A couple of weeks ago, a K friend told me about raising the fuel cap to increase the tank capacity. He had seen the idea on an American forum.

I couldn't find any details and I can't find any reference to the idea on our site, so I looked at the fuel cap and came up with this scheme.

The alloy ring to which the cap fixes in the petrol tank is about 13mm thick. The fuel cap seal is about 7mm below this ring, so I figured that if I lifted the cap 8mm, I would be able to get a useful amount of extra petrol in the tank.





My 'lifting' ring is 116mm OD x 91mm ID x 8mm thick and I used a thick gasket between the ring and cap. The standard cap seal remains in place below the new ring.
Four new 20mm long M4 countersunk screws are needed.



Before fitting the ring, I had filled the petrol tank about 5 miles from home.
Assuming about 1/2 litre had been used in that 5 miles and I was able to get just under 2 litres in my 'new' tank, I can now get something like an extra 1.5 litres of fuel on board. (That's at least another £2 worth in the UK)

There is still quite a volume of expansion space remaining in the tank in case that sort of thing worries you.

Now it could mean a shorter walk if I run out of petrol..........or a longer walk because I went past the last filling station.

Paul.

Nice one Paul.

The American forum where this idea of raising the gas cap comes from is the IBMWR.ORG
Your modification has a double advantage.
First it increases the capacity of the tank, but the best one, it gets rid of the recessed filler.
When it's raining, the water always sits around the filler neck and goes into the tank as soon as you open the cap. With your solution, the water has very little chance to enter the tank and furthermore to create inside corrosion. (This is the reason why a lot of K100 aluminum tanks are leaking on the front right).
The only think having to be check is the overfill pipe inside the tank. You don't want the extra 1.5 liters to drip on the road. (2 pipes and hoses under the tank)
CF

Top job Paul, you are a man of many talents, as CF said it also removes the water trap well worth copying is that one.



BIG D

Did you machine it yourself or did you manage to find one off the shelf? May have to phone the local metal dealer and see how much he will charge so i can make one up myself...

A respected 'local member' of our forum has been making the fuel cap ring raising device for some time. His design uses two fuel-safe O-rings for which there are grooves machined into the aluminium. It will soon be fitted to my bike as well.

I smell another long Down Under roadtrip coming up. Here's to further range!

Guest in the House wrote:A respected 'local member' of our forum has been making the fuel cap ring raising device for some time.

Let me guess...
Would that be Bert 2.0?

Crazy Frog wrote:

Guest in the House wrote:A respected 'local member' of our forum has been making the fuel cap ring raising device for some time.

Let me guess...
Would that be Bert 2.0?

Nuh, I have to keep him anonymous lest he be swamped for orders. He'd likely freak if the members asked him to make them one too.

I'd be interested to know how high he lifts the cap GITH.
Paul.

sidecar paul wrote:I'd be interested to know how high he lifts the cap GITH.
Paul.

It sits just slightly higher than the cap does in your image, Paul. I'd say it's about a litre improvement, perhaps a tad more. As I am preparing my bike for a roadtrip I will post a photo of it once I source the two O-rings, possibly later today.

It lifts the cap 10mm and I use 3mm O rings. I only fill if I intend to use the fuel up straight away as it will drip out the overflow if left on the side stand. I dont put the hole for the drain as it isnt needed any more.

Thanks Rick,

Paul.

With my newly painted tank (which I haven't fitted yet) I re-visited this idea to do a white petrol cap.

Being white it would show up the odd joint betwixt the ring and cap, so I've made a ring to fit the taper of the cap edge.




This was then screwed to the cap with 3...4BA (well BA is a metric based thread) screws all set in JB weld epoxy.


A coat of paint then covers all the irregularities.



And when fitted to the tank it makes a neater fitting (well I think so!)

 

A friend of mine once said "You should get out more", then he thought about it and commented "But you do!"

Keep riding and playing,
Paul.

That is basicly what I make and use O rings top and bottom to seal it and dont have a hole for the drain as it isn't really needed.

great job paul

How BMW gets away calling these "touring" bikes (even putting the moniker on the saddle bags) with just a five gallon tank is beyond me.

how is there room for expansion ,? and how do you stop the fuel from flowing out the overfill tube?

k-rider,
There's still a fair volume of air in the top of the tank when full.
 
If you remove the cap you will see that the lower edge of the cap mounting ring fixed to the tank is a good 20mm below the top of the tank. All we are doing is lifting the petrol cap so that we can fill the tank to this edge. (The cap seal is about 10mm below this edge as standard.)

