Auxiliary Fuel Tank – BMW G650GS 2011
BMW have recently introduced the G650GS single cylinder enduro motorcycle (the German for motorcycle is ‘motorrad’ – hence BMW Motorrad). This motorcycle is a continuation of their very successful F650GS (single cylinder) which stopped production for Europe in 2007. Realising their mistake in not continuing production, the updated G650GS was born for 2011. This note focuses on the smaller fuel tank capacity of 14 litres total, of the G650GS as compared to the 17 litre capacity of the F650GS and my installation of a gravity fed 12 litre auxiliary fuel tank. This approach will also apply to any of the BMW motorcycles with an under seat fuel tank as the fuel access point to the main fuel tank will be common to these bikes.
The low fuel warning light comes on with 4 litres left in the tank, which is after 155 miles at 70 mpg. When travelling in any remote areas of the British Isles, for me, this lower range is a nuisance as you are not guaranteed to easily find a petrol station now that many have shut in favour of the big super markets. The fitting of this auxiliary tank will increase the range to over 400 miles making searching for fuel a much lower priority.
Equipment – ‘the bits and pieces’
The tank is a USA Tour Tank (16” x 8”) which will hold 12 litres. It is fitted with a roll-over valve/tank vent which is ‘Td’ in with the existing tank roll-over valve/vent tube. The fuel flow from the auxiliary tank to the main tank is through a 90deg elbow, a fuel stop-tap, a fuel filter and a non-drip fuel connector making the trans-shipping of the fuel to a fuel can or to another motorcycle an easy and safe activity.
The vent from the auxiliary tank is joined to the main tank pipe using a ‘Y’ connector which then vents to below the motorcycle in the usual way.
The existing roll-over valve/tank vent is replaced with a purpose built and designed aluminium plate which holds a roll-over valve/tank vent and a fuel tank 90deg union sourced from the aero-industry. The photographs show all of the important aspects of this installation and my warning to everyone is that designing and installing fuel systems can be a dangerous activity and do not undertake the work unless you are capable of fuel systems pipe work and mechanical installations.
My original F650GS was fitted with a Metal Mule rear rack to which I engineered the fitting of a Peli Case. I have re-installed this to the new G650GS. The tank is secured to the rear rack with two substantial mild steel ‘L’ brackets (bar 1” x ¼”) bolted to the rear rack. The standard Tour Tank securing loops bolt on to the ‘L’ brackets. There are sufficient clearances to allow the seat to be removed and replaced without any modifications to the motorcycle. Complete removal of the auxiliary tank will leave no trace of its installation.
Before starting this installation, ensure that you have all of the components and do a ‘walk through’ of how you are going to tackle the whole job. Care needs to be taken when ensuring no fuel leaks, the routing of fuel lines to reduce any possible mechanical failure and most important, when removing the existing fuel roll-over valve/vent that nothing falls into the main tank especially any of the six securing Torx-bolts before the new plate is in position. Access to the rear seat-lock compartment and the removal of the seat also needs to be considered so the choice of a rear rack becomes a high priority.
Watch your Threads and Pipe Diameters
BSP is British Standard Pipe thread. (parallel thread and 57deg pitch)
NPT is National Pipe Taper. (tapered thread and 60deg pitch)
Inside pipe diameters can be 6mm (1/4inch) and/or 8mm (5/16inch).
Outside pipe diameters (od) can be up to 14mm for an inside diameter (id) pipe of 8mm.
ALWAYS use either PTFE tape or LocTite 567 on threads to prevent leaky joints.
ALWAYS use hose clips or cable ties on barb and push-on fittings.
4.55 Litres = I Imperial Gallon, 3.79 Litres = 1 US Gallon
For this installation I used 6mm id hoses and fittings. The gravity flow for 6mm fittings is approx 45 seconds per litre.
The photographs show the finished installation and a view of the tank access plate made from 1.6mm thick alloy sheet cut, drilled and filed, but no CNC this time.
Some helpful links: (June 2011)
Tour Tank, USA for tanks and the main accessory parts
Demon Tweeks for fuel cut-off valve and hose fittings
Your local plumbers merchant for PTFE tape
Your local electronic store for cable ties and Halfords for Velcro ties
Other suppliers of fuel system accessories:
Goodridge Hose and Fittings – another source of fuel pipe fittings
Earl's Performance Products – many fuel related parts
Mark Raybould ©
The new G650GS
Aux Tank ready to GO!
Peli case removed
The new access plate with rollover valve/vent and fuel access
If you have any comments, please PM me.
To prevent any air locks in the venting system, each tank will have its own separate vent tube. During fuel transfer with both filler caps closed, the main tank is expelling air whilst the aux tank is inhaling air. A stale mate could arise and prevent the flow of fuel.
The tank's earthing lug has been connected to the chassis of the bike which will reduce any static buildup on the tank.