekend using Locktite Radiator & Fuel Tank Repair Kit.  There were two areas with 7 holes in all on the left side. The photos below show the largest corroded area. It was fairly easy to do.

1. Clean off the area to the bare metal.
2. Remove corroded metal and indent the holes. I used a centre punch. Only need to knock it in so there is an indentation about 1-2mm.
3. Mix tank repair as per instructions and apply to holes. Flatten out as much as possible.
4. Cut back repair material as much as possible. I used a fine flat file
5. Fill with two-pack body filler
6. Sand back.

My tank will be getting a resparay next year so I just left it at that and covered it over with some black duct tape for the time being.

Really nice to see this demo. Thanks for the post man. It gives me great confidence now on doing my own (should I need to . . which I probaly will)

The tank is aluminum and I think Alumiweld welding rods are the best solution to repair leaks from pin holes and seams. Alumiweld is easy to use if you have a torch. I've seen videos of repairing large holes in aluminum boats with Alumiweld.

Regards