Archive of BMW Motorrad Club Cape (2006 - 2019)

I have wanted to do this many times. Do you know that vehicles are designed to have "free space" after you have filled up (by law)? The idea is that fuel comes out of an under ground tank (cold) and is then pumped into a fuel tank - in the case of most bikes this means you are putting cold liquid on-top of a stove plate (hot engine). Obviously the fuel is going to expand - drastically. If you fill your tank to the brim and then ride a short distance before you stop. You have hardly used any fuel AND the engine is up to temperature. Best case, your fuel will expand and run out off the over flow pipe and spill onto the ground, encasing your whole bike in petrol fumes. As I said this is best case, worst case something will cause a spark ..... Now you see why I have not done this conversion yet. The only time you fill your bike to the brim, is when you are about to set off on a looooong journey - imediately. I never fill up my bike when I get home after a long trip, I wait for the next morning and fill it up before I set off to work - yes it is a shlepp, but safe. In the late 80's I did a long trip on a CB 550 4K, then filled up 40 m from home. 10 minutes later the fuel over flowed - DIRECTLY onto the HOT engine!! The next hour was nerve racking, fortunately no ignition.

If you do this hole drilling thingie, how much more petrol do you really get extra in your tank? and is it really that worth it? I don't know "stupid questions", could some one please clarify. (I would go for PADLANGS, explanation rather.)

The idea is not to get more into the tank, it just goes quicker with the last 3 or 4 litres. One should of course not fill right to the top, this will result in a petrol spill when you close the cap. Your overflow pipe should also be were it is supposed to be, ending almost on the floor and not on the engine or exhaust. The reason why we have the reducer in the tank is not to stop us from filling it up completely, it came into place when the lead free petrol had to be used. It is supposed to stop the thicker nozzle of the leaded petrol from reaching into the tank. If you remember the old bikes, ( my last one before BMW was a Honda 900 Bol 'Dor) they had a big open fuel cap and you could always fill it to the top, especially since the filler cap was sitting at the highest point of the tank. The Filler cap of the BMW is however recessed so that you cannot fill the tank to the highest point.

Hi Wolf. Interesting point about the unleaded petrol being the reason for the "extra bit". It would be interesting to know if any manufacturer went for a narrower opening, without the dropped section. It would also be good to know when the law came into being that is intended to prevent one from filling a tank all the way to the top. This is not really an issue on a road bike, but I can see that sometimes you would want to stretch the range on off road trips.

Yep I am guilty of drilling a hole in the tank neck,A 6 mm nog al, otherwise it still takes too long to fill. As those more technically inclined will know an electrical drilling machine does create sparks when switched on and of course petrol fumes are most vunerable in that state, so you are placing you and the bike in a rather dangerous situation, THINK before you try out this modification. I guestimate an additional 1,5 litres of fuel in the tank, at 17,0km/ltr. that is an extra 25kms.of travel, possibly more because by this time you are really knyping. At the end of day it's about the comfort of that additional "reserve". Bum in the saddle, always.