Paul.

ohh, i see, strangely enough i can only fill the tank to 20mm under the fillercap hole , before it runs out of the overfill tube, is that normal or
is it possible to bent some pipes inside the tank? 

sidecar paul wrote:k-rider,
There's still a fair volume of air in the top of the tank when full.
 
If you remove the cap you will see that the lower edge of the cap mounting ring fixed to the tank is a good 20mm below the top of the tank. All we are doing is lifting the petrol cap so that we can fill the tank to this edge. (The cap seal is about 10mm below this edge as standard.)

Paul.

Hi k-rider,
That sounds like the breather/overflow pipe may be split or broken away from it's fitting in the top of the tank.
Here's a picture of the pipe which is solidly fixed to something (I couldn't find a small mirror to have a proper look) just in front of the filler cap hole.


 

Paul.

I lifted mine 11mm and it will dribble but only on the side stand. I usually dont fill it to the limit unless I want the extra and if I am going to be riding off right away.

RicK G wrote:I lifted mine 11mm and it will dribble but only on the side stand. I usually dont fill it to the limit unless I want the extra and if I am going to be riding off right away.

Easy way to fix that Rick is to fit a sidecar and remove the stand completely.

I should look at lifting the fuel cap myself.  More range is always good.

Al

hi paul
thanks for the nice pic, i will have to check it out this weekend, cant remember what mine looks like

sidecar paul wrote:Hi k-rider,
That sounds like the breather/overflow pipe may be split or broken away from it's fitting in the top of the tank.
Here's a picture of the pipe which is solidly fixed to something (I couldn't find a small mirror to have a proper look) just in front of the filler cap hole.


 

Paul.

I have just ordered a piece of aluminium plate from the bay of evil, and will spend a happy afternoon chain drilling to create a lifting ring.  I must say that the potential increase in range is not my principle aim; after the wettest winter since records began, all I want to do is prevent water from draining into the tank when I open the filler cap.

Is your cap on backwards?

Should lift from the front of the bike and hinge at the back.
There is a drain hole on the left that should drain most if not all the water.
Check the top seal.

The cap is facing the correct way, but I shall check the drain hole - thanks Rossko.

Often the gasket happen to be wrong mounted (easily done when you're in a hurry)
.....when changing the fuel filter.

I have made quite a few and use O-rings top and bottom and do away with the OEM gasket. The top O-ring is the same as the oil filter cover and the bottom is about 122mm OD.  Sometimes if the tank has had a few coats of paint it needs to be carved away.

I made my lifting ring this morning by chain drilling 5mm holes through a 10mm slab of aluminium that I bought from eBay.  I paid £17.50 for the metal, but there will be enough for two rings.  It will make me happy to be able to not let the K100LT get all jealous of the 1100 with its lifting ring.

The ring has had a coat of etch primer ready for some black paint tomorrow.  I cut a nice, thick gasket from some gasket paper, and the new 4mm countersunk stainless steel Allen screws are on their way.  The tank is already off the bike because of all the other work I am doing, so tomorrow I will drain it completely to remove any water that got into the tank.

Thanks to those of you who poineered this modification.

Chain drilling.......that's dedication, xpc.    I suppose someone else was using your lathe.   

Well done,
Paul.

aye ! indeed paul
awesome effort

Sidecar Paul, I wish that I did have a lathe.  It is on the list of things I would buy, if money were no object, but in its absence I have to resort to chain drilling.  Yes, it is laborious, and the part needs careful finishing with a file, but it is done.  I will have made two lifting rings, and still have change from £20; that kind of satisfaction drives me on as I stand next to the pillar drill, ankle deep in swarf, for hour after hour. 

Excuse my ignorance.  What is chain drilling?

Drilling holes close together so as to have a cut, in this case a hole that is far bigger than any drill he has will go.

Brickrider, I marked out an 86mm circle on some 10mm thick aluminum, and then another concentric 121mm circle.  I then centre-punched some marks for the drill to start on along these scribed circles, and then started drilling many, many 5mm holes very close together.  When that part was completed, I just joined one hole to the next with a hacksaw.  One ends with a vary roughly finished part that then needs to be finished by filing smooth, but at least you do not have to be a lathe owner, or go to a local engineering company with an open wallet.

I admire you patience! I'm not sure I need the extra volume in my tank however, knowing water is unlikely to enter the tank when the cap is opened would be a nice thing! I'll go out on a limb here and openly wonder if BMW's design of the cap didn't fall short of the mark.
After this mod, the cap sits notably proud of the tank, correct? Does this cause any issues with using a tank bag?

I have one on my K1100 without problems for the tank bag.