Replacement for cracked F8 fuel tank

[JRWooden]

Originally Posted by Pomo

I'm having a tank-ectomy done on Friday. If I don't get kicked out of the "kitchen" I'll try to peek over their shoulders and see what it looks like inside.

Get them to cut it in half!

[Pomo]

Definitely two pieces, an inner bladder and the outer shell. You can remove the gas cap and see it pretty clearly there.

[JGoody]

After reading the thread I'm still trying to understand the cause. If there's a bladder then there is no contact with fuel to the outer shell so it's not the Ducati problem where the ethanol causes the tank to develop bulges. If it's expansion then it would be easy to reduce the volume of the bladder or adjust the shape to allow a little clearance. If it's stress related fracture due to vibration etc then why wouldn't it be beefed up a bit in the areas where they crack? So what's going on here?

[ebrabaek]

Originally Posted by JGoody

After reading the thread I'm still trying to understand the cause. If there's a bladder then there is no contact with fuel to the outer shell so it's not the Ducati problem where the ethanol causes the tank to develop bulges. If it's expansion then it would be easy to reduce the volume of the bladder or adjust the shape to allow a little clearance. If it's stress related fracture due to vibration etc then why wouldn't it be beefed up a bit in the areas where they crack? So what's going on here?

I personally think that it is in the casting of the outer case. If temps and or mix is not right, the areas that will give in first, are the areas of stress....... Which is the extreme angles. I have not heard of any other cracking except those. Hard angles. Why some do and some don't , only explanation I can come up with is just inconsistency in production. I though for sure that cooking my tank in the hot desert southwest would have killed mine. But nothing. Got mine back in 2009. Many in ethanol areas are reporting no cracking. So it is not that either. There are no patterns, and with such, I claim inconsistent casting.

[COracer]

So I'm buying an '09 with the cracks, it is out of the three year warranty. Does anyone know if indeed this is covered for the 5 year fuel/emissions warranty? Has anyone reported leakage or is this strictly cosmetic?

Anxiously awaiting the cutaway of one...

[ebrabaek]

Originally Posted by COracer

So I'm buying an '09 with the cracks, it is out of the three year warranty. Does anyone know if indeed this is covered for the 5 year fuel/emissions warranty? Has anyone reported leakage or is this strictly cosmetic?

Anxiously awaiting the cutaway of one...

I have heard of many who got theirs replaced as " good faith " from BMW. Have you tried to ask your local dealer.... Or.... is this the one your buying from...???

[Pomo]

Originally Posted by COracer

So I'm buying an '09 with the cracks, it is out of the three year warranty. Does anyone know if indeed this is covered for the 5 year fuel/emissions warranty? Has anyone reported leakage or is this strictly cosmetic?

I had mine replaced last week, just a little under 6 months past the three year warranty. I got it done "good faith", but I'm also the original owner of the bike. The guy I talked to at the dealer said that was definitely a factor in getting not only the cost of parts covered, but also the labor. You might get lucky on parts if you have a nice dealer, but based on what I heard it would be somewhat surprising if they covered the labor.

I don't know if I'd classify it as it "strictly" cosmetic, it may indeed weaken the fuel tank. But the cracks will not instantly cause fuel leaks.

Originally Posted by COracer

Anxiously awaiting the cutaway of one...

I don't have a cutaway, but here are pictures of where the fuel pump and filler neck are mounted.

[COracer]

Thanks for the info gents, picking it up tomorrow from a private party. Bike has just under 12k on it and he had the 12k service done at a local dealer in November. While he hadn't noticed it and they didn't tell him about it, the RO has tech notes that the tank is cracking and he was upfront and told me about it when I looked at the bike.

I will probably try to get it replaced even though it seems it may happen again from what everyone is saying. Worst case I see a few on forums and Ebay for sale with no cracks from parted bikes, I wouldn't mind doing it myself, need to learn the ins and outs of the bike eventually.

[Pomo]

Originally Posted by COracer

I will probably try to get it replaced even though it seems it may happen again from what everyone is saying. Worst case I see a few on forums and Ebay for sale with no cracks from parted bikes, I wouldn't mind doing it myself, need to learn the ins and outs of the bike eventually.

There's some kind of special tool used to remove/install the fuel pump. You could probably rig something up though.

Edit: the tank comes off pretty easily, but you have to remove the subframe from the bike as the tank slides over the front of it. Makes sense when you see it.

[LukasM]

I have swapped many subframes and tanks, no special tools needed. The ring for the fuel pump can be unscrewed by tapping it with a screwdriver/chisel and a small hammer.

[JRWooden]

Just one note of caution. When working around fuel systems be careful of sparks.
Catastrophies are very rare, but having seen one in a garage I worked in many years ago ...
I never want to see another one.

I have a piece of brass rod that I use when I need to "persuade" something tied into a fuel system.
Copper and alloys containing copper (brass, bronze, Monel metal (copper-nickel alloy), copper-aluminum alloys (aluminum bronze), are all non-sparking. A hunk of copper water supply pipe can usually be found without much trouble.

I'll be the first to say that the risk is very small, but if the tank went boom it would really screw up the rest of your day

[twizted1]

Originally Posted by Pomo

I don't know if I'd classify it as it "strictly" cosmetic, it may indeed weaken the fuel tank. But the cracks will not instantly cause fuel leaks.



I don't have a cutaway, but here are pictures of where the fuel pump and filler neck are mounted.

After seeing these pictures, the tank is a one piece design. The white & black that you are seeing are merely different layers of the tank which is very likely blow molded. The white is likely going to be virgin material with no color added, the black is likely virgin and reground material with color added. If the tank design/fab is similar to the tanks that I worked with at a fuel tank manufacturer will be multiple layers of material with a layer of less permeable material sandwiched between the inner and outer layers of material.

If the tank is of the construction I am describing, there is no separation between the white & black material shown in the picture.

*former engineer at a fuel tank manufacturer

[JRWooden]

Originally Posted by twizted1

After seeing these pictures, the tank is a one piece design. The white & black that you are seeing are merely different layers of the tank which is very likely blow molded. The white is likely going to be virgin material with no color added, the black is likely virgin and reground material with color added. If the tank design/fab is similar to the tanks that I worked with at a fuel tank manufacturer will be multiple layers of material with a layer of less permeable material sandwiched between the inner and outer layers of material.

If the tank is of the construction I am describing, there is no separation between the white & black material shown in the picture.

*former engineer at a fuel tank manufacturer

Cool! An expert!

So is a crack that starts in the outer black layer of the tank likely to stop at the interface, or at least be slowed down, due perhaps to the layer of less permeable material between the inner and outer layer?
Is the less permeable material (in between) just a coating or does it have some real thickness to it that you could see if you examined the tank closely?

[runnin4melife]

So why are they cracking?

[twizted1]

Originally Posted by JRWooden

Cool! An expert!

So is a crack that starts in the outer black layer of the tank likely to stop at the interface, or at least be slowed down, due perhaps to the layer of less permeable material between the inner and outer layer?
Is the less permeable material (in between) just a coating or does it have some real thickness to it that you could see if you examined the tank closely?

I've not been in the industry in 5 years now...but from the best of my memory, the layer thicknesses were dependent on the customer requirements and testing. A crack that started in any layer would eventually propagate through. The crack may "stop" for a time, but will eventually crack the next layer.

All my input is based on the one company I worked for in the fuel tank industry, BMW's tanks may be built/designed/molded in a different process or using different materials than I have experience with.