I have a 32ltr petrol tank off a R100 gs.My question is, can It be modified to hold an extra 2 imperial gallons /9lts,by welding some extra sheet steel to the bottom on both sides of the tank.If so,will the original tank be able to take the extra weight of fuel, or will it possibly split some where.
Obviously if that is the case,what mods are req to strengthen the tank and where on the tank.

I doubt you'll get a definite answer on this one - not likely anyone's done it before, though you never know.

My best guess - no problem - remember that the tank is strong enough to take a heavy tank bag, and I've NEVER heard of a tank splitting from a too-heavy tank bag.

You could always just add something in the center of the tank for support to be safe - kind of a rubber pillar in the center of the frame tube to add one more contact point.

There are loads of large tanks out there, might be worth a look before you start welding. Welding fuel tanks is not fun, you'll need a really good welder who's done tanks before.

Let us know how it works out!

__________________
Grant Johnson

Seek, and ye shall find.
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One world, Two wheels.
www.HorizonsUnlimited.com

Interesting project! I thought of doing this to the stock tank on my R80 G/S, which is very small (a whooping 23 liters if I recall correctly..). I think the reality of doing it would be quite difficult, even if you weren't to worried about appearences. One of the challenging parts is re-sealing the metal sufficiently to prevent rusting. If you go ahead with it, there is a product designed to seal the inside of the tank (The BMW tanks I have owned had it). This keeps corrosion to a minimum. I have done welding on tanks before - it is very difficult to get a good seal, as the metal is thin and even hairline cracks will leak a surprising amout of fuel.

Personally, if it was me, I'd sell the PD tank (which should be easy, they are in demand) and purchase an Acerbis 43 liter tank.

However, that is the boring route - much more interesting to modify you own tank! Good luck, I'm interested to hear how you get on with it.

It is not impossible to expand(nothing is impossible as the saying goes) the capacity.I still have to see my welder to get his opinion on the practicalities of doing a satisfactory job.
I will let you all know what happens.

hi there,
the guy i bourght my r80gs had a photo of his first r80gs in his shed which had an expanded pd on it.
he said he bourght if of a guy who expanded it to do the finke rally in australia.
he couldn't remember how much it was expanded by, 40l ish.
he rode the thing all over australia with no problems, so i wouldn't be too worried about it holding the extra fuel.
chris

I'm sure it is possible, but maybe it's better to buy a 43L Acerbis? It is better attached to the frame and the cost is not that bad (500€).

I had the same problem with my little Dakar (skinny calf that she is) now do I pay for the £1500 Touratech tanks, spends days fitting them OR do I buy and use 2 x 5lt jerry cans @ £5 fot both?

Which one did I go for? there are two kinds of project:

1. Much needed and balanced between usefulness time and money
2. The other is a waste of all the above for little gain

Decide which one this fits into in your view and work from there.

The voice of reason

Give some thought to the safety aspect. That goes for a modified tank and cans of petrol. The tank will be untested and could possibly fail in harsh use or accident with dire results. Cans of fuel can be holed if not carried correctly or pressurized in the sun.

Petrol is dangerous stuff if handled badly.

Steve

My thoughts exactly.
The problem with the BMW mounted tank is that it only rests on a small pipe behind the steering head and on two rubbers at the back. For the 19l tank this is more than sufficient but by the time you increase the weight to that of 32 litres of fuel I become doubtful of how secure it is. besides the mounting provide no support for sideways movement on the tank.
The Accerbis or HPN 43L tank have added supports that fit on the down tubes of the main frame and rest on rubbers on top of the main tube. It also bolts to the mounting in the back, much more secure than the flimsy wire clip on the BMW tanks.
It will not take any modification if fitted to a pre 87 GS and some work to the seat of Post 87 bikes and on the 100GS you will have to relocate the cooler.
The tank itself are fitted by mounting three bolt-on brackets to the main frame and can be done in less than an hour.

keep standard tank, carry fuel in jerry cans. that way if you have an 'off' its probably safer.
also if you have "modified" your tank or had it modded and not told your insurance company..........and it leaks and sets fire to your bike..... they wont pay. (Most Insurance companies are OK if you tell them what you do, but some get snotty and want engineers reports and then try to hike the premiums) anyway thats my 2ps worth... Jerry cans r less hassle!

Save the extra money for travelling.which is what a bike is for!!!!!!!!!!!

just start welding! i would sugest maybe some internal bracing to reduce flexing, but dont see why it wouldnt hurt, also maybe make it a split tank so just in case one did tear or crack youd still have a spare tank.