First, I’m a bit embarrassed to be on the forum when I’ve not posted for a year or so. To be fair, I’ve done naff all motorcycling in the last year either.
O.K. To the point. Took the tank of the Aprilia Trail a couple of weeks back to play"hunt the ignition fault" and set the plastic fuel tank down on a bit of carpet still with 10 litres of fuel inside. And there it languished for about ten days as other things (Mrs. O.) intruded. Fixed the fault, ran in a couple of cables for accessories and then came to re fit the tank.
Once on the front mounts the rear mounting holes in the tank lugs don’t line up with the frame lugs by about 8/10 mm. So we are not talking “a bit tight” here. It’s as if the tank has grown. Nonsense? The tank top “glove box” screw holes don’t line up with the threaded inserts in the tank top either, so it has grown.
Mark (MH Motorcycles, Bromley) tells me he had the same problem with his Husqvarna some years back and he’s also heard of the same problem with KTM’s. Seems the tanks are fine while held in place but if not restrained they react with the dubious unleaded fuel inside and change shape. The answer to avoid this is to drain the tank before removing it. (Good knowing this now!)
The answer might be to heat up the tank and get it on to its mountings p.d.q. and then wait for it to set.
Anybody tried this? Anybody had this problem? Got any other answers to the problem?
This gets very confusing , why is there 2 threads now for the same thing ?
I have had this issue . there are 2 ways I have won the war , once on a Aprillia Falco and on KTM Superduke .
Falco … drained all fuel from the tank , set tank in the garage near the warmest wall , left for one week … tank had shrank back to original size and popped straight back on with no issues .
KTM , fitted new improved tank mounts with slots to allow for expansion and contraction … sorted .
Ooohhh yeah and Welcome Back … been like you have never gone … or never missed you … or no that sounds bad … Glad yer alive … Nope that sounds worse should have stuck with the first thing .
Thanks NumNum. I was hoping that you’d still be here as you were always the source of practical wisdom. (And some amusing posts.)
Now I’ve got the tank decently emptied, I’ll give it a bit of a warm to get rid of as much vapor as possible and park it under the radiator in the back room. And hope Mrs. O doesn’t notice!
If that don’t work, what do you think of the idea of building a ply box and using the steam cleaner (wet heat, no chance of it going boom) to heat it 100 deg C and slapping it back in place while still warm?
I would hope you really do not have to do that , strange enough it is water that causes the issue .Left to dry out your tank will return to actual size intended by aprilia .
It’s all something to do with ethanol, phase seperation , water, molecules to a size that allows it to pass into the plastic . Some moisture = good as increases shock absorbancy … too much= bad as causes size changes .
Long term cure for the bikes was always every week without fail going out and if they had not been ridden … give em a good shake to mix the fuel .
I was a little concerned when I got the KTM 990SMT. I’d read a lot on American forums covering plastic or spun nylon fuel tanks, it’s been a major headache with some Ducatis. The general consensus as NumNum has stated is that it seems to be related to ethanol content in fuel. This is the reason that I tend to fill the KTM with Super, no other benefit other than lower ethanol content.
I had this problem with a Ducati Multistrada I owned. The only permanent solution is to get a replacement tank and get it lined with a substance called Caswell. Caswell UK are based up in Cambridgeshire and at the time I recall they would do your tank for you.
It is a problem with ethanol in fuel. I wrote to a lot of the fuel companies at the time to discover who added ethanol to their petrol. You basically can’t use anyone’s ordinary unleaded, or Shell V-Power, or any supermarket petrol station high-octane unleaded. BP Ultimate, Texaco Super and Esso Super were ethanol free a few years ago.
Totally agree with Kevsta re Super unleaded. The left hand tank on my KTM 990Adv has grown to the point that I had to modify the lower mount and drop the hole down 10mm. And the tank on the Tuono was a bit snug last time I replaced it :w00t:
Hmm. First I agree that it’s the additives in lead free petrol that are the root cause, but if you follow through all the posts/links/forums (thanks NumNum for giving me the American starting point) you will discover that 1: you have half a days reading and 2: the problem is not quite directly the additives and 3: you need a degree in physical chemistry to fully understand the science.
I don’t have one of those so I’ll give you the short version:
One or the other of the additives in lead free fuel takes up water like blotting paper.
The water stays suspended in the fuel all the while the bike is in use and the fuel being agitated.
Leave the tank static and the water separates out.
The tanks are made of a plastic called polyamide (PA), a form of low grade nylon.
PA absorbs water and expands.
Manifestations vary from twisting, buckling, rippling and growing or combinations of.
Acerbis who make a lot of tanks for Aprilia, Ducati, KTM and many others reportedly advise motorcycle manufacturers that PA is not a suitable material for fuel tanks for bikes going to countries using lead free petrol. But is is the cheapest material Acerbis offer.
But there may be a cure.
Drain and dry out the fuel from the tank and keep the tank warm to drive the water from the PA. (It leaves almost as easily as it goes in. They say.) A fortnight in the sun seems to work well and sets in a reversion process. England. November. Sun?
My tank now sits on a 35C heat pad which I can run for years before the £1920 cost of a new tank has been used up. It would be better in the airing cupboard but bringing a petroleum fuel tank into the house negates my house fire insurance.
I travel in hope.
Oh, the American reckon that the tank inner coating, noted in a previous post, is the way to go to avoid the problem.
The tank sat on it’s heat pad for three weeks as I was busy cranking up a new construction site that was only walking distance from where I live.
By last Sunday the tank hardly even smelt of petrol so I stuck it in the downstairs bog and put a heater in there to bring the temperature up to 40 odd deg.C and left is there for 4 hours.
Took the warm tank down to the garage, banged it on the bike and there had been enough reversion to get the tank fixing bolts into the frame lugs and the nuts started on the threads.
Nothing ventured… I tightened everything up and (thought I’d) pulled the tank back into shape.
Now, there is a lot of bodywork hung off the Aprilia tank. None of it quite fitted properly. But it did fit o.k. once me and the Dremel had a word with it. (All of the “adjustments” are hidden.)
All back together!
Just awaiting a couple of bits from internet orders and then I can find out whether the new Anakee II tyres bought just before all this started last month were worth the money.
Interesting month without the bike. I don’t ride too much these days but being without a bike for a month was like having all your shoes stolen.
Worse, I had to use the bus once! Fine when I got on as I live only two stops from the end of line where the bus turns around so it was empty. Then the damn fool driver keeps stopping to pick up other people. What a daft arrangement. Surely a chap deserves better than this.
